fournier and borgomano 2007

AUTHORS

Francois Fournier � Formation de Rechercheen Evolution - Centre National de la RechercheScientifique 2761, Laboratoire de Geologie desSystemes Carbonates, Case 67, Universite deProvence, 3, Place Victor Hugo, F-13331 MarseilleCedex 03, France; [email protected]

Francois Fournier received his M.Sc. degrees fromthe Nancy School of Mines (France) and from theInstitut Francais du Petrole and a Ph.D. in car-bonate sedimentology from the University ofProvence in Marseilles (France). After a short ex-perience in oil companies as an exploration ge-ologist in France and Angola, he joined the Geologyof Carbonate Systems Laboratory (Marseilles,France) as lecturer in 2005. His research focuses onthe relationship between sedimentology, diagene-sis, and seismic reflections in carbonate reservoirs.

Jean Borgomano � Formation de Rechercheen Evolution - Centre National de la RechercheScientifique 2761, Laboratoire de Geologie desSystemes Carbonates, Case 67, Universite deProvence, 3, Place Victor Hugo, F-13331 MarseilleCedex 03, France

Jean Borgomano obtained a Ph.D. in carbonategeology in 1987 at the University of Provence inMarseilles (France). In 1988–2003, he workedat Shell as senior carbonate geologist in variousexploration and production Shell companies.He is currently a professor at the University ofProvence and the director of the Geology ofCarbonate Systems Laboratory. His research fo-cuses on the geological characterization and nu-merical modeling of carbonate reservoir archi-tecture and properties.

ACKNOWLEDGEMENTS

This work was funded by Shell Philippines Ex-ploration B.V. We gratefully acknowledge Shell,Chevron-Texaco, and the Philippine NationalOil Company for the access to data and the per-mission to publish this work. This paper signifi-cantly benefited from stimulating discussionswith many Shell staffs in research and opera-tional business units. We thank M. Joachimski(Erlangen University) for carbon and oxygen iso-tope analyses and the Laboratory of IsotopeGeochemistry at the Vrije Universiteit (Amster-dam) for Sr isotope ratio measurements. Re-viewers Richard Worden, Art Saller, and DavidEby gave constructive suggestions for the im-provement of the manuscript.

Geological significance ofseismic reflections and imagingof the reservoir architecturein the Malampaya gasfield (Philippines)Francois Fournier and Jean Borgomano

ABSTRACT

The integration of petrographic analyses of cores and thin sections,

petrophysical measurements, and well logs demonstrates that varia-

tions in acoustic impedance in the Malampaya buildup (upper Eo-

cene to lower Miocene, offshore northwest Palawan) are related to

vertical changes in porosity and pore type, which are dominantly

controlled by diagenetic processes. The Nido Limestone was subdi-

vided into 10–50-m (30–150-ft)-thick units characterized by spe-

cific diagenetic patterns and petrophysical properties (diagenetic

units). The alternation between tight and porous diagenetic units

is mainly controlled by meteoric diagenesis (leaching and pedogen-

esis) and by late-burial cementation and leaching. Well-to-seismic

ties show that the main seismic reflectors within the buildup in-

terior reflect the boundaries between diagenetic units. Most of the

negative amplitude reflectors are related to unconformities, where-

as positive amplitude reflectors have a more questionable chrono-

stratigraphic value and may represent the bases of cemented lenses

that can crosscut time lines. Comparison with other southeast Asian

Tertiary buildups indicates different origins of seismic reflections

related to distinct patterns of diagenetic evolution. The identification

of such seismodiagenetic units and of their controlling factors is of

paramount importance for the architecture and the petrophysical

characterization of carbonate reservoirs.

INTRODUCTION

Seismic reflection imaging has become an unparalleled geophysical

method to image subsurface architecture of carbonate systems (e.g.,

Belopolsky and Droxler, 2004; Eberli et al., 2004) and to assess the

AAPG Bulletin, v. 91, no. 2 (February 2007), pp. 235–258 235

Copyright #2007. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received April 26, 2006; provisional acceptance July 6, 2006; revised manuscript receivedAugust 21, 2006; final acceptance October 16, 2006.

DOI:10.1306/10160606043

factors controlling their evolution (e.g., Bachtel et al.,

2004; Isern et al., 2004; Fournier et al., 2005). Seismic

reflection images result from the interaction between

seismic waves and subsurface rocks. Seismic reflectors

are the interference composites resulting from several

contrasts in acoustic impedance (Sheriff, 1977). In car-

bonate sedimentary systems, diagenetic processes sig-

nificantly modify the pore network and the mineralogy

of the primary sediments, therefore affecting their

acoustic properties (Eberli et al., 2003).

The seismic sequence stratigraphymethod is based

on the assumption that seismic reflections follow de-

positional surfaces and erosional unconformities (Vail

et al., 1977), and therefore, they have chronostratigraphic

significance. However, several studies on seismic mod-

eling showed that this assumption is not always valid,

especially when abrupt depositional facies changes oc-

cur (Stafleu and Sonnenfeld, 1994; Zeng and Kerans,

2003), or when seismic resolution is limited (Rudolph

et al., 1989). In addition, meteoric or burial-diagenetic

alteration of carbonate rocks does not necessarily con-

form to depositional bodies. This implies that acoustic

impedance interfaces and, therefore, seismic reflectors

can potentially crosscut depositional surfaces and can-

not be necessarily predicted by sequence-stratigraphic

models.

Hence, it is necessary to carefully study the origin

of the reflections and to validate the basic assumption

of the seismic-stratigraphic method prior to any sedi-

mentologic and stratigraphic interpretation of the seis-

mic data.

The objectives of this article are (1) to identify the

processes that controlled the evolution and the spatial

distribution of petrophysical properties of the Malam-

paya carbonate reservoir; (2) to evaluate the relative im-

pact of depositional facies, diagenetic processes, tectono-

stratigraphic evolution, and seismic resolution on the

seismic imaging of these carbonates; and (3) to evaluate

the chronostratigraphic value of the seismic reflections.

LOCATION AND GEOLOGICAL SETTING

The Malampaya oil and gas accumulation is located in

the deep-water Block Service Contract no. 38, offshore

Palawan (Philippines), at a depth of 3000m (10,000 ft)

below present sea level (Figure 1), within a northeast-

southwest–oriented carbonate buildup. Like several hy-

drocarbon accumulations in the north Palawan block, the

Malampaya reservoir occurs within the upper Eocene

to lower Miocene Nido Limestone (Sales et al., 1997;

Williams, 1997). The field was discovered in 1989 and

contains a 56-m (180-ft)-thick oil rim (29.4jAPI) and

a 650-m (2000-ft)-thick gas column (Neuhaus et al.,

2004). The gas has been produced since October 2001

by means of a subsea manifold and five deviated wells.

Nido Limestone deposition was initiated during the rift-

ing phase of the South China Sea (late Eocene to early

Oligocene). In the middle Oligocene (magnetic anom-

aly 11), the South China Sea sea-floor spreading started,

and the Calamian-north Palawan-North Borneo micro-

continent, bearing theNido carbonate buildups, drifted

southward (Briais et al., 1993). During the last of the

early Miocene, sea-floor spreading ceased as a result

of the collision between the north Palawan block and

the accretion wedge of the Paleogene subduction zone

of north Cagayan (Briais et al., 1993; Schluter et al.,

1996). Carbonate development in the area stopped in

response to downwarping of the northwestern part of

the block and extensive clastic supply from the uplifted

Palawan Island (Fulthorpe and Schlanger, 1989). Since

Figure 1. Depth map (in meters subsea) of the top Nido Lime-stone and location of wells in the Malampaya gas field (modifiedfrom Grotsch and Mercadier, 1999) within Block SC 38, offshorePalawan, Philippines.

236 Significance of Seismic Reflections in Carbonates: Malampaya Gas Field

the early middle Miocene, the Malampaya carbonate

buildup has been progressively buried below 2000 m

(6500 ft) of terrigenous deep-marine sediments (Pagasa

and Matinloc formations). Deep-burial conditions are

expressed by elevated present-day formation tempera-

tures (100–170jC) in the Nido reservoir.

Grotsch andMercadier (1999) proposed amodel of

growth history of the Malampaya buildup using three-

dimensional (3-D) seismic data and relatively sparse core

and sidewall samples from 4 wells (Malampaya [MA]-1

to MA-4). This model was refined by Fournier et al.

(2005) using a newly acquired high-resolution seismic

survey and a comprehensive set of well data from 10wells

(MA-1 toMA-10). Fournier et al. (2005) subdivided the

Nido carbonates into 11 units (Figure 2) and showed that

the Malampaya growth history was largely controlled

by tectonic deformation. In addition, using core data

fromwells MA-5 andMA-7, Fournier et al. (2004) docu-

mented meter-scale parasequences attributable to high-

frequency relative sea level changes. These authors

showed that the petrophysical properties of the inner-

shelf carbonates are strongly controlled by meteoric dis-

solution and cementation associated with high-frequency

subaerial exposure events.

Except for the lowermost part of the Malampaya

carbonates (upper Eocene) where a significant amount

of quartz grains is present, the Nido Limestone min-

eralogy is almost exclusively calcitic. Only very occa-

sional dolomite cements, formed during the burial dia-

genesis, were found in the western flank and in the

western part of the buildup interior (Fournier et al.,

2005).

DATA AND METHODS

The data set consists of a 3-D seismic survey acquired

by Shell Philippines in 2002 and well data from 10 wells

(MA-1 to MA-10). Cores were recovered from wells

MA-2,MA-3,MA-4,MA-5,MA-7, andMA-9. Analyses

and interpretations of cores, thin sections, well logs, and

seismic data were performed by the authors in the Car-

bonate Laboratory of the Marseille University (France)

and with the Carbonate Team at Shell International

Figure 2. (a) Trace display of an arbitrary line across the northern area of the Malampaya buildup and the main seismic reflectors;(b) stratigraphic framework of the Nido Limestone in Malampaya. TWT = two-way traveltime.

Fournier and Borgomano 237

Exploration and Production B.V., Rijwijk (Netherlands).

Carbon and oxygen isotope ratios were measured at

the University of Erlangen, and strontium isotope mea-

surements were performed at the Vrije Universiteit in

Amsterdam. High-density 3-D seismic data were ac-

quired in 2002. The present work is founded on pre-

stack depth-migrated data, with a zero-phase signal.

The seismic polarity is defined as follows: Negative

amplitude means a downward increase in acoustic im-

pedance (positive reflection coefficient). To tie the wells

to the seismic data, synthetic seismograms were calcu-

lated in the SynPakmodule of the SMT (SeismicMicro-

Technology, Inc.) KingdomSuite software, using awave-

let extracted from the original seismic data. Acoustic

impedance profiles are computed from velocity and den-

sity logs, and the time-depth conversion was produced

integrating sonic-derived velocities.

The definition of depositional facies, seismicmark-

ers, and stratigraphic subdivisions is based on the

previous work by Fournier et al. (2005), with minor

modifications (Figure 2). Carbon, oxygen, and stron-

tium isotope analyses on whole-rock samples were used

to support diagenetic interpretations and datings. Ap-

proximately 500 porosity and permeability measure-

ments on core-plug samples are also integrated in this

study. Porosity logs were also calculated using density

logs and fluid corrections.

The following workflow was adopted to assess the

geological significance of seismic reflections in the Ma-

lampaya buildup interior:

1. Diagenetic study based on petrographic description

of cores and thin sections, cathodoluminescence, and

interpretation of carbon and oxygen isotope ratios

2. Interpretation of the relationships between sediments,

diagenetic products, and petrophysical properties

(porosity and permeability)

3. Calibration of the well-log signature relative to the

depositional and diagenetic patterns

4. Identification of the diagenetic units on the basis of

well data; these are defined as carbonate rock in-

tervals characterized by a pattern of diagenetic evo-

lution, a range of reservoir and acoustic properties,

and a specific well-log signature

5. Well-to-seismic ties

6. Determination of the relationship between diage-

netic unit boundaries and seismic reflections, as well

as the study of the tuning effect; the chronostrati-

graphic values of the seismic reflections are evalu-

ated using the stratigraphic results by Fournier et al.

(2004, 2005)

RESULTS

Diagenetic Evolution of Inner-Shelf Carbonates

Diagenesis has greatly modified the petrophysical prop-

erties of Malampaya carbonates in the buildup interior.

Diagenetic features described in core and sidewall sam-

ples from wells MA-1, MA-2, and MA-5 are shown

in Figure 3, and the chronology of diagenetic events is

summarized in Figure 4.

The diagenetic evolution of the inner-shelf carbon-

ates can be summarized as follows:

1. Early marine diagenesis: Precipitation of isopachous

rims of fibrous to bladed calcite within coarse-grained

bioclastic grainstones occurred in the marine phre-

atic environment. Geopetal infills of homogeneous

or peloidal micrite within mud-poor sediments are

commonandcanbe considerednearly syndepositional.

2. Meteoric diagenesis: Repeated subaerial exposure

events are reported from the late Oligocene and

early Miocene by Fournier et al. (2004). Exposure

surfaces are expressed by pedogenic features, such

as rhizoliths, pisoids, and laminated calcrete crusts.

Intense leaching of bioclasts and matrix below ex-

posure surfaces led to the formation of dissolution

vugs. Intergranular and moldic pores are commonly

partially occluded by fine-grained blocky cements of

nonferroan blocky calcite, which could represent

phases of meteoric phreatic cementation. Petro-

graphic observations of thin sections do not allow the

determination of whether blocky calcite cements are

all of meteoric-phreatic origin, or if they also include

late-burial cements. Large macrovugs are occasion-

ally rimmed by multilayered anisopachous fibrous

or botryoidal cements, interpreted as speleothems.

3. Late-burial diagenesis: Very coarse-grained calcite

blocky spars commonly occlude preexisting dis-

solution vugs or fractures and could be interpreted

as forming under late-burial conditions. They are par-

ticularly abundant within the wells located at the

vicinity of the western buildup margin (i.e., wells

MA-1, MA-7, MA-8). In MA-1, rare saddle dolomite

cements represent the youngest phase of porosity

occlusion. Matrix micrite commonly displays mod-

erate and sporadic microspar replacement of mi-

crite attributable to burial transformation, although

a meteoric origin is not excluded.

The scarcity of direct evidence of burial dissolu-

tion in Malampaya makes it difficult to evaluate its


Figure 3. Synthetic chart showing biostratigraphic ages, well-log data, diagenetic features, and d13C profiles (PDB = Peedee belemnitestandard) from wells MA-1, MA-2, and MA-5; the main sedimentary units are reported (m SS = meters subsea).


contribution to the present-day reservoir properties.

Corrosion of late-burial cement was observed within

the southwestern flank of the buildup, in well MA-3

(Fournier et al., 2004). Very minor matrix leaching

overprinting stylolites is reported fromMA-2. The del-

icate preservation of alveolar septal structures within

rhizoliths in MA-5 cores suggests that later dissolu-

tion stages probably did not affect significantly the

innermost part of the Malampaya shelf. However,

closer to the western margin of the buildup, dissolu-

tion vugs with noncemented walls are found in well

MA-7 (Figure 5b), coexisting with vugs occluded by

speleothems and coarse-grained blocky calcite. This

could be interpreted in two different ways: (1) The

noncemented vugs have a low connectivity, thus pre-

venting an efficient circulation of saturated fluids; or

(2) the vugs have a late origin and formed after the

latest phase of cementation. Vuggy porosity develop-

ment under deep-burial conditions has been document-

ed in other Tertiary southeast Asian carbonate build-

ups (Saller and Vijaya, 2002; Esteban and Taberner,

2003; Zampetti et al., 2003, 2005; Sattler et al., 2004).

In addition, although the present data set did not al-

low us to clearly establish the timing of hydrocarbon

migration, the function of high hydrocarbon satura-

tions in the preservation or enhancement of porosity

(Worden and Heasley, 2000) in the eastern and central

areas cannot be ruled out. Finally, fractures are encoun-

tered systematically within tight horizons, thus indi-

cating a control of cementation phases (meteoric and/

or burial) on the spatial distribution of fractures.

Origin and Identification of Diagenetic Units

Diagenetic units are defined as carbonate rock inter-

vals characterized by (1) a specific diagenetic history,

(2) a range of reservoir and acoustic properties, and

(3) a specific well-log signature.

On the basis of petrographic analysis on cores and

thin sections, well-log patterns, and petrophysical mea-

surements, the Nido carbonates were subdivided into

diagenetic units that are grouped into five main types.

They are characterized in Figure 6 in terms of litholo-

gy, pore type, diagenetic evolution, reservoir, and well-

log patterns.

Type Ia and Ib Diagenetic Units

The type Ia unit refers to quartz-rich packstones (bio-

micrite) with variable matrix content. Primary poros-

ity is completely occluded by blocky calcite cements.

Type Ib units are related to high-energy grainstone

(biosparite) facies with well-developed isopachous rim

cements. Residual pores are commonly occluded by

Figure 4. Ideal parageneticsequence of the Nido car-bonates in Malampaya.


Figure 5. Diagenetic features, porosity and permeability laboratory measurements, and carbon and oxygen isotope ratios in coredsections (a) in well Malampaya-5 (cores 1 and 2), located within a type IIIa diagenetic unit; and (b) in well Malampaya-7 (cores 1 and 2 ),located within a type IIIb diagenetic unit. Diagenetic units are defined as carbonate rock intervals characterized by their specificdiagenetic history, a range of reservoir and acoustic properties, and a specific well-log signature (see Figure 6).


Figure 6. Characterization of the diagenetic units in terms of lithology, diagenesis, petrophysical properties, and well-log pattern. Porosity is derived from density logs and fluid corrections.

242

Significanceof

SeismicReflections

inCarbonates:

Malam

payaGas

Field

blocky spar cements of meteoric and/or burial origin.

Type Ia and Ib units are devoid of dissolution features

and do not appear to be affected by repeated subaerial

exposure events. Reservoir quality of these units is poor,

with porosity less than 15% and permeability less than

100 md.

Type II Diagenetic Units

Type II units are characterized by very little diagenetic

alteration, with rare dissolution and cementation fea-

tures. They represent intervals of protected inner-shelf

sedimentation, dominated by wackestone to packstone

textures (biomicrite), that are not interrupted by re-

peated subaerial exposure (Fournier et al., 2004). How-

ever, slight microspar replacement of micrite occurs

locally within the matrix. Matrix microporosity (pore

space between micrite crystals) is the dominant pore

type. These units display low vertical and lateral varia-

tions of reservoir properties. Porosity values are high,

averaging 24%, whereas permeability is moderate, with

values typically less than 50 md.

Type IIIa and IIIb Diagenetic Units

Type IIIa and IIIb units represent intervals of cyclic

inner-shelf sedimentation, dominated by wackestone

to packstone textures (biomicrite) and marked by re-

peated subaerial exposures. Dissolution vugs and cal-

cretes are abundant features in both types of units.

Type IIIa and IIIb units differ by the amount of blocky

calcite cement. Whereas paleosol-related and vuggy

porosity are preserved in type IIIa units, blocky calcite

cements, of meteoric and/or burial origin, largely oc-

clude the pore space in type IIIb units. Figure 5 compares

two cored sections within a type IIIa unit (Figure 5a;

MA-5 well, cores 1 and 2) and a type IIIb unit (Figure 5b;

MA-7, cores 1 and 2). In both cases, the cored interval

is subdivided into meter-scale parasequences (Four-

nier et al., 2004), and most of them are bounded by

exposure surfaces displaying paleosol features. The

MA-5 cores 1 and 2 (type IIIa diagenetic unit) are

mainly composed of porous, mud-rich carbonates in-

terbedded with a few thin layers containing blocky

spar cements. The highest porosity (>28%) and per-

meability values (>500 md) are related to rhizolith-

and/or macrovug-bearing intervals (Figure 7B-b). In

the MA-7 cores (type IIIb diagenetic unit), meter-

thick tightly cemented beds alternate with more po-

rous and permeable layers. Tight intervals correspond

to paleosol horizons inwhich root-related pore space has

been completely occluded by coarse-grained blocky cal-

cite cements of probable burial origin (Figure 7B-c, e).

Within porous intervals, cements are more rare, and

vugs with noncemented walls coexist with vugs filled

with speleothem cements (Figure 7B-a, d, f ). The ver-

tical evolution of diagenetic features and petrophysical

properties in MA-7 cores is interpreted as follows

(Figure 7A): (1) High-porosity and high-permeability

layers form during subaerial exposure events as a re-

sult of rhizolith and dissolution vug development;

(2) locally, the pore space is partially occluded by

fine-grained blocky calcite, and vugs are rimmed by

speleothems in later phases of subaerial exposure;

(3) saturated deep fluids circulate preferentially with-

in high-permeability paleosol horizons and precipitate

blocky-calcite cement, during the late-burial phase, oc-

cluding most of the pore network; and (4) in a later

phase, corrosive fluids could have formed dissolution

vugs within the residual permeable intervals. Various

processes leading to carbonate dissolution in a burial set-

ting have been proposed. Burial dissolution does not

necessarily involve large fluid fluxes. For Mazzulo and

Harris (1992), brines chargedwith organic acids, carbon

dioxide, and/or hydrogen sulfide derived from organic

matter degradation and thermochemical sulfate re-

duction are the most likely fluids responsible for buri-

al dissolution of carbonates in a burial setting. Thermo-

chemical sulfate reduction is known to be responsible

for the partial dissolution of carbonates in deep-burial

settings at temperatures greater than 100–140jC (Wor-

den et al., 1995;Machel, 1998;Worden et al., 1998) that

are consistent with present-day formation tempera-

tures (100–170jC). In addition, Esteban and Taberner

(2003) demonstrated, from different carbonate-reservoir

case studies, that corrosion occurs mainly after the ces-

sation of pressure solution and results from the mix-

ing of formation fluids and externally sourced fluids

at higher temperatures. The external fluids could be

warmer hydrothermal fluids rising from depth as in

the Tertiary limestones of the Bombay Basin (Minero

et al., 2000; Esteban andTaberner, 2003) or compaction

waters from the shales overlying the carbonate build-

up, as suggested in the Liuhua platform (Sattler et al.,

2004). In the case of Malampaya, additional stable iso-

tope studies of cement stages and fluid-inclusion analy-

ses should be performed to clarify the origin of the cor-

rosive fluids.

Reservoir properties are highly variable in bothunit

types. Type IIIa units have a porosity modal value be-

tween20 and25%, andpermeability is commonly greater

than 100 md, whereas in type IIIb units, the porosity

modal value is between 5 and 10%, and permeability

rarely exceeds 100 md.


Figure 7. (A) Model of porosity evolution within the type IIIb units; (B) (a) core photograph showing a dissolution vug rimmed byspeleothems, Malampaya-7; (b) well-preserved, root-related porosity (alveolar septal structures) within rhizoliths, microphotograph,Malampaya-5; (c) occlusion of root-related pores by coarse-grained blocky calcite (bc), microphotograph, Malampaya-7; (d) dissolutionvug partially occluded by micritic geopetal infill (gi) and speleothems (sp); later dissolution cavities are present (lp), microphotograph,Malampaya-5; (e) core photograph within rhizoliths (Rhiz.): root-related pores or dissolution vugs are partially to completely occludedby blocky calcite or speleothems (sp), Malampaya-7; (f) core photograph showing the coexistence of vugs filled with speleothems (sp)and vugs with non-cemented walls (V.), Malampaya-7.


Influence of Depositional Facies on the Evolutionof Petrophysical Properties

Figure 8a–c display porosity-versus-permeability graphs

for the three dominant depositional facies of the early

Miocene buildup interior (echinoderm and red-algal

wackestone, foraminiferal and red-algal packstone, and

coral, red-algal, and foraminiferal packstone). The fol-

lowing observations can be highlighted regarding these

graphs:

1. The three dominant facies have very similar ranges

of porosity (24–28%) and permeability (5–20 md),

when they are not affected by dissolution or cemen-

tation processes (dominant matrix microporosity).

2. Dissolution and cementation processes, vuggy po-

rosity development, and pedogenesis can affect any

of the three main facies.

3. For a given type of diagenetic alteration, ranges of

porosity and permeability are very similar in the

three dominant facies (see envelopes for root-related

pore types and vuggy plus root-related pore types).

In contrast, grainstones have a specific diagenetic

evolution because marine fibrous rims and later blocky

cements commonly occlude most of the primary in-

tergranular pores. In the lower Miocene Malampaya

inner shelf, grainstones (Figure 8d) are relatively rare

and have low porosity (<20%) and low permeability

(<10 md).

Figure 8. Porosity-permeability plots as a function of dominant pore type and depositional facies for Malampaya-5 and Malampaya-7early Miocene samples; (a) echinoderm, and red-algal wackestone; (b) foraminiferal, and red-algal packstone; (c) coral, red-algal, andforaminiferal packstone and floatstone; (d) foraminiferal and red-algal grainstone. Boxes represent the maximum ranges of values for agiven pore type, considering all depositional facies.


In conclusion, because mud-bearing carbonates are

dominant, depositional facies apparently have only a mi-

nor impact on the present-day petrophysical properties

in the Malampaya buildup interior. Variations in po-

rosity, permeability, and pore type aremainly related to

dissolution, cementation, and pedogenetic processes.

Acoustic Properties of Diagenetic Units

The first step in determining the geological significance

of a seismic reflector is to correlate rock velocity with

other parameters such as porosity. Figure 9A and B

display graphs of sonic velocity in well MA-1 versus

porosity. In gas-saturated carbonates (at constant gas

saturation >90%) from type IIIa and IIIb units, graphs

show a major scattering of velocity values at a given

porosity (Figure 9B). InMalampaya as in other carbon-

ate reservoirs, pore-fill fluids have only a moderate ef-

fect on acoustic velocity (Neuhaus et al., 2004). This

lowsensitivityof acoustic velocity to fluid content is shown

in Figure 9C, where P-wave (= compressional wave)

velocity (Vp) values from gas-saturated carbonates

display the same scatter as in a water-saturated interval.

This indicates a relative inefficiency of the pore system

with regard to the P-wave propagation, probably in

relation to pore geometry and size. P-waves propagate

predominantly within the carbonate matrix and bypass

most of the pore network. Anselmetti and Eberli (1993,

1997) demonstrated that variations in velocity at equal

porosity are mainly controlled by pore types. The large

scattering in acoustic velocity in type IIIa and IIIb units

is the result of vertical heterogeneity in pore-type

distribution and diagenetic evolution. Within these

intervals, the dominant pore type varies vertically

from matrix microporosity to moldic and vuggy po-

rosity, with variable calcite cement content. In type II

units, velocities also exhibit significant deviations, al-

though dissolution features and cements are rare or

absent. Variable intensity of matrix neomorphism

(microspar replacement of micrite) in these mud-rich

intervals could be responsible for the scattered values of

velocity. In type Ib intervals, acoustic velocity varies with

porosity without significant scattering, thus reflecting a

low pore-type diversity, with porosity being related

Figure 9. Petroacoustic properties in well Malampaya-1: (A) sonic velocity (Vp)-versus-porosity plot for unit type Ia and Ib sampleswithin the water-bearing reservoir; (B) sonic velocity (Vp)-versus-porosity plot for samples located within the gas-bearing reservoir intype II, IIIa, and IIIb diagenetic units; (C) sonic velocity (Vp)-versus-porosity plot for type II and IIIb diagenetic units. Plotting symbolsindicate the pore-fluid nature. (D) Histograms of the acoustic impedance for the different diagenetic unit types.


only to the abundance of cement occluding the primary

interparticular porosity. Velocity in the type Ia unit

appears relatively insensitive to porosity changes.

Diagenetic unit types exhibit significant differ-

ences in acoustic impedance values (Figure 9D):

� Type Ia: very high acoustic impedance (>14 �106 kg m�2 s�1) because of very low porosity

values caused by calcite cementation and lack of dis-

solution features� Type Ib: high acoustic impedance (>10 � 106 kg

m�2 s�1) because of partial to complete occlusion

of intergranular primary porosity by marine fibrous

and meteoric to burial blocky calcite� Type II: low acoustic impedance (7–8 � 106 kg

m�2 s�1) attributed to high matrix porosity and

absence of cement-occluding pore space� Type IIIa: low acoustic impedance (8–9 � 106 kg

m�2 s�1), mainly related to high porosity levels

with paleosols and dissolution vugs� Type IIIb: high acoustic impedance (11–12 � 106

kg m�2 s�1) correlated with a low average porosity

value, resulting mainly from the intense cemen-

tation by a blocky spar of intervals that have pre-

viously undergone meteoric leaching and pedogenic

alteration

Most of the type IIIa and IIIb diagenetic units are

located within the oil- or gas-bearing reservoir, thus

implying a significant decrease in density in porous

intervals. We postulate that hydrocarbon content has

contributed to enhance the contrast between porous

type IIIa units and dominantly tight type IIIb intervals.

Seismic Imaging of Diagenetic Units

Origin of Seismic Reflectors

Synthetic seismograms were calculated to tie well and

seismic data (Figure 10). A good fit is obtained between

the synthetic seismogram calculated for wells MA-1,

MA-2, and MA-5 and the actual seismic data. Bound-

aries between diagenetic units are related to the highest

reflection coefficients (in absolute value) and generated

the main seismic reflectors within the buildup interior.

Amplitude value and polarity depend on the nature

and relative position of the bounding diagenetic units.

Table 1 summarizes the relationship between seismic

reflectors and the type of petrophysical boundary. A

well-to-well correlation of the diagenetic units is shown

in Figure 11.

Some positive amplitude reflectors are discontin-

uous and have only a very small lateral extent. For

example, Figure 12 shows the progressive disappear-

ance of the M20.0 reflector. In well MA-1, this re-

flector represents the base of a type IIIb diagenetic unit

that is marked by intense burial cementation of pre-

viously exposed and leached carbonates. Farther to the

east, this cemented carbonate body laterally changes

into a type IIIa diagenetic unit, and in well MA-5, the

cemented levels are very thin and rare (see Figure 5a).

Such a lateral change in diagenetic unit type is caused by

an eastern decrease in burial blocky cement cementa-

tion, thus suggesting a possible control of the western

margin fault in the circulation of late-burial fluids. A

similar fluid flow control by a fault was suggested by

Story et al. (2000) in the Liuhua 11-1 carbonate res-

ervoir (offshore China). In Figure 13B, a similar feature

is observed, with the eastward thinning of the tightly

cemented SC2.1-IIIb unit (lower part of the intra-Nido

interval; sensu Grotsch and Mercadier, 1999) seismi-

cally expressed by the disappearance of the C21.0 re-

flector between the MA-1 and MA-5 wells.

Except for the carbonate buildup base and top

that represent lithological boundaries, seismic reflec-

tors mark envelopes of rock bodies that are charac-

terized by similar petrophysical and petroacoustic

properties predominantly controlled by their specific

diagenetic evolution.

The carbonate base is imaged by a continuous, highly

positive amplitude reflector resulting from a lithologi-

cal contrast between sub-Nido sandstones (Paleocene–

Eocene) and tight Eocene carbonates. The seismic char-

acter of the carbonate buildup top is more variable. In

the buildup interior, carbonate buildup is expressed by

a continuous negative amplitude reflector represent-

ing a lithologic contrast in acoustic impedance between

tightly cemented limestones and overlying clastics. Near

the eastern margin and in the eastern flank, the car-

bonate top is represented by an envelope of various re-

flector terminations (Figure 2), thus expressing a lat-

eral change in reflection coefficient polarity (Neuhaus

et al., 2004). Other Tertiary carbonate buildups display

boundaries that are not expressed by a continuous seis-

mic reflector; e.g., SalalahBasin,Oman (Borgomano and

Peters, 2004), and Luconia Province, offshore Sarawak,

Malaysia (Bracco Gartner et al., 2004).

Impact of Tuning Effect on Seismic Imaging of Diagenetic Units

A careful study of the contribution of individual reflec-

tivity interfaces to the total seismic signal is required

to evaluate the accuracy of the diagenetic unit imaging.


Figure 10. Well-to-seismic tie. (a) Shape and amplitude spectrum of the wavelet extracted from the seismic data within the carbonate buildup: the spectrum shows frequenciesbetween 5 and 65 Hz, with 30 Hz the strongest but not overdominant; (b–d) synthetic panels compared with the actual seismic data for wells Malampaya-1, Malampaya-2, andMalampaya-5, respectively. Synthetic seismograms were calculated using the extracted wavelet. mMD = meters, measured depth.

248

Significanceof

SeismicReflections

inCarbonates:

Malam

payaGas

Field

As explained by Sheriff (1977), most reflections are

the composite interferences of several interfaces. Petro-

acoustic properties in Malampaya carbonates display

rapid vertical variations, particularly with type IIIa

and IIIb units. Individual synthetic seismic responses

at reflectivity interfaces are calculated (Figure 13A)

using a 30-Hzmodewavelet, extracted from the seismic

signal within the carbonates (see Figure 10). Internal

Table 1. Relationship between Diagenetic Unit Boundaries and Seismic Reflectors in the Malampaya Buildup Interior

Bounding Diagenetic Units

Reflection Coefficient

Corresponding Seismic Reflection

Lower Unit Upper Unit Polarity Examples

Pre-Nido clastics Type Ia Negative Peak Base Nido

Type Ia Type II Positive Trough R10.1

Type Ib Type II Positive Trough R20.1

Type II Type Ib Negative Peak R20.0

Type II Type IIIb Negative Peak C11.0, C21.0, M11.0, M12.0

Type IIIb Type IIIa Positive Trough C11.1, M12.1, M20.1, M30.1

Type IIIa Type IIIb Negative Peak C22.0, M20.0, M30.0, M40.0

Type IIIa Type II Positive Trough C12.1

Type IIIb Pagasa clastics Positive Trough M.40.1

Figure 11. Correlation panel of the diagenetic units between wells Malampaya-1, Malampaya-2, Malampaya-5, Malampaya-7, andMalampaya-8. Inset map represents the depth of the top Nido Limestone and the location of wells. mTVDSS: meters total verticaldepth subsea.


reflectivity interfaces within diagenetic units typi-

cally represent bases and tops of 1–10-m (3.3–33-ft)

intervals of thick, tightly cemented, or leached porous

carbonates (see MA-7 cores, Figure 5b). Nevertheless,

Figure 12a shows that they have only a minor influence

on the total seismic response because severely destruc-

tive interference occurs. The reflectivity interfaces at

the boundary between two diagenetic units are the

main contributors to the final composite signal. How-

ever, interferences can occur between these major inter-

faces, and an analysis of the tuning effect is needed to

establish the validity of the use of seismic reflectors in

delineating diagenetic bodies. Figure 14 shows that, in

well MA-1, petrophysical unit thicknesses are com-

monly close to the tuning thickness. Most of the unit

boundaries constructively interfere, thus implying that

amplitude anomalies are created, with peak-to-trough

amplitude values higher than expected, but without sig-

nificant discrepancy between apparent and actual peak-

to-trough time thickness. As a consequence, in most

cases, it will be possible to reconstruct with accuracy

diagenetic body thickness and morphology from the

interpretation of seismic reflectors after time-to-depth

conversion. Nevertheless, units SC2.1-IIIb, SC2.2-IIIa,

and SM3-IIIb-2 are too thin to be correctly imaged, and

negative interferences occur between the top and base.

DISCUSSION

Are Seismic Reflection Time Lines in Carbonates?

Seismic-stratigraphic interpretation is based on the as-

sumption that seismic reflections are generated by

stratal surfaces or erosional unconformities (Vail et al.,

1977) and have therefore a chronostratigraphic value.

Despite its crucial economic and academic importance,

studies questioning this paradigm are rare (Schlager and

Stafleu, 1993; Tipper, 1993; Anselmetti et al., 1997).

In Malampaya, seismic reflections signify bound-

aries between carbonate bodies that have been affected

Figure 12. (a) Trace display ofan arbitrary line crossing wellsMalampaya-1 and Malampaya-5 and showing the correspon-dence between seismic reflec-tors and the diagenetic units;the M20.0 reflector displays anabrupt disappearance betweenMalampaya-1 and Malampaya-5. (b) Sr isotope measurementon bulk carbonate samples;abrupt change in the Sr isotoperatio occurs at the top of theSM2-IIIb and SM3-IIIb-2 diage-netic units, thus suggestingsignificant time gaps. (c) Diage-netic unit correlation betweenMalampaya-1 and Malampaya-5; the SM2-IIIb diagenetic unitpinches out between Malam-paya-1 and Malampaya-5. mMD= meters, measured depth.


by distinct diagenetic evolutions, thus conferring spe-

cific petroacoustic and reservoir properties. By integrat-

ing the diagenetic, petrophysical, and seismic response

analyses and stratigraphic results by Fournier et al. (2004,

2005), the chronostratigraphic value of seismic reflec-

tions can be assessed.

Only negative amplitude reflectors (expressing a

downward increase of acoustic impedance) can be in-

terpreted as having a stratigraphic significance. Table 2

summarizes the chronostratigraphic significance of

the negative amplitude seismic reflectors. Some of the

corresponding surfaces can be unambiguously inter-

preted asmajor unconformities (sensuMitchum, 1977)

on the basis of significant breaks in the vertical and lat-

eral evolution of depositional facies and diagenetic pat-

tern (e.g., reflectorsR20.1,C11.1,C12.1,C22.1,M11.1,

or M40.1). In addition, reflectors M20.1 and M30.1

(Figure 12) are related to surfaces representing signif-

icant hiatuses as suggested by the abrupt shifts in Sr iso-

tope ratios (Wheeler andAharon, 1991).Nevertheless,

Figure 13. (A) influence ofvertical changes in acousticimpedance within the diageneticunits: (a) high-amplitude reflec-tions are related to SM1.2-IIIbbase and top, whereas internalreflection coefficients are inter-fering destructively and havelow contribution to the com-posite trace. (b) Highest ampli-tude reflections are related toSC2.2-IIIb top and SC2.1-IIIbbase; base and top of the SC2.2-IIIa unit are not fully resolved,and the composite signal re-sulting from the internal reflec-tion coefficients mentioned onthe right interfere moderatelywith SC2.2-IIIb top and SC2.1-IIIb base. (B) Trace display of anarbitrary line crossing wellsMalampaya-1, Malampaya-2,and Malampaya-5 and showingthe correspondence betweenseismic reflectors and the dia-genetic units; the M20.0 reflec-tor progressively disappearsbetween Malampaya-1 andMalampaya-5. (C) Diageneticunit correlation betweenMalampaya-1, Malampaya-2,and Malampaya-5; the SC2.1-IIIb diagenetic unit pinchesout between Malampaya-1 andMalampaya-5 and betweenMalampaya-5 and Malampaya-2.MD: measured depth.


for some other negative amplitude reflectors (R10.1,

M12.1), no direct chronostratigraphic or sedimento-

logic evidence supports their interpretation in terms

of unconformity or stratal surface. In the Malampaya

buildup interior, major unconformities can be either

related to phases of tectonic deformation (tilting and/or

folding) or by uniform falls in relative sea level (Fournier

et al., 2005). Such unconformities may contain time

lines, but no time lines will cross them.

In contrast, except for the base carbonate reflec-

tor, positive amplitude reflectors mark the bases of cal-

cite cement precipitation and, in the absence of further

high-resolution biostratigraphic or chemostratigraphic

datings, they cannot be rigorously considered as time

lines. The abrupt eastward pinch-out of the 40-m

(130-ft)-thick SM2-IIIb body (Figure 12) implies that

the diagenetic unit boundary probably crosscuts time

lines because no significant changes in paleowater

depth (Fournier et al., 2004) occurred within the build-

up interior at this time. In addition, during the early

Oligocene unit SC1.1, the vertical succession of depo-

sitional facies suggests an eastward-prograding system

(Fournier et al., 2005, p. 200). This prograding unit is

topped by an exposure surface imaged by the reflector

C11.1; the upper part of the SC1.1 unit contains abun-

dant meteoric and/or burial cements (type IIIb diage-

netic unit). The C11.0 reflector marks the base of these

cemented zones and is roughly parallel to the C11.1 un-

conformity. As a consequence, the C11.0 reflector prob-

ably crosscuts the different prograding clinoforms form-

ing the SC1.1 unit and, therefore, crosscuts time lines

(Figure 15). Although meteoric and burial diagenesis

have been largely controlled by stratigraphy, diagenetic

unit boundaries are not always parallel to stratigraphic

boundaries. As a consequence, some seismic reflectors

crosscut time lines because diagenetic transformations,

particularly burial cementation, have not perfectly fol-

lowed stratigraphy.

Figure 14. Study of the tuning effect in well Malampaya-1: (a) diagenetic units, upscaled acoustic impedance curve, and reflectioncoefficients in well Malampaya-1; (b) Actual time thickness versus apparent time thickness (solid line) and versus normalized peak-trough amplitude (dashed line); curves are calculated using the wavelet extracted from the seismic data (see Figure 10). Diageneticunit bases and tops are always interfering; most of the unit thicknesses are close to the tuning thickness, thus inducing significantamplitude anomalies. TWT = two-way traveltime; TVD = true vertical depth.


Implications for Reservoir Architecture andReservoir Performance

Malampaya seismic reflectors image envelopes of car-

bonate bodies affected by a coherent set of diagenetic

transformations instead of depositional surfaces. Pick-

ing the seismic reflectors in Malampaya consequently

leads to the definition of seismodiagenetic units in-

stead of sedimentary bodies or depositional stratigraph-

ic sequences (sensu Mitchum, 1977).

Because Malampaya reservoir properties are main-

ly controlled by the nature and the intensity of dia-

genetic alterations, 3-D picking of the seismic reflec-

tions will provide not only envelopes of porous and tight

units that are laterally continuous in 3-D, but also en-

velopes of dominant pore types. The highest hierar-

chical levels of the reservoir layering can therefore be

constructed in 3-D, when diagenetic unit thickness

is greater than tuning thickness. However, the use of

seismic acoustic impedance inversion for the construc-

tion of 3-D porosity models is complicated for two

reasons: (1) acoustic impedance is not only related to

porosity but also to pore type, particularly in vuggy

intervals; and (2) the tuning effect between the top and

base of the diagenetic units induces significant ampli-

tude anomalies.

The layering of the reservoir into seismodiage-

netic units also has implications for the permeability

model of the reservoir. Figure 6 shows that the different

diagenetic units are related to distinct porosity-versus-

permeability behavior. For example, type II and IIIa units

have the same porosity mode (20–25%), but perme-

ability values differ significantly because they com-

monly reach 100 md in type IIIa units and rarely exceed

50md in type II units. Such differences are related to

the nature of the dominant pore type (type II: matrix

micropores; and type IIIa: vugs and root-related pores)

and, therefore, to the diagenetic evolution.

The interpreted reservoir architecture from seis-

mic and static well data suggests the presence of dense

and relatively tight diagenetic units that correspond to

flat lenses and sheets in 3-D. These diagenetic units

Table 2. Stratigraphic Significance of Seismic Reflectors in the Malampaya Buildup Interior

Seismic Reflector

Bounding Diagenetic BoundariesStratigraphic

Significance

Arguments and References

Lower Unit Upper Unit

M40.1 Type IIIb Pagasa clastics Drowning surface Severe deepening in Malampaya-8 (Fournier

et al., 2005, p. 207)

M30.1 Type IIIb Type IIIa Unconformity Significant hiatus revealed by Sr isotopes (this

paper, Figure 11)

M20.1 Type IIIb Type IIIa Unconformity Significant hiatus revealed by Sr isotopes (this

paper, Figure 11)

M12.1 Type IIIb Type IIIa ?

M11.1 Type IIIb Type II Unconformity Top of cyclically exposed carbonates, overlain

by deeper deposits (Fournier et al., 2005)

C22.1 Type IIIb Type II Unconformity Top of cyclically exposed carbonates

Above: deepening in environment

C12.1 Type IIIa Type II Unconformity Top of cyclically exposed carbonates, overlain by

deeper facies, in Malampaya-1, Malampaya-2,

and Malampaya-5 (Fournier et al., 2005, p. 205)

C11.1 Type IIIb Type IIIa Unconformity Exposure surface marking the top of a prograding

unit; evidences of tectonic deformation prior to

SC1.2 deposition (Fournier et al., 2005, p. 200)

R20.1 Type Ib Type II Unconformity Tilted platform top, evidenced by eastward

deepening in environments of overlying SC1.1

deposits (Fournier et al., 2005, p. 200)

R10.1 Type Ia Type II Unconformity? Possible significant hiatus: Tc stage (letter-stages

classification of larger foraminifera) could be

missing?


can be locally stacked vertically and form apparent con-

tinuous strata, but individually, they are not laterally

continuous at the scale of the Malampaya buildup.

Regarding the possible compartmentalization of the

reservoir, they can therefore be considered as baffles

for vertical and 3-D fluid displacement and not as ver-

tical barriers. The systematic presence of open vertical

fractures within these dense diagenetic units enhances

their vertical permeability at the reservoir scale. The

initial reservoir conditions (pressure gradients and flu-

id contacts) confirm that the Malampaya field is not

compartmentalized.

Given the previous considerations, the gas pro-

duction, especially from the crest of the buildup, can-

not be affected by the presence of these dense dia-

genetic units. One should, however, realize that such

reservoir architectures would have more impact in

other settings on the reservoir performance in the case

of oil production.

Comparison with Other Tertiary Carbonate Buildupsfrom Southeast Asia

Tertiary carbonate buildups of southeast Asia are of

considerable economic importance because they are

major hydrocarbon targets both offshore and onshore

(Sun andEsteban, 1994;Howes, 1997;Williams, 1997).

Although displaying very similar features in terms of

age, general morphology, and biological assemblages,

many differences exist with regard to the growth pat-

tern, the evolution of the petrophysical properties,

and the origin of seismic reflections. In Figure 16,

Malampaya is compared with the early Miocene up-

per Zhujiang platform (Liuhua 11-1 field), offshore

China (Erlich et al., 1990; Wagner et al., 1995; Sattler

et al., 2004; Zampetti et al., 2005), and the early to

middle Miocene Luconia buildups, offshore Sarawak,

Malaysia (Epting, 1980, 1989; Zampetti et al., 2003,

2004).

Figure 15. (a) Trace display of an arbitrary line crossing wells Malampaya-1, and Malampaya-5. It shows the correspondencebetween seismic reflectors C11.1, C11.0, R20.1, and the diagenetic units; (b) well correlation showing the prograding unit SC1.1(modified from Fournier et al., 2004) and the SC1.1-IIIb diagenetic unit. The lower boundary of this type IIIb diagenetic unit crosscutsdepositional surfaces. Around well Malampaya-2, the SC1.1-IIIb diagenetic unit is too thin, and destructive interference occursbetween the top and base.


Figure 16. Comparison between the Malampaya buildup, the upper Zhujiang platform (offshore China), and the Luconia platforms (offshore Malaysia).

FournierandBorgomano

255

In the three carbonate systems, petrophysical and

petroacoustic properties are controlled by secondary

porosity formation under meteoric and/or late-burial

conditions. Therefore, seismic reflections mark, in the

three cases, boundaries between diagenetically con-

trolled tight and porous units. The main differences

between the three examples involve the origin of the

acoustic contrasts between the diagenetic and litho-

logic units and the chronostratigraphic significance of

such contrasts.

Origin of the Porous versus Tight Units

In the Luconia and Liuhua 11-1 buildups, impedance

contrasts aremainly induced by deep-burial leaching and

cementation (Zampetti et al., 2003; Sattler et al., 2004).

InMalampaya, although late-burial cementation is also

a major factor in the development of tight units, the

spatial distribution of late cements is mainly inherited

from the meteoric diagenetic history. Indeed, high-

frequency exposure events are reported in Malam-

paya and are responsible for the development of high-

permeability paleosol-related intervals, of probable

major importance for fluid circulation during the late-

burial diagenesis. In contrast, even if several exposure

surfaces are reported from Luconia and Liuhua, no

evidence of high-frequency subaerial exposure and as-

sociated paleosol development exists. In the Liuhua 11-1

field, the porosity spatial distribution is controlled by

bedding-parallel aquitards of depositional origin (Sat-

tler et al., 2004) that diverted the circulation of deep-

burial corrosive fluids.

Differences in tectonic evolution and subsidence

regime can be invoked to explain the presence of cy-

clically exposed carbonates in Malampaya, in contrast

to Luconia and Liuhua 11-1 buildups. Indeed, in Ma-

lampaya, Fournier et al. (2005) documented significant

synsedimentary folding, tilting of the carbonate build-

up, and repeated exposure events that could be related

to episodic pulses of tectonic deformation. In addition,

climatic differences (amount of rainfall, seasonality)

between the three buildups can also explain the distinct

diagenetic patterns (intensity of leaching and cementa-

tion, paleosol development) during subaerial exposure

phases.

Stratigraphic and Depositional Significance

Seismic reflectors fromLuconia and Liuhua carbonates

still conform to depositional architecture, despite the

dominant burial-diagenetic origin of the acoustic im-

pedance contrasts. InMalampaya, only negative ampli-

tude reflectors have a stratigraphic value.Nevertheless,

they markmajor unconformities and do not necessarily

conform to primary depositional stratal surfaces or

stratal envelopes. Indeed, deformation, tilting, and ero-

sion could have occurred below such unconformities.

In addition, positive amplitude reflectors are of disput-

able chronostratigraphic value in Malampaya because

they are only related to bases of cemented zones, and

some of them (C11.1,C21.0,M20.0) probably crosscut

depositional surfaces.

The imaging of the primary depositional architec-

ture is problematic in Malampaya as in other Tertiary

carbonate buildups. For example, although the vertical

succession of depositional facies suggests an eastward-

prograding system during the earlyOligocene unit SC1.1

(Fournier et al., 2005, p. 200), only the unit top un-

conformity is imaged, and prograding depositional sets

are not visible on seismic data. The inability to image

primary depositional features is related to (1) the severe

overprinting of the primary acoustic properties during

meteoric and burial-diagenetic phases and (2) resolution

effects because possible acoustic contrasts at the top

and base of the depositional strata are too close com-

pared to the seismic signal wavelength.

CONCLUSIONS

1. The reservoir layering into porous and tight diage-

netic units is mainly inherited from the successive

meteoric and burial-diagenetic transformations.

During repeated phases of subaerial exposure, high

porosity-permeability meter-scale intervals formed

as a result of the development of root-related pore

networks in paleosols and dissolution vugs. In later

diagenetic phases, burial water flow circulated pref-

erentially through the high-permeability intervals

formedduring subaerial exposure. They precipitated

blocky calcite cements, thus forming tight horizons,

particularly in the western margin of the buildup

interior, in the vicinity of the main fault. Finally, a

later phase of deep-burial leaching may have locally

enhanced porosity between tight horizons by creat-

ing dissolution vugs. Within intervals that have not

undergone subaerial exposure,matrixmicroporosity

(pore space between micrite crystals) is the domi-

nant pore type.

2. Seismic reflectors in Malampaya more likely image

seismodiagenetic units instead of stratigraphic se-

quences or sedimentary bodies. Most of the nega-

tive amplitude reflectors are related to unconformi-

ties and have therefore a stratigraphic significance.


Positive amplitude reflectors have a more question-

able chronostratigraphic value and can potentially

crosscut time lines.

3. Three-dimensional picking of the seismic reflections

gives a direct insight into the reservoir architecture,

although the primary depositional architecture of

the carbonate system is poorly imaged. Constructive

interference occurs between the top and base of the

diagenetic units, thus generating amplitude anoma-

lies without significantly altering the time geometry

of the acoustic interfaces.

4. As suggested by Tertiary buildups from southeast

Asia, seismodiagenetic interpretation of 3-D seismic

data, based on a genetic classification of seismic re-

flectivity, could therefore represent an alternative

to the conventional seismic-stratigraphic approach

in carbonate systems.

REFERENCES CITED

Anselmetti, F. S., and G. P. Eberli, 1993, Controls of sonic velocityin carbonates: Pure and Applied Geophysics, v. 141, p. 287–323.

Anselmetti, F. S., and G. P. Eberli, 1997, Sonic velocity in carbonatesediments and rocks, in F. J. Manfurt and A. Palaz, eds., Car-bonate seismology: Society of Exploration Geologists, Geo-physical Development Series, v. 6, p. 53–74.

Anselmetti, F. S., G. P. Eberli, and D. Bernoulli, 1997, Seismicmodeling of a carbonate platform margin (Montagna dellaMaiella, Italy): Variations in seismic facies and implications forsequence stratigraphy, in F. J. Marfurt and A. Palaz, eds., Car-bonate seismology: Society of Exploration Geologists, Geo-physical Development Series, v. 6, p. 373–406.

Bachtel, S. L., R. D. Kissling, D. Martono, S. P. Rahardjanto, P. A.Dunn, and B. A. MacDonald, 2004, Seismic stratigraphicevolution of the Miocene–Pliocene Segitiga Platform, EastNatuna Sea, Indonesia: The origin, growth and demise of anisolated carbonate platform, in G. P. Eberli, J. L. Massaferro,and J. F. Sarg, eds., Seismic imaging of carbonate reservoirs andsystems: AAPG Memoir 81, p. 309–328.

Belopolsky, A. V., and A. W. Droxler, 2004, Seismic expressions ofprograding carbonate bankmargins:MiddleMiocene,Maldives,IndianOcean, inG. P. Eberli, J. L.Massaferro, and J. F. Sarg, eds.,Seismic imaging of carbonate reservoirs and systems: AAPGMemoir 81, p. 267–290.

Borgomano, J. R. F., and J. M. Peters, 2004, Outcrop and seismicexpressions of coral reefs, carbonate platforms, and adjacentdeposits in the Tertiary of the Salalah Basin, South Oman, inG. P. Eberli, J. L. Massaferro, and J. F. Sarg, eds., Seismic imag-ing of carbonate reservoirs and systems: AAPG Memoir 81,p. 251–266.

BraccoGartner, G. L.,W. Schlager, and E.W. Adams, 2004, Seismicexpression of the boundaries of a Miocene carbonate platform,Sarawak, Malaysia, in G. P. Eberli, J. L. Massaferro, and J. F.Sarg, eds., Seismic imaging of carbonate reservoirs and systems:AAPG Memoir 81, p. 351–365.

Briais, A., P. Patriat, and P. Tapponnier, 1993, Updated interpre-tation of magnetic anomalies and sea floor spreading stages in

the South China Sea: Implications for the Tertiary tectonicsof southeast Asia: Journal of Geophysical Research, v. 98,p. 6299–6328.

Eberli, G. P., G. Baechle, F. Anselmetti, and M. Incze, 2003, Factorscontrolling elastic properties in carbonate sediments and rocks:The Leading Edge, v. 22, p. 654–660.

Eberli, G. P., J. L. Masaferro, and J. F. ‘‘Rick’’ Sarg, 2004, Seismicimaging of carbonate reservoirs and systems, in G. P. Eberli,J. L. Massaferro, and J. F. Sarg, eds., Seismic imaging of car-bonate reservoirs and systems: AAPG Memoir 81, p. 1–9.

Epting, M., 1980, Sedimentology of Miocene carbonate buildups,central Luconia, offshore Sarawak: Bulletin of the GeologicalSociety of Malaysia, v. 12, p. 17–30.

Epting, M., 1989, TheMiocene carbonate buildups, central Luconia,offshore Sarawak, in A. W. Bally, ed., Atlas of seismic stra-tigraphy: AAPG Studies in Geology 27, p. 168–173.

Erlich, R. N., S. F. Barrett, and B. J. Guo, 1990, Seismic andgeologic signature of drowning events on carbonate platforms:AAPG Bulletin, v. 74, p. 1523–1537.

Esteban, M., and C. Taberner, 2003, Secondary porosity develop-ment during late burial in carbonate reservoirs as a result ofmixing and/or cooling of brines: Journal of Geochemical Ex-ploration, v. 78–79, p. 355–359.

Fournier, F., L. F. Montaggioni, and J. Borgomano, 2004, Paleo-environments and high-frequency cyclicity in the Cenozoicsouth-east Asian shallow-water carbonates: A case study fromthe Oligo-Miocene buildups of Malampaya (offshore Palawan,Philippines): Marine and Petroleum Geology, v. 21, p. 1–22.

Fournier, F., J. Borgomano, and L. F. Montaggioni, 2005,Development patterns and controlling factors of Tertiarycarbonate buildups: Insights from high-resolution 3D seismicand well data in the Malampaya gas field (offshore Palawan,Philippines): Sedimentary Geology, v. 175, p. 189–215.

Fulthorpe, C. S., and S. O. Schlanger, 1989, Paleo-oceanographicand tectonic setting of early Miocene reefs and associated car-bonates of offshore southeastAsia: AAPGBulletin, v. 73, p. 729–756.

Grotsch, J., and C. Mercadier, 1999, Integrated 3-D reservoir mod-eling based on 3-D seismic: The Tertiary Malampaya andCamago buildups, offshore Palawan, Philippines: AAPG Bul-letin, v. 83, p. 1703–1727.

Howes, J. V. C., 1997, Petroleum resources and petroleum systemsof SE Asia, Australia, Papua New Guinea, and New Zealand, inJ. V. C. Howes and R. A. Noble, eds., Proceedings of anInternational Conference on Petroleum Systems of SE Asia,Australasia: Indonesian Petroleum Association, p. 81–100.

Isern, A. R., F. S. Anselmetti, and P. Blum, 2004, A Neogenecarbonate platform, slope, and shelf edifice shaped by sea leveland ocean currents, Marion Plateau (northeast Australia), inG. P. Eberli, J. L. Massaferro, and J. F. Sarg, eds., Seismic imag-ing of carbonate reservoirs and systems: AAPG Memoir 81,p. 291–307.

Machel, H. G., 1998, Gas souring by thermochemical sulfatereduction at 140C: Discussion: AAPG Bulletin, v. 82, p. 1870–1873.

Mazzulo, L. J., and P. M. Harris, 1992, Mesogenetic dissolution: Itsrole in porosity development in carbonate reservoirs: AAPGBulletin, v. 76, p. 607–620.

Minero, C. J., M. Esteban, R. Sarmiento, and H. Kumar, 2000,Burial porosity reservoirs in Bassein Formation, Bombay Basin,offshore India: AAPG Bulletin, v. 84, p. 1465–1466.

Mitchum, R.M., 1977, Seismic stratigraphy and global changes of sealevel, part 11: Glossary of terms used in seismic stratigraphy, inC. E. Payton, ed., Seismic stratigraphy— Applications to hy-drocarbon exploration: AAPG Memoir 26, p. 205–212.

Neuhaus, D., J. Borgomano, J.-C. Jauffred, C. Mercadier, S. Olotu,


and J. Grotsch, 2004, Quantitative seismic reservoir charac-terization of anOligocene–Miocene carbonate buildup:Malam-paya field, Philippines, inG. P. Eberli, J. L. Massaferro, and J. F.Sarg, eds., Seismic imaging of carbonate reservoirs and systems:AAPG Memoir 81, p. 169–183.

Rudolph, K. W., W. Schlager, and K. T. Biddle, 1989, Seismic modelsof a carbonate foreslope-to-basin transition, Picco di Vallandro,Dolomite Alps, northern Italy: Geology, v. 17, p. 453–456.

Sales, A. O., E. C. Jacobsen, A. A. Morado, J. J. Benavidez, F. A.Navarro, and A. E. Lim, 1997, The petroleum potential ofdeep-water northwest Palawan Block GSEC 66: Journal ofAsian Earth Sciences, v. 15, p. 217–240.

Saller, A. H., and S. Vijaya, 2002, Depositional and diagenetichistory of the Kerendan carbonate platform, Oligocene, centralKalimantan, Indonesia: Journal of Petroleum Geology, v. 25,p. 123–150.

Sattler, U., V. Zampetti, W. Schlager, and A. Immenhauser, 2004,Late leaching under deep burial conditions: A case study fromthe Miocene Zhujiang carbonate reservoir, South China Sea:Marine and Petroleum Geology, v. 21, p. 977–992.

Schlager, W., and J. Stafleu, 1993, Pseudo-toplap in seismic modelsof the Schlern-Raibl contact (Sella platform, northern Italy):Basin Research, v. 5, p. 55–65.

Schluter, H. U., K. Hinz, and M. Block, 1996, Tectono-stratigraphicterranes and detachment faulting of the South China Sea andSulu Sea: Marine Geology, v. 130, p. 39–78.

Sheriff, R. E., 1977, Limitations on resolution of seismic reflectionsand geological detail derivable from them, in C. E. Payton, ed.,Seismic stratigraphy— Applications to hydrocarbon explora-tion: AAPG Memoir 26, p. 3–14.

Stafleu, J., and M. D. Sonnenfeld, 1994, Seismic models of a shelf-margin depositional sequence: Upper San Andres Formation,Last Chance Canyon, New Mexico: Journal of SedimentaryResearch, v. 64, p. 481–499.

Story, C., P. Peng, C. Heubeck, C. Sullivan, and J. Dong Lin, 2000,An integrated geoscience and reservoir simulation study of theLiuhua 11-1 field, South China Sea: 32nd Annual OffshoreTechnology Conference Transactions, Houston, p. 1–11.

Sun, S. Q., and M. Esteban, 1994, Paleoclimatic controls onsedimentation, diagenesis and reservoir quality: Lessons fromMiocene carbonates: AAPG Bulletin, v. 78, no. 4, p. 519–543.

Tipper, J. C., 1993, Do seismic reflections necessarily have chrono-stratigraphic significance?: Geological Magazine, v. 130, p. 47–55.

Vail, P. R., R. G. Todd, and J. B. Sangree, 1977, Seismic stratig-raphy and global changes of sea level: Part 5— Chronostrati-graphic significance of seismic reflections, in C. E. Payton, ed.,Seismic stratigraphy— Applications to hydrocarbon explora-tion: AAPG Memoir 26, p. 99–116.

Wagner, P. D., D. R. Tasker, and G. P. Wahlman, 1995, Reservoirdegradation and compartmentalization below subaerial uncon-formities: Limestone examples from west Texas, China, andOman, in D. A. Budd, A. H. Saller, and P. M. Harris, eds., Un-conformities and porosity carbonate strata: AAPG Memoir 63,p. 177–195.

Wheeler, C. W., and P. Aharon, 1991, Mid-oceanic carbonate plat-forms as oceanic dipsticks; examples from the Pacific: CoralReef, v. 10, p. 101–114.

Williams, H. H., 1997, Play concepts— Northwest Palawan, Philip-pines: Journal of Asian Earth Sciences, v. 15, no. 2–3, p. 251–273.

Worden, R. H., and E. C. Heasley, 2000, Effects of petroleum em-placement on cementation in carbonate reservoirs: BulletinSociete Geologique de France, v. 171, p. 607–620.

Worden, R. H., P. C. Smalley, and N. H. Oxtoby, 1995, Gas souringby thermochemical sulfate reduction at 140jC:AAPGBulletin,v. 79, p. 854–863.

Worden, R. H., P. C. Smalley, and N. H. Oxtoby, 1998, Gassouring by thermochemical sulfate reduction at 140jC: Reply:AAPG Bulletin, v. 82, p. 1874–1875.

Zampetti, V., W. Schlager, J. H. van Konijnenburg, and A. J. Everts,2003, Depositional history and origin of porosity in a Miocenecarbonate platform of Central Luconia, offshore Sarawak: Bul-letin of the Geological Society of Malaysia, v. 47, p. 139–152.

Zampetti, V., W. Schlager, J. H. van Konijnenburg, and A. J. Everts,2004, Architecture and growth history of a Miocene carbonateplatform from 3D seismic reflection data; Luconia Province,offshore Sarawak, Malaysia: Marine and Petroleum Geology,v. 21, p. 517–534.

Zampetti, V., U. Sattler, and H. Braaksma, 2005, Well log andseismic character of Liuhua 11-1 field, South China Sea; re-lationship between diagenesis and seismic reflections: Sedi-mentary Geology, v. 175, p. 217–236.

Zeng, H., and C. Kerans, 2003, Seismic frequency control oncarbonate seismic stratigraphy: A case study of the KingdomAbo sequence, west Texas: AAPG Bulletin, v. 87, p. 273–293.


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