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Copyright 2007, Society of Petroleum Engineers

This paper was prepared for presentation at the 2007 SPE International Oil Conference andExhibition to be held in Veracruz, Mexico, 27-30 June 2007.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paperfor commercial purposes without the written consent of the Society of Petroleum Engineers isprohibited. Permission to reproduce in print is restricted to an abstract of not more than

300 words; illustrations may not be copied. The abstract must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.Box 833836, Richardson, Texas 75083-3836 U.S.A., fax 01-972-952-9435.

Abst ractElectric, acoustic, and nuclear logs, as well as rock properties

information from cores and downhole tests, such as leakoff,minifrac, hydraulic fracturing, and pressure buildup, are

normally available in the gas fields in Northern Mexico. The

existing information was used to fully determine rockproperties and to select the optimum perforating technique to

minimize formation damage and to help produce gas from this

type of reservoir.

The critical drawdown and formation compressibility were

evaluated based on the integration of rock mechanicalproperties from dipole sonic and from density logs with core

analysis information determining proper dynamic-to-static

calibration parameters.

The process to design the perforating technique tomaintain a balance between hole diameter for future hydraulic

fracturing and maximum penetration to reduce the skin

damage in this type of reservoir is presented in the paper. The

results from different wells, as well as the advantages anddisadvantages of the technique, are compared.

Introduction The main objective of the perforating process is to establish

communication to the reservoir to be able to have productionefficiently and effectively. This process is particularly

important in the low permeability, overpressured tight gas

formations even so it is apparently simple because most of theformations require hydraulic fracture for commercial

production. In fact, it has been a challenge when selecting the

perforating technique to maintain a balance between charge

penetration, hole size, and reservoir pressure for some well

completions. If the perforating technique is not optimized forthe particular reservoir, the results of the initial flow test,

fracture extension, and well production are, in most of the

cases, more expensive and less efficient.

In the case of overpressured tight gas reservoirs, theapplication of geomechanical models and field experience has

shown that the best technique is nearbalance perforating. The

same applies for high porosity and permeability reservoirs

where there is tendency to have sand production if extremeunderbalance techniques are used. In the case of fractured or

anisotropic reservoirs, the best technique is nearbalance

oriented perforating.

Well Perforating and Recent DevelopmentsWell perforating began over 70 years ago with the

development of various systems to establish communication

between the cased wellbore with the formation. The objectiveof any system is to achieve the maximum flow efficiency for

the particular reservoir while keeping the skin damage to a

minimum.

One of the first systems was bullet perforating, which wasconceived and patented in 1926. This system had some

drawbacks because the bullet remained in the perforation

tunnel and penetration was poor but, on the contrary, the

flowing efficiency was relatively good because the perforation

tunnel with the shape of a near uniform cylinder.In January 1945, Ramsey C. Armstrong founded Wel

Explosives Company (Welex) and, in 1946, the shaped charge

was introduced into the oil industry. The principle of shapedcharge perforating was developed in WWII for armor piercing

shells used in bazookas to destroy tanks. This new technology

allowed the oil producers to have some control over the

perforation design (penetration and hole size) to optimize

productivity. When compared to the bullet system, the shaped

charge perforation tunnel is a conic cylinder and the linerdebris is either dispersed through the entire tunnel or flowed

back into the well.12

In general, it was observed that the wellsperforated using the jet perforator system had higher flow

rates than the wells perforated using the bullet perforator

system because the penetration of the first system was largerthan the other system.3

A shaped charge is basically composed of the charge case

liner, main explosive, and the secondary explosive. The jet

perforating system includes the shaped charges, detonatingcord or primacord, and the electric or pressure detonator

(Figure 1). In general, the angle of the liners cone controls the

penetration and the entry hole size, as well as the explosive

power.45

This technology has been subject to continuousimprovement throughout the years. The recent introduction of

simulators using fast computers to design systems optimizing

SPE 108480

Geomechanical Applications for Near-B

alance and Dynamic Underbalance PerforatingTechnique in Overpressured Gas Zones in Burgos BasinHumberto Campos,Pemex, andSergio Martinez, Hugo Pizarro, Calvin Kessler, and Juan Torne,Halliburton

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2 SPE 108480

charge interference and the use of other metals for the jet has

contributed to the increase in penetration and perforating

efficiency. The development and introduction of fast pressure

gauges at beginning of this century allowed the analysis if theevents occurring almost instantaneously during the jet

perforating process (Figure 2).

The introduction of flow laboratories (Figure 3) where

rock samples are subject to actual downhole conditions,

including reservoir pressure, overburden pressure, andeffective stress, allowed the evaluation of the performance of

standard charges in any specific reservoir.6 In addition, it ispossible to customize the design of charges for any specific

application, optimizing the results (Figure 4).

There is a great deal of information related to design and

selection of perforating systems for various reservoir

conditions, depending on the production objectives andtechniques. This paper presents an overview of the these

techniques and reviews the experience of integrating the

reservoir parameters and geomechanical information with the

charge performance and mechanical condition of the wells toplan the perforating job. This type of integration will help to

improve the perforating job performance and any additionalapplications performance, such as hydraulic fracturing in theoverpressured tight gas reservoirs in Northern Mexico.

Underbalance Perforating. The underbalance perforating

technique was introduced very early in the development ofvarious perforating techniques7. It was more highly developed,

however, after the successful introduction of tubing conveyed

perforating (TCP) in the 1970s as a method of inducing an

initial surge period to clean the perforation and minimize theskin damage.

As early as 1956, Allen and Worzel7 showed that

overbalance perforating resulted in a less effective

perforation because the perforation tunnel was filled withcrushed sand, charge debris and pieces of metal from the

liner in addition to formation matrix plugging near the

perforating tunnel, even after the backflow from the formation

(Figure 5). Based on these observations, they recommendedperforating with some differential into the wellbore. In 1969,

Terry Walker, Jack Brown, and George Briggs conducted tests

with an average of 500 psi underbalance, using hollow steel

carrier (HSC) guns. They observed that the atmosphericpressure inside the carrier was an important factor for

additional cleanup of the perforations, especially in gas

reservoirs where the formation damage during the perforationwas larger because of the change in fluid compressibility.7

After the successful introduction of the TCP technique

(which allowed larger differential pressure into the wellbore),

King et al.8completed a study of at least 90 wells to determine

the minimum underbalance required for a proper cleanup ofthe perforations, considering that excessive differential

pressure can cause the casing to collapse or the formation to

disaggregate. They observed that in formations withpermeabilities in the range of 1md to 900md, there was an

exponential relationship between formation permeability and

minimum underbalance required to have clean perforations(linear relationship in the log-log plot). The procedure used

includes the comparison of production when damage was

removed using acid after the perforating job for gas and oil

wells, as shown in Figure 6. Most of the tests were performed

using an average underbalance of 1,000 psi with a maximum

of 2,000 psi for oil wells and 3,000 psi for gas wells. Over

50% of the time, however, acid did improve production in gaswells above 2,000 psi and below 2-4md. The results of this

experiment have been used for several years to design

underbalance perforating jobs either in TCP or wireline

perforating. In several cases, extreme underbalance pressure

have been used in low permeability formations with limitedsuccess because, as King stated, at low permeabilities, there

may not be sufficient flow through the formation matrix to

clean the perforations.(King et al., 1986)

In some depleted reservoirs, perforating with the wel

flowing as another underbalance technique that has beenintroduced successfully to improve the cleanup of the

perforations and the reservoir communication.

Extreme Overbalance Perforating. After the introduction o

the TCP technique and the development of low permeability

reservoirs that required additional stimulation to have

commercial production rates, various techniques, such as

extreme overbalance perforating, were considered tocomplement the underbalance perforating technique. The

technique was initially presented in 1993 by Oryx Energy and

ARCO as an means of minimizing problems encounteredduring the hydraulic fracturing of some specific reservoirs.9

In general, the basic technique used in TCP operations

involves pressurizing a large portion of the tubing with gasover a column of fluid. During the perforation, the fluid is

injected into the formation, creating small fractures around the

wellbore in consolidated formations (Figure 7). A variation of

this technique was developed in 1997 with the introduction of

propellants that generate high pressure gas during theexplosion of the gun.

In principle, this technique has applications mostly in lowpermeability formations to pass the damage zone when there inot enough underbalance, in pre-hydraulic fracture treatment

to break down the formation and to enhance the natura

fractures communication to the wellbore.912 In medium- tohigh-permeability formations, there is usually a surge in

pressure at the beginning, but the production declines to

normal rates after the induced fractures are closed because

there is no material placed to keep them open.

Nearbalance Perforating. The nearbalance perforating

technique is based in the application of a small underbalance

(less than 500 psi) while using HSCs to induce an additiona

drawdown pressure when the jets are passing through thecarrier steel wall, casing, cement, and formation.

In 1969, Terry Walker, Jack Brown, and George Briggs

presented an evaluation of this technique using 500 psi as anaverage underbalance pressure and HSCs with satisfactory

results, except that in some cases, there was sand flow. This

probably occurred because the critical drawdown pressure was

exceeded.7

The static and dynamic behavior during the clean-up phaseas a product of transient and steady-state flow has been

observed and documented in various papers.13

Some unconventional reservoirs are sensitive to a highunderbalance condition during the perforating and production

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SPE 108480 3

phases because the rock strength and stress can induce either a

shear failure (sand production) or rock grain texture damage in

the vicinity of the perforation tunnel. The optimumunderbalance condition related to geomechanical properties of

the reservoir has recently been documented in various

papers. 1320It has also been observed that in low permeability

gas reservoirs, very high underbalance values (4,000 psi) arenot required to clean gas cores at irreducible water

saturation.16 In gas cores saturated with brine (which is the

case for tight gas reservoirs), increasing the underbalance to

2,000 psi did not improve flowing efficiency.17

When rock properties information is available, optimizingthe balance between uniaxial compressive strength (UCS)2021

and critical drawdown pressure values with the reservoir

pressure and length of the HSC gun at atmospheric pressure todesign the perforating job has proved to add value to the

reservoir performance and the subsequent hydraulic fracturing

operations.

Extreme Underbalance Perforating. The extreme

underbalance perforating technique began to be used recently

in Indonesia for natural flow gas reservoirs. It is based onworking at the maximum safe underbalance before the criticaldrawdown pressure is reached to perforate the well and

achieve maximum flow and minimum skin.2224

This technique has also been successfully used in themedium- to high-permeability gas reservoirs in the Burgos

basin for several years, but it did not produce the same results

in the deep overpressured tight gas sands.

Dynamic Underbalance Perforating. Dynamic underbalanceperforating is the latest perforating technique, based on

controlling the transient pressure behavior when the jet is

going into the reservoir with the wellbore.6, 25 Highly

sophisticated software has been developed that is capable ofpredicting the behavior of the pressure and fluid within

fractions of seconds after the charges are initiated until they

reach steady state. This development allowed the design of therequired volume and specific timing to generate the required

dynamic underbalance for the specific formation while

keeping the near balance condition, which is the ideal

condition for the reservoir rock, as showed in recentpapers.2021 Normally, the flowing performance using this

technique is much better because of the effective removal of

fines from the crushed zone, the optimum tunnel shape (Figure

8), and an instantaneous surge that permits better flowperformance without damaging the rock around the wellbore.

Simulations for standard static underbalance and nearbalance

dynamic underbalance are shown in Figures 9 and 10respectively.

Oriented Perforating. The oriented perforating technique has

been used and documented for hydraulic fracturing

applications (Figure 11) when the reservoir is known to besubject to horizontal stress difference of at least 8% because of

tectonics or nearby faults in the Burgos basin. The need to use

this technique is more acute in deep tight gas reservoirs where

fracture pressure gradients sometimes exceed 0.9 psi/ft and theanisotropy effect is reflected in large values for tortuosity and

friction.2628 A historical case in the Burgos basin was

previously documented and is shown in Figure 12.

Another application for this technique includes sandcontrol in highly stressed reservoirs or in horizontal or highly

deviated wells.2930

Near Balance Perforating in Burgos BasinOverpressured Tight Gas ReservoirsThe gas reservoirs in Burgos basin are usually overpressured

sand reservoirs between 1,000mts and 5,000mts in depth with

a porosity range from 12.5 to 24% average and permeability

from 0.01md to 2 md.It is standard practice to hydraulically fracture the wells

after they are completed, using a monobore type of completion

design. The typical completion is 3.5 in. or 4.5 in. tubing in6.125 in. borehole, which gives up to 1.5 in. cement sheet in

some cases (Figure 13).

The wells are drilled using oil based mud that is, in some

cases, as heavy as 2.2 gr/cc. Any gas kick is usuallydocumented with the equivalent mud weight. This information

is used to determine the reservoir static pressure. (Flowing

pressure is usually very low because these are tight gasformations with low permeability and high irreducible watersaturation.) The standard practice includes verifying whether

or not there is pressure and gas flow on surface after the

perforating job is completed to proceed with the injection tesand the hydraulic fracture job.

The penetration and efficiency of the charges is a function

of several parameters related to the charge itself and the

reservoir conditions. The parameters related to charge areusually controlled in the selection of the charge for the

specific application. The parameters related to the reservoir

condition include the formation compressive strength (UCS or

UniAxial Compressive Strength is usually selected, but the

actual formation compressive strength depends on theconfining pressure), reservoir pressure, and matrix rock

texture, as shown in Figure 14. In the case of tight gas sands

the design for the perforating jobs is oriented to provideeffective reservoir communication while maintaining the

required conditions for hydraulic fracturing (entry hole and

phase orientation). The standard perforating methodology

consisted in completing the well with treated water andperforating in uncontrolled underbalance condition. Thi

method was successful in most of the shallow wells, but in

deep wells the underbalance reached sometimes up to 9,000

psi (above the critical shear pressure as found recently basedon rock mechanics core analysis). The flowing gas pressure

however, reached zero very rapidly after opening the well

Some wells flow intermittently at very low flowing pressuresafter a mini-frac procedure was performed, which indicates

large formation damage either during the drilling or

perforating phase. The need to perform hydraulic fracturing

was normally good enough to remove the perforating skin

damage and provide good reservoir communication untideeper wells were drilled and other problems were

encountered in the hydraulic fracturing, such as very high

tortuosity and friction, fracture screen-out, casing collapse

rapid decrease in production, and formation backflow.Mechanical properties analysis for some of the reservoirs

shows that the critical pressure was almost 60% of the actua

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4 SPE 108480

reservoir pressure while high friction angles were observed.

The changes in the formation compressive strength exceed

three times UCS when the confining pressures change

1,800psi and six times the UCS for 5,600psi confiningpressure (Figure 15).

This particular rock condition presents a challenge because

the required underbalance needed to clean up the perforating

tunnel and remove the damage zone will exceed the critical

drawdown pressure. This situation will create an instantaneousvery high load impact on the rock that results in grain crushing

around the wellbore, in addition to the damage induced by theperforating jet (Figure 16). For this particular rock type, the

ideal condition is to perforate the rock at balanced reservoir

condition because the formation compressive strength is

equivalent to the UCS. Based on the geomechanical model,

this condition is more easily achieved when the pressure insidethe wellbore is near that of the reservoir.

Taking into consideration that in tight gas reservoirs the

procedure to clean perforations using the underbalance

technique gives in the best of the cases partial results asdocumented by King et al.in 1986 and other authors in recent

years, it was decided to have optimum penetration and tunnelcondition perforating using the Near Balance PerforatingTechnique. In addition, the first interval was perforated using

the longest possible carrier to have an additional underbalance

uncontrolled dynamic pressure at a controlled static

underbalance condition in the order to 200 to 500 psi asdocumented previously by Terry Walker, Jack Brown, and

George Briggs in 19697and Larry Salz in 1974.14

The downhole performance of the perforating guns largely

depends on charge to casing clearance, formation strength,formation effective stress, (correlating overburden and

reservoir pressure), hydrostatic pressure, and casing

strength.3235 In addition, the target lithology, grain size, and

matrix distribution also affects the downhole performance ofthe charges. These factors, however, are still difficult to

consider in simulations and are still under investigation.

Mechanical Restrictions. Normally the 2in. Hollow SteelCarrier is used for wells completed in 3.5in. tubing or re-

perforating jobs, the 2.5 in. carrier is used in 4.5 in. tubing and

new wells completed with 3.5in (2.993 in. nominal ID) when

perforations are done with fluid up to the surface valvesbecause the maximum expansion of the gun after firing in

these conditions is 2.625 in.

Charge Performance. In this particular case, the preferred

perforating system is HSC in 2 in. or 2.5 in. size. The average

API 19B charge performance for these systems shows a

penetration of 18.3 in. and 26.5 in., and an average entry hole

of 0.22 in. and 0.32 in. respectively (Figure 17). The minimumrequired entry hole for the selected charges is 0.21 in. to

prevent bridging of the fracture proppant as previously

documented (Figure 11). The clearance is controlled in bothcases. In the smaller case, however, the carrier provides some

clearance to have good charge performance. The charges,

primacord, and detonator used were of the HMX type, rated at4000F for 1 hour.

Rock Properties. The rock mechanical properties analysis

was performed for some of the wells in the area. The results

show that the static-to-dynamic calibration factor for Youngs

modulus is close to 0.25 and 0.85 for Poissons ratio(Generally the Youngs modulus ratio can be as high as 0.9 in

shallower reservoirs with larger permeability, but we observed

an average ratio of 0.4 to 0.6 in shallower tight gas reservoirs)

The UCS and confined Mohr Coulomb rock mechanics tests

show that the friction angle averages 39 degrees with 1,500 pscohesion pressure, but the rock compressive strength increase

from 6,500 psi UCS to 30,000 psi for 5,600 psi confinemenpressure (Figure 18). The increase in rock strength associated

with the change of confinement pressure (which is similar to

having underbalance or overbalance larger than 2,000 ps

during the wellbore-reservoir pressure stabilization transient)

is reflected in a reduction of charge penetration, as reported byvarious studies.3233 There are several relations for

determination of the compressive strength based on porosity

measurements, but most of them show large variations over

the same porosity range. A particular one developed forBurgos is presented, but still a large scattering is observed

(Figure 19).

Geomechanical Condition. In a simple manner, perforating

performance is a function of the effective stress defined as the

difference between overburden and formation pressure

Reductions as large as 25% in penetration are observed whenthe effective stress varies from 0 to 15,000 psi.

In the case of the deeper tight gas reservoirs, the effectivestress ranges between 3,000 psi and 6,000 psi. When

compared to the rock properties, we can observe that the

critical pressure from Mohrs circle is an average 60%, which

gives a high probability of shear failure if large underbalance

perforating is used.In the case of the well D-101, the overburden pressure was

as high as 13,776 psi at 4,000mts. The reservoir pressure

calculated from gas entry during the drilling process was

approximately 9,000 psi and the critical reservoir pressure wasestimated as 4,399 psi.

The maximum drawdown based on actual rock condition

can be estimated from Griffith criteria and the Mohr-Coulombcriteria.

The Griffith criteria provides an estimation of the critica

shear failure condition from a relationship between the radiastress and the pore pressure when the medium stress is close to

the reservoir pressure which is the case for overpressured tighgas reservoirs. In general, if Sm = ( S1+ S2+ S3) / 3 ,

Toct= ( 8 * St* Pp)

Where, Stis a function of the UCS of the rock. In the case of

the well D-101, the CDP value was estimated as 6,241 psiwhich gives a static drawdown maximum close to 2,791 psi.

The Mohr-Coulomb criteria gives a CDP value of 5,402

psi for a maximum drawdown of approximately 4,198 psi.

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SPE 108480 5

If the well is completed with treated water, the static

underbalance will be approximately 3,300 psi, which is too

close to the critical pressure of the reservoir and shear failurecould be induced if the well is perforated in this condition.

Based on this, it was recommended to apply an additional

3,000 psi on surface before the detonation of the gun. It was

verified that the pressure after perforating increased byapproximately 350 psi. The flowing pressure of the well was

controlled to be higher than the critical value before the

hydraulic fracture job was performed successfully (Figure 20).

Perforation Job Planning and Performance Prediction PerfPro

TM. There are various software models used to predict

the performance of the charges. In this particular case,

PerfProTM

software was used because it is one of the latestmodels that includes API 19B tests and it is based on actual

tests over different rocks. Parameters were selected based on

the reservoir information previously reviewed in this paper.

The results are presented in Figure 21.

Effect of the Empty Space in the HSC in Nearbalance

Perforating. The amount of additional underbalance for a2.5in OD and 6mts length hollow steel carrier under reservoirconditions with 300 psi static underbalance exceed 1,000 psi

additional dynamic underbalance as shown in Figure 10.

The comparison of the pressure transient response betweena static underbalance condition and the dynamic nearbalance

condition shows that the static pressure recovering is marginal,

indicating skin or formation damage, while the second one

shows a good recovery to the original reservoir pressure.This evaluation was performed using the specialized

software SurgeProTM. For dynamic underbalance applications,

this process is performed during the planning and design

phase, depending on actual reservoir conditions. Special

chambers and devices are used to control drawdown duringthe transient time.

Conclusions and Recommendations

The integration of all the reservoir information and theteam work proved to be successful to optimize results and

production.

The application of this methodology has been animportant factor in the effective evaluation of reserves,

testing and production of the deep tight gas reservoirs inBurgos Basin.

The recommendation for perforating overpressured tightgas reservoirs specially in deep reservoirs for the

hydraulic fracturing during the completion processinclude the following steps:o Plan and design the well using a simulator, such as

PerfProTM,if possible.

o Plan to use at least 6mts of 2.5 in. HSC wheneverpossible for the first interval.

o Perforate 60 degree phase or perform orientedperforating if the stress field for the particular well

is known.

o Prevent static underbalance drawdown larger than500 psi.

o Either increase the control fluid weight orpressurize the well before the perforation of the

first interval. The intervals that follow should be

perforated before flowing the well and releasing

the pressure that keeps the balance wellborereservoir.

o Wait for a few minutes after the detonation of theperforating gun to allow for the stabilization of the

fluids downhole.o While flowing the well after the completion of the

perforating job, prevent any drawdown below the

critical reservoir pressure.

o Whenever possible, use the dipole sonic orstandard sonic and density information to calculatethe modules and calibrate them using field

correlations. The RockXpertTM

software usually

provides good correlation to determine criticasanding pressure and fracture pressure. This wil

also indicate the extension of the hydraulic fracture

and will help in the design of the job to optimize

results.

The problems related to sand screen-out, tortuosity, andfriction while performing the hydraulic fracture were

drastically reduced after the general use of thenearbalance perforating technique.

The nearbalance perforating technique, integratinggeomechanical properties of the formation with actua

well conditions, is a helpful method to maintain goodperforating efficiency without additional cost in large

volume operations such as the Burgos basin.

AcknowledgementsThe authors would like to thank PEMEX and Halliburton

for permission to publish this paper. We would like torecognize the participation of PEMEX and the service

companies in the application of this type of technology to add

value to the client.

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and resulting Impact on the New RP43, SPE 18242

35. Behrmann, L.A. and Halleck, P.M.: 1988, Effects ofWellbore Pressure on Perforator Penetration Depth, SPE18243

36. Wesson, D.S., Gill, B.C., and Navarrete, M.: 1991Improved System Test for Perforators, SPE 22813

37. Bell, W.T. et al.: 1999, Predicting Downhole ShapedCharge Gun Performance Viability of Method, SPE60129

38. Halleck, P.M. et al.: 1991, Prediction of In-Situ ShapedCharge Penetration Using Acoustic and Density Logs,SPE 22808

AuthorsHumberto Campos is the Chief of Well Services

Department in Activo Burgos PEMEX. Humberto holds anElectronic Engineering degree from Instituto Tecnologico de

la Laguna, and a Master Degree in Science from Instituto

Politecnico Nacional, Humberto has been working forPEMEX for more than 27 years since 1980 when he stared in

Poza Rica District as a flied operations engineer and later in

different locations Veracruz, Comalcalco, Mexico City and

Reynosa.

Sergio Martinez is a Technical Advisor in Reynosa

Sergio has been more than 20 years in different positions in

Welex and Halliburton Logging Services working in MexicoUSA and Italy. Sergio has occupied different operational and

management positions

Calvin Kessler, is the Reservoir Deliverability andProducibility Manager for Wireline & Perforating Service

Line at Halliburton Energy Services. He has a BS PE and MS-

Mining from New Mexico Institute of Mining and

Technology. He is a member of SPWLA, SPE, API, AADE

and CCSG, and has more than 32 years of experience with

Halliburton.

Hugo Pizarro is the Perforating, TCP and Slick LineTechnical Specialist for Halliburton Energy Services Wireline

and Perforating Product Service Line in Latin America. Hugo

holds an Electronic Engineering degree from UniversidadPolitecnica de Venezuela. Hugo has been working for

Halliburton for more than 17 years since 1990 when he started

in HRS and in 1995 he moved to HLS in Venezuela. Hugo ha

worked in different positions from field operations until

management and technical support.

Juan Torne is the technical manager for Halliburton

Energy Service Wireline and Perforating Product Service Linein Latin America, Juan holds an engineering degree from

Universidad del Cauca in Colombia. He is a member o

SPWLA and SPE, and has been with Gearhart and Halliburton

for over 22 years. He has worked in Venezuela, IndonesiaEgypt, and Mexico in various positions, from field operations

technical and interpretation support, operations management

and technical marketing,

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SPE 108480 7

Figure 1 Jet Perforating Shaped Charges Figure 2 Jet Perforating Sequence

Figure 3 Dynamic Perforating Evaluation Lab

Shaped charges Jet Perforating

Liner

Explosive

Main Load

Charge

Case

Explosive

BoosterPowder

LinerLiner

Explosive

Main Load

Explosive

Main Load

Charge

Case

Charge

Case

Explosive

BoosterPowder

Detonating

Cord

Detonating

Cord

Detonating

Cord

DetonatorDetonatorDetonator

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8 SPE 108480

Figure 4 Flow Efficiency as function of Perforating System

Figure 5 Crushed Zone

Effect of the technique used

on the Perforation Tunnel

Experiment f or same charge and same conditionsincluding pore pressure and effective stress tocompare the effect of +/- 3500psi U/O pressure

Perforation Damage Zone

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SPE 108480 9

Figure 6 Kings Underbalance Experiment

Figure 7 Extreme Overbalance Technique

Perforation breakdown and fracturing

Propellant burn gas expansion

Perforation event

Hydrostatic head

PressurePSI

Time - seconds

Pressure-MPa

2000

10000

8000

6000

4000

12000

0 0.005 0.01 0.015 0.02 0.025

20

30

40

50

10

60

70

80

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10 SPE 108480

Figure 8 Dynamic Underbalance Technique

Figure 9 Static Underbalance Downhole Pressure Transient

Dynamic Underbalance and Fast Gauge Response

Static Underbalance of 3000psi Tight Gas Formation

Observe that pressure did not recover for long time

as observed in the field Minimum Back Flow

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SPE 108480 11

Figure 10 Near Balance Dynamic Pressure Transient

Figure 11 Oriented Perforating applied to Hydraulic Fracturing Design

Near Balance Dynamic Perforating Technique

Observe the controlled draw down above the criticalpressure and the formation flow back transient

response in a low permeability tight gas reservoir

6000

5000

4000

3000

2000

200

150

100

50

0

-5010 20 30 40 50 60 70 80 90 1000

Breakdown

Pressure(psi)

WidthFunctionDur

ingFractureExtension

Perforation Orientation Angle, degrees from Fracture Orientation

Breakdown Width Function

Abbas et al .

Simulation using Perf-Pro for12% porosity, 360

0F reservoir

temperature and 15,747 psi

Gun 1: 2-1/2" Millennium

Gun/Charge Type 2-1/2" Millennium Avg Formation Penetration 9.06 inGun Position Eccentered Avg Exit Hole Dia 0.27 inShot Phasing 180 deg

Shot No. 1 2Orientation, deg 0.0 180.0Gun Clearance, in 0.0 1.33Formation Penetration, in 8.87 9.25Exit Hole Dia 1st Csg, in 0.31 0.26

Simulation using Perf-Profor 12% porosit y, 3600F

reservoir temperature and15,747 psi formation

com ressive stren th

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12 SPE 108480

Figure 12 Hydraulic Fracturing Historical Case

Figure 13 Well D-101 Mechanical Description

INICIPERF.:05-FEBRERO-03TERM. PERF: 16-MAYO-03INICIO TERM: 01-JUNIO-03

INICIPERF.:05-FEBRERO-03TERM. PERF: 16-MAYO-03INICIO TERM: 01-JUNIO-03148 m

COLUMNA GEOLGICA

AFLORA

PROF. PROGRAMADA: 4261 m

EOCENOSUP.JACKSON SUP.

403 m

MIOCENOCATAHOULA

1219 m

OLIGOCENOFRONO MARINO

OLIGOCENOVICKSBURG

1940 m

2246 m

EOCENO SUP.JACKSON MED.

Activo de Exploracin Reynosa

Operacin GeolgicaEXPLORACIN Y PRODUCCINREGIN NORTE

Activo de Exploracin Reynosa

Operacin GeolgicaEXPLORACIN Y PRODUCCINREGIN NORTE

EXPLORACIN Y PRODUCCIN

REGIN NORTE

E.M.R. = 94.46 m

19 m

POZO: D-101E.M.R. = 64.88 m

4258 m

2693 m

1151 m

PROF. TOTAL: 4261 m

INTERVALOS ATRACTIVOSPARA PRUEBAS DE PRODUCCIN

AGOSTO 24, 2004Shg

A 3529 m, GL = 569 UDens. de 2.01 A 1.93 gr/cmA 3529 m, GL = 569 UDens. de 2.01 A 1.93 gr/cm

A 3006 m, GL = 228 UDens. de 1.88 A 1.81 gr/cmA 3006 m, GL = 228 UDens. de 1.88 A 1.81 gr/cm

A 2225 m, GL = 200 UDens. de 1.45 A 1.43 gr/cmA 2225 m, GL = 200 UDens. de 1.45 A 1.43 gr/cm

3815 m

3825 mP.P. 1: DISP. (31-07-04); Pi= 4000 psi (281 Kg/cm),

Pf= 4500 psi (316 Kg/cm)

P.P. 2:3525 m

3540 m

3345m

3360 m

P.P. 3:

2254m

2270 m

P.P. 4:

PROGRAMA: TOMAR RPC Y MUESTRA

TR. 13-3/8 ,Q-125, 53.5 lb/pie.

T.R. 9-5/8 ,P-110 y Q-125, 53.5 lb/pie.

T.R. 20 K-55, 94 lb/pie.

T.L. 4 1/2, P-110, 15.1 lb/pie

DISP: (11-08-04);PI= 900 psi (63Kg/cm),Pf= 1500 psi (105 Kg/cm)

PP-No intv m T/D (seg) Rt(0HMS) (%) Sw(%)

PP-1 3815-3825 2.725 6 10-13 65

PP-2 3525-3540 2.560 6-10 10-13 60-70

PP-3 3345-3360 2.46 6-8 1012 60-70

PP-4 2254-2270 1.671 4-8 12-15 60-80

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SPE 108480 13

Figure 14 Charge Performance as a function of Reservoir Conditions

Figure 15 Rock Mechanical Properties Analysis

Penetration as (target)

Target

Compressive

Strength

(psi)

Effective

Stress

(psi)

Penetration*

(in) Comments

Concrete 6,600 0 15.49 Benchmark surface shot

Berea 7,000 100 10.25 Reduction due to sandstone

Berea 7,000 1,500 9.21

Reduction due to increase

effective stress

Nugget 13,000 100 6.68

Reduction due to increased

strength

* 2-1/8" Capsule Charge

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14 SPE 108480

Figure 16 Rock Failure in Burgos Basin as a function of the Effective Confinement Pressure

Figure 17 API 19B Test for the Shaped Charge HSC System

0.20

0.22

0.24

0.26

0.28

0.30

0 2,000 4,000 6,000 8,000 10,000

PNC, psi

Porosidad

Poral Elastic Region

Poral Failure RegionShear and Crush Failures

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SPE 108480 15

Figure 18 Mohrs Coulomb Rock Mechanics Core Analysis

Figure 19 Compressibility vs Porosity

D-1

1

10

100

0.06 0.10 0.14 0.18 0.22 0.26 0.30

Porosidad

cfeb

ac

+

=

1

Compresibilidad,

1/psix106

Compresibilidad,

1/psix106

1

10

100

0.06 0.10 0.14 0.18 0.22 0.26 0.30

Porosidad

Newman (C & H)

Newman (Horne)

Burgos

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16 SPE 108480

Figure 20 Well Perforating Model

Figure 21 Performance comparison based on Compressive Strength

Overburden

Reservoir Pressure

Hydrostatic Pressure

WHP>0

CS 6480psi

Ph = Pr (UCS)

CS 15068psi

Ph < Pr (1800psi)