lecture - 02 feb 21 2015 saturday.unlocked

Department of Earth & Environmental Sciences,

Bahria University, Karachi Campus

www.bahria.edu.pk By: M. Hammad [email protected]

3D SEISMIC INTERPRETATION (GEO3D SEISMIC INTERPRETATION (GEO--518)518)

M. S (Geophysics)M. S (Geophysics)

By InstructorBy Instructor

M. Hammad ManzoorM. Hammad Manzoor

February 21, 2015 (Saturday)February 21, 2015 (Saturday) Lecture # 2Lecture # 2Lecture # 2Lecture # 2



Hydrocarbon Hydrocarbon Exploration Overview Exploration Overview

By Utilizing By Utilizing


Geophysical MethodsGeophysical Methods



Key elementsKey elements


Key to find HydrocarbonsKey to find Hydrocarbons

Subsurface Mapping TechniquesSubsurface Mapping Techniques


The Constraints of EconomicsThe Constraints of Economics

ConclusionsConclusions


Bahria University, Karachi CampusKEY ELEMENTS

First objective in exploration is to identify the geological

situations where accumulations of Hydrocarbons are possible.

From geological studies we know that these situations are

characterized by five features:

Source rock

Reservoir rock


Reservoir rock

Migration path

Trap

Seal


Bahria University, Karachi CampusSource Rock

This is likely to be a thick shale, containing organic material.

We hope that this rock and its organic content were

deposited under airless conditions (favorable for the preservation of

the organic material), that it became rapidly buried, and that it

"cooked" at a favorable temperature for a sufficient time.

The nature of the petroleum generated depends on the


The nature of the petroleum generated depends on the

temperature history and on the origin of the organic material; woody-

plant detritus and/or very high temperatures tend to yield gas, while

marine detritus and/or moderate temperatures tend to yield oil.


Bahria University, Karachi CampusSource Rock




Source Rock

Geophysical Methods Response

In the context of the source rock, then, the task of our geophysical

methods is to reveal:

The Rock Type;

The Volume;


The Volume;

The Conditions of Deposition;

The Temperature/Burial History; and

The Original Organic Content.

Geophysical methods can make some contribution to all these

factors except the last.


Bahria University, Karachi CampusReservoir Rock

This is likely to be a porous sandstone or carbonate. We hope

that this rock is very extensive, very porous and very permeable.

The original porosity depends on grain character and

depositional conditions; this porosity may be destroyed by

cementation, or enhanced by solution or chemical change.

The original permeability depends on the size between


The original permeability depends on the size between

grains; this permeability may be destroyed by cementation, or

enhanced by natural fracturing.

Further, we know that (particularly in sandstones) the

permeability is seldom uniform; it tends to be largest in the direction

of the water flow from which the rock grains were deposited.


Bahria University, Karachi CampusReservoir Rock




Reservoir Rock


In the context of the Reservoir rock, then, the task of our geophysical

methods is to reveal:

The Type of Rock;

Its Thickness, Extent and Volume;


Its Thickness, Extent and Volume;

The Conditions of Deposition and the shape

The Present Porosity; and

The Present Permeability.

Geophysical methods can make some contribution to all these

factors except the last.


Bahria University, Karachi CampusMigration

Migration path for the petroleum to move from the source

rock to the reservoir rock. This may be a permeable rock (such as the

silty rock), or a permeable zone of fracture.




Migration Path


Although geophysical methods allow no measure of permeability,

they can sometimes indicate the likelihood of such permeable paths.

However, the problem is complicated by the fact that we are asking

for a permeable path at the appropriate time in the past; it need not


for a permeable path at the appropriate time in the past; it need not

be permeable now.


Bahria University, Karachi CampusTrap

We need a trap. In Figure we see the classical anticlinal trap,

and filled upto the spill point.



Bahria University, Karachi CampusStructural Trap

In structural traps such as this the reservoir rock itself may

be widespread, and the search is for vertical closure; this may be

supplied by four-way dip (a dome) or by a combination of dip and

faulting.



Bahria University, Karachi CampusStratigraphic Trap

In stratigraphic traps, however, the reservoir is naturally

limited in some way, and the search is for indications of these limits.

Examples are the uncomformity trap




In stratigraphic traps, Reef Example;




In stratigraphic traps, Sand Filled Channels Example;



Bahria University, Karachi CampusTrap Suits Examples




Trap


In the context of the Trap, then, the task of our geophysical methods

is to reveal:

The Dip of the Reservoir Rock;

The Presence of Trapping Faults; and/or


The Presence of Trapping Faults; and/or

A Three-dimensional picture of the reservoir body

The great successes of geophysical methods in the past have been

in the search for structural traps. To a smaller extent, and with much

less certainty, geophysics is now contributing to the search for

stratigraphic traps.


Bahria University, Karachi CampusSeal Rock

This may be an impermeable cap-rock (such as a thick layer

of salt, or an unfractured shale, or a dense and unfractured

limestone).

Alternatively, the seal may be a fault, in which sealing

minerals have been precipitated from compaction water escaping up

the fault.

In stratigraphic traps it may be a lateral transition a facies


In stratigraphic traps it may be a lateral transition a facies

change from a permeable reservoir rock to an impermeable

sealing rock


Bahria University, Karachi CampusSeal Rock


THE SAND BAR THE SAND BAR THE SAND BAR THE SAND BAR



Seal Rock


In the context of the Seal rock, then, the task of geophysical methods

is to reveal:

In Case of Structural Traps:


The Nature of The Rock Above the Trap;

The Risk of Fracturing in That rock; and

The Risk that such a system of fractures vents, directly or

indirectly, to the surface;



Seal Rock


In Case of Fault Traps:

The Likelihood that the fault is chemically sealed; or

The Risk that the fault vents, directly or indirectly, to the

surface;


surface;

In Case of StratigraphicTraps:

The Likelihood that any Critical Unconformity is sealed; and

The Likelihood that lateral Facies changes represent a seal.



A SituationA Situation







A Situation - Geophysical Methods

Let us suppose that we do find a situation having the

necessary features: source; reservoir; migration path; trap and

seal.

There is another matter, the geological history, which we

should explore before we drill. For example, let us look again at

the rock layers.


the rock layers.

First, we notice their parallelism; this is telling us that at one

time (after the start of deposition of the cap rock) the layers were

flat and horizontal




Second, we notice that the present structure suggests both

folding and tilting (or regional dip); now we ask which came first

the folding or the tilting?

For if the tilting came first and was followed by migration of

all the oil and gas before the folding


Think Over

It.




THEN THE TRAP OF IS OF NO INTEREST TO US

IT IS BARREN.




ThanksThanks


ThanksThanks

lecture - 02 feb 21 2015 saturday.unlocked

Documents

bahria university

karachi campusreservoir

rock type

hammad manzoorfebruary

hammad manzoorm

source rock reservoir

karachi campuskey elements

original organic content