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Majalah Ilmiah UNIKOM

Vol.6, No. 2

183

H a l a m a n

NUMERICAL COMPUTATION STUDY OF SEISMIC WAVE IN

FRACTURED RESERVOIR ROCK USING MATLAB 6.5.1

USEP MOHAMAD ISHAQ

Jurusan Teknik Komputer

Universitas Komputer Indonesia

Fractured reservoir rock becoming important study recently, it is due to the high de-

mand of oil and gas. Some of fractured reservoir are basement rock, carbonate as well

as vulcanic rock. They have two kinds of porosity, primary and secondary porosity. The

primary porosity is caused by matrix and frame, and it is much smaller compared to

secondary porosity that caused by fractured zone. Elastic isotropy is assumed in most

cases of seismic analysis, processing and interpretation. Anisotropic especially trans-

verse isotropic behavior of seismic velocity, however, is found to exist in most crustal

and subsurface media especially in fractured reservoir rock. In this research, some

studies are done to investigate the effect of saturation on three types of fracture: iso-

tropic, vertical transverse isotropic and horizontal transverse isotropic rock. They are

studied using analytical model through extended Gassmann modeling and seismic

core physics laboratory. The analytical model of fractured zone is derived by extending

Gassmann equation for anisotropic model, it is known as Brown-Korringa equation.

This equation model the effect of fluid saturation in anisotropic fractured reservoir

rock. The samples of fractured rock are built from fractured sandstone in several condi-

tions, such as: isotropic, vertical transverse isotropic and horizontal transverse iso-

tropic. Then, they are measured in high pressured laboratory with several types scenar-

ios, such as variation of both overburden and pore pressure, several types of satura-

tion: SWIRR (saturated water irreducible), full water saturated and light oil saturated.

The results of numerical modeling show that in traverse isotropic media, both of P and

SV wave increase due to the fluid inclusion. The SH wave velocity is unaffected by fluid

inclusion. These results are different compared to isotropic Gassmann equation’s as-

sumption that S wave velocity is not sensitive to fluid substitution. Experimental studies

confirmed the results. In isotropic sample, P wave velocity increase around 25% to

52% with water inclusions, and 12% to 41% due to light oil inclusions. On vertical trav-

erse isotropic (VTI) media, P wave increase up to 34% due to water saturation, and in

horizontal traverse isotropic (HTI) media increase around 13% to 17%. Several types of

AVO responses due to the fluid inclusion in fractured reservoir rocks are also presented

also in this paper.

Fluid in fractured rock, extended Gassmann, seismic core measurement

I. Introduction

Many factor influencing seismic velocity in

medium such as: pressure, fluid content,

porosity, temperature, clay content and ani-

sotrophy degree. One of anistrophy type is

transverse isotrophy that is generally repre-

sented by Thomsen parameter

1)

. Anisotropy

medium is caused by two factors, they are:

intrinsic factor and fracture type

2)

.

Alamat korespondensi pada Usep Mohamad Ishaq, Jurusan Teknik Komputer Universitas Komputer Indonesia, Jalan

Dipati Ukur 114, Bandung 40132. Email: ishacovic@gmail.com .

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