WELCOME

Investigation of Fluid Properties and Their Effects

on Seismic Response for Reservoir Characterization

of Fenchuganj Gas FieldBy

S. M. ARIFUL ISLAMSUST SPE STUDENT CHAPTER

BANGLADESH

• Introduction• Objectives• Location and Map• Geology• Data Sources• Methodology• Result and Discussion• Conclusion• Future Work

CONTENTS

Seismic data is commonly used for interpretation and evaluation of structural or stratigraphic features in the subsurface. Modern advancements in seismic exploration have examined the effect of fluid and rock properties on seismic attributes. These advancements may provide improved reservoir characterization and analysis.

INTRODUCTION

To study the fluid properties and their seismic significance, a number of published predictors are used to model reservoir data.

To predict fluid properties by using the Batzle and Wang (1992) model.

To predict rock and bulk properties by using the Gassmann-Biot model as a function of the saturating fluids.

To predict seismic response from the layered rock properties using Zoeppritz’ equations.

OBJECTIVES

The Fenchuganj Gas Field belongs to the Fenchuganj Upazilla of Sylhet district. It is situated at distance of about 40 km south of Sylhet town, bounded by Longitude E 90053’- 920 and Latitude N 24030’-24037’ which is 30 km long and 8 km wide.

LOCATION AND MAP

The Fenchuganj structure is situated in the transition zone between the central Surma Basin and the folded belt in the east and is closest to the eastern margin of the central Surma Basin. It is surrounded by different gas fields with Miocene reservoirs, such as Kailas Tila in the north, Beani Bazar in the east and Rashidpur in the south. It is separated in the north from Kailas Tila and in the south from the Batchia anticline by a clear saddles. From available geological and geophysical data of the Surma Basin, it appears that the Fenchuganj structure is the third highest structure after Chattak and Atgram in the Surma Basin.

GEOLOGY

GEOLOGY (CONT’D)

Fenchuganj is a comparatively young structure and contemporaneous with Atgram, Chattak and Dupi Tila structures and older than Kailashtila, Beani Bazar, Sylhet etc. Available data suggests that the structural growth of this structure began after deposition of the Upper Marine Shale (uppermost Miocene) and at the beginning of the Dupi Tila a small dip closure anticline had already taken shape. It is believed that the main anticlinal shaping and uplifting took place during and after Dupi Tila time which climaxed in the erosion of the base of the Dupi Tila within the crestal part. Finally, this resulted in the faulting of the structure, creating a reverse fault, and making the eastern flank of the anticline steeper.

It is most likely that the structural growth is still continuing.

GEOLOGY (CONT’D)

• The well log data that are used in this paper are provided by Geological Division and Geo-physical Division of Bangladesh Petroleum Exploration and Production Company Limited (BAPEX).

• The well log data from Fenchuganj Well-3 (Gamma, Resistivity, Sonic, Porosity, Density in LAS format)

DATA SOURCES

METHODOLOGY

METHODOLOGY (CONT’D)

Application of Batzle and Wang (1992) Model for Varying Saturation and Constant Pressure

RESULT AND DISCUSSION

Application of Gassmann-Biot Model for Varying Saturation and Constant Pressure

• Velocity vs. Saturation• Bulk Density vs. Saturation• Acoustic Impedance vs. Saturation• Poisson’s Ratio vs. Saturation• Acoustic Impedance vs. Poisson’s Ratio• P-wave Velocity vs. Bulk Density• S-wave Velocity vs. P-wave Velocity

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)Velocity vs. Saturation

RESULT AND DISCUSSION (CONT’D)Bulk Density vs. Saturation

RESULT AND DISCUSSION (CONT’D)Acoustic Impedance vs. Saturation

RESULT AND DISCUSSION (CONT’D)Poisson’s Ratio vs. Saturation

RESULT AND DISCUSSION (CONT’D)Acoustic Impedance vs. Poisson’s Ratio

RESULT AND DISCUSSION (CONT’D)P-wave Velocity Vs. Bulk Density

RESULT AND DISCUSSION (CONT’D)S-wave Velocity Vs. P-wave Velocity

Application of Batzle and Wang (1992) Model for Varying Saturation and Pressure

Fluid Modulus vs. Pressure at Different

Saturation Condition

Fluid Density vs. Pressure at Different

Saturation Condition

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

Application of Gassmann-Biot Model for Varying Saturation and Constant Pressure Field

P-wave Velocity vs. Pressure at Different Saturation Condition

Poisson’s Ratio vs. Pressure at Different Saturation Condition

Acoustic Impedance vs. Pressure at Different Saturation Condition

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)

Amplitude versus Offset (AVO) Modeling of Fenchuganj Gas Field

AVO Modeling from Reservoir Condition and Conditions due to Change of Saturation and Pressure

AVO Modeling Between Shale Zone and Gas Saturated Sand

RESULT AND DISCUSSION (CONT’D)

RESULT AND DISCUSSION (CONT’D)MODELING FROM RESERVOIR CONDITION

RESULT AND DISCUSSION (CONT’D)MODELING FROM RESERVOIR CONDITION

RESULT AND DISCUSSION (CONT’D)MODELING BETWEEN SHALE AND GAS ZONE

RESULT AND DISCUSSION (CONT’D)MODELING BETWEEN SHALE AND GAS ZONE

• Increase of water saturation affects fluid properties by increasing the fluid density, modulus and velocity

• The compressibility of fluid decreases as the water in fluid increases

• As temperature increases, the velocity and density of the fluid decreases

• Fluid bulk modulus increases as bulk density increases in varying saturation with constant pressure condition.

• In the saturating rock frame velocity, density, acoustic impedance and Poisson’s ratio increases as saturation increases in varying saturation with constant pressure condition.

• Fluid modulus increases as water saturation increases and decreases as pressure decreases. Again it decreases though the production path in varying saturation and pressure condition.

• Fluid density increases as water saturation increases and decreases (very little) as pressure decreases. Again it increases through the production path in varying saturation and pressure condition.

CONCLUSION

• In the saturating rock frame P-wave velocity increases as water saturation increases and decreases as pressure decreases. Again it decreases through the production path in varying saturation and pressure condition.

• In the saturating rock frame Poisson’s Ratio increases as water saturation increases and decreases as pressure decreases. Again it decreases through the production path in varying saturation and pressure condition.

• In the saturating rock frame Acoustic Impedance increases as water saturation increases and decreases as pressure decreases. Again it decreases through the production path in varying saturation and pressure condition.

• AVO modeling between reservoir condition and conditions due to change of saturation and pressure shows the negative amplitudes and indicates gas saturated zone.

• AVO modeling between upper shale zone and gas saturated sand shows negative amplitude and indicates gas saturated zone.

• This total work gives reservoir engineering decisions and forecasting throughout the production.

CONCLUSION (CONT’D)

• We have investigated fluid properties and their effect on seismic response on the major two gas saturated layers of Fenchuganj Gas Field.

• It is necessary to investigate the total reservoir including minor gas saturated zone if the gas production from those zones are economically viable.

FUTURE WORK

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