An integrated study for seismic structural interpretation and reservoir estimation of Sawan gas field, Lower Indus Basin, Pakistan

Muhsan Ehsan; Muhammad Arslan Shakeel Toor; Muhammad Iqbal Hajana; Nadhir Al-Ansari; Amjad Ali; Ahmed Elbeltagi

doi:10.1016/j.heliyon.2023.e15621

An integrated study for seismic structural interpretation and reservoir estimation of Sawan gas field, Lower Indus Basin, Pakistan

Heliyon. 2023 Apr 20;9(5):e15621. doi: 10.1016/j.heliyon.2023.e15621. eCollection 2023 May.

Authors

Muhsan Ehsan¹, Muhammad Arslan Shakeel Toor¹, Muhammad Iqbal Hajana¹, Nadhir Al-Ansari², Amjad Ali³, Ahmed Elbeltagi⁴

Affiliations

¹ Department of Earth and Environmental Sciences, Bahria School of Engineering and Applied Sciences, Bahria University, Islamabad, 44000, Pakistan.
² Civil, Environmental and Natural Resources Engineering, Lulea University of Technology, 97187, Lulea, Sweden.
³ School of Earth Sciences, Zhejiang University, Hangzhou, Zhejiang, China.
⁴ Agricultural Engineering Dept., Faculty of Agriculture, Mansoura University, Mansoura 35516, Egypt.

Abstract

The information about the subsurface structure, type of fluids present in the reservoir, and physical properties of the rocks is essential for identifying potential leads. The integrated approach of petrophysical analysis, seismic data interpretation, seismic attributes analysis, lithology, mineralogy identification, and Gassmann fluid substitution were used for this purpose. The structural interpretation with the help of seismic data indicated the extensional regime with horst and graben structures in the study area. The two negative flower structures are cutting the entire Cretaceous deposits. The depth contour map also indicate favorable structures for hydrocarbon accumulation. The four possible reservoir zones in the Sawan-01 well and two zones in the Judge-01 well at B sand and C sand levels are identified based on well data interpretation. The main lithology of the Lower Goru Formation is sandstone with thin beds of shale. The clay types confirm the marine depositional environment for Lower Goru Formation. The water substitution in the reservoir at B sand and C sand levels indicated increased P-wave velocity and density. The water substitution affected the shear wave velocity varies slightly due to density changes. The cross plots of P-impedance versus Vp/Vs ratio differentiate the sandstone with low P-impedance and low Vp/Vs ratio from shaly sandstone with high values in the reservoir area. The P-impedance and S-impedance cross plot indicate increasing gas saturation with a decrease in impedance values. The low values of Lambda-Rho and Mu-Rho indicated the gas sandstone in the cross plot.

Keywords: Contour mapping; Hydrocarbon bearing zones; Lower Goru formation; Petrophysical analysis; Rock physics; Seismic attributes; Seismic data interpretation.