Shale Gas Potential of Lower Cretaceous Sembar Formation in Middle and Lower Indus Basin, Pakistan

  • Nazir Ahmad
  • Javed Mateen
  • Kashif Shehzad Chaudry
  • Nasar Mehmood
  • Fahad Arif

Abstract

Natural gas production from tight shale formations, known as “shale gas”, has become an important source of natural gas in the world due to technological advances and rapid increases in natural gas prices as a result of significant supply and demand pressures. Pakistan is facing big challenges in meeting its ever growing energy needs due to expanding population and economic growth. It is necessary to exploit unconventional energy resources along with conventional ones to meet the country energy requirement. Here, we investigate shale gas potential of Lower Cretaceous Sembar Formation within a large area of Middle and Lower Indus Sub-basins. The study includes the organic richness, hydrocarbon generative potential, shale thickness and distribution, subsurface depth of studied interval, maturity, volume of hydrocarbon generated and retained per section and reservoir characteristics of Sembar shales. Geochemical data show that the TOC of the formation range from 0.55 wt. % to 9.48 wt. % with present day generation potential of 0.14 to 18.69 mg HC/g rock. The average TOC of immature samples is 1.0 wt.% with generation potential of 2.88 mg HC/g rock and hydrogen index (HI) of 240mgHC/g TOC(type III and II/III). Gross thickness of the formation ranges from less than 50mto more than 1000mwith an average of 300min the study area. Subsurface depth (top of the formation) varies between 1000mto 5000min platforms to foredeep areas. Overburden thickness, geothermal gradient, Tmax and Vitrinite Reflectance data place the formation in oil, wet and dry gas windows at the depths of 2500 m, 3200m and 3400mrespectively. Based on original generation potential and average source rock thickness, volume of generated hydrocarbon (gas equivalent) is 242 bcf/section. By taking expulsion (50% of the generated volume) into account and conversion of retained oil into gas through secondary cracking, the retained volume is 103 bcf/section. Average porosity of the formation at reservoir level (3400mto 4000 m) is 6.0%. Mineralogically, the formation is composed an average of 42% quartz, 47% clay, 10% calcite and 1% pyrite. Depth for shale gas exploitation in platform areas is about 3500 m, where as in foldbelt regions, it varies between 1000mto 3000 m.

Published
2013-06-01
Section
Articles