Shale oil exploration from paleocene-early eocene sequence in Cambay Rift Basin, India

Abstract

Shale gas and oil constitute an important unconventional resource of hydrocarbons stored in organic rich, matured fine grained sedimentary rock. The organic rich source rock, on deep burial, results in conversion of organic matter into oil and natural gas. A major part of the hydrocarbons is expelled, migrated and entrapped in ideal locales constituting conventional accumulations in the basin. The residual quantities retained within the original source rock constitute the unconventional shale gas and oil plays. The gas and oil in shale are held as free hydrocarbons within natural fractures, pore spaces and some gas are stored as adsorbed gas on the organic matter. The shale, characterized by low matrix permeability, requires hydrofracturing for shale gas and oil production. A pilot Shale gas and oil well (Well-X) is drilled in Broach-Jambusar block of Cenozoic Cambay Petroliferous basin is drilled and extensive core has been collected in the Cambay Shale section of Paleocene-early Eocene age. Detailed shale specific geological, minerological, geochemical, petrophysical, geomechanical, desorption and adsorption isotherm studies etc are carried out and are synthesized for prospect evaluation.The Cambay Shale is moderately fissile, silty with presence of occasional fractures. The average Total Organic Content (TOC) is around 2.9wt%. The shale is characterized by high clay (kaolinite and chamosite) content of around 55%with average quartz content around 29%.The shale resistivity is 1.5-4.0 ohm-m. Based on integrated analysis, a zone of 60 m was hydrofractured and it yielded oil (API gravity: 40.0).Transgressive- Regressive cycle analysis of the shale section has been attempted for better understanding of the unconventional plays.