Hydrocarbon Prospectivity in the Stratigraphic Traps within Cambay Shale, Broach Sub Block, Cambay Basin, India
Broach sub block lies in between Mahisagar and Narmada river of South Cambay Basin.Gandhar and Jambusar are the two prolific oil and gas producing fields in this block. Most of the discovered oil was found in Hazad sands of Middle to Upper Eocene age.But some oil was also produced from the sands within Cambay Shale formation of Paleocene to Early Eocene. An attempt has been made to predict the hydrocarbon distribution and prospectivity of thesesands.An analogy was inferred from Linch sands in North Cambay basin.
The Cambay shale was deposited during Paleocene to Early Eocene. Five to twelve layers of dirty, partly lithic sands are present in the Cambay shale and have been considered as potential exploration target for petroleum exploration. The Cambay Shale is having maximum thickness of approx 2800 m in N-S oriented Tankari depression which is 8 km wide and is the main kitchen for hydrocarbon generation.The formation progressively pinch out on both sides of the depression. On the eastern margin Cambay shale pinches out and shows a progressive onlap.On the western margin which corresponds to present day Gulfof Cambay,Hazad transgresses the Olpad formation which is observed in one of the well.A methodology was adopted to critically examine the well data, seismic data,depositional environment,thickness distribution of Cambay Shale and the sand provenance.
Based on the studies carried out,it is envisaged that Cambay shale was deposited during major marine transgression and the sand within it,under short regressive cycles.The seismic events correspond to this unit shows high amplitude reflections. This unit is penetrated in one of the wells in the Nada area and its encountered number of hydrocarbon shows. The main depositional lobe is present in the western edge of the block, close to the present day shoreline.In the Malpur,Barkhodra,Nada area,two wells had shown oil and gas indications.
The potential hydrocarbon target are high amplitude events which comprises of sand and shale alternations.These sands occurs as pinch out in northwestern and southeastern flank of Tankari low.The paleoriver system in the NE of the area played and important role in bringing the sediments along pre existing paleozoic or older faults.The number of prolific sands present in the Cambay shale are well within the oil window with insitu entrapment conditions and can be targeted for hydrocarbon exploration.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009