Evaluating Carbonates Embedded in Anhydrites to Identify Better Reservoir Sections: A Case Study

Abstract

The Gotnia and Hith formations in the State of Kuwait were deposited in an intrashelf basin and they are characterized by regionally widespread deposition of cyclic evaporites. These consist of alternating halite and anhydrite-limestone units. The anhydrite is mostly interbeded with fossiliferous, argillaceous limestones and is exploratory target. The success of one well drilled to test the potential of these carbonates have confirmed the existence of good reservoirs associated with them. A study was done in the onshore part to assess the potential of these carbonate reservoirs. The major play elements for exploration of these carbonate bands were studied as a pre-cursor to increased exploratory activity. The challenges associated with the high pressure and high temperature environment of these formations has led to non-availability of open hole logs. The paucity of well data therefore puts more emphasis on optimum use of the seismic data. Effort has been made to integrate the available data with seismics to identify high priority areas. These carbonates may act as self charging hydrocarbon system or as good reservoirs holding hydrocarbons migrating from the nearest sources. The major source underlying Gotnia is Najmah Shale and the one overlying Hith is Basal Makhul Shale within regionally named “Sulay” formation. The objective of the present work was therefore, to identify the places where carbonates with better reservoir properties exist and also have the possibility of being charged through faults connected to the nearest sources. The amplitude based attributes coupled with impedance were used to identify the areas of better reservoir development. Various discontinuity attributes were studied to look for the faults that were likely to connect the reservoir sections with the sources. Mathematical blending of seismic attributes was also used successfully to enhance the visibility of the discontinuities. The fractures are likely to be better developed along the faults. Therefore accurate fault delineation helped in identifying areas of higher fracture densities. Ant tacking was used on different volumes to identify subtle discontinuities and the higher density of discontinuities was interpreted as the indicator of fracture corridors. All these elements were later integrated and “Lead Areas” were identified for further studies to generate prospects.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015