Abstract: Petroleum Geology and Sequence Stratigraphy of the Upper Jurassic - Mid Cretaceous Goru - Sembar play in Pakistan and Rajasthan (India)

Copestake, P.; Slatford, M.; and Blakeley, I. - IEDS Ltd.

In the Indus region of Pakistan, the main proven reserves had been thought to reside in Lower Tertiary carbonate reservoirs, until the Lower Cretaceous Goru Formation sandstone play was discovered by Union Texas' Lower Indus Basin Khaskeli #1 in 1981. By 1997 the operator had made a total of 49 Lower Goru - Sembar discoveries in the area. State company OGDC has also had success in the play just to the north with discoveries such as Bobi #1 (1988).

Extension of the play northwards into the Middle Indus Basin was proven with Lasmo's Kadanwari #1 Lower Goru gas discovery in 1989, which has since been followed by several other gas discoveries including OMV's early 1998 Sawan #1, which is the largest gas discovery in the Lower Goru to date, with reserves estimated in excess of 1 TCF.

Across the Indian border to the east, in the Jaisalmer Basin (Rajasthan), hydrocarbons had been known in Lower Cretaceous reservoirs since ONGC had drilled Khara Tar #1 in 1964, but were not proven in commercial quantities until Oil India discovered gas in the Pariwar Formation at Tanot (1988) and Dandewala (1989).

The present study was undertaken to provide a regionally unified understanding and mapping of these occurrences, utilizing a database of 58 wells tied to a regional seismic grid (13,000km 2D).

The reservoir interval has been subdivided into 15 genetic sequences/subsequences, ranging from Berriasian to Turonian in age. Biostratigraphy was used to subdivide and correlate the sequences, tied to a well based sequence evaluation incorporating geochemistry and sedimentological data.

Deposition of the reservoir sandstones and interbedded source rocks took place in a passive margin region formed during the rifting of the Indian plate from the eastern margin of Africa during the break up of Gondwanaland. Deposition of a series of major offlapping fluvio-deltaic wedges was initiated in the earliest Cretaceous (Berriasian), at the base of Sequence 2, at a time of major basin expansion possibly equating to the final split of India/Madagascar from Africa.

Play fairway analysis subdivides the overall package into three main play groupings (Sequences 1 - 3, 4 - 6, 7 - 9), defined by effective major regional topseals which occur at maximum flooding surface condensed sections above regressive reservoir units. Main reservoirs occur in Sequences 4 to 6 and are primarily of fluvio-deltaic origin. Source rocks are present in six sequences (2 to 7), from a kerogen of mixed terrestrial and algal origin.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil