Dennis R. Prezbindowski¹, Jennifer L. Beall¹, Stewart D. Griest¹, Michael W. Waite²
(1) Texaco, Houston, TX
(2) Saudi Arabian Texaco, Kuwait

Abstract: Reservoir Development in Giant Ratawi Oolite Fields (Lower Cretaceous), PNZ, Saudi Arabia and Kuwait

The Lower Cretaceous Ratawi Oolite is a prolific limestone in the Partitioned Neutral Zone, located between the Kingdom of Saudi Arabia and the State of Kuwait. It is productive in the giant Wafra and South Umm Gudair fields with over a billion barrels of cumulative oil production. The Ratawi Oolite is composed of stacked, shallowing upwards, carbonate cycles deposited on a broad, shallow platform. Reservoir porosity consists of primary and secondary pores developed in heterogeneous skeletal/peloidal grainstones, packstones and wackestones. Reservoir porosities and permeabilities range from 18 to 25 percent and 10’s of millidarcies to more than a darcy, respectively. Reservoir studies, 3-D and 2-D seismic interpretation and exploration experiences indicate that reservoir potential in the Ratawi is dependent on structure. Ratawi depositional facies patterns, as well as secondary porosity overprints, are related to paleotopography and relative sea level changes. Grain-dominated (high primary porosity) facies were deposited in association with paleotopographic highs. Sediments deposited off the flanks of structures are muddier, with little primary macro porosity developed. Paleotopographic highs consist of anticlines formed over basement fault blocks. These structures developed prior to Ratawi deposition, as demonstrated by the onlapping relationship of the Sulaiy and Ratawi sediments. The same structural elements grew intermittently throughout the Mesozoic-Tertiary to form the prominent structures trapping hydrocarbons today at Wafra and South Umm Gudair Fields. Recognition of the dynamic relationship between carbonate deposition, relative changes in sea level, structurally influenced paleotopography and reservoir development in the Ratawi Oolite are important in enhancing future exploration success.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana