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TYLER, NOEL, Bureau of Economic Geology, University of Texas at Austin, Austin, TX

Abstract: Increasing Oil and Gas Recovery in Depositionally Complex Reservoirs

Reservoir architecture, the internal structure and interrelations of component facies that compose sandstone and carbonate reservoirs, plays a profound role in governing recovery from oil and gas reservoirs. Facies are the fundamental building blocks of reservoirs and as such either foster or hinder reservoir drainage, impart heterogeneity to the reservoir, and provide the flow units through which the reservoir drains. Reservoirs characterized by complex facies architecture are invariably inefficiently drained as a result of intrareservoir stratigraphic entrapment of recoverable hydrocarbons. These are the reservoirs in which reserve growth will be attained.

Mature, densely drilled fields in Texas are a magnificent natural laboratory to assess the magnitude and residency of the remaining oil and gas resource. Even in this highly drilled province, oil reservoirs on secondary production average only 40% recovery, and remaining bypassed and untapped mobile oil amounts to one-fifth of the original oil in place. In less densely drilled areas of the United States this remaining mobile oil resource is even higher.

It is estimated that between 80 and 100 billion barrels of movable oil will remain at abandonment in heterogeneous reservoirs in the United States. Innovative strategies, such as advanced reservoir imaging, drilling, and completion technologies, are being developed for successfully locating, and producing, this undrained nonresidual oil. However, critical to the successful deployment of any advanced recovery technology is the detailed knowledge of the internal architecture of the target reservoir. Furthermore, by identifying the geological distribution of moveable oil, a better understanding of the geological constraints on enhanced oil recovery is gained as well. Recent field redevelopment projects in Texas, the Gulf of Mexico, and South America emphasize the importance, and promise, of geologically targeted deployment of recovery technologies in mature, historically low- to moderate-recovery reservoirs. 

AAPG Search and Discovery Article #90922©1998-1999 AAPG International Distinguished Lectures