Victoria L. French¹
(1) Texaco Exploration and Production, Inc, Midland, TX

Abstract: The predictive relationship of productive San Andres carbonate shoal bodies as determined from outcrop and subsurface study

The West Jordan unit, located along the eastern margin of the Central Basin platform (CBP) in west Texas, provides an excellent subsurface example substantiating the predictive nature of compartmentalized reservoir zones documented within equivalent San Andres shoal facies in outcrop. Detailed reservoir characterization of the productive West Jordan area has determined that primary reservoir intervals are comprised of isolated carbonate shoal/barrier bar facies, which are separated by a series of lower permeability intershoal deposits. The distribution of shoal and intershoal facies results in considerable reservoir compartmentalization that is closely associated with productive and nonproductive areas within the reservoir as indicated by cumulative production data. Chronostratigraphic study of equivalent outcropping strata has established the effect of accommodation space and resulting depositional environments to the overall geometry developed within these shoal bodies.

Recent outcrop study along the Algerita Escarpment and Guadalupe Mountains of eastern New Mexico and west Texas has demonstrated a relationship between sequence hierarchy and facies architecture resulting from varying accommodation space. This model can be utilized to enhance reservoir predictability in the subsurface. Chronostratigraphic relationships along the outcrop illustrate that considerable variations occur within depositional environments and shoal body geometries as a result of changing accommodation conditions during eustatic sea level fluctuations.

The quantification of shoal geometries within the West Jordan unit further substantiates the predictive nature of these shoal bodies. Understanding controls on shoal development is a valuable predictive tool for similar fields along the CBP, which lack the core and well control to adequately map these facies resulting in significant reservoir compartmentalization.

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