Though economically rewarding the Upper Jurassic Cotton Valley Lime (CVL) Reef play of East Texas challenges exploration strategies and drilling technologies. CVL buildups underlie a thick Bossier Shale section; reef penetrations are as deep as 17,000 ft. and overpressured to 16,000 psi. Consequently, coring is risky and recovery has been minimal. However, well cuttings are usually available and valuable in constructing a sequence stratigraphic framework in which to evaluate reef occurrence, distribution, and temporal-spacial relationships. Information from reef and non-reef cuttings was compiled to create descriptive lithology logs which were integrated with open hole logs. The combined data was used to establish diagnostic criteria for recognizing, and ultimately predicting depositional facies (e.g. reef, reef flank, off-reef, and shoal).

This study demonstrates the value of well cuttings for enhancement and verification of stratigraphic correlations, expansion of regional play concepts, and refinement of depositional models. Although interpretations are limited by the quality and nature of cuttings, the incorporation of this type of data has contributed to understanding controls on distribution, composition, and reservoir characteristics of various reef types, and in evaluating facies, fabrics, diagenesis, and porosity in individual wells/buildups.

Porosity development (primary and secondary microporosity, and secondary dissolution porosity) in CVL buildups is controlled primarily by facies composition and presence or absence of framework and binding organisms. By making thin sections on CVL drillsites, Sonat has been able to make real time qualitative estimates of productivity in individual buildups. The Sonat Mobil Evaluation Lab (SMEL) is used to facilitate on-site grain and depositional facies identification for early detection of buildup facies and to insure complete penetration of reefal buildups.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah