New Model for Halokinetically Controlled Patch Reef Systems: A Case Study From the Fairway Field, a Major Aptian Reservoir in the East Texas Basin
The Fairway field is a major (410 MMbbl) Aptian reservoir in the East Texas Basin that produces from a James Limestone reef complex. It contains a complex mosaic of reefs, reef-derived grainstones, shallow subtidal packstones/wackestones, and oyster/rudist biostromes. Facies prediction is limited because of significant lateral and vertical heterogeneity characteristic of reef systems. Previous attempts at characterizations of the Fairway field have not fully considered the effect of eustatic fluctuations, antecedent topography, concurrent halokinesis, and resultant changes in depositional environment. This work assesses facies progressions from a sequence stratigraphic perspective, placing emphasis on syndepositional halokinetic movements in modifying the generalized south-facing shelf model. Reconstructing step-by-step depositional history improves predictive frameworks for reservoir facies in the Fairway field and other analogous halokinetically controlled reef systems (GOM, UAE, Iran) by providing context for lateral and vertical facies heterogeneity. Isopach maps of the Pearsall Fm reveal antecedent topography present at the onset of the James Limestone that filled by end of carbonate deposition. Strata thicken to the NW for all members of the Pearsall Fm, reflecting the development of a salt withdrawal basin associated with the breached La Rue diapir. Strata thin to the SW, SE, and NE in the Pine Island Shale and James Limestone. The Fairway field is centered over what was likely a NW-facing U-shaped embayment on the margin of a topographic high generated by uplift of the Brooks, Brushy Creek, and Boggy Creek salt pillows. Patch reefs initially grew within the embayment and around its margin, achieving greater vertical accretion on the edge adjacent to the basin and producing a system similar to that observed in modern atolls. During highstand, reefs contacted wave base and were eroded, filling the embayment with sediments that are now the primary reservoir facies. Salt pillow migration may have also contributed to reduction in accommodation. Later transgression resulted in deposition of low-energy, shallow shelf wackestones with chondrodont and rudist biostromes. In addition to highlighting the importance of antecedent topography and development of sequence stratigraphic frameworks, the Fairway field patch-reef complex is an excellent case study for understanding heterogeneity in a halokinetically controlled localized shoaling area on a broad shelf.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019