Summary

During the appraisal phase of a shale play it is critical that appraisal wells are representative of the target formation, and that well productivity is not impacted by localized features which do not represent the majority of the acreage position. This paper discusses a case study set in the Permian Basin in which thirteen Wolfcamp shale wells were drilled in an ∼30 sq. mi study area. Several of these wells were in fact determined not to be representative of typical Wolfcamp Shale well performance. Using this well set we will discuss the impact a fault and its associated deformation zone had on well performance. 3D seismic, microseismic, image logs, chemical tracers, water geochemistry, and production data were all integrated in this study and will be used to demonstrate the findings.

Using coherence and curvature attributes extracted from 3D seismic volumes, a lineament was mapped and interpreted as a right-lateral strike-slip fault, terminating in a horsetail splay. Natural fracture occurrence, interpreted from horizontal well image logs, correlates with these structural features. Average fracture density calculated for nine horizontal wells increases systematically towards the fault. Further, a meaningful correlation was established between average fracture density for each well and the production data. The correlation between average fracture density and oil production remained positive up to a point, above which production rates declined markedly. Using these two relationships, production rates in the additional wells, which did not have image log data, were predicted successfully.

The two wells drilled in close proximity to the fault demonstrated significantly higher water production and water-oil-ratios. Oil production from these two wells underperforms the peers in the study area. Both wells were drilled in a north to south direction, parallel to the major fault. Microseismic events adjacent to the fault line-up with the synthetic fault splays and display increased event magnitude. Water-based chemical tracers indicate higher water production rates from the intensely fractured splay region while water geochemistry shows a distinct signature that is attributed to the fault zone. This signature is discrete from offset wells which are further from the fault system. These findings have provided an explanation for the anomalous performance of these two wells and given guidance to the required fault offset in the field development plan.

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