Mass balance of generation, retention, and production for the Wolfcamp-sourced hydrocarbon in the Permian Delaware Basin: Insight on remaining recoverable resource and expulsion efficiency

Abstract

Detailed quantification of basin-wide hydrocarbon (HC) masses from generation to production is necessary for a quantitative petroleum system analysis, and ultimately, for accurate resource estimation. Such quantified HC masses must be balanced following the fundamental laws of mass conservation. Mass balance is particularly important for unconventional-conventional petroleum systems in which expulsion efficiency (EE) is a critical parameter defining HCs in place, within the source rock (SR) interval and outside. This study performs an HC mass balance assessment aiming primarily to obtain insights on the remaining recoverable and EE, applied to the Wolfcamp Formation (Fm) in the Permian Delaware Basin. Calculated generated HC volumes from the Wolfcamp Fm based on the assumed 3D geologic model and p90/50/10 SR properties are 878/2107/4514 billion barrels of oil equivalent (BBOE). The mass balance is performed with three calculation scenarios: (1) inversion of EE (based on the United States Geological Survey [USGS]-estimated remaining recoverable HC in the Wolfcamp Fm), (2) forward calculation with multiple assumed EE, and (3) HC expulsion simulation. The mass balance with the inversion of EE indicates that the p90/50/10 of 58%/62%/69% overall EE is required for the Wolfcamp Fm to achieve the USGS-estimated remaining recoverable HC of 35/78/140 BBOE. Both mass balance with forward calculation and expulsion simulation predict overall lower p90/50/10 EE of 50% and 30%/56%/75%, respectively, thus resulting in higher than the USGS-estimated remaining recoverable HC in the Wolfcamp Fm in most scenarios. All of the mass balance calculations are also consistent with the interpretation of Wolfcamp unconventional play as a self-sourced play. This workflow is an efficient tool for taking a quantitative look at the petroleum system, especially related to the possibilities of generated HC distribution in the system. The calculated mass balance can serve as a reference in modeling unconventional systems and resources.