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Clastic Facies and Reservoir Characterization Through a Sequence Stratigraphic Production Decline Curve Analysis: Example Frio Formation, Jim Wells and Nueces Counties, South Texas


As petroleum fields mature, the initial information employed for their exploration is augmented and refined by the addition by improved spatial information, e.g. from additional borehole petrophysics, core, 4D seismic, etc. However, there is also substantial geologic information of value imbedded within the temporal data, specifically the production data itself. If integrated into a geologic perspective, these historic data can potentially optimize hydrocarbon extraction by generating infill drilling prospects or recompletions of previously bypassed, behind-pipe hydrocarbon-saturated zones. This study investigates the value of production decline curve analysis (PDCA) as one such ad posteriori tool for evaluating a relationship between reservoir elements and their associated depositional environments when coupled to a sequence stratigraphic partitioning of clastic fluvial-shallow marine reservoirs. For the past 80 years, the Oligocene-Miocene Frio Formation progradational wedge has continued to be a major oil and gas producer. While numerous regional geological and geophysical studies of this mature petroleum system have been conducted, less numerous are studies which can provide high-resolution reservoir characterization placed within a sequence stratigraphic approach. Characteristic petrophysical log motifs of 113 wells in the adjacent Captain Lucey and Richard King Fields of Jim Wells and Nueces counties correlated and constrained with biostratigraphy and the global sea level curve reveal the overprint of fourth order autocyclic processes of regression and transgression within a general third order allocyclic relative sea level fall. Five lowstand system tract reservoir sand environmental assemblages sealed by transgressive shale depositional environments in this part of the Frio wedge were identified: LST Delta 1, Delta Plain Distributaries, Distributary Crevasse Splay, TST Barrier Island, and LST-TST Delta 2. The Oligocen-Miocene Frio in these Jim Wells and Nueces county fields reveal on the overprint upon a slowly subsiding shelf of fourth order autocyclic processes of regression and transgression within a general third order allocyclic relative sea level fall. In particular, these results show strong relationships between PDCA and depositional environments in the Frio of South Texas. In general, results from this work point to the potential utility of PDCA depositional facies linkages as a reservoir performance predictor in fields elsewhere.