Dynamic-To-Static Permeability Ratio Provides Valuable Insights of Reservoir Architecture and Heterogeneity in Complex Hydraulically Fractured Reservoirs

Matrix permeability is a key parameter to predict reservoir deliverability and ultimate recovery in tight gas reservoirs. Since it is a multiscale property, its values can significantly change with the scale of the medium under investigation. Well-log evaluation and core measurements provide pore- to meter-scale static measurements exclusively representative of the borehole vicinity, whereas well testing provides kilometer-scale dynamic permeability under multiple assumptions such as rock and fluid properties. This paper demonstrates how discrepancies between static and dynamic calculations of reservoir permeability present an opportunity to validate models of reservoir quality and lateral connectivity away from boreholes. The lack of a simple relationship between static and dynamic permeability is a valuable observation to help understand reservoir architecture and to promote multidisciplinary integration. The process starts with the assessment of static permeability (at the borehole); we used extensive sedimentary and petrographic data to quantify the effects of depositional facies, mineral composition, and diagenetic overprint on porosity-permeability functions. This permeability model was compared to machine-learning (ML) permeability calculated from wireline logs to provide additional consistency checks and coverage in areas where core was unavailable. Absolute permeabilities were converted to effective permeability using unsteady-state relative permeability testing. The primary source of dynamic permeability is pressure transient analysis (PTA) from pressure buildup tests in shut-in wells. Over 20 wells with tests achieving radial flow provided validation for gas-effective permeability thickness. Since PTA does not densely cover the field, we used rate transient analysis (RTA) from over a 100 wells to derive a pseudo-PTA permeability. This approach included the calculation of original gas in place (OGIP), which is the most reliable parameter from RTA, using a flowing material balance (FMB) and then corroborated results by type curve analysis. We finally derived correlations between PTA-derived permeability and RTA-derived OGIP as an additional proxy for dynamic permeability in wells with more than 6 months of production. The ratio between dynamic and static permeability provides valuable insights into reservoir architecture and heterogeneity away from boreholes. Ratios below unity reflect the preservation of interbedded thin mudstones, which provided silica to occlude pore space and throats of nearby sandstones with quartz cement during diagenesis. Mudstones and cemented sandstone shoulders provide additional tortuosity that greatly reduces connected gas volumes identified by transient analysis. Ratios above unity represent fewer preserved mudstone layers and overall better sandstone quality; even though the sandstone thickness can be lower, the dynamic permeability and connected volumes are consistently larger. Lower gross thickness is associated with less accommodation space in the proximity of basement highs. This setting promoted the removal of interbedded mudstones (and associated damaging effects on reservoirs) and boosted reservoir lateral connectivity. The understanding of dynamic and static permeability ratios and their linkage to the diagenetic overprint on depositional architecture contribute to identifying undeveloped resources (i.e., infill drilling) as well as better prediction of initial reservoir performance in new wells.