Depleted-State Interwell Pressure Communication in a Stacked Shale-Oil Pad: Passive Pressure Monitoring and Controlled Fracture-Representation Tests

Summary

Development of stacked shale-oil pads increasingly depends on how depletion propagates between wells and vertically adjacent landing intervals, yet interference is still commonly interpreted at the well or pad scale. For this study, we used an instrumented pilot within the Qingcheng hydraulic fracturing test site (HFTS), where two producers are bracketed by two shut-in monitoring wells equipped with downhole gauges, to resolve depleted-state interwell pressure communication at the monitoring-system scale. The data set comprises nine monitoring systems, including six isolated systems in Monitor A and three systems in Monitor B. Core and borehole observations show clustered hydraulic fractures and widespread bedding-parallel discontinuities in the monitored interval. The passive pressure responses, acquired about 18 months after production onset, were characterized with direct observational descriptors. Total pressure declines span 0.3–3.8 MPa across the nine systems over about 200 days. A 23-day shut-in and restart of one producer, together with wellbore operations and late rate reductions, produced responses within about a day to a few weeks in some systems and no resolvable response in others. At the current well configuration, some intervals already operate in a clear interwell pressure-communication regime, whereas others remain closer to local depletion behavior. A calibrated numerical model of the monitored study area with core-constrained stage-scale fracture counts is then used in controlled fracture-representation tests. A single-equivalent-fracture representation underpredicts the delayed cycle-sensitive response. Stage-scale multifracture geometry improves the matches, but in the fixed-parameter subtractive tests, it does not reproduce that response while preserving the weak-response behavior. Within the tested model family and parameterization, the most consistent matches are obtained when a limited set of laterally continuous, weakly conductive, and pressure-sensitive bedding-parallel pathways is included. In this study, we provide a field workflow that links direct fracture evidence, passive pressure monitoring, and controlled fracture-representation tests, which show that interwell pressure communication alone is not a sufficient indicator of effective drainage in spacing and interference decisions for stacked shale-oil development.