Interlayer Crossflow Behavior in Vertically Heterogeneous Edge-Water Gas Reservoirs

To address the challenges of nonuniform water invasion fronts and complex interlayer interference during the development of vertically heterogeneous edge-water gas reservoirs, this study integrates laboratory experiments with numerical simulations. First, a depletion experiment under edge-water drive was conducted using a self-developed large-scale 2D physical model operating under high-temperature and high-pressure conditions, equipped with a nonintrusive acoustic-electrical monitoring system. Based on the experimentally obtained dynamic pressure and fluid production data, a quantitative characterization method for interlayer crossflow that accounts for dynamic water saturation was established. Subsequently, a numerical model, rigorously calibrated through history matching, was employed to systematically examine the effects of aquifer size, production rate, and reservoir sequence on water invasion behaviors and crossflow characteristics. The results indicate that (1) the large-scale physical experiment confirmed that the high-permeability layer serves as a preferential flow path for edge water invasion. After water breakthrough occurred in this layer, the gas production rate dropped sharply while water production surged, precipitating drastic variations in interlayer and intralayer pressure differentials. Interlayer crossflow persists throughout the development process, primarily characterized by gas recharging from the medium- and low-permeability layers into the high-permeability layer. Quantitative calculations normalized to the total reservoir hydrocarbon pore volume (HCPV) reveal that the high-permeability layer (K3) acted as a macroscopic gas sink, receiving a cumulative gas influx equivalent to 22.35% of the total HCPV. Concurrently, the low-permeability (K1) and medium-permeability (K2) layers supplied this crossflow, experiencing gas outflows representing 11.58% and 10.76% of the total HCPV, respectively. (2) Numerical studies show that a larger aquifer size results in a faster water invasion velocity, earlier water breakthrough, a shorter water-free production period, and a lower recovery degree, while the intensity of interlayer crossflow is relatively weakened due to the rapid pressure maintenance in the high-permeability layer. Conversely, a lower production rate extends the water-free production period, delays water breakthrough, intensifies interlayer crossflow, and leads to a higher recovery degree. Reservoir sequence significantly dictates the water invasion pattern and sweep efficiency. In Fining-upward Sequence reservoirs (characterized by high permeability at the bottom), edge water preferentially fingers through the bottom high-permeability layer, whereas Coarsening-upward Sequence reservoirs are prone to top-water fingering. This study quantifies the gas–water two-phase interlayer interference mechanism under heterogeneous conditions. Furthermore, based on the numerical model calibrated by history matching, the effects of aquifer size, production rate, and reservoir sequence on development performance are systematically investigated. The methodologies and findings of this work provide effective tools for predicting water invasion behaviors, thereby offering a theoretical basis for the efficient development of vertically heterogeneous edge-water gas reservoirs.