Sand Production Mechanisms in Sandstone Gas Reservoirs during Cyclic Injection-Production with Variable Water...

Formation water is common when using depleted reservoirs to build underground gas storage, which causes serious sand production problems during the periodic injection-production operation of natural gas. Current research focuses on the sand production of the reservoir in the single-phase case. Little attention is paid to the sand production caused by injection and production in water-bearing reservoirs. To fill this gap, this study reveals the sand production mechanism of reservoir rocks under two-phase flow conditions using alternating displacement. The critical sand production pressure difference of the core under different water saturations was first experimentally measured and compared with the results under single-phase flow conditions. Results show that the critical sanding pressure difference of water-bearing cores is generally higher than that of dry cores. Then, the impacts of water saturation on sand production during cyclic injection-production in sandstone gas storage were experimentally evaluated as well. The sand production shows a nonmonotonic trend of increasing first and then decreasing when the water saturation is 0%-85%, with a peak at 30% water saturation. Experiments also show that the change of sand production is controlled by the number of alternating displacement cycles. Within the range of 15-30 alternations, the growth rate of core permeability and sand production decelerates. Beyond 30 alternations, a notable increment is observed with further increases in alternations. This research finding has significant value for the construction and operation of gas storage facilities in water-bearing sandstone reservoirs.