Improving Tight Gas Recovery from Multi-pressure System During Commingled Production: An Experimental Investigation

Abstract

Commingled production has been widely used as an efficient production method in gas field. However, the interlayer interference of gas flow seriously restricts the improvement of gas recovery. Presently, there are several investigations on commingled production characteristics of multi-pressure system gas reservoirs, but no corresponding improved production methods have been proposed. In this study, commingled production characteristics were studied by conducting simultaneous production (simultaneously opening all gas layers for production) simulation experiments. Subsequently, the mechanism of eliminating interlayer interference was revealed by conducting progressive production (progressively opening each gas layer for production) simulation experiments. Then, the effect of interlayer pressure difference on the gas recovery was studied to evaluate the improvement effect of gas recovery. Finally, the effects of initial temperature and pressure on gas recovery were explored to judge the applicability of the progressive production. All experiments were conducted with full-diameter cores of tight sandstone under conditions of temperature, pressure and gas–water saturation similar to those of the actual reservoirs. Experimental results showed that the gas produced by the high-pressure layer may flow back to the low-pressure layer through the interconnected pipeline at outlet end, thereby inhibiting the production capacity of the low-pressure layer and the gas recovery during commingled production. The progressive production method effectively avoids the occurrence of backflow, reduces the effect of interlayer interference, balances the production contribution ratio of different layers and improves the total gas production and recovery efficiency. The progressive production can improve the gas recovery of all gas layers; however, the improvement effect on the low-pressure layer is much better than on the high-pressure layer. The gas recovery from the low-pressure layer to the high-pressure layer increased by 2.62%, 2.23%, 1.41% and 1.23%, respectively. The increase in interlayer pressure difference can intensify interlayer interference and reduce the gas recovery of both simultaneous and progressive production. However, the greater the interlayer pressure difference (2, 3 and 4 MPa), the better the improvement effect of the progressive production in gas recovery (2.04%, 2.66% and 3.61%). The progressive production is effective for multi-pressure system with different initial temperatures and pressures.