非线性渗流对低渗气藏采收率的影响

Effect of nonlinear percolation on recovery factor of low permeability gas reservoirs

低渗透气藏开发过程中普遍存在非线性渗流,研究非线性渗流对采收率影响对于合理开发此类气藏具有一定意义。选取塔里木某低渗透气藏的岩心开展不同渗透率和含水饱和度条件下的非线性渗流实验,实验表明低渗透气藏存在启动压力梯度和较强的应力敏感性。渗透率越低、含水饱和度越高,启动压力梯度越大,应力敏感性越强,非线性渗流特征越明显。非线性渗流对低渗透气藏采收率有较大影响。启动压力梯度越大、应力敏感性越强的气藏,最终地层废弃压力越高,采收率越低。在低渗透气藏开发部署时,尽量寻找较高渗透率和较低含水饱和度的储层,优先开发。同时,井网加密调整、储层改造、降低含水饱和度也是提高低渗透气藏采收率的有效途径。

Non-linear seepage generally exists in the development of low permeability gas reservoirs. It is meaningful to study the effect of non-linear seepage on recovery factors for reasonably exploiting these low permeability gas reservoirs. Cores from the Tarim gas field are adopted and non-linear seepage experiments are conducted under different permeabilities and different water saturations. The experiment results show that low permeability gas reservoirs exhibit a start- up pressure gradient and strong stress sensitivity. The lower the permeability and the higher the water saturation, the larger the start-up pressure gradient, the stronger the stress sensitivity, and the more obvious the non-linear seepage behavior. Non-linear seepage impacts the recovery factor of low permeability gas reservoirs strongly. With the increase of start-up pressure gradient and stress sensitivity, the abandonment pressure of the gas field rises, and the recovery factor declines. During the development and deployment of low permeability gas reservoirs, the area with high permeability and low water saturation should be exploited firstly. Furthermore, well pattern infilling, reservoir stimulation and reducing water saturation are the effective methods to improve the recovery factor of low permeability reservoirs.