裂缝性低渗气藏水平井不稳定产量递减探讨

针对气体在低渗储层中低速流动时存在启动压力梯度的问题，开展了渗流模型建立、求解及定性分析研究。采用低速非达西渗流机理，建立了考虑启动压力梯度的裂缝性低渗气藏水平井不稳定渗流模型，求解了数学模型并绘制了水平井产量递减典型曲线。该渗流模型最终求取的是定压生产条件下低渗气井的不稳定产量解，为采用图版拟合法评价储层参数提供了理论依据。启动压力梯度等相关参数对递减曲线的影响分析表明，启动压力梯度越大、储层物性越差，流动越困难，水平井产量越低，产量递减曲线位置越低；弹性储容比越小，基质窜流发生越早，产量导数曲线上的下凹部分持续时间越长，下凹程度越深；窜流系数越小，产量导数曲线上的下凹部分出现时间越晚，窜流越难发生。

Investigation of Unstable Production Decline in Fractured Low-Permeability Gas Reservoir Horizontal Wells

With respect to the problem of starting pressure gradients during the low-speed flow of a gas from low-permeability gas reservoirs, a flow model was constructed, solved, and qualitatively analyzed. Using a low-speed non-Darcy flow mechanism, a model of the unstable flow in fractured low-permeability gas reservoir horizontal wells was constructed with the starting pressure gradient taken into account. The mathematical model was solved and a typical curve of production decline in the horizontal wells was plotted. The last solution of this flow model, that is, the unstable production of low-permeability gas wells under constant pressure production conditions was used to provide the theoretical basis for the use of graph fitting methods to assess the reservoir parameters. Analysis of the effects of the starting pressure gradients and other related parameters on the production- decline curve showed that as the starting pressure gradient increased, the storage properties became poorer, the flow became more difficult, the horizontal well production decreased, and the production decline curve shifted downward. With the decrease in the elastic storage ratio, the matrix channeling occurred earlier, the concave down portion of the production derivative curve increased in duration, and the degree of the downward concavity increased. When the channeling coefficient decreased, the concave down portion of the production-derivative curve shifted later and the channeling occurred less easily.