缝洞型底水气藏水平井水侵动态数学模型与影响因素研究

Research of Mathematical Model and Influencing Factors of Water Invasion Performance for Horizontal Well in Fractured-vuggy Gas Reservoirs with Bottom Water

在含有底水的气藏开发过程中,随着气体的采出,气井井底压力逐渐降低,底水会发生向上锥进的现象,严重影响产气。因此若能预先求得气井水侵动态,这对于开发底水气藏具有重要的意义。同时,与常规底水气藏不同,缝洞型底水气藏呈现出三重介质的特性,溶洞和天然裂缝较发育,其非均质性较强,气体渗流的过程更为复杂。通过采用渗透率变异处理储层中裂缝、溶洞的发育,考虑到裂缝和溶洞的存在仅改变了储集层的渗透率,同时在均质底水气藏水平井水锥动态计算方法的基础上,利用渗透率变异理论建立了缝洞型底水气藏临界产量和水锥突破时间公式,并对其影响因素进行了分析。根据所得公式可以近似求解缝洞型底水气藏中水平井的临界产量、见水时间以及见水位置,可用来指导实际缝洞型储层水平井的合理开发,延缓开发过程中底水锥进,延长见水时间,同时还可以确定见水位置为后续压锥及堵水调剖的实施提供依据。通过建立的数值模拟模型以及实际生产数据,验证了本方法研究的可靠性,数值模拟结果从直观上展示了缝洞型底水气藏水平井水锥研究的正确性。

In the development process of gas reservoirs with bottom water, water coning up is easy to happen with the production of gas and well bottom pressure decreasing, which has a strong impact on gas production rate. So if water invasion performance can be predicted in advance, that really has important meaning to develop gas reservoirs with bottom water. Meanwhile, comparing with conventional gas reservoirs with bottom water, fractured-vuggy gas reservoirs with bottom water have the characteristic of triple porosity, fractures and vugs are developed resulting in high heterogeneity and the seepage process of gas is more complex. According to using the permeability variation to deal with the development of fractures and vugs in fractured-vuggy gas reservoirs with bottom water, the absence of fractures and rugs just changes the reservoir＇s permeability. What＇s more, on the base of the horizontal well bottom water coning performance in the single-porosity reservoir, the critical rate equation and the water breakthrough time equation are established in the use of the permeability variation theory, with their influencing factors analyzed. These equations obtained can be used to calculate the critical rate and the water breakthrough time of the horizontal well and to predict the water breakthrough position of fractured-vuggy gas reservoirs with bottom water, which can guide the development of field fractured-vuggy gas res- ervoirs with bottom water and determine reasonable gas production rate and prolong the water breakthrough time and then guide the implement of follow-up water shutoff and profile control method. The established numerical simulation model and the actual production data verify that the method is reliable and the numerical simulation result directly shows the right of the water coning up study in fractured-vuggy gas reservoirs with bottom water.