裂缝—孔隙型有水气藏水侵动态变化规律及关键参数计算方法

为了实现裂缝—孔隙型有水气藏的高效开发,需要掌握水侵的动态变化规律。为此,基于π定理,引入了反映水侵动态变化特征的无量纲参数进行水侵动态物理模拟实验方案设计;选取四川盆地川中地区某裂缝—孔隙型有水气藏储层全直径岩心开展水侵动态物理模拟实验,然后通过数值反演将实验结果转换为有水气藏水侵动态评价参数,进而研究裂缝—孔隙型有水气藏水侵动态变化规律,并建立水侵动态评价关键参数及水体体积的计算方法 ;在此基础上,以四川盆地中坝气田上三叠统须家河组二段气藏为例,进行水侵动态分析及水体规模评价。研究结果表明:①裂缝—孔隙型边、底水气藏水侵与产气同步发生,无水采气期井底压力与天然气采出程度呈线性关系,气藏产出地层水后水侵速度加快、水气比快速上升,最后趋于稳定的较高水气比;②无水采气期井底压降速率与稳定水气比主要受水体体积的影响,而单位压降气采出程度和稳定水气比又可用来评价水体体积;③建立了裂缝—孔隙型边、底水气藏无水采气期稳定单位压降气采出程度、稳定水气比与水体规模互相解释评价方法。结论认为:①气藏水侵生产动态曲线与岩心模拟水侵动态实验结果具有很好的一致性,根据已知的水体体积,可以预测无水采气期单位压降气采出程度、稳定水气比;依据稳定水气比,可以预测气藏水体体积,预测结果与生产动态具有很好的一致性;②该研究成果可以为裂缝—孔隙型有水气藏水侵动态预测和整体治水提供理论支撑。

Change laws of water invasion performance in fractured–porous water-bearing gas reservoirs and key parameter calculation methods

In order to develop fractured–porous water-bearing gas reservoirs efficiently, it is necessary to understand the change laws of water invasion performance. Based on the π theorem, this paper adopted the dimensionless parameter that can reflect the change characteristics of water invasion performance to design the physical simulation experimental scheme of water invasion performance. The full-diameter cores taken from the reservoir of one certain fractured–porous water-bearing gas reservoir in the central Sichuan Basin were selected to carry out physical simulation experiment of water invasion performance. Then, by virtue of numerical inversion, the experimental results were converted into evaluation parameters of water invasion performance in water-bearing gas reservoirs. Afterwards, the change laws of water invasion performance in fractured–porous water bearing gas reservoirs were investigated, and the method for calculating key water invasion performance evaluation parameters and aquifer volume was established. Finally, water invasion performance analysis and aquifer size evaluation were conducted with the gas reservoir in the second Member of Xujiahe Formation, Upper Triassic in the Zhongba Gasfield of the Sichuan Basin as an example. And the following research results are obtained. First, in fractured–porous gas reservoirs with edge and bottom water, water invasion and gas production occur simultaneously. Before water production, there is a linear relationship between bottomhole pressure and reserve recovery degree. After water production, water invasion speeds up and the water–gas ratio (WGR) rises rapidly and finally approaches to a stable WGR of higher level. Second, the bottom hole pressure drop rate before water production and the stable WGR are mainly affected by the aquifer volume, and the degree of reserve recovery per unit pressure drop and the stable WGR can be used to evaluate the aquifer volume. Third, a method for mutual interpretation and evaluation of the aquifer size and the reserve recovery degree per unit pressure drop before water production and the stable WGR of fractured–porous gas reservoirs with edge and bottom water is established. In conclusion, the water invasion performance curve of the gas reservoir agrees with the core simulation experimental results. Based on the known aquifer volume of a gas reservoir, the stable reserve recovery degree per unit pressure drop before water production and the stable WGR can be predicted; and on the basis of the stable WGR, the aquifer volume of a gas reservoir can be predicted. The prediction results are in line with the production performance, providing a theoretical support for water invasion performance prediction and overall water control of fractured–porous water-bearing gas reservoirs.