邻井干扰条件下的多井压力恢复试井分析方法

Pressure buildup analysis in multi-well systems under interferences from adjacent wells

储层渗透性高、井间连通性较好的气藏,其本质是一个多井系统,气藏投产后,测试井的压力恢复资料容易受邻井的影响,压力导数曲线在中晚期会出现明显的"下掉"或"上翘"特征。单井试井分析方法往往将此特征解释为边界的影响,不当的解释结果可能会对生产决策产生误导。为了正确认识多井连通储层的试井特征、甄别疑似边界特征,采用有效井径的概念,建立了无限大均质储层多井系统中测试井井底压力的动态模型,其中测试井考虑表皮效应和井筒储存效应,邻井不考虑表皮效应与井筒储存效应。通过Laplace变换方法,得到了Laplace空间下以Bessel函数表示的精确解,建立了邻井同时生产或同时关井这两种情形下的试井典型曲线图版,进而建立了相应的多井压力恢复试井分析方法。长期渐近解理论分析结果表明:1上述两种情形下,压力恢复导数曲线呈现台阶状上升特征,出现多个径向流水平线,每个水平线高度与第一个水平线高度的比值为测试井与产生影响邻井无量纲产量的代数和;2当邻井一直生产且对测试井产生干扰时,测试井压力恢复导数曲线在中后期呈现下掉特征。

Some gas reservoir has high permeability, and good interwell continuity. This kind of gas reservoir actually can be regaraed as multi-well system. After gas reservoir put into production, pressure buildup data is easily affected by offset wells. Middle or late period of pressure derivative curve will be downwarping or upwarping obviously. This kind of characteristic curve would be interpreted as bound- ary effect based on normal pressure buildup analysis theory. Incorrect analysis will provide incorrect information for misleading develop- ment and production decision. In order to clarify reservoir characteristic and identify pressure buildup characteristics by offset effect, the dynamic model of bottom-hole pressure in the multi-well system of infinite homogeneous reservoirs is derived with the parameter of ef- fective radius. Skin and wellbore storage effect are considered for testing well in the model. But skin and wellbore storage are ignored for offshet well. With Laplace transform method, the exact solution to Bessel function in the Laplace space is obtained. Two type curves are plotted for online or offline simultaneous with offset wells. In addition, the type curve characteristics are analyzed and the related method of pressure buildup analysis is established. Under both scenarios mentioned above, analysis on long-term asymptotic theory for solutions shows that the pressure derivative curves rise step-likely, and there appears a multi-radial flow stabilization line. The ratio of each sta- bilization line height to the first stabilization line height is the algebraic sum of the dimensionless production combined testing well and effective offset well. In the meanwhile, the pressure derivatives curves descend under the scenario of test well buildup when offset wells are producing simultaneously.