启动压力梯度对低渗气藏不稳定渗流特征的影响  

Impacts of start-up pressure gradient on features of transient seepage flow in low-permeability gas reservoirs

作　　者：张小龙 杨志兴 ZHANG Xiaolong;YANG Zhixing(Research Institute of CNOOC（China）Co.,Ltd.-Shanghai Branch,Shanghai 200335,Chin)

机构地区：[1]中海石油(中国)有限公司上海分公司研究院,上海200335

出　　处：《油气井测试》2018年第3期7-13,共7页Well Testing

基　　金：国家重大专项"东海厚层非均质性大型气田有效开发关键技术"(2016ZX05027-004)

摘　　要：为了准确描述启动压力梯度对低渗气藏不稳定渗流特征的影响,在广义达西定律基础上,通过考虑启动压力梯度的非达西渗流特征,分别建立了无限大、圆形封闭及圆形定压外边界低渗气藏的不稳定渗流数学模型。采用格林函数法获得各渗流模型的拉普拉斯空间解析解,利用Stehfest数值反演算法,将拉普拉斯空间解反演变换得到实空间解,通过实例绘制了不同启动压力梯度下的无限大低渗气藏井底压力与时间的双对数曲线。研究发现,气井定产量生产时,当启动压力梯度分别为0、0.001MPa/m、0.003MPa/m及0.005MPa/m,生产97h后,井底压力分别下降16.6%、19.6%、26.3%、33.4%,表明启动压力梯度越大,对井底压力影响越显著,井底压力下降越快,地层能量衰竭越严重,低渗储层动用越困难,单井有效动用范围越有限。该特征分析对加深启动压力梯度对低渗气藏不稳定渗流机理的研究与认识有一定的借鉴。To accurately reflect the impacts of start-up pressure gradient on features of transient seepage flow in low-permeability gas reservoirs,the mathematical models for transient seepage flows in low-permeability gas reservoirs with infinite,circularly enclosed and circular constant-pressure outer boundaries were built on the basis of general Darcy＇s law,and with consideration to non-Darcy flow features of start-up pressure gradient.By using the Green＇s function,the Laplace spatial solutions of these models were derived.Then,with the Stehfest numerical inversion algorithm,the Laplace spatial solutions were inverted to derive the analytical solutions in real space.Finally,the log-log curve of bottom-hole pressure and time for infinite low-permeability gas reservoirs with different start-up pressure gradients were generated for certain examples.As revealed by the research results,when the gas well with start-up pressure gradient of 0,0.001 MPa/m,0.003 MPa/m and 0.005 MPa/m produces at a single rate for 97 h,the bottom-hole pressure reduces by 16.6%,19.6%,26.3% and 33.4%,respectively.Obviously,the higher the start-up pressure gradient is,the more significant the impacts on bottom-hole pressure are,the faster the bottom-hole pressure drops,the more severely the formation energy depletes,the more difficult the development of low-permeability reservoirs is,and the more limited the effective well drainage area is.The study results can provide necessary references for deeply identifying the impacts of start-up pressure gradient on transient seepage flow in lowpermeability gas reservoirs.

关 键 词：启动压力梯度 低渗气藏 非达西渗流 不稳定渗流 渗流模型 压力动态分析 

分 类 号：TE353[石油与天然气工程—油气田开发工程]