鄂尔多斯盆地现今地应力测量及其在油气开发中的应用

油气田开发中实施水力压裂措施、部署和优化注采井网必须考虑现今地应力方向、大小及其分布规律.通过岩石声发射法、钻孔井臂崩落法、古地磁定向岩石差应变法以及岩石压缩等实验方法,测定了鄂尔多斯盆地伊陕斜坡区现今主应力大小和方向,并以吴旗探区为例,讨论了现今地应力在油气开发中的初步应用.认为伊陕斜坡区不同深度砂岩的现今最大水平主应力(δ1)值介于20.3～60.01MPa之间,与深度线性相关性好,相关系数=0.952;现今最大水平主应力方向为NE-NEE-近EW向,由盆地西南(西)向东北(东)方向逐步偏转变大.在现今应力状态下,吴旗探区中生界延长组长6储层NNE-NEE向裂缝系统在水力压裂过程中将首先启动张开并连通,最先形成有效主渗流通道,随着外界流体压力逐步增大,NW及NWW向裂缝系统可成为次级渗流通道;同时认为长61储层人工裂缝扩展方位约为NE-SW向,压裂缝为沿最大水平主应力方向延伸的垂直裂缝,且井孔相对稳定.

Measurement of the present earth stress of Ordos Basin and its applications in oil and gas exploitation

The direction,magnitude and distribution of present earth stress must be taken into account in hydraulic fracturing of oil wells,planing and optimizing of injection-production pattern in oil and gas field exploitation.The direction and magnitude of the present earth stress of Yi-Shaan slope zone in Ordos Basin are determined by many methods such as rock acoustic emission,borehole breakouts,differential strain analysis by paleo-magnetic orientation of rock,as well as rock compression experiment and so on.And the applications of the present earth stress in oil and gas exploitation are discussed taking Wuqi explorative area as a case.The measurement results show that the present maximum horizontal principal stress(δ1)value is in the range of 20.30～60.01 MPa according to the memory of the sandstone in different depth in Yi-Shaan slope zone,it has good linear correlation to depth,and correlation coefficient is 0.952;the direction of the present maximum horizontal principal stress is NE-NEE-near to EW.Deflection gradually becomes bigger from the southwest(west)to the northeast(east)in the basin.In the state of present stress,NNE-NEE crack system in Chang 6 reservoir of Yanchang Formation in Wuqi exploration area will firstly open and connect in the process of hydraulic fracturing and the main effective seepage channels are formed at the first.With the gradually increasing of the outside fluid pressure,the microcrack system in the directions of NW and NWW can form the secondary seepage channels.At the same time,it is held that the spreading direction of the artificial crack in Chang 61 reservoir is about NE-SW,the artificial crack is vertical one along the direction of maximum horizontal principal stress,and so drilling holes are relatively stable.