水平井地层电阻率各向异性校正方法研究

Research on Anisotropy Corrections of Horizontal Well Formation Resistivity

水平井井眼轨迹与地层的相对位置经常变化,造成常规测井仪器在水平井中的响应机理发生改变,地层电阻率测井表现出各向异性特征。在砂泥岩剖面中,当井眼与地层层面相交或离层面不远时,其距离小于仪器的探测范围,常规测井仪器不足以正确识别单个地层,探测到的是砂泥岩互层,在层界面上表现出宏观各向异性,测量值是砂岩和泥岩的综合反映;当井眼远离层面时,其距离大于仪器的探测范围,仪器探测到的是单一的砂岩地层,在层内表现出微观各向异性,测量值反映的是砂岩的特性。据此,综合水平井和邻近直井测井资料描述井眼轨迹与地层的空间展布,确定井眼轨迹与层界面的几何关系,提取井眼轨迹到层界面的距离,采用砂/泥岩薄互层模型进行地层电阻率各向异性校正。其效果良好,具有一定的推广价值。

Because the relative position of horizontal well trajectory to formation often changes in a horizontal well, which leads to the change of response mechanism of normal well logging tools in the well, the response of well logging is different to that in the vertical well. The main different character is anisotropy of the formation resistivity. In sand/shale profile, when the horizontal well trajectory intersects the formation interface or is near to the interface, the distance is less than logging tools＂ probing radius, so the tool can＇t correctly identify a single formation, its response is a comprehensive reflection of both sand formation and shale formation, this phenomenon is macroscopic anisotropy; When the horizontal well trajectory is far from the formation interface, its distance is greater than the logging tools＂ probing radius, so the tool can indentify the single sand formation, reflects property of the sand formation. This phenomenon is microcosmic anisotropy. With all the above ideas, and the horizontal well and near vertical wells＂ log data are used to describe the horizontal well trajectory＇s spatial distribution, determine the location relationship between well trajectory and formation interface and detect the distance from well trajectory to the formation interface. With the help of the sand/shale model, we can correct the formation resistivity anisotropy. The correction method is good and has a certain useful value.