泥浆侵入各向异性地层阵列侧向测井响应数值模拟

泥浆侵入和地层各向异性都会造成阵列侧向测井不同探测深度曲线的分离，而曲线分离是地层参数反演的关键。为此，采用三维有限元方法模拟泥浆侵入条件下各向异性地层的阵列侧向测井响应特征，研究各向异性、泥浆侵入、井斜、围岩等因素对测井曲线分离的影响。结果表明：①直井条件下阵列侧向测井响应曲线主要受地层层理方向电阻率的影响；随着地层倾角的增大，垂向电阻率的贡献增大；对于无限厚各向异性地层，RLA1~RLA5曲线间在低角度情况下呈负差异，高角度时呈正差异，翻转角约为60°。②在一般情况下，泥浆侵入对阵列侧向测井曲线分离的影响大于各向异性。③对于泥浆侵入各向异性储层，不同探测深度曲线间的差异特征杂乱，不能单纯利用曲线差异识别油、水层。④层状泥浆侵入各向同性地层，随着井斜角的增加，受低阻围岩的影响，曲线分离程度减小；当侵入深度不大（0.1~0.4m）时，随着井斜角的增加，曲线分离程度增大。研究成果对阵列侧向测井资料处理及储层评价具有借鉴意义。

Numerical simulation of array laterolog responses in anisotropic formation with mud invasion

Mud invasion and formation anisotropy can cause the separation of array laterolog curves with different investigation depths.The curve separation is the key to the inversion of formation parameters.Based on 3D finite element method(3D-FEM),the array laterolog responses in anisotropic formation with mud invasion were simulated and the affection of anisotropy,mud invasion,wellbore deviation and surrounding rock on the curve separation was studied.The following conclusions were drawn.①In vertical wells,array laterolog curves are mainly affected by the resistivity along bedding direction.With the increment of stratigraphic dip angle,the contribution of vertical resistity increases.In infinite thick anisotropic formation,there is a negative separation among the curves (RLA1~RLA5) with different investigation depths,when the angle is small.When the angle is large,the separation is positive.The critical angle is around 60°.②The influence of mud invasion on curve separation is obviously greater than that of anisotropy.③For anisotropic reservoirs with mud invasion,the difference characteristics among the curves with different investigation depths are messy,which makes it difficult to identify reservoir fluids (oil or water) using the differences among the curves.④For isotropic formations with layered mud invasion,the curve separation degree decreases with the increment of well deviation angle,affected by low-resistivity surrounding rocks.When the mud invasion is not deep (0.1~0.4m),the curve separation degree increases with the increment of well deviation angle.The achievements of the study on array laterolog responses in anisotropic formation with mud invasion have referential significance for data processing and reservoir evaluation.