随钻电阻率测井的各向异性影响及校正方法研究

随钻测井(LWD)是在钻井过程中实时测量井眼穿过地层的各种岩石物理参数,其电阻率测井的影响因素包括井眼、仪器偏心、井轴与地层的相对倾角、地层电性各向异性、围岩、电介质和泥浆侵入等,若不对这些原始数据进行必要的校正处理,就可能失去随钻测井的地层评价意义。在诸多的影响因素中,地层电性各向异性和相对倾角对大斜度井和水平井的随钻电阻率测井影响最大。目前,对随钻测井曲线进行环境影响校正的方法主要有图版法和计算机自动校正法。校正图版是根据理论计算或实验结果做出的,不适合于逐点对所有井段的地层进行较全面的环境影响校正。自动校正法主要是根据理论研究或对解释图版曲线采用拟合校正公式,而实现自动校正。本文分析了随钻电阻率与各向异性和相对倾角的关系,对校正图版曲线采用最优拟合得到校正公式,来实现随钻电阻率测井的各向异性的自动校正,效果良好,值得推广应用。

The Anisotropic Effect and Correction Method in Logging-While-Drilling (LWD) Resistivity Logging

LWD is to measure all kinds of petrophysical parameters of the borehole through formation at real time while drilling.The influencing fac- tors of its resistivity logging include borehole,eccentricity of instrument,relative inclination between well axle and formation,anisotropy of formation electrical properties,adjoining rock,dielectric and mud invasion,etc.If these raw data were not corrected necessarily,there would be no significance for LWD formation evaluation.Among these factors,the anisotropy of formation electrical properties and relative inclination have the maximum effect on LWD resistivity well logging in high-inchnation wells and horizontal wells.At present,the correc- tion methods of environmental effect for LWD curves are mainly chart method and computer autocorrection method.The calibration chart method is worked out according to the theoretical calculation or experimental result,which is not adapted to the comprehensive environ- mental effect correction of point by point to all of the intervals of the formation.The autocorrection method is carried out mainly according to the theoretical researches or fitting correction formula to the curves of the interpretation chart.The paper analyses the relationship between LWD resistivity and anisotropy and relative inclination.A correction formula,which has gained good effect,has been got by fitting the curves on the calibration chart to realize anisotropy autocorrection in LWD resistivity well logging.It is worth generalizing.