摘要：
侧向类测井电阻率曲线的极化角对地质构造的解释、地层界面的判断有很大帮助,但也会导致电阻率曲线失真且产生假薄层特征,因此通过正演计算明确影响极化角的因素可以提高油气层评价的准确性.运用三维有限元法建立了层状介质模型,探讨了围岩电阻率、钻井液电阻率、侵入带特性、仪器特性、层厚、井径和井斜角等因素对阵列侧向测井曲线极化角的影响.正演计算表明,目的层电阻率与围岩电阻率的比值大于4时,极化角更加尖锐且幅值急剧增加;钻井液电阻率主要影响极化角的形态,钻井液电阻率越大极化角越尖锐;侵入带对极化角的影响较复杂,要综合考虑侵入带电阻率与侵入深度来判断;仪器探测深度对极化角形态的影响不大,仪器纵向分辨率越高,极化角越平缓且幅值越小;井径越大,极化角越不明显;当地层厚度小于仪器纵向分辨率时,阵列侧向测井曲线极化角消失,随着层厚增大,极化角幅值变大但趋于平缓;当井斜角大于60°时,极化角基本消失,且井斜角越小,极化角越明显.研究结果表明,围岩电阻率、仪器纵向分辨率和层厚对极化角的影响尤其明显,这可为现场正确利用极化角进行油气储层解释提供指导.%The polarizing angle of a laterolog curve is helpful in the interpretation of geological struc-tures and the assessment of formation interfaces,but the distortion of the resistivity curve and the features of"false thin layers"can also occur.Therefore,it is of great significance for evaluating oil and gas reser-voirs to identify the influencing factors of the polarizing angle by using a forward calculation.Three-di-mensional finite element numerical simulation is used to set up a layered media model,which facilitates e-valuating the influence of a series of factors on polarizing angle characteristics,such as the surrounding rock resistivity,drilling fluid resistivity,invasion zone characteristics,instrument characteristics,layer thickness, well diameter,well angle,etc.The forward calculation results showed that when the ratio of the resistivity of the target rock to that of the surrounding rock is greater than 4,the polarizing angle will be sharper and the amplitude increased rapidly.They also showed that the resistivity of drilling fluid mainly affects the shape of the polarizing angle so that the greater the resistivity of drilling fluid,the sharper the polarizing angle.The influence of invasion zone on the polarizing angle is more complex.Well designers should care-fully consider the invasion resistivity and depth.The detection depth of the instrument has little effect on the polarizing angle shape,but the higher the vertical resolution of instrument,the flatter the polarizing an-gle,and the smaller the amplitude.Further,the bigger the well diameter,the less obvious the polarizing an-gle is.Revealingly,when the formation thickness is less than the vertical resolution of the instrument,the polarizing angle of the array laterolog disappears.With the increase of formation thickness,the polarization angle becomes larger,and it tends to be flat.However,when the angle of inclination is more than 60°,the polarizing angle basically disappears.Likewise,the smaller the inclination angle,the more obvious the po-larizing angle.The research results indicated that the effect of surrounding rock resistivity,instrument ver-tical resolution,and layer thickness had the most obvious effect on the polarizing angle.This could provide guidance for the correct application of the polarizing angle to interpret oil and gas reservoirs.
