地层电性各向异性对电阻率测井的影响

Influence of the Electrically Anisotropic Formation on Resistivity Logging

测井解释中的各种公式和理论大多建立在地层各向同性的基础上,过去的井眼都是以直井为主,这些公式、理论几乎能够满足生产的需要。随着定向井在生产中的地位逐渐提升,地层电性各向异性的影响也逐渐凸现出来。通过各种模型的正演模拟,可以看出地层电性各向异性对定向井,特别是大斜度井和水平井的测井响应影响较大,并且各向异性地层的电阻率值随着井斜角或各向异性地层中交错层理倾角的增大而增大,但总是介于hσ和(σhσV)1/2之间的。同时根据测井曲线上的一些组合响应,可以判断出井下各向异性地层的存在与否。电性各向异性的存在使以往经典的Ar-chie公式从标量形式拓展到张量形式,但同时也增加了求解的复杂性。

Most of the formulae and theories in logging interpretation are on the basis of isotropy of formation. Because the holes are mainly vertical in the past, these formulae and theories can almost meet the demands of the production. However, the influence of the electrically anisotropic formation emerges gradually along with the importance of directional well in the production. Through the forward modeling for a great variety of models, it is revealed that the electrically anisotropic formation greatly influences the logging responses to the directional wells, especially to the highly deviated wells and the horizontal wells. The resistivity of the electrically anisotropic formation increases along with the dip angle increasing and is always between the value σh and （σhσv）^1/2. According to the combination responses on the logging curves, we can know whether the electrically anisotropic formation exist in the hole or not. The existence of the electrical anisotropy makes the classic Archie formula from the scalar quantity to the tensor, and the complexity of solving the problem is also increasing.