异常感应测井的环境影响解释

Abnormal Induction Log Response Caused by Special Environment.

利用感应测井仪器响应的有限元求解方法，研究了地层条件和井眼环境对电阻率测井结果的影响，在存在低阻围岩和高侵的一般情况下，中感应测井响应ＲＩＭ要大于深感应测井响应ＲＩＤ，且二者都低于地层真电阻率。但是，用淡水泥浆钻井对地层形成高侵时，在侵入前沿会出现一个低电阻率区域，它对测井响应会产生一种异常影响，即使存在低阻围岩，也有可能导致ＲＩＭ＜ＲＩＤ这一异常现象，现场测井和模拟计算结果都证实了这一点。本文的计算方法可以有效地计算同时存在上下围岩、井眼和复杂侵入条件下的视电阻率，它为解释地层条件和井眼环境对测井结果的一般影响和一些测井异常现象提供了理论依据。

The effects of the formation and the wellbore environments on the induction log responses are studied by the Finite Element Method (FEM). The FEM can be used effectively to calculate the resistivity responses when the bed, wellbore and invasion were present. For the case of low resistivity shoulder bed and high resistivity invasion zone, the response of medium induction logging RIM would be greater than that of deep induction logging RID. Both RIM and RID are less than the true resistivity of formation. However, if the fresh water mud filtrate were used in drilling, a low resistivity annulus could be formed in the front of the invasion zone. This annulus would lead to a special phenomenon with the result of RIM<RID even if the low resistivity shoulder beds exist. The present calculation model is used to simulate special results that were shown in a field logging. The simulation and the field data were in good agreement. The present results not only provide a general explanation for the formation and the wellbore environments, but also give reasonable interpretations on some strange phenomena.