裂缝性地层呼吸效应特征实验研究

Experimental study on the characteristics of respiration effect in fractured formations

摘要:

裂缝性地层钻进时，由于井筒压力波动导致的地层呼吸效应易被误判为溢流而采取不必要的压井措施，严重影响钻井安全。为此，研制了可用于模拟裂缝性地层呼吸效应的实验装置，探索了钻井液循环压力、裂缝张开压力和岩石类型对钻井液漏失与返排特征的影响。研究表明，裂缝性地层呼吸效应是一种可逆性漏失，其发生过程为漏失-拟稳态-返排。随着钻井液循环压力的增加，钻井液最大漏失量和返排量均增加；随着裂缝张开压力的增加，钻井液最大漏失量增加，而返排量减少；相对于砂岩和灰岩，特低孔低渗的花岗岩的漏失量更大，而返排量更小。研究结果为分析深部裂缝性地层呼吸效应特征、区别其他工况而采用正确措施等提供了理论基础。

Abstract:

When drilling deep fractured formation， the formation breathing effect caused by wellbore pressure fluctuation is easy to be misjudged as overflow and unnecessary killing measures are taken， which seriously affects the drilling safety. Therefore， an experimental equipment was developed to simulate the breathing effect of fractured formation. A series of experiments were carried out to analyze the effects of drilling fluid circulation pressure， fracture opening pressure and rock type on the characteristics of drilling fluid leakage and flowback. The results show that the fractured breathing effect is a reversible leakage， and the whole process of its occurrence is leakage-“quasi-steady”-flowback. With the increase of circulating pressure of drilling fluid， the maximum leakage and return amount of drilling fluid increased. With the increase of fracture opening pressure， the maximum leakage amount of drilling fluid increases， but the return amount decreases. Compared with sandstone and limestone， granite with extremely low porosity and low permeability has larger leakage and smaller return amount. The research results provide a theoretical basis for analyzing the characteristics of fractured breathing effect of deep fractured formation and adopting correct measures to distinguish other operating conditions.