深水浅层钻井呼吸效应机制及影响因素分析

Analysis of the breathing effect mechanism and influencing factors during drilling in deepwater shallow formations

钻井呼吸效应常被误判为井涌而采取错误的措施,使呼吸效应强度增加。为明确深水浅层呼吸效应机制,基于深水浅层高孔高渗和裂缝不发育的特点,建立多孔弹性介质渗流模型,模拟深水浅层钻井呼吸效应过程,分析地层参数(弹性模量、泊松比、渗透率和孔隙度)、钻井液性能(塑性黏度和动切力)和井底压差对深水浅层钻井呼吸效应的影响。结果表明:深水浅层钻井呼吸效应属于渗透性诱导机制,使部分钻井液残留在地层中,具有瞬时性,可分为漏失、拟稳态和返排3个阶段。低弹性模量、低泊松比、高孔高渗的地层更容易发生渗透性呼吸效应。加入降滤失剂和膨润土、使用低密度钻井液、采用低排量的钻井方式和控压钻井技术等,可以降低渗透性呼吸效应强度。该结果为深水浅层安全高效钻井提供指导。

The breathing effect during drilling is often misjudged as kick and the wrong measures are taken,which leads to the enhancement of the breathing effect and seriously affects the efficient and safe drilling in deepwater shallow formations.To clarify the breathing effect mechanism during drilling in deepwater shallow formations and master the characteristics of leakage and flowback,a porous elastic medium seepage model is established to simulate the process of this kind of breathing effect based on the characteristics of high porosity and high permeability and lack of fractures in deepwater shallow formations.The effects of formation parameters(elastic modulus,Poisson's ratio,porosity and permeability),drilling fluid properties(plastic viscosity and yield value)and bottom hole pressure dif ference on breathing effect are analyzed.The results show that the breathing effect during induced in drilling in deepwater shallow formations belongs to the permeability-induced mechanism and is transient,which can be divided into three stages:leakage,pseudo-stability and flowback,resulting in part of the drilling fluid remaining in the formation.The formation with low elastic modulus,low Poisson's ratio and high porosity and high permeability is more prone to permeability breathing effect.This kind of breathing effect can be reduced by adding filtrate reducers and bentonite,using low density mud,and using low-displacement drilling method and management pressure drilling technology.The results provide guidance for safe and efficient drilling in deepwater shallow formations.