Study On Highly Inhibitive Water-based Drilling Fluid Used In Long Shale Segment

The paper is a comprehensive study of the highly-inhibitive water based drilling fluid,which used for solving the bore-well instability in long shale interval of horizontal wells.After analyzing the characteristics of shale-gas production zone and mechanism of bore-well instability,it also explored the bore-well stability of clay and shale wells,examined evaluation approaches of high-sealing drilling mud,searched various types of additives.Then,researchers tested the highly-inhibitive WBM,and its result has met the requirement both in lab and on site.The paper first analyzed the major components and its characteristics of shale,the property of clay mineral,etc.On this basis,it further studied the mechanism of bore-wall instability in shale wells and thus,established the methods and approaches of examining bore-wall stability in shale wells.By conducting traditional tests like fluid loss test and core in flow equipment test and innovative tests like micro layer simulation and micro fracture simulation,it also delivered major emphasis on the instant sealing and anti-sloughing capacity of shale.To compare between empty mud(without agent)and agent mud,the paper measured the sealing and anti-sloughing methods suitable for shale.During the experiment phase,researchers selected RLC-101 and CEL and YH-150 as the plugging agent on the basis of sealing mechanism,and SP-80 and JY-1 as emulsifiers after studying the emulsifier’s stability and emulsification mechanism.The designed formula of highly-inhibitive WBM used in long shale interval.After testing the rheological property,lubricity,specifications and the sealing capacity of mud cake,the drilling fluid is suitable for adopting in field.In Changning and Weiyuan gas field,this WBM had shorter reaming time,lower well diameter enlargement ratio and better performance compared with traditional poly-sulphur and potassium poly-sulphur drilling fluid system.The fluid has high-efficiency and environmental-friendly,shedding meaningful social benefit for the future development of shale-gas.