Research And Application Of Shale Gas Water-based Drilling Fluid In Changning Area

At present,the shale oil-based drilling fluid system is relatively mature and widely used in actual drilling construction.However,oil-based drilling fluid also faces the problems of high drilling cost and serious environmental damage.Therefore,major oil companies and scientific research institutions at home and abroad have been seeking a low-cost,low-pollution,high-performance water-based drilling fluid to replace the current oil-based drilling fluid,and have achieved some application results in related experimental wells.However,in the application of horizontal well deviation section and long horizontal section in shale formation,it is still unable to solve the problems of high friction and high torque caused by the change of shale bottom structure and strength,as well as the complex downhole problems such as rapid deviation variation and easy collapse of shaft lining during the construction of horizontal well deviation section.Based on the research of water-based drilling fluids at home and abroad,this paper studies and analyses the shale water-based drilling fluids,and studies a drilling fluid system suitable for shale area development.Firstly,the related literature of water-based drilling fluid at home and abroad is investigated and summarized,and the geological structure characteristics of Changning area in Sichuan Province are studied and analyzed in detail.Then,taking Longmaxi Formation shale in Changning area as the target formation,the sealing ability of inclination-making section and horizontal well section of shale gas reservoir in drilling process is weak.The problems of large filtration capacity,poor inhibition and lack of lubrication performance were comprehensively analyzed and studied.The types of main treatment agents and the optimum dosage range of drilling fluid were determined by optimum selection experiments.The plugging agent was MAX-SHIELD,the dosage range was 3%-4%;the inhibitor was PEG,and the dosage value was 3%;the filter reducer was PAV-LV.The additive is 0.6%～0.7%.LATIRATE is selected as lubricant,and the range of additive is 3%～4%.Then,through compatibility experiments,the final formula of shale water-based drilling fluid is determined as follows:3%NV-1+0.3%KOH+3%PEG+3%MAX-SHIELD+0.6%PAC-LV+3%LATIRATE+5%RSTF+4%SMP-I+barite.Using the sand bed experiment,high temperature and high pressure experiment,shale expansion experiment,shale recovery experiment,shale invasion experiment,and adhesion coefficient test experiment are designed to evaluate the sealing performance,inhibition performance,anti-invasion performance and lubrication performance in detail.The experimental results show that the water-based shale drilling developed in this paper is effective.The liquid has good sealing,inhibiting,rheological,filtration reduction and lubricating properties.Finally,the field application of Ning A well in Changning block shows that the water-based drilling fluid system developed in this paper has good cuttings carrying capacity,good adaptability to Longmaxi shale,good plugging and collapse prevention performance,and achieves the expected results...