Research On The Drilling Fluid For Long Openhole Safe Drilling Of Large Segment In Baka Coal Bed

Baka Area is located in Kekeya tectonic zone of in Taipei depression hills,Turpan-Hami Basin.Since the formation is staggered by coal,sand and shale,some underlying fracture were developed.The pressure bearing capacity of the formation were low.So some complex accidents were caused such as wellborn instability and collapsing,drilling choking and well leakage.In order to reduce such incidents,shorten the drilling cycle,a technical study is carried out by this paper about safe drilling fluid of long openhole completion in large segment of coal bed in Baka Area.The mineral components of Baka Area are analyzed and evaluated by X-ray diffraction analysis and Scanning Electron Microscopy(SEM)and lithology and physical characteristics becomes clear.A study on instability type and the instability mechanism of formation is carried out.Using the lithology research results of Kekeya tectonic zone,formation instability types(coal rocks instability and shale rock instability)is defined.Through extensive both theoretical and experimental research on two kinds of instability mechanism,five factors can be summarized as the origin of the two kinds of instability mechanism,which are physical factors,chemical factors,mechanical factors,machine factors and mechanical and physical combination factors.The performance of common two kinds of blocking agents and five kinds of shale inhibitor is analyzed and evaluated,and a comparative experiment about the common additives with a new strong seam sealer CBD-2 and potent inhibitors BCY-3 is carried out.Performance evaluation results show that that blocking agent CBD-2 has excellent sealing performance and filtration wall building performance,and the inhibit performance of the BCY-3 is better than the other treatment agent candidatesThe reasonable amount of blocking agents CBD-2 and inhibitors BCY-3 is evaluated by an orthogonal experiment.The optimal dosage is fixed by comparing the rheological properties,the hydration inhibition performance and blocking formation properties in different dosage,which the CBD-2 addition amount is 3%(mass volume ratio)and BCY-3 2%(mass volume ratio)in the system.Comprehensive performance evaluation is carried out for safe drilling drilling fluid system of long openhole completion in large segment of coal bed in Baka Area.The results show that the new formulation has a stronger seam sealing and inhibitory and its overall performance is significantly better than the active recipe.Through the application test in KE21-PING1 well,the drilling fluid formulations optimized reflects good sloughing suppression and blocking ability and this study is true and effective.