The Design Of The Drilling String And The Casing String In The Stepped Horizontal Well

The stepped horizontal well is a kind of special horizontal well which develops on the foundation of the conventionality horizontal well, its horizontal segment can rise and fall many times at vertical section, cross the oil layer of different depth, can also cross the oil layer of dissimilarity direction many times inside the horizontal plane of the same depth. Because wellhole curvature distribute anomaly at the horizontal segment , it will make increase the friction of the drilling string or the casing string , and bring some difficulty to drilling and the well completion, it can't add press on the drill bit , breach the drilling string in early days and the tube string could not descend well bottom etc. complicated circumstance. In order to resolve the technique problem of drilling string (casing string )'s friction and passing ability evaluation and turntable driven rotational speed which influence engineering design and construction, it need commence from whole drilling string mechanics analysis and, aim at the steppedl horizontal wellhole track characteristics, apply gap element method to analyse force-bearing on the drilling string . The calculate internal forces and stress of drilling string ,and calculate the contact friction between drilling tool and bore hole face, thus complete an ability evaluation on drilling string's passing and calculation of turntable driven rotational speed;According to the casing string working state, select whole casing string for the researched object, fully considering structure and top and bottom boundary of the casing string, and enteral-pressure load , emphasized to consider contact friction nonlinear between casing string and bore ,and centralizer's elastic deformation , a nonlinear static model of whole casing is built;According to casing string interal forces any well deepth generalized stress ,outside-inside press ,we can calculate the casing string strength; According to the casing string total friction and axial force, we can analysis the casing string's friction. Based on an overall consideration of casing string strength and friction resistance, we can eventually complete the passing ability evaluation in the casing string. provide a theory basis for drilling design and construction of crime scene. Practice proves that applying this theory method can lower complicated risk of drilling and raise drilling speed.