Casing design for horizontal well cementing

Long radius horizontal wells and some medium radius horizontal wells can be cased for cementing. The main problem in the design of horizontal well casing is whether the casing can pass through the curved section safely.

(1) Casing strength design. In the process of casing running in horizontal well, it bears axial bending load, uplift and down pressure load under normal overpressure. Therefore, the casing design strength of horizontal wells is one grade higher than that of conventional vertical wells (or directional wells). For example, the steel grade J55 casing with a wall thickness of 7.72mm is used for vertical wells, and the steel grade N80 casing with a wall thickness of 7.72mm is used for horizontal wells, When lifting the maximum tonnage, the safety factor of tensile strength shall not be less than 1.80, and the safety factor of casing tensile strength shall not be less than 1.5.

(2) Calculation of various resistances during casing running. The resistance during casing running is mainly composed of two parts: one is the local resistance when passing through sharp bend, which is determined by the borehole conditions, and the main influencing factor is the maximum full angle change rate of the well; the other is the friction resistance between casing and wellbore, which is determined by casing gravity equivalent to horizontal displacement length and friction coefficient between casing and wellbore. Whether the casing can run smoothly depends on whether the self gravity (floating weight) of the casing is greater than the resistance of the above two parts. In Jing'an oilfield, the vertical depth is 1 900 m, the horizontal well displacement can reach 600 m, and the casing can enter the well smoothly. The length of the horizontal section can be greatly increased by using the anchor to increase the axial downward pressure. Casing running to the designed well depth at one time is the premise of cementing operation. In Sichuan, before casing running, theoretical design and simulated drifting technology are adopted to solve the problem of casing running.