... difference in force, Ib Differential force, Ib = downward force, Ib - upward force. lb Differential force, lb = 77371b - 84301b Differential force = -693 Ib Therefore: Unless the ... 54.58psi x 140.5 sq in. Upward force = 76681b d) Differential = downward force - upward force force, lb 7737 Ib 7668 lb Differential = +691b force Drilling Fluids 91 Barrels ... Therefore, approximately 55 psi would be required to break circulation. References API Specification for Oil- Well Cements and Cement Additives, American Chenevert, Martin E. and Reuven...