Lost-Circulation Control Material Yields Successful Cementing Operation and Achieves Good Zonal Isolation in Middle East Region

Abstract

Abstract While drilling an 8.5 in. open hole in the Umm Shaif field, an unexpected fault was encountered across formation ARAB-D2, increasing losses from 15.0 to 40.0 bbl/hr. Initial losses were managed using mud lost-circulation material (LCM) pills; however, losses were observed again while running the liner. It was decided to cement the liner to secure the shoe, with the expectation of being required to perform a remedial operation. The liner was cemented with all precautions to help prevent further loss. By systematically introducing enhancements to the cementing and liner running practices and optimizing the fluid (cement/spacer) design using the latest technology fiber system in the spacer, it was possible to achieve the objective to control losses during the cementing operation. Additionally, securing the shoe and isolating the reservoir zone while preparing for a top-of-liner squeeze and liner perforation, if necessary, to squeeze cement in poorly isolated zones was achieved. Three-dimensional (3D) placement simulator software was used to model the flow rates and the equivalent circulating density (ECD) during the operation, and sensitivity runs were performed to observe worst-case scenarios at different loss rates to optimize volumes, rates, etc. Once the spacer crossed the loss zone, lost-circulation additives (composed of a blend of various additives) began bridging across the zone, enabling the cement slurry to reach the top of liner, where it circulated excess cement. The tagged hard cement above the top-of-liner log exhibited good isolation to the reservoir formation, no remedial operations were necessary for the shoe and top of liner, and no perforations were necessary. Spacer fluids are an environmentally acceptable blend of carefully selected materials, including coarse and tough LCM, fibers, and medium-sized, resilient angular materials. These fluid systems help mitigate losses when cementing across weak, unconsolidated, or fractured formations and carry materials with both high-pressure integrity and compressibility to help ensure tolerance to modifications in fracture size, caused by differential pressure fluctuations, without the materials being dislodged or allowing collapse. These materials are stable and insoluble in water. The spacer fluid system breaks the emulsion of oil-based drilling fluid, water wetting the casing pipe and the formation in preparation for cement bonding. Additionally, such materials resist intermingling of fluids at the interface in the fluid train.