Optimized Deepwater Cement Design for Record-Length Expandable Liner

Abstract

During a sidetrack operation out of 9 7/8-in. casing on a deepwater well in Green Canyon Block 243, Gulf of Mexico, unexpected hole conditions were encountered that required the use of an additional casing string. The decision was made to run a 7 5/8 × 9 5/8-in. expandable liner in the 8 1/2 × 9 1/2-in. wellbore. The liner would expand to provide an inside diameter of 7.71 in., allowing space for a 7-in. production liner in the targeted interval. The 6,867-ft liner (pre-expansion length) is currently the world record for the longest expandable liner set to date and presented several challenges for cement job design. The liner would be cemented conventionally before the expansion operation. Expansion time was calculated to be approximately 17 hours, allowing the fluid time for the primary lead cement, with a safety factor, to exceed 19 hours. The tail cement had to exhibit good compressive strength around the shoe track, and the operator specified top of cement (TOC) at 17,000 ft to protect a secondary pay zone. Slurry properties were simulated to meet fluid times required for the liner expansion. Standard API lab tests used for cement testing were modified to accommodate this lengthy operation. The expandable liner was set at 20,605 ft measured depth (MD) and 19,930 ft true vertical depth (TVD) with a maximum hole angle of 36°. The liner was cemented successfully using an extended thickening-time lead slurry mixed at 15.7 lb/gal, followed by a 16.2-lb/gal tail slurry with a shorter pumping time to achieve good strength at the liner shoe. After drilling out the liner, the operator obtained a 16.8-lb/gal equivalent (PPGE) formation integrity test (FIT) and resumed drilling to the target depth. The cement-evaluation log showed excellent bonding behind the expandable liner with TOC at 17,000 ft as planned. Operational details and cement design considerations are provided in the paper. Emphasis is placed on wellbore configuration, expandable installation procedures, and hole preparation, a full understanding of which is the beginning of a successful cement job. Introduction The Aspen field is located in a prolific development area in the Green Canyon Block 243 in 3,000-ft water. This field development has been in progress since 2000 with five major production horizons drilled in the area. Through high-rate production, certain sands have seen some depletion and thus significant pressure regressions have been observed throughout the productive intervals. Operators following proper equivalent circulating density (ECD) management and using synthetic- based drilling fluids with optimized particle-size distributions to maximize the sealing of depleted sand packages have achieved success. This case-history well was a re-entry sidetrack to reach a lower objective known to be in a narrow pore pressure/fracture gradient window because of the pressure-depleted interval. The planned completion program consisted of sidetracking out of the original wellbore through a 10 ¾ × 9 7/8-in. tieback at 14,000 ft and directionally drilling an 8 ½-in. pilot hole to planned TD (Fig. 1). The hole would subsequently be opened to a 9 ½-in. hole size to run a 7 5/8-in. production liner. During the drilling operations through the production interval, wellbore pressures indicated that it would not be possible to continue without encountering significant losses. To still reach lower objectives and complete with a 7-in. production liner, the use of a 7 5/8 × 9 5/8-in. expandable liner installation became critical to the success of the well. Because there were secondary completion objectives behind this installation, it was also critical to obtain a top of cement (TOC) back to 17,000 ft as well.