New Solutions for Subsalt-Well Lost Circulation and Optimized Primary Cementing

Abstract

Abstract Drilling and cementing operations in certain subsalt wells in the Gulf of Mexico (GOM) and other areas have long challenged operators and contractors. These wells have thick, deep salt formations with shear zones just above and below the salt, resulting in high unexpected costs during drilling. Such formations are often referred to as "rubblized" or "disturbed" shale zones. One theory proposes that, during geologic periods, the movement of adjacent salt formations induces shearing stresses that cause deformation, brittle failure, and fracturing in the surrounding shales. Costly drilling problems in these zones are primarily caused by the narrow margins between pore and fracture pressures that result in severe lost circulation, hole instability, and high-pressure kicks. Some of these wells also exhibit uncontrolled gas flows and underground water flows. Many GOM deepwater blocks and shelfblocks have massive salt structures and potential hydrocarbon reservoirs, but the trouble costs and difficulties associated with drilling these wells have forced operators to plug and abandon some wells and completely avoid others. Conventional lost-circulation and hole-stabilization treatments have been minimally successful in many subsalt wells. However, new wellbore-stabilization and cementing programs designed for subsalt wells can help ensure well control and integrity during drilling and production operations. This paper provides information for helping to improve subsalt drilling operations and lower well-construction costs. In addition, the failures and successes of lost-circulation treatments performed during drilling operations in shear and salt zones will be explained. Primary cementing operations that help provide costeffective zonal isolation and well integrity in these zones are presented, as well as best practices and proposals for cement-slurry design and mud displacement. Laboratory studies and cost comparisons that help justify replacing traditional materials and procedures with these cementing programs are also presented.