James F. Heathman

Plug Cementing: Horizontal to Vertical Conditions

This paper presents an in-depth study of cement plug placement that was conducted with large-scale models for the improvement of plug cementing practices and plug integrity. Common hole and workstring geometries were examined with various rheology and density ratios between the drilling fluid and cement. The critical conditions dictating the difference between success and failure for various wellbore angles and conditions were explored, and the mechanisms controlling slurry movement before and after placement are now better understood. An understanding of these mechanisms allows the engineer to better tailor a design to specific hole conditions. Controversial concepts regarding plug-setting practices have been examined and resolved. The cumulative effects of density, rheology, and hole angle are major factors affecting plug success. While the Boycott effect and an extrusion effect were observed to be predominant in inclined wellbores, a spiraling or roping effect controls slurry movement in vertical wellbores. Ultimate success of a cement plug can be obtained if allowances are made for these effects in the job design, provided all other previously published recommended placement practices are followed. Results ofthis work can be applied to many sidetracking and plug-to-abandon operations. Additionally, the understanding of the fluid movement (creep) mechanisms holds potential for use in primary and remedial cementing work, and in controlling the placement of noncementitious fluids in the wellbore.

Conformance-While-Drilling Technology Proposed to Optimize Drilling and Production

Oilfield operators must face challenges of safe and efficient drilling, long-term well integrity, and optimum reservoir production in almost every area of the world. These challenges usually become apparent during drilling in zones with adverse conditions such as unwanted influx of high-pressure water/gas, crossflows, chemical sensitivity, low mechanical strength, low pore pressure and lost circulation. Drilling these trouble zones can substantially impact well economics by adding costs for lost rig time and extra materials. These conditions can result in poor primary cementing that will jeopardize well integrity above the producing reservoir, and production can suffer. Many of these negative conditions of high water/oil and gas/oil ratios, scaling, and skin damage that affect production can be prevented during drilling by the use of reservoir conformance technology. This technology uses chemical and mechanical systems for water/gas shut off and thief-zone plugging. Conformance systems have been applied in thousands of wells after the well has been on production, and in most of the cases, after the well integrity has been severely impaired due to unwanted water/gas production or associated corrosion and scaling. On the other hand, conformance while drilling (CWD) techniques (using chemical squeezes to shut off water and gas influx) have been applied in only a relatively small number of wells; however, use of this technology should increase in the future since new and emerging CWD technology is improving the process with a wider performance range of chemical systems, placement techniques/tools, and real-time predictive methods and tools. The intent of this paper is to describe the old and new chemical systems, their properties, applications, and placement techniques, and finally, a new drill-string tool designed for jet injection of treatments for hole consolidation and restoration of washed out holes to gauge size. Also mentioned are new logging while drilling (LWD) tools designed to measure pore pressures at the bit to correlate to seismic data for prediction of stratigraphy, lithology, and types of structures. These new LWD tools and future logging developments will help determine when to apply CWD. Development of other technologies that will facilitate and accelerate implementing of CWD technology is also discussed and will include wellbore stabilization software designed to predict the need for CWD and show the optimum type of CWD system for a specific zone while drilling. Field test results of both the old and new CWD technology are included in this paper. Initial lab and field tests show encouraging trends toward favorable impact on drilling and production operations, which include a recent success in stabilizing an infamous rubble zone. CWD enhancements used in drilling and producing 14 lateral wells are explained. A CWD system that eliminated lost circulation in drilling a pay zone with oil-based mud allowed the operator to complete a prolific well rather than having to abandon the prospect, which had been the original prediction. Underbalanced drilling technology to prevent formation damage in pay zones has been further enhanced by use of CWD systems to shut off water influx above the pay zone.