Conversion of Mud to Cement

Abstract

Abstract A dependable method for converting fluid into a cementitiuos slurry has been sought for many years. Recent advancements in copolymer technology have made it possible to introduce Portland cement directly into drilling fluid while maintaining control over the rheology of the resultant slurry. For purposes of brevity, converted drilling fluid as described herein will be referred to as mud-to-cement, or MTC. Conversion of drilling mud into a cement slurry has several unique advantages. As examples, conversion of spent drilling mud reduces disposal costs. Secondly, the superior compatibility into MTC significantly improves annular displacement efficiency by controlling the flocculation that normally results when drilling mud and cement contact. Thirdly, MTC makes the most benefit of manpower, equipment, time and materials by consolidating services at the rig site. Consolidation of drilling mud and cementing technologies to cut costs while improving the quality of completions is the underlying topic of discourse in this paper. In addition to presentation of the slurry design paper. In addition to presentation of the slurry design process, laboratory data, mixing and handling concepts process, laboratory data, mixing and handling concepts and case histories are discussed. Also, several important avenues of potential savings are suggested. Applications in a variety of locations using different types of completions have all been successful both operationally and from the standpoint of results. Introduction The basic purpose of cementing a wellbore is to return the annulus to as near the original state as possible. In general, this means removal of all drilling mud from the annulus and replacement with a contiguous cement sheath. Cement should provide at least four basic functions:zone isolation,casing support,formation support, andcasing corrosion protection. The more complete the removal and replacement process, the more complete will be the provision of process, the more complete will be the provision of these four required functions. It is in this critical removal replacement process, however, that convention all cementing practice has often failed. The reason for that failure can be best explained as follows. Drilling mud and cement slurry are incompatible and formed a gelled mass when intermixed. Therefore, conventional cementing practice usually calls for a preflush or spacer fluid to separate mud and cement. preflush or spacer fluid to separate mud and cement. However, some spacer fluids available on today's market are incompatible with either mud or cement. Many spacer fluids are overwhelmed when all three slurries are commingled. A good spacer should have the dispersion power necessary to reduce the viscosity of such mixtures back to a level near that of the original fluids involved. Otherwise, large quantities of clabbered or severely gelled mixture will remain in the annulus. As a result, expensive remedial cementing is often required to correct inferior primary cementing applications. To reduce the problems associated with mud and cement incompatibility into a cementitiuus slurry has been developed. Converting drilling fluid into a cement slurry has been a topic of research for many years. IN 1970, a Portland cement based formulation was introduced by Wyant et al., but it had a complex formulation, was very sensitive to temperature, and did not incorporate an adequate dispersant. Even so some field applications were done. Another formulation employing a magnesium based drilling fluid was introduced by Miller et al. in 1975. P. 485