Acid-soluble magnesia cement (MC) was used in production zones to plug perforations temporarily to reduce brine losses during completion and workover operations. This has resulted in substantial savings for operators. The cement has also been used to reduce potential formation damage. This paper describes some of the characteristics of the cement, field applications, and results.
IntroductionBarthel 1 described the first applications of MC in Iran to cure severe lost circulation during drilling in production zones with an acidremovable cement. This differed from the use of conventional lostcirculation materials (LCM's), such as calcium carbonate or sized salt pills, which are not setting cements and therefore do not develop compressive strength. Conventional LCM's have several disadvantages in production zones.1. Many are potentially damaging to formations. 2. Some LCM's (e.g., mica) can distort production logs. 3. They can be removed prematurely by subsequent well operations, causing the seal to be broken and further losses.4. They can block or interfere with downhole tools and completion equipment.Curing lost circulation relies on blocking formation fractures, channels, or pores with bridging materials, usually with a selected mixture of coarse and fine particle sizes. Introducing blocking material into a production zone will usually result in impairment of subsequent production. If the blocking material can be removed, however, it may not result in permanent formation damage.Drilling, production, and reservoir engineers have a keen interest in and responsibility to optimize production in the most cost-effective manner possible. Thus, attention has been focused on formation damage and ways to prevent it, resulting in the development of "nondamaging" drill-in fluid systems and the increasing use of solids-free completion brines. Losses of these fluids or their filtrates into the formation can cause formation permeability reductions. 2 Even minute quantities of fines from unfiltered water or brines can damage cores. These fluids can cause such chemical reactions in formations as "salinity shock," where formation fines are released or the fluids form precipitate fines when mixed with formation fluids. MC can reduce potential damage by providing a means of substantially reducing losses of mud, drill-in fluid systems, and solids-free completion brines. The following procedure should be followed.1. MC solids bridge on the formation face or fracture to stop most losses.2. The MC solids cement together to develop a compressive strength that resists or prevents dislodgement better than other LCM's. The cemented solids further seal the cement's permeability to prevent seepage losses.3. Me removes with relative ease by drilling or fluid-flow erosion out of the wellbore, and then backflush or acidize. This allows application in producing and injection zones.The MC described in this paper has been used in this procedure for openhole drilling applications since 1975. Since 1985, MC has been used successfully in a similar pro...