Circulation, lost

During drilling operations sometimes large volumes of drilling mud are lost into a formation. In this case normal mud circulation is no longer possible and the fluid level inside the borehole will drop, creating a potentially dangerous situation as described below. The formations in which lost circulation can be a problem are ... 

Lost circulation materials are flake, fiber, or granular-shaped particles. Each type is sold individually, often in two or more size grades, or two or more materials of different shapes may be sold as a blend (133—136). Materials of different shapes and sizes are often blended into the mud at the well site. 

Usually special solids, such as nut shells, limestone, expanded perlite, etc., are added to the drilling muds to fill or clog rock fractures in the open hole of a well. Most of these lost circulation materials can shorten the life of pump parts. They are especially hard on valves and seats when they accumulate on the seats or between the valve body and the valve disc. 

Sand content of the mud is reported in percent by volume. Also reported is the point of sampling, e.g., flowline, shaker, suction, pit, etc. Also, solids other than sand may be retained on the screen (lost circulation material, for example) and the presence of such solids should be noted. 

Air-gas drilling usually increases drilling rate by three or four times over that when drilling with mud as well as one-half to one-fourth the number of bits are required. In some areas drilling with air is the only solution these are (1) severe lost circulation, (2) sensitive producing formation that can be blocked by drilling fluid (skin effect), and (3) hard formations near the surface that require the use of an air hammer to drill. 

Lost circulation. Maintain colloidal content to provide good filtration properties, low density, and thick mud. Viscosity pill and lost circulation materials. Care in use of meclianical equipment. 

SANDS Low pressure. Water or mud blocking. Loss of crude or diesel oil used as completion fluid. Minimum filtration rate water-base muds. Minimum filtration rate water-base emulsions. Miminum filtration rate oU-base emulsions. Oil-base muds. Inhibited muds. Minimum weight muds. Crude oil or diesel oil. Add oil-soluble lost circulation material. 

Coral reef. Dolomite. Fractured shales. Lost Circulation. Withdraw tooU slowly to prevent swabbing action. 

Intermediate casing strings are cemented to seal off abnormal pressure formations and cover both incompetent formations, which could cave or slough, and lost circulation formations. 

Lost circulation. A cement plug can be placed adjacent to a zone of lost circulation in the hope that the cement slurry will penetrate and seal fractures (see Figure 4-406). 

Other methods propose to use materials that interact in the fissures of the formation to form a plug of increased strength. Lost circulation additives are sunamarized in Table 1-12. 

Anionic Association Polymer. Another type of lost circulation agent is a combination of an organic phosphate ester and an aluminum compound, for example, aluminum isopropoxide. The action of this system as a fluid loss agent seems to be that the alkyl phosphate ester becomes crosslinked by the aluminum compound to form an anionic association polymer, which serves as the gelling agent [1488]. 

Permanent Grouting. Lost circulation also can be suppressed by grouting permanently, either with cement [37,409] or with organic polymers that cure in situ. 

Initially glass microspheres were used in the 1970s to overcome severe lost circulation problems in the Ural Mountains. The technology has been used in other sites [1189]. Hollow glass beads reduce the density of a drilling fluid and can be used for underbalanced drilling [1199-1201]. Field applications have been reported [73]. 

Fiber-containing cement was initially developed as a high-strength material that could be used to line a borehole [1789]. Several relatively simple and cheap spin-off applications of fiber cement were identified, such as the use of fiber cement in cement plugs for borehole stabilization and as a lost circulation material. Several companies are already applying or offering fiber cement for these purposes in the field, in both organic fibers and metal fibers [372,1077, 1682-1684]. 

Additives and mixtures to reduce or prevent lost circulation Density-increasing or weighting agents Free water control and solid suspending agents Spacers and chemical washes or preflushes Specialty cement blends... 

Vinyl monomers are used as such and are allowed to polymerize in place to form a gel. This technique is used to enable a solution to gel slowly, even at high temperatures. An aqueous solution of a vinyl monomer is mixed with a radicalforming initiator and optionally with a dispersant. The initiator decomposes at elevated temperatures and initiates the polymerization process. In this way, a gel is formed in place. Radical polymerization is sensitive to molecular oxygen. For a more pronounced delay, polymerization inhibitors may be added to the solution in small amounts. The technique is used in the treatment of subterranean formations, especially for plugging lost circulation in drilling operations, particularly at elevated temperatures. 

M. L. Allan and L. E. Kukacka. Calcium phosphate cements for lost circulation control in geothermal. Geothermics, 24(2) 269-282, April 1995. 

B. D. Burts, Jr. Lost circulation material with rice fraction. Patent US 5118664, 1992. 

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