Reference

Lightweight cement slurry and method of use

Lightweight cement slurry and method of use. Copening, Ward L. (Dow Chemical Co., USA). U.S. US 4415366 A 15 Nov 1983, 5 pp. Cont. of U.S. Ser. No. 241,339, ab (English). (United States of America). CODEN: USXXAM. CLASS: IC: C04B015-02. NCL: 106086000. APPLICATION: US 82-420655 21 Sep 1982. PRIORITY: US 81-241339 6 Mar 1981. DOCUMENT TYPE: Patent CA Section: 58 (Cement, Concrete, and Related Building Materials) Foamed, thixotropic hydraulic cement slurries are prepd. for cementing of subterranean voids, esp. oil or gas wellbores penetrating weak underground formations which are broken by slurries of ordinary d. The thixotropic properties are preferably imparted by CaSO4.0.5H2O. Sufficient surfactant is included to permit the bubbles, av. diam. f1.5 mm, to remain as discrete entities until the slurry hardens. Thus, a thixotropic slurry with d. 9 ppg (lb/gal) was used to set a plug in a 44.5 in. open borehole in a limestone formation which would not stay filled with an 8.4 ppg brine. The base slurry consisted of a blend of 14 CaSO4.0.5H2O and 100 parts cement with ~2% CaCl2 setting accelerator and 57 parts thereof were blended with 100 parts bay brine with d. ~8.4 ppg and contg. ~0.5 parts surfactant (ethylene oxide adduct with di-sec-butylphenol).There are some commonly used reagents with their cas registry numbers 31291-60-8 and 26499-65-0 in this article. In the pumping of an initial base slurry involving ~1100 sacks of cement, N2 was to be pumped into the slurry 25 ft downstream at ~65 parts N2/100 parts slurry. The N2 was inadvertently pumped at a much faster rate, causing escape of the gas after placement, so that only 7 ft of fill was placed. Another 950 sacks of cement-hemihydrate blend were mixed with water to a slurry of 14.6 ppg and N2 was introduced at the nominal rate, giving ~90-100 std. ft3 N2/barrel of slurry and resulting in a foamed thixotropic slurry with downhole d. ~8.2-8.8 ppg. This gave a fill of ~140 ft consisting of a foamed lightwt. plug sufficiently strong to support a 3rd stage of unfoamed 14.6 ppg thixotropic slurry representing the desired amt. of fill. .