API Oilwell Cementing Practices

Abstract

Summary Throughout the years, the API Cement Standardization Committee 10 hasstrived to provide the drilling industry with the latest technology as appliedto cement specifications and testing of down-hole materials. Twenty-twoeditions of these standards and specifications and more than 25 technicalpapers and bulletins have been published. Perhaps this committee's mostsignificant achievement is a new textbook covering worldwide cementingpractices. Chapters written by practices. Chapters written by recognizedexperts from major oil and service companies who usually are active in API workdeal with everything from primary cementing to the plugging of wells. This bookalso contains a complete bibliography of papers and patents to 1990. Noteworthypapers and patents to 1990. Noteworthy in the text is a survey of more than 300fields worldwide, covering casing programs, drilling fluids, and cementingpractices. Many worthwhile and useful statistics may also be found therein. This paper highlights the latest in cementing and findings from these surveysof drilling and completion practices. Introduction Most of the several thousand wells drilled and completed annually throughoutthe world-some produce oil or gas and some are dry-are cased, with the casingset in the borehole and surrounded by cement. Literature on cementingtechnology dates from the early 1920's. Most of this cementing information, however, represents practices used after World War II. In 1937, the practicesused after World War II. In 1937, the API established its first committee tostudy the use of cement downhole. A few cement testing laboratories werealready equipped with strength-measuring apparatus and stirring devices todetermine the fluidity or pumpability of cement slurries at downholepumpability of cement slurries at downhole temperatures. Many changes havetaken place in cement standardization, cement testing, and field practices, particularly in drilling below practices, particularly in drilling below 10,000ft. API Cement Standardization Committee 10 has played a significant role inall phases of cement technology R and D. In 1990, experts within the industryand on Committee 10 finalized the text Worldwide Cementing Practices, whichattempts to consolidate the various cementing technologies currently used. Highlights of the various chapters and authors' opinions are summarizedherein. Role of Standardization In the Manufacture and Use of Cement Portland cement is produced by partially Portland cement is produced bypartially fusing powdered blends composed of limestone with materials likeclays, shales, blast-furnace slag, siliceous sands, iron ores, and pyritecinders. From a chemical standpoint, pyrite cinders. From a chemicalstandpoint, these blends may be considered to be mixtures of the oxides ofcalcium (CaO), aluminum (Al O), silicon (SiO), magnesium (MgO), iron (Fe O), Potassium (K O), and sodium (Na O). During heating to about 2,700 deg. F, theseoxides combine to form calcium silicates and aluminates (commonly referred toas "clinker") that can react with water to form a hydrated product withcementitious properties. The paste product with cementitious properties. Thepaste of Portland cement and water will harden under water and in air. Becausethis paste can set under water, Portland cement is known as a hydraulic cement. When hydraulic cements set and harden by reacting chemically with water, thisreaction, called hydration, forms a stonelike mass. Hydration begins as soon ascement contacts water. Each cement particle forms a type of growth on itssurface that gradually spreads until it links up with the growth from othercement particles or adheres to adjacent substances. Thus, progressivestiffening, hardening, and strength development result. The stiffening of wellcement slurries can be recognized by an increase in consistency that depends ontime, temperature/pressure conditions, and the composition and fineness of thecement and slurry formulations. Test procedures and specifications for theperformance of various types of Portland cement in construction work aremaintained by the American Society of Testing Materials (ASTM). The oilindustry determined that the ASTM tests were inadequate for determining theperformance of cements in wells because they were made under conditions unlikethose encountered in well cementing operations. In 1952, the national APIcommittee adopted standards for six classes of cements used in oil- andgas-well cementing operations. The first tentative standard in 1953, designatedAPI Std. 10A, was entitled API Specification for Oil-Well Cements. Thestandards for six API classes of well cements covered chemical requirements, determined by ASTM procedures, and physical requirements, determined inaccordance with procedures outlined in API RP 10B and procedures outlined inAPI RP 10B and ASTM. The petroleum industry mostly purchases cementsmanufactured in accordance with API classifications. API has published thesestandards since 1953, when the first national standards on cements for use inwells were issued. These specifications are reviewed annually and revisedaccording to the needs of the oil industry. Specifications do not cover all theproperties of cements over broad ranges of depth properties of cements overbroad ranges of depth and pressure. They do, however, embody a realistic methodof classifying Portland cement for use in wells by specifying the requiredproperties. P. 1364