Erik B. Nelson

3 Cement Additives and Mechanisms of Action

Publisher Summary This chapter summarizes the major categories of well cement additives, their principal benefits, chemical compositions, and mechanisms of actions. The physical and chemical phenomena with which the additives contend are discussed in the chapter. Portland cement systems are routinely designed for temperatures ranging from below freezing in permafrost zones to 700°F (350°C) in thermal recovery and geothermal wells. Well cements encounter the pressure range from near ambient in shallow wells to more than 30,000 psi (200 MPa) in deep wells. In addition to severe temperatures and pressures, well cements are often designed to contend with weak or porous formations, corrosive fluids, and overpressured formation fluids. Over 100 additives for well cements are available, many of which can be supplied in solid or liquid forms. Eight categories of additives are generally recognized, which are, accelerators, retarders, extenders, weighing agents, dispersants, fluid-loss control agents, lost circulation controlling agents, and speciality additives.

2 Chemistry and Characterization of Portland Cement

Publisher Summary This chapter deals with the physical and chemical properties, and the performance of the remarkable material, which are crucial to every facet of well cementing technology. The chapter reviews the manufacture, chemical composition, hydration chemistry, and classification of Portland cements. Well cementing exposes Portland cement to conditions far different from those anticipated by its inventor. Cement systems must be designed to be pumped under conditions ranging from below freezing in permafrost zones to greater than 1,000° F (538°C) in some thermal recovery wells. After placement, the cement systems preserve their integrity and provide zonal isolation during the life of the well. It is possible to accommodate such a wide range of conditions through the development of additives which modify the available Portland cements for individual well requirements.

9 Thermal Cements

Publisher Summary This chapter discusses thermal cements. The chemistry of thermal cements is also presented and data are provided to illustrate the long term performance of typical systems. The proper mixing and placement of well cements rely upon the application of electrical and mechanical technology. The physical and chemical behavior of well cements changes significantly at elevated temperatures and pressures. Corrosive water zones and very weak formations are common in thermal wells. The three principle types of wells that encompass thermal cementing are deep oil and gas wells, geothermal wells, and thermal recovery wells. Portland cement, Class J cement, silica-lime systems, and high-alumina cement are used to complete thermal wells. The chapter uses cement compounds with special chemical notation.

7 Special Cement Systems

Publisher Summary This chapter discusses cement technologies specific to problems as slurry fallback, lost circulation, microannuli, salt formations, permafrost, and corrosive well environments. As the technology of well cementing advanced, certain problems were encountered for cement systems. Thixotropy describes the property exhibited by a fluid system under shear, which develops a gel structure and becomes self-supporting when at rest. Portland cement systems containing water-swellable clays as bentonite, which develops gel strength, and exhibit some degree of thixotropic behavior. After each static-dynamic cycle, the gel strength and yield point tend to increase. Thixotropic cements can be prepared by the addition of water-soluble crosslinkable polymers and a crosslinking agent. Good bonding between cement and pipe, and between cement and formation are essential for effective zonal isolation.