Thermal Expansion of Cement and Well Integrity of Heavy Oil Wells

Abstract

Proper well construction involves long-term integrity; thus, accurate characterization of the physical properties of set cement systems is mandatory. Chemical stability, compressive strength, and permeability are commonly the main parameters determined for oilfield cement systems. The knowledge of these properties is most often enough to estimate if a cement system will maintain well integrity. However, some hydrocarbon recovery processes are highly aggressive toward the cement sheath. Under thermal processes for recovery of heavy oil, such as steam-assisted gravity drainage (SAGD) or cyclic steam stimulation (CSS), the well temperature can reach up to 350°C. The casing expands during the heating-up phase, and this outward expansion increases the stress on the annular cement sheath. Under such conditions, simulations show that a key intrinsic thermal property, the linear coefficient of thermal expansion (LCTE), is equally as important as the other physical properties to maintain well integrity. To determine the LCTE of set cement, one needs to understand the thermal-expansion theory of solid materials. An experimental setup for measuring this parameter for set cement has been developed, and essential precautions for performing accurate measurements have been formulated. The LCTE of cement is a critical parameter in the development of new cement technologies for high-temperature (HT) well applications; the chemical composition of the cement system and the curing conditions can affect the LCTE of oilfield cement systems. Improved understanding of this critical parameter has allowed significant improvement of the reliability of cement systems used in these hostile environments and provides better solutions in the form of thermally responsive cement systems.

Experimental study on the thermal expansion property and mechanical performance of oil well cement with carbonaceous admixtures

“…2.3.2 Thermal expansion coefficient measurement. Recently, most of the studies have been focused on the thermal expansion property of the hardened cement paste under the water-saturated condition, and the measured temperature is between 20 and 80 C. 5,18,21 Considering the anhydrous condition in the dry layers and the high temperature in the thermal recovery well, the thermal expansion coefficient of the set cement was measured by a horizontal thermal expansion coef-cient dilatometer, and the cement specimens were heated from 24 C to 300 C at an increasing rate of 1 C per minute, allowing the temperature distribution of the specimen to become uniform; then, the CTEs of the specimen at different temperatures were obtained by the computer. The schematic of the experimental setup for the CTE measurements is shown in Fig.…”

“…2 Chemical stability, mechanical properties, and permeability are commonly the main parameters determined for characterizing the oileld cement systems. 5 In the course of the thermal production process, steam is injected into the reservoir through the wellbore and heats it up to reduce the viscosity of heavy oil. The temperature of the oil reservoir sometimes increases to 250 C or even over 300 C. However, when the temperature is above 110 C, the C-S-H gel in the cement paste begins to transform into another hydrate product, a dicalcium silicate, which has a denser structure, and leads to an obvious volumetric shrinkage of the cement.…”