Development and economic appraisal of a lightweight zeolite cement blend for high temperature - high pressure oil and geothermal wells

Abstract

With ever-increasing global energy demand, it is of vital importance that technology consistently meets industry requirements. As high temperature-high pressure reservoirs become more and more profitable, the energy industry can be expected to exploit them. Hence, a versatile cement system that can be used in such reservoirs would need to be capable of ensuring well integrity under such conditions. However, in order to overcome most of these challenges, cement systems are often too dense to pump into a formation without damaging it. Therefore, a lightweight cement is needed. One promising means of delivering a lightweight cement that meets these rigorous demands is to replace a portion of the API cement with a natural pozzolan such as a zeolite. The zeolite cement blend developed in this project has a density of 13.5 ppg, far lower than the 17 to 18 ppg cements that would otherwise be used. Through a trial and error process of replacing portions of API class H or G cement with six different zeolites, an acceptable zeolite cement blend was found, along with the necessary system of additives to ensure that it performed within existing specifications for oil well cements. Each of the cement blends was subjected to high temperature-high pressure testing of consistency behavior, fluid loss, and compressive strength, along with studies of modification with carbonation. This study also endeavored to show that such a cement system was economically viable. This was done using a number of case studies including both oil and geothermal wells. The cement costs of the cement were found by studying each component. The associated costs associated with the cement were subjected to a Monte Carlo simulation to reflect better the variability expected in a well job. By adding the two, and comparing the cost with a similar job carried out with a standard class H cement, the economic viability of the cement was established. In addition, the cost per kilowatt-hour and projected revenues for the geothermal projects were calculated to show that it made financial sense to use the zeolite cement blend.