Holistic Design of Cement Systems to Survive CO2 Environment

Abstract

Cement systems that can survive in the CO2 environment are needed in various applications. Examples of these applications include:producers: CO2 in the reservoir is produced along with the hydrocarbons,injectors: CO2 is injected for sequestration and/or enhanced oil recovery, andproducers and injectors: produced CO2 can subsequently be injected for the purpose of enhanced oil recovery/sequestration. However, the carbonation of Portland cement is a well-documented, thermodynamically favorable process. When CO2 or carbonic acid comes in contact with Portland cement, it initially reacts with it to form water-insoluble calcium carbonate. Longer term, the presence of water dissolved with CO2 (or carbonic acid), if allowed to contact the cement sheath, can dissolve the calcium carbonate to bi-carbonate, which then could be displaced if a flow channel were to be present or formed during the life of the well. This can threaten long-term effective zonal isolation. A dual level solution is required to effectively address this challenge. As a first level, the potential for CO2 to enter the cemented annulus and contact the cement sheath is minimized, by placing the cement slurry in the entire annulus, reducing the permeability and endowing the set sheath with the properties necessary to withstand the well events. The second level involves reducing the amount of material in the set cement sheath that is reactive to CO2. This holistic approach has worked well in practice. Both the physical and chemical integrity of the cement sheath is addressed using this approach. Following the design logic described above, a cement system with improved resistance to CO2 environments was created by 1) designing a reduced-permeability cement sheath to withstand well operations with low cement hydration volume shrinkage and 2) optimizing the cement slurry formulation so that its hydration products have a lower amount of materials that are reactive to CO2. This cement system was then tested in the laboratory under expected in situ conditions and optimized for different well situations before placement in the field. The cement systems have been successfully placed in anumber of wells and these wells are all operating as required with no loss of zonal isolation reported. The design approach, laboratory test procedure and results from laboratory and field are presented and discussed in this paper. Introduction Technologies associated with carbon capture and storage (CCS) are coming more and more to the forefront as the world tackles long-term trends for increasing global energy demand coupled with the need to address the challenge of associated CO2 emissions (Fig. 1). In addition, it has been estimated that 40% of the world's remaining gas reserves contain more than 2% CO2. In considering how to deal with CO2 emissions, the scale of the task ahead cannot be underestimated. Global CO2 emissions are projected to rise from less than 20 thousand million tons in 1980, to wells in excess of 30 thousand million tons by the year 2030. CCS is one way in which it is hoped CO2 emissions to the atmosphere can be reduced. Currently four largescale CCS projects are operating around the world, each separating around 1 million tons of carbon dioxide per year from produced natural gas: Sleipner and Snohvit in Norway, Weyburn in Canada (with the carbon dioxide sourced in the United States), and In Salah in Algeria. In considering these numbers it is easy to see that as many as 10,000 Sleipner-sized projects might be required by the year 2030 if CCS were the only method selected to reduce CO2 emissions to 1980 levels.

An Experimental Study on Effects of Static CO2 on Cement under High-Pressure/High-Temperature Conditions

“…The interaction between cement and CO 2 in the rocks has gained significance in recent years Moroni et al 2009;Brandl et al 2010;Le Guen et al 2008). Geological storage of CO 2 in depleted and partially depleted oil fields has gained increasing global interest as an economically viable means of reducing CO 2 emissions, while recovering extra oil.…”

“…Numerous studies have been conducted by researchers globally to help understand the mechanism of carbonation in portland cement Moroni et al 2009;Duguid 2008). When cement hydrates, the major products formed during the hydration reaction are calcium hydroxide (portlandite), calcium-silicate-hydrate (C-S-H), ettringite, and monosulfate.…”

Application of anticorrosive materials in cement slurry: Progress and prospect

“…in the well are simulated indoors. Moroni et al (2009) carried out indoor cement paste corrosion simulation experiments in the high-concentration CO 2 environment in Kashagan Oilfield, Kazakhstan, under the experimental conditions of 93 °C, 14 MPa, and 3 MPa CO 2 partial pressure. It is found that the paste cement paste will form a large amount of CaCO 3 when exposed to CO 2 , which will produce huge expansion stress in the cement sheath and crack it during expansion.…”

Long-Term Study of Effects of CO2 Exposure on Cement Integrity Under Downhole Conditions

“…Geological storage of CO 2 in depleted and partially depleted oil fields has gained increasing global interest as an economically viable means of reducing CO 2 emissions, while recovering extra oil. Numerous studies have been conducted by researchers globally to help understand the mechanism of carbonation in portland cement Moroni et al 2009;Duguid 2008). Cement systems designed for these wells need the sealing capability to provide long-term zonal isolation.…”

“…The interaction between cement and CO 2 in the formation has been an area of interest in recent years Moroni et al 2009;Brandl et al 2010;Le Guen et al 2008). When cement hydrates, the major products formed during the hydration reaction are calcium hydroxide (portlandite), calciumsilicate-hydrate (C-S-H), ettringite, and monosulfate.…”