Geopolymer as well cement and its mechanical integrity under deep down-hole stress conditions: application for carbon capture and storage wells

Abstract

With regard to the safety, environmental impact and sustainability of carbon capture and storage (CCS) projects, the integrity of injection and production wells plays a major role. In a CCS project, mechanical integrity of well cement should be maintained to sustain the required mechanical strength throughout the life of an oil/gas and CO 2 sequestration well. One of the major issues with existing Portland cement based oil well cement is cement degradation in CO 2 -rich environment. On the other hand, geopolymer cement possesses excellent acid resistant characteristics, shows higher mechanical strength and durability and demonstrates lower permeability. Therefore, this research work focused on studying the mechanical integrity of geopolymers under two different down-hole conditions: (1) effect of CO 2 on mechanical behaviour of geopolymers and (2) hydraulic fracturing of geopolymers to study the mechanical integrity under down-hole stress conditions. To study the mechanical integrity under CO 2 rich environment, geopolymers were tested in CO 2 chamber at a pressure of 3 MPa for up to 6 months and compressive strength and microstructural testings were conducted. It was noted that strength values of geopolymers did not change significantly in CO 2 environment for 6 months. There were only about 2 % variations in compressive strength values in CO 2 compared to the initial strength value. Scanning electron microscopy (SEM) test results revealed that there is no significance variation in the microstructure of geopolymer after 6 months in CO 2 . For hydraulic fracturing experiment, four different tests were conducted with various injection pressure (P in ), axial stress (r 1 ), confining pressure (r 3 ) and tube length (30 and 40 mm). Geopolymers could not be fractured in any of the four tests, in which maximum values of P in of 23 MPa and r 1 of 59 MPa were used. There was no fracture development in geopolymers despite maximum ratios of P in /r 3 of 3.8 and r 1 /r 3 of 13.3 was tested. Tests could not be repeated with higher ratios of P in /r 3 and r 1 /r 3 due to the limitation with the triaxial set-up used. Since there is no fracture development in geopolymers at higher ratios of P in / r 3 and r 1 /r 3 , it is concluded that required mechanical integrity can be observed when geopolymers are used as well cement.

Factors Affecting the Compressive Strength of Geopolymers: A Review

“…Geopolymers, in the family of inorganic aluminosilicate binder, has received extensive interests because of high temperature resistance [70,[102][103][104][105], low permeability [106][107][108][109][110], strong bonding and good durability [51,[111][112][113], excellent chemical corrosion resistance [114][115][116][117][118], and environmental friendliness [119,120], etc. Some of the uses that have been investigated for alkaline activated materials are: as sustainable construction material [121][122][123][124][125][126], mine backfilling [127,128], porous spheres as novel pH buffers [129,130], bricks [71,112,131,132], porous thermal insulation material [133], as road material [134], for immobilization of toxic metals and nuclear waste management [135][136][137][138][139][140], coatings for concrete [141]…”

A Review of Potential Cementing Systems for Sealing and Support Matrices in Deep Borehole Disposal of Radioactive Waste

“…The potential for using geopolymers for well cementing has been recently explored by Nasvi and co-workers [54][55][56][57][58] in laboratory-based studies. Other researchers are now exploring the use of this system, particularly where CO 2 sequestration is being considered, as the system is not readily carbonated [59].…”

Comparison of Salinity Dependent Mechanical Behaviours of Geopolymer and OPC: An Application to CCS and Oil / Gas Wells

“…All over the world, anthropogenic emissions of greenhouse gases have been a major concern with carbon dioxide (CO 2 ) playing a major role in these greenhouse gas emissions [1]. Hence, it is essential to reduce carbon dioxide emissions if global warming is to be effectively reduced.…”

“…In a CO2 rich environment, Portland cement will be unstable and will have reduced strength, cement degradation, and increased permeability and will be subjected to chemical attacks [7]. On the other hand, researchers [1,3,8] have found that geopolymer possesses excellent acid resistant characteristics, high strength and low shrinkage compared to OPC. Geoploymer is an aluminasilicate cementitious material, which can be synthesized by mixing the source material (fly ash, metakaolin, slag etc.)…”

“…Geoploymer is an aluminasilicate cementitious material, which can be synthesized by mixing the source material (fly ash, metakaolin, slag etc.) with a strong alkaline solution (a combination of NaOH and Na2SiO3) [1,9,10]. Hence in the current study, geopolymer was used as the well-cement.…”