Mechanical behaviour of wellbore materials saturated in brine water with different salinity levels M.C.M. Nasvi a , P.G. Ranjith a, * , J. Sanjayan b , A. Haque a , Xiao Li c a Deep Earth Energy Lab, Monash University, Building 60, Victoria 3800, Australia b Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Victoria, Australia c Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China article info Article history: Received 27 February 2013 Received in revised form 29 November 2013 Accepted 3 December 2013 Available online 13 January 2014 Keywords: Acoustic emission Brine Geopolymer Fly ash Well cement abstract In any carbon capture and sequestration (CCS) project, well cement plays a vital role as it provides the required zonal isolation and well integrity. Typical wellbore materials including well cement and for- mation rock will be exposed to a range of saturation mediums such as water and brine with different salinity levels. To date, ordinary Portland cement (OPC)-based well cement has been used. However, its survival has been questioned under CO 2 sequestration conditions, as it experiences cement degradation and strength reduction in saline water. Therefore, this experimental work investigates the mechanical characteristics of geopolymer (G) as well cement and sandstone (S) as formation material. The me- chanical behaviours of G, S and GeS composite materials in fresh water (W) and two concentrations of brine water (BW), 5% NaCl (5% BW) and 15% NaCl (15% BW), were studied. Based on the results, it was found that G, S and GeS samples experience strength reduction in W and BW. However, the reduction rate of G is almost half of that of OPC-based oil well cement. In addition, the strength reduction rates of G and GeS were less in 15% BW compared to Wand 5% BW, due to the lower alkali leaching rates from G in BW compared to W. Therefore, saline aquifers with high NaCl content are always favourable for G well cement. The S samples showed constant strength reduction regardless of the saturation medium, and hence NaCl does not show any significant effect on the mechanical behaviour of quartz-rich sandstone. The crack propagation stress thresholds were higher for G and GeS saturated in 15% BW compared to 5% BW. The S samples did not show major variation in crack propagation stress thresholds in W and BW. The ARAMIS strain measurement results showed that the maximum strain that wellbore materials experi- ence at failure reduces with the introduction of brine. In addition, G and GeS undergo splitting failure, whereas S experiences shear failure in W and BW. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction There have been many scientific studies focussing on the reduction of global warming, and carbon dioxide (CO 2 ) is one of the main greenhouse gases causing global temperature rise. The major threats of global warming will be the inundation of low-lying coastal zones due to the melting of polar ice caps, regional de- creases in food production, the deterioration of eco-systems, and the spread of diseases [1]. Of all greenhouse gases, CO 2 is respon- sible for 64% of the greenhouse gas effects [2]. Geo-sequestration of CO 2 is considered to be one of the largest scale mitigation methods to combat greenhouse gases produced from coal-powered plants, petroleum and oil recovery projects, cement production and iron and steel production [3e5]. The sequestration wells play a major role in the success of any sequestration project, as well as integrity should be maintained for efficient sequestration. Well integrity can be obtained by providing zonal isolation, which depends on the well cement as it is used for primary cementing (between the casing and the caprock) and secondary cementing (inside the casing). To date, ordinary Portland cement (OPC) has been used as well cement. However, there are many problems associated with the current practice, such as cement degradation, lack of chemical and acidic resistance, durability concerns, leakage, and strength reduction in high salinity environments [6,7]. According to an enhanced oil recovery (EOR) survey, of the total of all CO 2 EOR wells (16,348) only 0.15% use non-Portland cement CO 2 zones. In North America, there are tens of thousands of abandoned, inactive, or * Corresponding author. Tel./fax: þ61 3 9905 4982. E-mail addresses: Mohamed.nasvi@monash.edu (M.C.M. Nasvi), ranjith.pg@ monash.edu (P.G. Ranjith), JSanjayan@groupwise.swin.edu.au (J. Sanjayan), lixiao@mail.igcas.ac.cn (X. Li). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2013.12.003 Energy 66 (2014) 239e249