WELLBORE STABILITY FOR CARBON SEQUESTRATION IN GEOLOGICAL FORMATION

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1. INTRODUCTIONThe increase of knowledge of the effect of CO2 on climate change has led scientists and engineers to investigate mechanisms to control global warming by decreasing the emissions of CO2 into the atmosphere. One promising approach is Carbon Capture and Storage (CCS). In CCS schemes, CO2 is captured from large-scale industrial emitters and transported to either be used (e.g. algae cultivation) or stored permanently in geological sites, where it is injected into rock geological formation. Research studies were undertaken on how to store CO2 in geological rock formations as different stresses, fractures and pressures during CO2 injection can compromise the storage capacity of the storage site. 2. AIM AND OBJECTIVES OF THE PROJECTThe main aim of the project is to develop a CO2 injection model which will consider the thermo-hydro-mechanical coupling effect on the wellbore stability caused by intermittent injection of CO2. The main objectives of this study will be as follows:* A robust elastic-plastic damage constitutive model will be proposed. The created model will consider the irregularity of CO2 pressure and temperature inside the wellbore.* The model will be implemented into the Finite Element Method (FEM) and calibrated by existing laboratory testing results from literature. The calibrated numerical method will be used to do more analysis for various wellbore design to seek the optimised design for intermediate CO2 injection to geological formations.* Different curves will be created relating the degree of damage around the wellbore to the effects of different loadings and temperature changes. These curves can be provided to the industry in order to improve future wellbore designs. 3. METHODOLOGYThe research would be accordingly comprised of four parts as follows: * During the first two years, a constitutive model of double porosity rock under complex loading conditions will be created. The created model will describe the flow of CO2 from the ship all the way down to the wellbore. It would be also capable to predict the near-field expansion of CO2. After a 6 month literature research and publishing a general review conference paper for "ARMA symposium in New York", the constitutive model in agreement with the supervisory team was decided to follow and upgrade the study of Ma and Zhao (2018) and Khalili and Valliappan (1996). So far, the governing equations of the model used by Ma and Zhao (2018) were studied carefully in order to be able to create the appropriate coding that can reproduce their results. MATLAB software will be used for the THM constitutive modelling. Bai's (2016) PhD dissertation and Khalili's et al. (2010) research were selected as a guideline for modifications on the constitutive equations of Ma and Zhao (2018) in order to include thermal effects in the model. This will give a robust THM constitutive model for fractured porous media/rock. * The final stages of the PhD project are to further improve the numerical model. The model will be calibrated using the results of existing laboratory results in literature. Finite Element Method [FEM] will be adopted. The calibrated model will be applied to further scenarios and working conditions. A more reliable wellbore design can then be proposed under various working conditions. ReferencesBai, Y. 2016. Coupled thermos-hydro-mechanical (THM) model for multiphase flow through deformable porous media with double porosity. PhD dissertation. Khalili-Naghadeh, N. and S. Valliappan. 1991. Flow through fissured porous media with deformable matrix: Implicit formulation. Water Resources Research, 27(7), pp.1703-1709.Khalili, N., A. Uchaipichat, and A. Javadi. 2010. Skeletal thermal expansion coefficient and thermo-hydro-mechanical constitutive relations for saturated homogeneous porous media. Mechanics of Materials, 42(6), pp.593-598.Ma, J., and G.F. Zhao. 2018. Borehole Stability Analysis in Fractured Porous Media Associated with Ela