Modelling Enhanced Gas Recovery by CO Injection in Partially-Depleted Reservoirs.

Abstract

Carbon Capture and Storage (CCS) is considered as an important solution for CO emission reduction, yet, the CO capture process is highly costly. Thus, combining Enhanced Gas Recovery (EGR) with CCS could potentially offset the costs via additional production of natural gas. Therefore, the objective of this P.hD. is to build a numerical model to simulate CO-EGR in partially-depleted gas reservoirs; in particular Centrica Plc's North Morecame gas field.

Our numerical model is based on the so-called Method of Lines (MOL) approach. MOL requires selecting a set of persistent Primary Dependent Variables (PDVs) to solve for. In this case, we chose to solve for pressure, temperature and component mass fractions. Additionally, MOL requires recasting of the governing equations in terms of the PDVs, which often requires the evaluation of partial derivative terms of the flow properties with respect to the PDVs. In this work, a method of analytical evaluation of these partial derivative terms is introduced. Furthermore, in a new approach, the mutual solubility correlations for mixtures of CO-HO and CH-HO, available in the literature, are joined together using straight lines as a ternary diagram, to form a ternary CO-CH-HO equilibrium model; the equilibrium-model's predictions matched well with the available experimental solubility data.

1D and 2D numerical simulations of CO-EGR were carried out. Overall, the 1D results were found to match very well with an existing analytical solution, predicting accumulation of a CH bank ahead of the CO plume and accurately locating the associated shock fronts while considering the partial miscibility of both CO and CH in HO. Based on the subsequent model predictions, in the North Morecambe field without drilling any additional wells, 0.6 out 2.3 BSCM, i.e., 26 of the remaining gas can potentially be recovered using CO-EGR.