Identification of oil reservoirs suitable for CO2-EOR and CO2 storage (CCUS) using reserves databases, with application to Alberta, Canada

Abstract

Carbon capture and storage (CCS) is a key technology which could be utilized to stabilize CO2 concentrations in the atmosphere. While all the components of integrated CCS systems exist and are in use today in the fossil-fuel extraction and refining industries, very few large-scale integrated CCS projects are currently in operation, due mainly to the high cost of implementation. For this reason, in the last few years the concept of CO2 capture, utilization and storage (CCUS) has been advanced, based on the premise that utilizing CO2 captured from anthropogenic sources, particularly in CO2 enhanced oil recovery (EOR) operations, would provide revenue that will, accordingly, reduce costs and facilitate deployment. When a large number of oil reservoirs are found in a particular region or jurisdiction, it is very difficult to ascertain which oil reservoirs are suitable for CO2-EOR by using detailed reservoir analysis and numerical simulations. In such cases, reserves databases may contain sufficient information to allow a region- or jurisdiction-wide identification (screening) of oil reservoirs suitable for CO2-EOR. Based on industry's experience to date with CO2-EOR, a set of 14 criteria has been developed to screen oil reservoirs in terms of their suitability for CO2-EOR, including operational and reservoir characteristics, and reservoir size. Using the published statistical analysis of the performance of 31 CO2-EOR operations in Texas, it is possible to estimate the incremental oil recovery factor and the net CO2 utilization factor for a given oil reservoir suitable for CO2-EOR, hence the incremental oil recovery and associated CO2 storage for that reservoir. In terms of CCUS, two additional screening criteria are introduced, which relate the size and location of large CO2 sources with respect to the location and potential CO2 storage capacity of a given oil reservoir suitable for CO2-EOR. If more than one oil reservoir meets these conditions for a particular large CO2 source, the reservoirs could be ranked using a weighted normalized parametric procedure that takes into account reservoir storage capacity in relation to the size of CO2 emissions from that particular source, the distance between the source and the reservoirs, and the depth of the reservoirs.The screening and ranking procedures for identifying oil reservoirs suitable for CO2-EOR and CO2 storage has been applied to Alberta, Canada, where there are close to 13,000 oil reservoirs recorded in the reserves database of the oil and gas regulatory agency. Application of the screening criteria identified 136 oil reservoirs in 85 oil fields that are suitable for CO2-EOR. The criteria that have the greatest impact on screening are oil gravity, minimum miscibility pressure and reservoir size. Second-order criteria in terms of impact are reservoir temperature and oil viscosity. Porosity and initial oil saturation have almost no effect, mostly because most reservoirs would normally satisfy these criteria. The cumulative incremental oil production at 2 HCPV injected CO2 in these 136 oil reservoirs is estimated to be 759, 1742 and 2858 MMSTB at P10, P50 and P90, respectively, with corresponding cumulative CO2 storage capacity of 213, 868 and 1742Mt CO2. Considering a maximum straight distance of 300km between any of the 38 large CO2 sources in Alberta and oil fields with reservoirs suitable for CO2-EOR, and a minimum storage capacity equivalent to 5 years of emissions leads to the identification of 29 oil fields that are suitable for both CO2-EOR and CO2 storage (i.e., CCUS).The methodology presented herein for screening oil reservoirs for CO2-EOR and CO2 storage can be applied to any region or jurisdiction in the world, possibly with some adjustments regarding some threshold values and weighting coefficients for reservoir ranking.