SPE-169084-MS Single Well Pilot Test of Near Miscible CO 2 Injection in a Kansas Arbuckle Reservoir J. S. Tsau and M. Ballard, SPE, University of Kansas Copyright 2014, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Improved Oil Recovery Symposium held in Tulsa, Oklahoma, USA, 12–16 April 2014. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract A recent study showed that CO 2 injection at pressures below minimum miscibility pressure (MMP) improves oil recovery with Arbuckle reservoir core samples at near miscible conditions. To demonstrate its applicability on a larger scale, a single well pilot test was designed to experimentally inject CO 2 into the Arbuckle formation at pressures below MMP to determine the efficiency of CO 2 displacement at near miscible conditions. The pilot test consists of a single-well chemical tracer (SWCT) test before and after CO 2 injection on a selected well producing from the Arbuckle formation. The reservoir operating pressure was 1,150 psi while the MMP of the oil was 1,500 psi at 106 °F (reservoir temperature). The first chemical tracer test was performed to determine the oil saturation in the formation prior to CO 2 injection. This was followed by injecting approximately 17 tons of CO 2 at pressures below MMP with a follow up water displacement, followed by a second tracer test performed to determine the remaining oil saturation. The oil saturation measured from the two tracer tests were 0.23 and 0.20, respectively. A reduction of oil saturation by 0.03 represents a 13% improvement of oil displacement which results from CO 2 injection at near miscible conditions. The test results indicate the potential of using near miscible CO 2 to improve oil recovery in Kansas Arbuckle reservoirs and others where MMP cannot be achieved. Introduction Arbuckle reservoirs are a significant resource in Kansas for Improved Oil Recovery (IOR). These reservoirs have produced an estimated 2.2 billion barrels of oil representing 35% of the 6.1 billion barrels of total Kansas oil production (Franseen et al., 2004). Because of the characteristic production history, Arbuckle reservoirs have been viewed as fracture-controlled karstic reservoirs with strong pressure support from either a bottom water or edge water aquifer, effectively naturally waterflooding the reservoir. The same report from Franseen et al. (2004) on various geologic aspects of the Kansas Arbuckle Group also postulated Arbuckle reservoirs are affected by their connectivity to underlying aquifer with a wide range of reservoir pressures. The data collected in the Bemis-Shutts field revealed significant variability of Drill-Stem Test (DST) shut-in pressures in the Arbuckle, which ranged from less than 200 to greater than 1,100 psi (Franseen et al., 2003). Such a wide range of well shut-in pressures implies that the reservoirs are either highly heterogeneous or are in various degrees of connectivity with the underling aquifer which leads to limitations of CO 2 miscible flooding in these Arbuckle reservoirs where miscibility is not achievable at the reservoir operating pressure. A recent study to assess near-miscible CO 2 displacement processes to improve oil recovery in Arbuckle reservoirs showed encouraging laboratory results. The core flooding experiment with Arbuckle reservoir core samples indicated at least 50% of the remaining oil in place can be recovered by injection of CO 2 at near miscible conditions where the pressure is below the Minimum Miscibility Pressure (MMP) at reservoir temperature (Bui et al., 2010). To demonstrate the applicability of near miscible CO 2 injection to improve oil recovery on a larger scale, a single well pilot test was designed to experimentally inject CO 2 into the Arbuckle formation at pressures below MMP to determine the efficiency of CO 2 displacement at near miscible conditions. The pilot test consists of a single-well chemical tracer (SWCT) test before and after CO 2 injection on a selected well producing from the Arbuckle formation. The chemical tracer test was