A substantial increase in oil production resulting from CO2 flooding has been clearly identified in two multi-pattern areas of the SACROC Unit. Analysis of the two areas permitted the identification of oil response to CO2 injection with greater accuracy than has previously been possible at SACROC. The areas include the 600 acre [2.43 × 10 (6) m2] Four Pattern Area (4PA) and the 2700 acre [10.93 × 10 (6) m2) Seventeen Pattern Area (17PA). Located in the Kelly-Snyder Field of Scurry County, Texas, the 50,000 acre [202.3 × 10 (6) m2] SACROC Unit is the world's largest CO2 miscible flooding project. The 4PA encompasses 24 wells arranged in four contiguous inverted 9-spot injection patterns. The area has been on pattern waterflood since 1972 and was at a 95 percent producing water cut when CO2 water-alternating-gas (WAG) injection was commenced in June 1981. An approximate 30% hydrocarbon pore volume (HPV) of CO2 was injected over a 5-year period at WAG ratios ranging from two to eight. CO2 injection ceased in May 1986 and the area has been on continuous water injection since that time. Incremental oil recovery attributable to CO2 injection is estimated currently to be at least 9% of the original oil in place (OOIP). This represents an estimated cumulative CO2 utilization of 9.5 Mft3 per barrel of incremental oil [1692 m3/m3]. Also on pattern waterflood since the early seventies, the Seventeen Pattern Area has exhibited an approximate 5% OOIP recovery after injecting 17% cumulative HPV CO2. CO2-WAG flooding in the 17PA began in May 1981. Currently, the cumulative CO2 utilization is estimated to be 9.7 Mft3 per barrel of incremental oil [1728 m3/m3]. This paper examines the methods used to determine CO2 mobilized oil response, describes how the effects of workovers and other "normal" field operations were accounted for, and evaluates the influence of activities in patterns adjacent to the study areas. Introduction A substantial increase in oil production resulting from CO2 flooding has been clearly identified in two multi-pattern areas of the SACROC Unit. The intent of this paper is to document that response. CO2 performance reported herein is that which has been observed under "normal" field conditions and operations. SACROC DESCRIPTION AND EARLY PROJECT PERFORMANCE The SACROC Unit has been the subject of a great many papers dealing with the reservoir description, the CO2 displacement process, CO2 transmission, performance of the CO2 project, and many other topics. The history provided below, therefore, is only a synopsis. Early History of the Kelly-Snyder Field Discovered in 1948, the Kelly-Snyder Field is located in Scurry County, Texas (Fig. 1). The discovery well, Standard of Texas Brown 2-#1, was drilled to 6,700 feet [2042 m], 9 miles [14.5 km] northwest of Snyder, Texas. The well flowed 530 bbl/D [84.3 m3/d] from the Canyon Reef formation. Further development drilling proved up an area encompassing some 84,000 acres [340 × 10 (6) m2]. To date this discovery represents one of the last billion-plus barrel reservoirs to be found within the continental U.S.A. Pertinent reservoir data and properties are summarized in Table 1. P. 27^

The Paleocene/Eocene age First Eocene dolomite reservoir is estimated to contain than 10 billion barrels of oil of which only a small percentage will be produced during primary development. Consequently, steam flooding is being investigated as an appropriate EOR option. A 1.25-acre, single pattern pilot (SST) and a 40-acre, 16 pattern pilot (LSP) are in progress. The detailed pilot area log, core, and seismic data provide a unique opportunity to assess reservoir heterogeneity. Analysis of temperature and petrophysical logs obtained in a temperature observation well located 35 feet from the SST injector show that a vertical barrier to steam migration exists. Two, relatively thick, very low porosity and very low permeability nodular evaporite-rich zones that were predicted to be the most likely barriers do not appear to be a vertical barrier. Instead, an interval characterized by numerous thin, cycle caps, characterized by muddy, finely crystalline dolomites interpreted to be tidal flat facies may be the vertical barrier. Each of these cycle caps also exhibit signs of subaerial exposure which may also contribute to the generally low porosity and very low permeability of the cycle caps. Detailed studies, including micro-permeameter measurements, quantitative mineralogical studies, and micro-CT scans were used to further characterize this interval. The geological assessments of heterogeneity are supplemented by a history-matched simulation model that suggests the evaporite-rich zones may have acted as short term baffles but that the vertical barrier to steam migration is coincident with the interval with abundant tidal flat cycle caps and exposure surfaces. Geological and other reservoir data obtained from the LSP suggest that similar vertical barriers may exist in the pilot area. Early steamflooding results show a very positive response to steam injection as well as multiple thermal "events" (most likely baffles rather than barriers) in the lowermost flooded zones at the LSP. The LSP data allows inferences to be made regarding the occurrence and distribution of lateral high permeability "connections" between injectors and producers as well as the overall reservoir response to steam injection. While the rapid temperature response observed in a few wells may reflect localized fractures or karst-like zones, numerical simulation using very fine grids (1.25 m cell size) shows that some of the LSP wells may experience very short breakthrough times without the need for fracture or karst-like zones.

This study presents an approach to exploit full potentials of a production logging run. In the proposed methodology, we seek layer flow contributions, reservoir parameter estimation, and well-performance optimization, in one logging operation. In particular, we match the entire wellbore pressure, temperature, and density profiles using a fully transient wellbore/reservoir simulator. In the proposed approach, perturbations can be created either from static or dynamic well condition. New formulations for these initial conditions for multirate tests with non-Darcy skin are presented. Field examples illustrate the notion presented in this work. P. 107

A large scale steamflood pilot test has been underway since 2008 in the first Eocene reservoir in the Wafra Field in the Partitioned Zone (PZ) between Saudi Arabia and Kuwait. The first Eocene is a carbonate reservoir and it is the shallowest reservoir in the Wafra Field with an average depth of 1,000 feet The primary objective of the pilot is to reduce technical and economic risk/uncertainty to determine whether full field steamflood development is feasible. The pilot consists of sixteen 2.5 acre inverted 5 spot patterns with associated steamflood and production facilities. The injection interval is the 1st Eocene "C" interval at a depth of 1300 ft. This is the first multi-pattern steamflood of a carbonate reservoir in the Middle East. This presentation will share the early results from the implementation of the pilot project. The production response to carbonate steamflooding will be shown along with examples of individual well production behavior. Early insights into carbonate steamflood response, variability of production response by pattern and the identification of operating issues associated with carbonate steamflooding will be shared. The success of the pilot test project has huge implications to not only the PZ, but to the entire Middle East region due to the vast amount of oil contained in reservoirs that would be considered targets for the steamflood process. Conclusions and lessons learned that can be drawn from carbonate steamflooding results to date in the pilot will also be shared in the presentation