Microscopic Rock Characterization and Influence of Slug Size on Oil Recovery byCO2 Miscible Flooding in Carbonate Oil Reservoir

摘要

Carbon Dioxide (CO2) has been recognized as a preferredrnmiscible solvent for Enhanced Oil Recovery (EOR) methods.rnMiscible flooding by CO2 has proven its positive effectivenessrnthrough numerous laboratory and field projects. The mainrngoals of this study are to provide microscopic reservoir rockrncharacterization, and optimize the selection and the effect ofrnCO2 slug size to be applied for carbonate oil field, U. A. E., onrnoil recovery by CO2 miscible flooding.rnScanning Electron Microscope (SEM) is used to providernaccurate description of the reservoir rock surface topography.rnThe SEM is used to attain the pore size distribution of thernrock. Energy Dispersive X-Ray Spectrometer (EDS) andrnInductively Coupled Plasma (ICP) are applied for detailedrnaccurate analysis of elements constituting the rock.rnFive flood experiments were performed to achieve the goals ofrnthis study. The first experiment was carried out usingrncontinuous CO2 flooding. Other three experiments usedrndifferent CO2 slug sizes of 0.15, 0.30, and 0.45 hydrocarbonrnpore volume and chased by actual reservoir brine. The fourthrnexperiment was carried out to evaluate the performance ofrnwaterflooding. All experiments were performed using actualrncrude oil injected into actual reservoir rock samples of almostrn23 cm length and 10 cm diameter. These samples werernsaturated at initial-oil-in-place condition and then subjected tornwater and/or CO2 floodings. The minimum miscibilityrnpressure (MMP) was calculated to be 3,700 psia using currentrncorrelations from literature. To secure good miscibilityrncondition, all experiments were conducted under injectionrnpressure of 4,200 psia and at 250 oF similar to the reservoirrncondition. The results indicated that water flooding recovered 66 % IOIPrnand a continuous CO2 miscible flood produced 96 % IOIP.rnFurthermore, the increase of slug size increases oil recoveryrnby CO2 miscible flooding, but the slug size of 0.15 HCPV isrnrecommended since the increment in oil recovery using largerrnslugs does not represent significant addition to the oil recoveryrnin comparison to applied smaller slug sizes.