Miscibility study of carbon dioxide injection to enhance oil recovery from Abu-Dhabi oil field Thani reservoire

The subject field in this study has been recognized among the largest offshore oil fields in the world, located in the Arabian Gulf 63 kilometers to the Northwest of Abu Dhabi, producing large quantities of crude oil and associated gas from three different carbonate reservoirs, Thani-I, II and IIII since 1963. In the early 1970's peripheral water injection scheme was adopted to maintain the reservoir pressure and sustain production. Simultaneously, partial waterflooding was applied to one sector of the field, but stopped soon after implementation shadowed by poor sweep efficiency and dramatic escalation of water-cut. Furthermore, hydrocarbon miscible gas injection was implemented in the year 2000 but stopped seven years later, due to high gas oil ratio and aspheltene deposition.;In light of such recovery complications, management is considering serious recovery measures to extend plateau production and meet long-term production from this field. Post initial screening phase, it became evident that CO 2 miscible injection is the most suitable way forward. Characteristics of the Thani-III reservoir are within the favorable range for both immiscible and miscible CO2 injection criteria set by Taber, Martine and Serigh. Thani-III reservoir is considered more homogenous, less fractured and with higher production potential than Thani-I and II, hence promoted to be the target of CO2 miscible gas injection.;This thesis aims to study the miscibility features of CO2 miscible injecton to enhanced oil recovery from Thani-III reservoir. Comprehensive simulation model is used to determine multi contact miscibility and suitable equation of state with CO2 as a separate pseudo component using one of the industry standard simulation software. Experimental PVT data for bottom hole and separator samples including compositional analysis, differential liberation test, separator tests, constant composition expansion, viscosity measurements and swelling tests for pure CO2 were used to generate and validate the model. In addition to that, simulation studies were conducted to produce coreflooding and slimtube experimental models, which are compared with the conclusions drawn from experimental results. Results of this study have shown comparable results with the lab experimental data in regards to minimum miscibility pressure (MMP) calculation and recovery factor estimation, where the marginal errors between both data sets were no more than 7% at its worst. For example, slimtube experimental results suggested 4230 psig as minimum miscibility pressure, where the simulation study EoS figure is 4130 psig and the slimtube simulation model results is 4180 psig. Similarly, coreflooding experimental data recovery factor at 1.2 PV injected solvent was 75% and a value of 72% recovery factor was obtained from the software single core model at same conditions of pressure and saturations.;Results from this study are expected to assist the operator of this field to plan and implement a very attractive enhanced oil recovery program, giving that other factors are well accounted for such as asphaltene deposition, reservoir pressure maintenance, oil saturation, CO2 sequestering and choosing the most appropriate time to maximize the net positive value (NPV) and expected project gain.