Increasing Oil Recovery with CO2 Miscible Injection: Thani Reservoir, Abu-Dhabi Giant Off-Shore Oil Field Case Study

Abstract

This paper aims to study the miscibility features of CO2 miscible injection to enhanced oil recovery from Thani-III reservoir. A Comprehensive simulation model was used to determine multi contact miscibility and suitable equation of state with CO2 as a separate pseudo component using one of the industry’s 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 were 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. 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.

Diffusion and swelling of CO2/light oil mixtures using pressure decay and CT-scan

“…Swelling test is a special PVT laboratory test and is the most common multi-contact PVT test (Aljarwan, 2012). During this test, a gas with known composition is injected into the oil at varying proportions (quantified in terms of molar percentage).…”

“…Here it is firstly important to differentiate miscibility from solubility. The first one is valid when two or more fluids form a single homogeneous phase in all mixed proportions while for the last one this happens only for a single level of proportions (Aljarwan, 2012). In addition to this, two miscible fluids will in the case of EOR present no interface and no capillary effect when in contact with porous media.…”

“…The last one has an important role on the recovery of residual oil at pore scale. At low solvent flow rates and long residence time, diffusion between CO 2 and oil interacts effectively to remaining unrecoverable oil, which is subsequently recovered by swelling (Aljarwan, 2012). Furthermore, the diffusion promotes mixing between the injected solvent and the oil, prevents viscous fingering, retards gas breakthrough and therefore improves the sweep efficiency for enhancing oil recovery (Guo et al, 2009).…”