Effects of Gas Additions to Deepwater Gulf of Mexico Reservoir Oil: Experimental Investigation of Asphaltene Precipitation and Deposition

Abstract

Conventional primary and secondary water flooding of Deepwater Gulf of Mexico (GOM) reservoirs typically result in substantial un-recovered oil providing an attractive target for enhanced oil recovery (EOR) processes. One of the challenges of applying EOR gas injection in these offshore reservoirs is the h igh oil asphaltene content. Anadarko Petroleum Corporation and Schlumberger have jointly investigated the effects of gas addition on the phase behavior of oil, especially its effect on asphaltene precipitation and deposition. The study focuses on the experimental results from various tests showing the instability of asphaltenes in oil from various gas injection scenarios. Three common EOR injection gases: nitrogen (N2), carbon dioxide (CO2) and methane (CH4) were studied. N- heptane was (n-C7) also included for comparison of solids phase behavior during depressurization. Most asphaltene laboratory testing use n-C7 at ambient conditions, whereas asphaltene precipitation occurs with change in pressure and temperature during reservoir depletion processes. The study collected PVT and flow assurance data for original live fluid and for additions of N2, CO2, CH4 and n- C7 at high pressure and temperature conditions. Measurements include asphaltene onset pressure (AOP), saturation pressure (Pb), swelling tests and asphaltene deposition tests. Other basic measurements of the corresponding dead oil include SARA analysis, viscosity, density and fluid characterization. Fluids from the field presented a compositional variation with a variety of asphaltene contents from 4 to 15.5%. Results of experimental flow assurance assessments revealed the black oil has high propensity for asphaltene precipitation due to addition of injected gas. The addition of N2, CO2 or CH4 significantly aggravates the asphaltene precipitation condition of these fluids. The comparison between the three gases showed that, when added in the same mole proportion, N2 was the strongest precipitant followed by CH4.

CO2-Fluid-Rock Interactions and the Coupled Geomechanical Response during CCUS Processes in Unconventional Reservoirs

“…Different injection gases have different effects on asphaltene precipitation. The injection of CH 4 , CO 2 , and N 2 will lead to asphaltene precipitation, among which N 2 has the most significant influence on asphaltene precipitation [171,172], followed by CH 4 [173].…”

Investigation of the Gas Injection Effect on Asphaltene Onset Precipitation Using the Cubic-Plus-Association Equation of State

“…Fluid-1 [20] Fluid-2 [20] Fluid-3 [40] Fluid-4 [20] Fluid-5 [20] Comp Table 5. Model parameters are calculated by correlating experimental data for 5 mol% gas injection case as shown in Fig.…”

“…Symbols (squares for upper onset, circles for bubble points) represent experimental data from Gonzalez et al[40]. (Plot-a) Lines for upper onset and bubble pressures for 0 mol% gas injection case are the correlations by CPA with ‫۶ۯ‬ / =3977-58536/T K, of HC =19.13 bar, ‫ۯۯ‬ / =7000K & ࢼ ‫۶ۯ‬ =0.05 (case-1/solid lines) and ‫۶ۯ‬ / =1887-33418/T K, of HC =19.13 bar for default values of ‫ۯۯ‬ / =3000K & ࢼ ‫۶ۯ‬ =0.05 (case-2/dashed lines).…”

Mechanistic study to investigate the effects of different gas injection scenarios on the rate of asphaltene deposition: An experimental approach

“…Asphaltene deposition during CO2 flooding in oil reservoirs has been extensively studied [21-23, 31, 32, 45-48]. However, few studies have been conducted examining the influence of N2 and CH4 flooding on the amount of asphaltene deposition [23,[49][50][51][52][53]. The kinetics of asphaltene deposition is an area of intense debate in the research community.…”