Geochemical Modeling of Oil-Brine-Rock Interactions during Brine-Dependent and Brine-CO2 Recovery Technique in Carbonate Petroleum Reservoirs

The brine-dependent recovery process involves the tweaking of the ionic composition and strength of the injected water compared to the initial in-situ brine to improve oil production. The recovery process has seen much global research efforts in the past two decades because of its benefits over other oil recovery methods. In recent years, several studies, ranging from laboratory coreflood experiments to field trials, admit to the potential of recovering additional oil in sandstone and carbonate reservoirs and has been well-explored on two frontlines, namely, brine dilution and compositional variation. However, many challenges have saddled the recovery process, such as disputes over the fundamental chemical mechanisms; difficulty with construction of a representative model to give reliable interpretation and prediction of the process, and these necessitate applicable solution. Therefore, this study explores the formulation of theory based on experimentally-observed behavior to couple equations of multicomponent transport and geochemical reactions. Mechanisms such as dispersion/diffusion, advection, instantaneous equilibrium reactions, and non-equilibrium rate-controlled reactions are captured in the construction of the numerical models. The DLVO theory of surface forces was also applied to rationalize potential determining ion interactions and to evaluate the contribution of each force component to the wettability change in the oil-brine-rock system and the characteristic oil recovery improvement. The model was applied to interpret recently-published results on the different approaches that have been explored in the application of brine-dependent recovery process in carbonate reservoir rocks. The focus being that identifying the dominant mechanisms responsible for the observed improved recovery will help substantiate the field application of the process. The study demonstrates that injected brines, containing potential determining ions depleted in NaCl, are more effective at improving recovery when it, and wettability alteration is much more pronounced at high temperatures. It was also illustrated that potential determining ion concentrations play a more significant role as compared to brine salinity reduction. The magnitude of the contribution of the electrostatic force to sustaining a stable water film increases with decreasing ionic strength, either through reduction of NaCl, Ca2+ or brine dilution, or increasing SO42- concentration. Mineral dissolution/precipitation is necessary for the pursuit of re-establishing equilibrium and should not be ignored in modelling different mineralogical carbonate rocks. The derived optimized thermodynamic parameters are demonstrated to be widely applicable. Although chalk and limestone differ by surface area and reactivity, the same thermodynamic parameters are applicable in modeling the recovery process in their respective reservoir rocks. There is a significant increase in relative injectivity for brine-CO2 recovery mainly due to more exposure to a higher amount of CO2-saturated-brin

Alkalinity Generation Constraints on Basalt Carbonation for Carbon Dioxide Removal at the Gigaton-per-Year Scale

The world adds about 51 Gt of greenhouse gases to the atmosphere each year, which will yield dire global consequences without aggressive action in the form of carbon dioxide removal (CDR) and other technologies. A suggested guideline requires that proposed CDR technologies be capable of removing at least 1% of current annual emissions, about half a gigaton, from the atmosphere each year once fully implemented for them to be worthy of pursuit. Basalt carbonation coupled to direct air capture (DAC) can exceed this baseline, but it is likely that implementation at the gigaton-per-year scale will require increasing per-well CO2 injection rates to a point where CO2 forms a persistent, free-phase CO2 plume in the basaltic subsurface. Here, we use a series of thermodynamic calculations and basalt dissolution simulations to show that the development of a persistent plume will reduce carbonation efficiency (i.e., the amount of CO2 mineralized per kilogram of basalt dissolved) relative to existing field projects and experimental studies. We show that variations in carbonation efficiency are directly related to carbonate mineral solubility, which is a function of solution alkalinity and pH/CO2 fugacity. The simulations demonstrate the sensitivity of carbonation efficiency to solution alkalinity and caution against directly extrapolating carbonation efficiencies inferred from laboratory studies and small-injection-rate field studies conducted under elevated alkalinity and/or pH conditions to gigaton-per-year scale basalt carbonation. Nevertheless, all simulations demonstrate significant carbonate mineralization and thus imply that significant mineral carbonation can be expected even at the gigaton-per-year scale if basalts are given time to react

Brine-Dependent Recovery Processes in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

Brine-dependent recovery, which involves injected water ionic composition and strength, has seen much global research efforts in the past two decades because of its benefits over other oil recovery methods. Several studies, ranging from lab coreflood experiments to field trials, indicate the potential of recovering additional oil in sandstone and carbonate reservoirs. Sandstone and carbonate rocks are composed of completely different minerals, with varying degree of complexity and heterogeneity, but wettability alteration has been widely considered as the consequence rather than the cause of brine-dependent recovery. However, the probable cause appears to be as a result of the combination of several proposed mechanisms that relate the wettability changes to the improved recovery. This paper provides a comprehensive review on laboratory and field observations, descriptions of underlying mechanisms and their validity, the complexity of the oil-brine-rock interactions, modeling works, and comparison between sandstone and carbonate rocks. The improvement in oil recovery varies depending on brine content (connate and injected), rock mineralogy, oil type and structure, and temperature. The brine ionic strength and composition modification are the two major frontlines that have been well-exploited, while further areas of investigation are highlighted to speed up the interpretation and prediction of the process efficiency

The codes and data generated in this study.

The codes and data generated in this study.</p

A cohesive approach at estimating water saturation in a low-resistivity pay carbonate reservoir and its validation

Abstract Carbonate reservoir characterization and fluid quantification seem more challenging than those of sandstone reservoirs. The intricacy in the estimation of accurate hydrocarbon saturation is owed to their complex and heterogeneous pore structures, and mineralogy. Traditionally, resistivity-based logs are used to identify pay intervals based on the resistivity contrast between reservoir fluids. However, few pay intervals show reservoir fluids of similar resistivity which weaken reliance on the hydrocarbon saturation quantified from logs taken from such intervals. The potential of such intervals is sometimes neglected. In this case, the studied reservoir showed low resistivity. High water saturation was estimated, while downhole fluid analysis identified mobile oil, and the formation produced dry or nearly dry oil. Because of the complexity of Low-resitivity pay (LRP) reservoirs, its cause should be determined a prior to applying a solution. Several reasons were identified to be responsible for this phenomenon from the integration of thin section, nuclear magnetic resonance (NMR) and mercury injection capillary pressure (MICP) data—among which were the presence of microporosity, fractures, paramagnetic minerals, and deep conductive borehole mud invasion. In this paper, we integrated various information coming from geology (e.g., thin section, X-ray diffraction (XRD)), formation pressure and well production tests, NMR, MICP, and Dean–Stark data. We discussed the observed variations in quantifying water saturation in LRP interval and their related discrepancies. The nonresistivity-based methods, used in this study, are Sigma log, capillary pressure-based (MICP, centrifuge, and porous plate), and Dean–Stark measurements. The successful integration of these saturation estimation methods captured the uncertainty and improved our understanding of the reservoir properties. This enhanced our capability to develop a robust and reliable saturation model. This model was validated with data acquired from a newly drilled appraisal well, which affirmed a deeper free water level as compared to the previous prognosis, hence an oil pool extension. Further analysis confirmed that the major causes of LRP in the studied reservoir were the presence of microporosity and high saline mud invasion. The integration of data from these various sources added confidence to the estimation of water saturation in the studied reservoir and thus improved reserves estimation and generated reservoir simulation for accurate history matching, production forecasting, and optimized field development plan