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The existence of propane (C3H8) in a CO2-oil mixture has great potential for increasing CO2 solubility and decreasing minimum miscibility pressure (MMP). In this study, the enhanced solubility, reduced viscosity, and lowered MMP of CO2-saturated crude oil in the presence of various amounts of C3H8 have been systematically examined at the reservoir conditions. Experimentally, a piston-equipped pressure/volume/temperature (PVT) cell is first validated by accurately reproducing the bubble-point pressures of the pure component of C3H8 at temperatures of 30, 40, and 50 °C with both continuous and stepwise depressurization methods. The validated cell is well utilized to measure the saturation pressures of the CO2-C3H8-oil systems by identifying the turning point on a P-V diagram at a given temperature. Accordingly, the gas solubilities of a CO2, C3H8, and CO2-C3H8 mixture in crude oil at pressures up to 1600 psi and a temperature range of 25–50 °C are measured. In addition, the viscosity of gas-saturated crude oil in a single liquid phase is measured using an in-line viscometer, where the pressure is maintained to be higher than its saturation pressure. Theoretically, a modified Peng–Robinson equation of state (PR EOS) is utilized as the primary thermodynamic model in this work. The crude oil is characterized as both a single and multiple pseudo-component(s). An exponential distribution function, together with a logarithm-type lumping method, is applied to characterize the crude oil. Two linear binary interaction parameters (BIP) correlations have been developed for CO2-oil binaries and C3H8-oil binaries to accurately reproduce the measured saturation pressures. Moreover, the MMPs of the CO2-oil mixture in the presence and absence of C3H8 have been determined with the assistance of the tie-line method. It has been found that the developed mathematical model can accurately calculate the saturation pressures of C3H8 and/or CO2-oil systems with an absolute average relative deviation (AARD) of 2.39% for 12 feed experiments. Compared to CO2, it is demonstrated that C3H8 is more soluble in the crude oil at the given pressure and temperature. The viscosity of gas-saturated crude oil can decrease from 9.50 cP to 1.89 cP and the averaged MMP from 1490 psi to 1160 psi at 50 °C with the addition of an average 16.02 mol% C3H8 in the CO2-oil mixture. [ABSTRACT FROM AUTHOR]

The Ordos Basin is the main tight gas‐producing basin in China. Under the background of strong heterogeneous physical property, there is still high porosity and permeability "sweet spot" in tight reservoirs. Feldspar dissolution exerts a significant effect on porosity/permeability, while its genetic mechanism is unclear, which restricts the prediction of effective reservoir. In this paper, genesis of feldspar dissolution and its effect on reservoir heterogeneity were studies. Carboniferous‐Permian Formation, which is the main gas‐producing strata in northeast margin of Ordos Basin, is taken as the target. Based on the methods of thin section observation, physical property test, inclusion, isotope and productivity analysis, mechanism of feldspar dissolution, and its positive modification to tight sandstone reservoir are studied. The results show that the target sandstone is dominantly made up of litharenite and feldspathic litharenite. About 98.6% of the samples possess permeability less than 1 mD, while 89.7% of the samples possess porosity less than 10%. The high porosity/permeability space within tight reservoirs is dominated by dissolved pores, accounting for more than 80% of the total pore space. The dissolution minerals are mainly associated with feldspar, and the amount of feldspar dissolution is positively correlated with porosity and permeability. According to the fluid chemical information of quartz overgrowth and ankerite (related to feldspar dissolution), feldspar dissolved pores are caused by organic acid derived from the thermal maturity of organic matter. According to production data, no daily production can be achieved in single well, when the porosity and permeability are less than 7% and 0.1 mD, respectively. However, once it exceeds this porosity/permeability threshold value, the production capacity is exponentially improved. Furthermore, when surface porosity of feldspar dissolution exceeds 7%, most values of the porosity and permeability exceed the threshold values of the allowable productivity, indicating that extensive feldspar dissolution is favorable factor for effective reservoir space development in tight reservoirs. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of water injection management practices for complex and impactful onshore and offshore carbonate reservoirs. It delves into the fundamental aspects of waterflooding design, surveillance techniques, and monitoring methods tailored for the unique challenges posed by carbonate formations. Two case studies from the Permian Basin in Texas and two from Lula Field offshore Brazil and Agbami Field offshore Nigeria are examined considering scientific principles into practice to provide insights into best practices, lessons learned, and strategies to maximize the benefits derived from real noteworthy waterflood operations. The paper underscores the significance of rigorous reservoir characterization, including understanding reservoir architecture, heterogeneities, fracture networks, fluid communication pathways, and rock–fluid interactions. It emphasizes the crucial role of integrated multidisciplinary teams involving geologists, reservoir engineers, production engineers, and field operators in ensuring successful waterflood design, implementation, and optimization. Through the case studies, the paper highlights the importance of designing pattern configurations, well placements, and injection/production strategies to the specific reservoir characteristics, continually optimizing these elements based on surveillance data. It also stresses the necessity of comprehensive data acquisition, advanced analytics, numerical simulations, and frequent model updates for effective reservoir management and decision-making. The paper is impactful in terms of the lessons learned from the actual case studies, and how can these be implemented in actual field projects. Different case studies documented in the paper provide the challenges facing them and how different authors have addressed their problems in unique ways. The paper distills the information and important findings from a variety of case studies and provides succinct information that is of immense value as a reference. Important findings of these case studies are connected using creativity and are innovative as they introduce unique techniques and establish successful ideas to create new value in terms of maximizing oil recovery. Most importantly, this paper explores the application of innovative technologies, such as intelligent completions, 4D seismic monitoring, and water–alternating gas (WAG) injection, which can significantly improve waterflood performance in complex carbonate reservoirs. In summary, the paper provides a thorough understanding of the factors contributing to the success and failure of waterfloods in carbonate reservoirs through case studies based on factually and technically sound operations. It documents guidelines for optimizing waterflood performance and reducing or eliminating the potential for failures, reinforcing positive results in these challenging yet invaluable hydrocarbon resources. [ABSTRACT FROM AUTHOR]

This paper focuses on the current application of machine learning (ML) in enhanced oil recovery (EOR) through CO2 injection, which exhibits promising economic and environmental benefits for climate-change mitigation strategies. Our comprehensive review explores the diverse use cases of ML techniques in CO2-EOR, including aspects such as minimum miscible pressure (MMP) prediction, well location optimization, oil production and recovery factor prediction, multi-objective optimization, Pressure–Volume–Temperature (PVT) property estimation, Water Alternating Gas (WAG) analysis, and CO2-foam EOR, from 101 reviewed papers. We catalog relative information, including the input parameters, objectives, data sources, train/test/validate information, results, evaluation, and rating score for each area based on criteria such as data quality, ML-building process, and the analysis of results. We also briefly summarized the benefits and limitations of ML methods in petroleum industry applications. Our detailed and extensive study could serve as an invaluable reference for employing ML techniques in the petroleum industry. Based on the review, we found that ML techniques offer great potential in solving problems in the majority of CO2-EOR areas involving prediction and regression. With the generation of massive amounts of data in the everyday oil and gas industry, machine learning techniques can provide efficient and reliable preliminary results for the industry. [ABSTRACT FROM AUTHOR]

Diagenesis is a double-edged sword of geochemical recordings. It makes us always doubt about the representativeness of many geochemical indicators, especially the isotope and mineral related. It also provides a window to explore the biogeochemical processes at the water–rock interface, which are related to the interactions between the hydrosphere, biosphere, and lithosphere. In this study, we identified microbial early diagenesis in lacustrine ostracods from the Songliao Basin 91.35 million years ago by using in situ mineralogical and carbon isotope analytical methods. Our results suggest multiple biological early-diagenesis processes and the formation of a ferric and methane transition zone (FMTZ) in the sulfate-poor pore water, which are conducive to the formation of dolomite and ankerite. These secondary carbonate minerals related to dissimilatory iron reduction and methanogenesis have heavier carbon isotopic compositions than the calcified ostracod shell in the water column and might bring interferences to the geochemical parameters of ostracods. [ABSTRACT FROM AUTHOR]