Progress and development direction of technologies for deep marine carbonate gas reservoirs in the Sichuan Basin

Influence of reservoir heterogeneity on water invasion differentiation in carbonate gas reservoirs

Chemical water shutoff agents and their plugging mechanism for gas reservoirs: A review and prospects

High-quality development of ultra-deep large gas fields in China: Challenges, strategies and proposals

Aiming to investigate the supercritical CO2 miscible flooding performance in heterogeneous reservoirs, the CO2 gas channeling experiments of parallel short cores (matrix) with different permeability ratios and parallel long cores with different fracture conductivities were carried out in this work. The influences of the permeability ratio and fracture conductivity on oil recovery and gas channeling were analyzed. The results show that reservoir heterogeneity plays a key role in enhancing oil recovery. The permeability ratio not only affects the oil output but also controls the gas breakout time and the oil production in the post-breakout stage. High-permeability cores have higher displacement efficiency than low-permeability cores, but gas breakthrough occurs earlier. The formation of dominant gas channels in high-permeability cores restricts the flow of CO2 into low-permeability cores, resulting in lower displacement efficiency of low-permeability cores. In the case of the existence of fractures, a rapid breakthrough of CO2 will occur, and as the conductivity of the fractures increases, the gas breakthrough time becomes shorter and the gas channeling in the fractures becomes more serious. When the fracture–matrix core permeability ratio reaches 37, the matrix core does not produce oil and gas. In the initial stage, as the fracture conductivity becomes stronger, the oil production rate becomes faster and most of the oil is recovered before gas breakthrough. The fractures are not only the channel of oil flow but also the main path of gas channeling. The recovery curve flattens out rapidly after CO2 breakthrough. As fracture conductivity increases, the recovery curve flattens out faster, resulting in poor ultimate recovery. This study is expected to provide theoretical guidance for miscible CO2 flooding in heterogeneous tight oil reservoirs. 

Influence of Heterogeneity and Fracture Conductivity on Supercritical CO2 Miscible Flooding Enhancing Oil Recovery and Gas Channeling in Tight Oil Reservoirs

Effective water influx control in gas reservoir development: Problems and countermeasures

Profitable development technology of the Changning-Weiyuan National Shale Gas Demonstration Area in the Sichuan Basin and its enlightenment

The molecular models of nanopores for major rock constituents in deep shale were constructed. The microscopic adsorption behavior of methane was simulated by coupling the grand canonical Monte Carlo and Molecular Dynamics methods and the effect of rock constituents was discussed. Based on the illite and kerogen nanopore models, the discrepancies in microscopic water distribution characteristics were elucidated, the effects of water on methane adsorption and its underlying mechanisms were revealed, and the competitive adsorption characteristics between water and methane were elaborated. The results show a similar trend in the microscopic distribution of methane between different shale rock constituents. Illite and kerogen slit pores have no significant difference in methane adsorption capacity. The adsorption capacity per unit mass of kerogen is greater than that of illite due to the smaller molar mass of the kerogen skeleton and its large intermolecular porosity. Illite has a greater affinity for water than methane. With increasing water content, water molecules preferentially occupy the high-energy adsorption sites and then overspread the entire pore walls to form water adsorption layers. Methane molecules are adsorbed on the water layers, and methane adsorption has little effect on water adsorption. Kerogen is characterized as mix-wetting. Water molecules are preferentially adsorbed on polar functional groups and gather around to form water clusters. In kerogen with high water content, methane adsorption can facilitate water cluster fusion and suppress water spreading along pore walls. In addition to adsorption, some water molecules dissolve in the kerogen matrix.

/pdf/molecular-simulation-of-methane-adsorption-in-deep-shale-6uym3i84.pdf

Molecular Simulation of Methane Adsorption in Deep Shale Nanopores: Effect of Rock Constituents and Water

Shale gas reservoirs are unconventional resources with great potential to help meet energy demands. Horizontal drilling and hydraulic fracturing have been extensively used for the exploitation of these unconventional resources. According to engineering practice, some shale gas wells with low flowback rate of fracturing fluids may obtain high yield which is different from the case of conventional sandstone reservoirs, and fracturing fluid absorbed into formation by spontaneous imbibition is an important mechanism of gas production. This paper integrates NMR into imbibition experiment to examine the effects of fractures, fluid salinity, and surfactant concentration on imbibition recovery and performance of shale core samples with different pore-throat sizes acquired from the Longmaxi Formation in Luzhou area, the Sichuan Basin. The research shows that the right peak of T2 spectrum increases rapidly during the process of shale imbibition, the left peak increases rapidly at the initial stage and changes gently at the later stage, with the peak of the left peak shifting to the right. The result indicates that water first enters the fracture system quickly, then enters the small pores near the fracture wall due to the effect of the capillary force, and later gradually sucks into the deep and large pores. Both imbibition rate and capacity increase with increased fracture density, decreased solution salinity, and decreased surfactant concentration. After imbibition flowback, shale permeability generally increases by 8.70–17.88 times with the average of 13.83 times. There are also many microcracks occurring on the end face and surface of the core sample after water absorption, which may function as new flowing channels to further improve reservoir properties. This research demonstrates the imbibition characteristics of shale and several relevant affecting factors, providing crucial theory foundations for the development of shale gas reservoirs.

/pdf/nmr-based-shale-core-imbibition-performance-study-1xez9hw3.pdf

NMR-Based Shale Core Imbibition Performance Study

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