Well-pattern optimization of CH4 transport associated with supercritical CO2 flooding

During CO2 displacement of CH4 in shale, competitive adsorption results in reduced pore space used for gas flow in shale, which is closely associated with the production capacity of shale-gas reservoirs. Thus, the present work investigates the effects of CO2–CH4 competitive adsorption on production capacity. Herein, a slit–pore model is developed in terms of gas storage (CO2 and CH4) and graphene pores using molecular dynamics and implemented via large-scale atomic/molecular massively parallel simulator. The effects of CO2 injection pressure, temperature, and velocity and of pore size on CO2–CH4 displacement and competitive adsorption properties are simulated and examined. Hence, the displacement efficiency of CH4 and the adsorption layer thickness of the CO2–CH4 binary mixture are determined. Moreover, based on a basic seepage model of planar linear flooding, the effect of CO2–CH4 competitive adsorption on production capacity is analytically investigated. Results demonstrate that the production capacity with consideration of adsorption layer thickness is less than that without consideration of adsorption layer thickness, illustrating that CO2–CH4 competitive adsorption behaviors are closely connected with permeability, flow rate, and production capacity of shale-gas reservoirs, especially for shale-gas reservoirs containing large numbers of pores and slits.

Effects of competitive adsorption on production capacity during CO2 displacement of CH4 in shale

Deng

Zhang

et al. 2022

Research on the seepage properties of coal with different particle size proppant under cyclic loading

Liu

Zhu

et al. 2023

The selection of proppant particle size significantly impacts the gas output and gas production period of the extracting coalbed methane (CBM). This study combines theoretical analysis and experiment, based on the in-situ stress distribution characteristics of the coal seam in Wangjiazhai Coal Mine, Guizhou Province, conducted artificially-fractures permeability testing with different particle size proppant combinations during the cyclic loading and unloading. The findings indicate that the coal sample with two particle sizes of proppant has more permeability and smaller stress sensitivity coefficient than the coal sample with a single proppant as effective stress increases, the coal sample with the maximum permeability and the smallest stress sensitivity coefficient is placed with proppant ratio of 20/40 mesh to 40/70 mesh is 1 to 3. The stress sensitivity coefficient and the permeability decreases with increasing the number of confining pressure cycles. The depth of proppant embedding increases has a hysteresis phenomenon with increasing the effective stress, and the coal sample with proppant ratio of 20/40 mesh to 40/70 mesh is 1 to 3 has the smallest embedded depth. The proppant will cause damage to the fractures surface of the coal seam. This study provides technical support for efficiently extracting the CBM resources that are difficult to exploit in Guizhou Province.

Adaptability and enhanced oil recovery performance of surfactant–polymer flooding in inverted seven-spot well pattern

2023

As one of the leading technologies for chemical enhanced oil recovery (cEOR), surfactant–polymer (SP) flooding technology has long attracted the interest of petroleum scientists and engineers. However, most of its application scenarios are based on the five-spot well pattern. The EOR potential in an inverted seven-spot well pattern is seldom ever recorded. The applicability of the SP system in the inverted seven-spot well pattern was examined based on the physical characteristics of Karamay Oilfield in China. The numerical simulation and the one-dimensional core flooding experiment were used to compare the sweep intensities and EOR abilities of the two well patterns. The migration law and the EOR ability of the SP system were assessed by a specially made one-third inverted seven-spot configuration. The main controlling factors and compatibility charts of SP flooding development in the inverted seven-spot well pattern were obtained. Results show that 61% of the region is represented by a weak swept state in the inverted seven-spot well pattern. The effective swept area is greatly increased by appropriately raising the viscosity and slug size of the SP system. Compared to constant viscosity injection, step-down viscosity injection further increases the sweep range and oil recovery. The inverted seven-spot well pattern has a greater swept area of the SP system than the five-spot one, but a weaker strength. Polymer concentration is the most effective factor of SP flooding in the inverted seven-spot well pattern, followed by oil viscosity and surfactant concentration. The study can broaden the application of the SP system in the inverted seven-spot well pattern.