A fracture/proppant system is used to mimic the interaction between the rock matrix and proppants during the process of fracture closing attributed to pore-pressure reduction during hydrocarbon production. Effects of rock type and bedding-plane direction are investigated. High-strength sintered bauxite proppants are placed in hydraulic fractures in sandstone and shale rock. There are two bedding-plane directions in shale rock: One is 90 , which is perpendicular to the fracture, whereas the other is 0 , which is parallel to the fracture. Increasing mechanical loading is imposed to close the fracture. Micrometer-scale X-ray tomography is used to visualize the internal structure. Cutting-edge image-processing methods are applied to extract patterns of both the fracture and matrix. A pore-scale lattice Boltzmann simulator, optimized with graphics-processing-unit parallel computing, is used to simulate the permeability tensor inside the fracture. Significant proppant embedment is observed in the sandstone rock when the effective stress is increased to 4,200 psi. Consequently, fracture porosity is reduced by nearly 70%, and permeability is reduced by two orders of magnitude. Embedded proppants are unable to create microscopic fractures on the matrix surface because of the low bonding strength between grains. In the shale rock with 90 bedding planes, when the effective stress is increased to 3,000 psi, significant microscopic fractures on the matrix surface are created because the lamination structure of the matrix is opened. In the shale rock with 0 bedding planes, noticeable microscopic fractures on the matrix surface are not observed until the effective stress is increased to 6,990 psi. Proppant embedment is insignificant because of the high bonding strength between fine grains. Significant anisotropy in the permeability tensor is observed during all experiments. This study is the first to use cutting-edge imaging and modeling methods to quantitatively study the interaction between proppants and the rock matrix during the stressincrease process. It has important applications, which help sustain production with adequate fracture conductivity in deep reservoirs (e.g., the Haynesville shale). Laboratory Materials and ApparatusAs illustrated in Fig. 1a, a cylindrical core plug (1-in. diameter and 2-in. length) was cut into two identical halves. The space between the two halves is the primary propped hydraulic fracture and hereafter is referred to as the primary fracture, in which 20-to 40-mesh high-strength sintered bauxite proppants were uniformly placed to form a monolayer. All the materials were retained in place by a cylindrical sleeve. Uniaxial mechanical stress was imposed to close the primary fracture (Fig. 1b) to mimic the

As more wells are drilled and completed in deeper reservoirs, various methods are being applied to overcome choking effects in propped fractures and enhance well productivity. Choking effects can result from permeability damage caused by fracturing gel residues, low proppant concentrations, proppant crushing from high closure stresses, or embedment/intrusion of formation materials into the proppant pack. This paper describes the laboratory testing of a new well stimulation method that can use low-quality sand for generating stable, highly conductive channels within a propped fracture to help maximize and maintain production of hydrocarbon from the formation reservoir to the wellbore.Mini-pillars of various particulate materials were formed by coating them with a tackifying agent or a curable resin and placing them in molds to be cured before testing. These mini-pillars were installed in conductivity cells using various layout configurations to determine the effect of closure stresses on pillar height, diameter expansion, conductivity measurements, and choice of particulate materials. Laboratory experiments were performed to evaluate the formation and stability of mini-pillars and proppant-free channels surrounding the pillars.The obtained results in this study indicate that flow capacity of conductive channels prepared from proppant pillars with low-quality sands was comparable to those prepared using high-quality sand or high-strength manufactured proppant. Proppant crushing was not observed to be a concern when applying fine particulates during this fracturing process because flow capacity of proppant-free channels between aggregate masses dominates flow through the propped fracture, making the formation of proppant pillars with high-quality sand or high-strength proppant unnecessary. As long as proppant pillars are held in place without being previously dispersed or broken up to ensure the integrity of proppant-free channels, low-quality sand or particulates can be a practical and economical source of solids material for preparing these proppant aggregates.

As more wells are drilled and completed in deeper reservoirs, various methods are being applied to overcome choking effects in propped fractures and enhance well productivity. Choking effects can result from permeability damage caused by fracturing gel residues, low proppant concentrations, proppant crushing from high closure stresses, or embedment/intrusion of formation materials into the proppant pack. This paper describes the laboratory testing of a new well stimulation method that can use low-quality sand for generating stable, highly conductive channels within a propped fracture to help maximize and maintain production of hydrocarbon from the formation reservoir to the wellbore.Mini-pillars of various particulate materials were formed by coating them with a tackifying agent or a curable resin and placing them in molds to be cured before testing. These mini-pillars were installed in conductivity cells using various layout configurations to determine the effect of closure stresses on pillar height, diameter expansion, conductivity measurements, and choice of particulate materials. Laboratory experiments were performed to evaluate the formation and stability of mini-pillars and proppant-free channels surrounding the pillars.The obtained results in this study indicate that flow capacity of conductive channels prepared from proppant pillars with low-quality sands was comparable to those prepared using high-quality sand or high-strength manufactured proppant. Proppant crushing was not observed to be a concern when applying fine particulates during this fracturing process because flow capacity of proppant-free channels between aggregate masses dominates flow through the propped fracture, making the formation of proppant pillars with high-quality sand or high-strength proppant unnecessary. As long as proppant pillars are held in place without being previously dispersed or broken up to ensure the integrity of proppant-free channels, low-quality sand or particulates can be a practical and economical source of solids material for preparing these proppant aggregates.

A fracture-proppant system is used to mimic the interaction between the rock matrix and proppants during the process of fracture closing attributed to pore pressure reduction during hydrocarbon production. Effects of rock type and bedding plane direction are investigated. High-strength sintered bauxite proppants are placed into simulated hydraulic fractures in sandstone and shale rock. There are two bedding plane directions in shale rock; one is 90°, which is perpendicular to the fracture, while the other is 0°, which is parallel to the fracture. Increasing mechanical loading is imposed to close the fracture. Micron-scale X-ray tomography is used to visualize the internal structure. Cutting-edge imaging processing methods are applied to extract patterns of both the fracture and matrix. A pore-scale lattice Boltzmann (LB) simulator, optimized using graphics processing unit (GPU) parallel computing, is used to simulate the permeability tensor inside the fracture. Significant proppant embedment is observed in the sandstone rock when the effective stress is increased to 4,200 psi. Consequently, fracture porosity is reduced by nearly 70%, and permeability is reduced by two orders of magnitude. Embedded proppants are unable to create microscopic fractures on the matrix surface because of the low bonding strength between grains. In the shale rock with 90° bedding planes, when the effective stress is increased to 3,000 psi, significant microscopic fractures on the matrix surface are created because the lamination structure of the matrix is opened. In the shale rock with 0° bedding planes, noticeable microscopic fractures on the matrix surface are not observed until the effective stress is increased to 6,990 psi. Proppant embedment is insignificant because of the high bonding strength between fine grains. Significant anisotropy in the permeability tensor is observed during all experiments. This study is the first to use cutting-edge imaging and modeling methods to quantitatively study the interaction between proppants and the rock matrix during the stress increase process. It has important applications, which help sustain production with adequate fracture conductivity in deep reservoirs (e.g., the Haynesville shale).