Modeling of Water Behavior in Hydraulically-Fractured Shale Gas Wells

Abstract

This study presents the modeling of water behavior in hydraulically-fractured of shale gas wells. A five layers model represents a hydraulically-fractured shale gas well was built in Sensor reservoir simulator through Pipe-It, integrated asset management software. Stress dependent permeability multiplier is applied in the model to represent the permeability enhancement in the zone close to the fracture face during the fracturing stimulation. An implicit black-oil logarithmic model with a total of grid number of 5,800 and thickness of 200 ft is used as the base case model. The horizontal well extends through the reservoir in x-direction. The fracture is located in the center of x-axis, while the tip of the fracture is in the middle of y-axis.Water behavior in the fracture for this study is represented by water saturation within the fracture grids. A better understanding of water behavior in the fracture and its effects on the production profile was obtained through several sensitivity cases, which include number of layers, perforation location, matrix permeability, gas production rate, and shut-in time.Based on the sensitivity tests, it was observed that high water saturation in the fracture is found when the perforation is located in the uppermost layer of the model. For matrix permeability sensitivity, the total kh for the model is maintained at a constant. Reservoir with high matrix permeability in the uppermost layer gives higher water saturation in the fracture. The varying gas production rates influence the water saturation in the fracture. Higher gas rates result in higher water saturation in the fracture. The water saturation profile analysis based on the rate sensitivity shows that a critical gas rate to feed the water from the matrix to the fracture is expected to exist. Water saturation profiles in the matrix have relatively the same profile according to shut-in sensitivity. These differing water saturation profiles on the shut-in sensitivity indicate delayed of water feed from the matrix to the fracture.Also, different perforation locations affect the water production profile, but not on the gas production profiles. Both gas and water production profiles are not significantly affected by different matrix permeability values. Rate sensitivity shows that higher gas rate results in higher total water production. Shut-In period also affects the production profiles. Gas and water productions are observed to decrease with an increased shut-in time due to the delay of production. It is noteworthy that the differences in total water productions are substantial. This is due to shut-in period after water injection reduces water recovery, as compared to immediate production after water injection.From the sensitivities applied to the model, water saturation in the fracture is generally affected by all sensitivity parameters, thus also affects production profiles. This study contributes to having a better understanding in the water behavior in the fracture and the production profiles of shale well gas.