Actual and Optimal Hydraulic Fracture Design in a Tight Gas Reservoir

Abstract

Designing hydraulic fracture stimulation to optimize well productivity requires knowledge of the initial reservoir pressure and permeability, the closure stress magnitudes in the reservoir and in bounding formations, a carrier fluid with a suitable leakoff coefficient, and rock properties such as the Young's modulus and the Poisson ratio that can be determined from a core sample. When key parameters are left unknown, the hydraulic fracture stimulation is likely to be severely suboptimal.This study integrates pressure buildup and production transient analyses with microseismic surveys and the recorded pumping schedule to estimate the above-mentioned parameters in previously fractured wells on production for up to 7 years from a tight gas reservoir.The first well drilled and completed in the block included a pressure buildup test that enabled accurate estimation of the initial reservoir pressure and permeability. A post-fracture buildup test was also conducted, and annual pressure buildup tests in 6 subsequent years showed continuous changes in the fracture morphology with fracture conductivity decreasing by a factor of 3 and fracture length increasing by about 50%. Many of the subsequent wells were drilled in 2 pattern well clusters, each designed to account for fracture propagation behavior indicated from a microseismic survey. A comparison with an optimal hydraulic fracture design intended to maximize well productivity indicates that most of the well stimulations were suboptimal with rate and cumulative production about ½ that of an optimized design based on the same proppant mass.The observed changes in fracture conductivity and length over time were unanticipated. Because such data are rarely recorded the variations in fracture morphology may be fairly typical and should be of considerable interest to pressure transient analysts. The production data analysis shows the difficulties in determining formation and fracture parameters when the transient response lacks radial flow. The fracture treatment analysis shows a comparison between the actual fracture treatment and one designed to maximize well productivity and clearly illustrates the potential for well improvement using modern hydraulic fracture design principles.

Hydraulic Fracturing Treatment Optimization for Low Permeability Reservoirs Based on Unified Fracture Design

“…However, the above works only focus on the optimization of fracture number, fracture spacing and fracture geometry dimensions. Treatment optimizations are not mentioned [62][63][64][65]. In order to satisfy the optimal fracture dimensions, the treatment parameters should also be optimized further.…”