Analysis of Gas Production from Hydraulically Fractured Wells in Naturally Fractured Reservoir Using Source Function Method
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According to the 2014 EIA statistics, natural gas production from shale and tight oil plays accounted for 48% of US natural gas production and this number is expected to grow to 69% in 2040. Natural fractures are commonly observed in these unconventional reservoirs. Multi-stage hydraulic fracturing in horizontal wells has been applied to develop these shale/tight sands. Natural fractures could be open during treatment or conductive even before treatment, providing a larger drainage by creating a complex network. It still remains a challenge to reasonably predict well performance in such a complex system, especially by honoring the distribution of natural fractures explicitly. This study presents a methodology based on Green’s source function and Fractal discrete fracture network (FDFN) model. Slab source is a plane source with finite thickness, which is a novel approach of classic source function by reducing the erroneous integration. The hydraulic and natural fractures together are represented by independent slab sources, and their influence on each other is considered, which is more realistic than summing the flow from each fracture as total flow. FDFN model was used to generate realistic natural fracture maps. Production from adsorbed gas, common in shale reservoirs, is also modeled using modified material balance equation. I applied our model to estimate the multi-stage hydraulic fractured horizontal gas well performance in synthetically generated naturally fractured reservoirs. An extended number of natural fractures were handled by introducing several approaches to speed up the calculation. A parametric study was conducted to delineate important parameters affecting well performance. Simulation results indicated that conductive natural fracture largely influence gas production in unconventional reservoirs. The characteristics of natural fractures, such as density, length and interaction with hydraulic fractures were found to be controlling parameters. It was also found that the inclusion of adsorbed gas could result in the total gas production increase up to 25%. Also, comparisons are provided with published or commercially available numerical and analytical approaches to verify the methodology of this study. The novelty of the method is in the ability to respect the previously identified fracture distribution explicitly, either hydraulic or natural, even if the fractures are non-orthogonal to the horizontal wellbore. Since the approach is semi-analytical, it is easy to use and solves the problem in reasonable time using standard computers.
Hwang, Yun Suk (2017). Analysis of Gas Production from Hydraulically Fractured Wells in Naturally Fractured Reservoir Using Source Function Method. Doctoral dissertation, Texas A & M University. Available electronically from