ANALYSIS OF GAS PRODUCTION FROM HYDRAULICALLY FRACTURED WELLS IN NATURALLY FRACTURED RESERVOIR USING SOURCE FUNCTION METHOD
根据2014年EIA的统计数据，页岩和致密油气区块的天然气产量占美国天然气产量的48%，预计2040年这一数字将增长至69%。在非常规储层中，通常发育有天然裂缝。水平井多级水力压裂是开发页岩/致密储层的有效技术。天然裂缝可能在压裂后被张开，有的甚至压裂前就具有传导率。合理预测如此复杂系统，尤其是考虑天然裂缝分布的气井产能仍然是一个挑战。 本研究提出了一种基于格林源函数和分形离散裂缝网络（FDFN）模型的方法。
ABSTRACT
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.
