Simulation and Analysis of Fracture Swarms Observed in the Eagle Ford Field Experiment

V. Sesetty, A. Ghassemi
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引用次数: 6

Abstract

Coring adjacent to a hydraulically fractured horizontal well in Eagle Ford shale by Conoco-Phillips has revealed several closely spaced parallel hydraulic fractures (separated only by few inches) propagating in the direction perpendicular to the wellbore axis. The number of observed hydraulic fractures greatly exceed the number of clusters according to the recent paper titled "Sampling a Stimulated Rock Volume: An Eagle Ford Example". The observed behavior is contrary to the conventional practice of hydraulic fracture modeling where often a single fracture from each perforation cluster. This assumption stems from a simplified concept of the stress shadow that inhibit the growth of multiple parallel fractures under very tight spacing. In this study we show that correct modeling can in fact capture the field observed fracture clusters or swarms of closely-spaced fractures. Numerical model based on displacement discontinuity method is used to simulate non-planar hydraulic fracture propagation. Fracture deformation, fluid flow and perforation friction are fully coupled. Fracture propagation from a single cluster consisting of 20 perforations under 1800 phasing spanning 5 ft is considered. The effect of controlling parameters such as far-field stress contrast, perforation properties, and fracture toughness on multiple hydraulic fracture growth from a cluster of perforations is studied. The results show that closely spaced fracture clusters or swarms can occur for a certain range of conditions and operational parameters. The in-situ stress contrast, perforations conditions, and injection rates exert a significant influence. Under the right conditions, closely-spaced fractures can extend to distances exceeding tens of feet from the wellbore. Early termination and/or coalescence of closely spaced fractures can also occur. To our knowledge, our modeling results are the only ones that can explain the data from the Conoco-Phillips field observations regarding the occurrence of fracture swarms. The resuts show that the assumption of a single fracture per cluster does not hold true under all conditions. Moreover, such assumption would significantly underestimate stimulated rock volume near the wellbore. Finally, our results capture the injection pressure data which can be used as a diagnostic tool to infer the perforation effectiveness (i.e., the number of perforations that are in contact with fluid flow).
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Eagle Ford油田试验观测裂缝群的模拟与分析
康菲公司在Eagle Ford页岩的一口水力压裂水平井附近取心,发现了几条紧密间隔的平行水力裂缝(相距仅几英寸),沿垂直于井筒轴线的方向延伸。根据最近一篇题为《对受刺激岩石体积取样:以Eagle Ford为例》的论文,观察到的水力裂缝数量大大超过了裂缝簇的数量。观察到的行为与传统水力压裂建模的做法相反,通常每个射孔簇中只有一条裂缝。这一假设源于一个简化的应力阴影概念,即在非常紧的间距下,应力阴影会抑制多条平行裂缝的生长。在这项研究中,我们表明,正确的建模实际上可以捕获现场观察到的裂缝簇或紧密间隔的裂缝群。采用基于位移不连续法的数值模型模拟非平面水力裂缝的扩展。裂缝变形、流体流动和射孔摩擦是完全耦合的。考虑了由20个射孔组成的单个簇在1800相位下跨越5英尺的裂缝扩展。研究了远场应力对比、射孔性能和断裂韧性等控制参数对射孔簇水力裂缝扩展的影响。结果表明,在一定的条件和操作参数范围内,可以产生紧密间隔的裂缝簇或裂缝群。地应力对比、射孔条件和注入速度是影响射孔效果的重要因素。在适当的条件下,紧密间隔的裂缝可以延伸到距井筒超过数十英尺的距离。紧密间隔骨折的早期终止和/或合并也可能发生。据我们所知,我们的建模结果是唯一可以解释康菲石油公司现场观察到的有关裂缝群发生的数据。结果表明,并非在所有条件下,每个簇只形成一条裂缝的假设都成立。此外,这种假设将大大低估井筒附近的受激岩石体积。最后,我们的结果捕获了注入压力数据,该数据可作为诊断工具来推断射孔有效性(即与流体接触的射孔数量)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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