Design and Analysis of Improved Swelling and Degradable Diverting Agent for Multistage Hydraulic Fracturing

K. Ikebata, Tomoki Onishi, K. Furui, S. Mandai, Y. Hirano, Yuya Kanamori, Bessie Psihogios, R. Taniguchi
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引用次数: 5

Abstract

Fracturing fluid diversion plays a crucial role in maximizing the well productivity of multistage fractured wells. Proper sizing and material design of diverting agents are key elements to effectively bridge and plug perforations and fractures during treatment. In this study, we present an improved design for a water-soluble diverting agent that can cover a range of fracture widths. In addition, a wellbore flow model that predicts the swelling and dissolution behaviors of diverting agents flowing from the surface to the fractures was developed for field applications. Butenediol vinyl alcohol copolymer (BVOH), which has elastic and sticking properties in water, is used as a diverting agent. Cylindrical pellets and smaller sized powder, made from the polymer, were mixed to bridge and plug hydraulic fractures. BVOH diverting agents were evaluated for slit widths of 1–4 mm with different pellet geometries using a high-pressure and high-temperature filtration apparatus. The swelling and dissolution rates depend on many parameters such as the temperature, dissolution time, crystallinity degree, and geometry. In this study, empirical correlations that predict the swelling and dissolution rates of BVOH polymers for various formulations were developed and implemented in a wellbore flow model that simulates fluid flow and heat transfer during pumping operations. A theoretical case study of a multistage hydraulic fracturing treatment was also presented to demonstrate the applicability and effectiveness of the treatment. The filtration test results with various diverting agent designs indicate that the length and diameter of the pellets affect the performance and effectiveness of the bridging and plugging fracture-like slits. Moreover, an optimum pellet size exists for different slit sizes. With modified pellet size and diameter ratios, wider slits of 3–4 mm can be effectively plugged by diverting agents with reduced leakoff volumes. The swelling and dissolution models correlated well with the experimental data, considering the temperature, dissolution time, and crystallinity degree. The case studies presented in this study illustrate that the models can predict the time required for the diverting agents to dissolve under field conditions and determine whether the diverting agents pumped into the well provide sufficient conditions for diversion. Furthermore, the study results indicate that the pump rate and injection conditions before pumping the diverting agent are key controlling factors in determining the dynamic downhole temperatures and thus affect the time required for the degradation of the diverting agent. In addition, a field trial result is presented to demonstrate the effectiveness of the swellable, BVOH diverting agent at low downhole temperatures, and hydraulic fracturing treatment in the Permian Basin. Swelling diverting agents exhibit a more elastic behavior than existing particulate diverting agents. Swelling polymers are less abrasive and thus reduce the risk of equipment damage during preparation and pumping. The wellbore flow simulator developed in this study helps stimulation engineers optimize material types, particle-size distribution, and concentration of diverting agents for various field applications.
多级水力压裂改进型膨胀可降解导流剂的设计与分析
压裂液的分流对多级压裂井的产能最大化起着至关重要的作用。在施工过程中,适当的转向剂尺寸和材料设计是有效桥接和封堵射孔和裂缝的关键因素。在这项研究中,我们提出了一种改进的水溶性转向剂设计,可以覆盖一定范围的裂缝宽度。此外,还开发了一个井筒流动模型,该模型预测了转向剂从地面流向裂缝的膨胀和溶解行为,可用于现场应用。丁烯二醇乙烯醇共聚物(BVOH)在水中具有弹性和粘接性能,被用作转流剂。由聚合物制成的圆柱形颗粒和较小尺寸的粉末混合在一起,以桥接和堵塞水力裂缝。BVOH导流剂的狭缝宽度为1-4 mm,具有不同的颗粒几何形状,使用高压和高温过滤装置进行了评估。溶胀和溶解速率取决于许多参数,如温度、溶解时间、结晶度和几何形状。在本研究中,开发了预测不同配方BVOH聚合物膨胀和溶解速率的经验相关性,并将其应用于模拟泵送作业过程中流体流动和传热的井筒流动模型中。以多级水力压裂技术为例,论证了该技术的适用性和有效性。不同导流剂设计的过滤试验结果表明,球团的长度和直径影响桥接和封堵裂缝的性能和效果。此外,对于不同的狭缝尺寸,存在一个最佳的球团尺寸。通过调整颗粒尺寸和直径比,可以通过减少泄漏量的转向剂有效地堵塞3-4 mm的更宽的裂缝。考虑温度、溶解时间和结晶度等因素,溶胀和溶解模型与实验数据吻合较好。本研究的实例表明,该模型可以预测暂堵剂在现场条件下溶解所需的时间,并确定泵入的暂堵剂是否为暂堵提供了充分的条件。此外,研究结果表明,泵送暂堵剂前的泵速和注入条件是决定井下动态温度的关键控制因素,从而影响暂堵剂降解所需的时间。此外,现场试验结果证明了可膨胀、BVOH转向剂在井下低温下的有效性,以及在Permian盆地的水力压裂处理。膨胀型转流剂比现有的颗粒型转流剂表现出更强的弹性。膨胀聚合物的磨蚀性较低,因此在制备和泵送过程中降低了设备损坏的风险。本研究开发的井筒流动模拟器可以帮助增产工程师优化各种现场应用的材料类型、粒径分布和暂堵剂浓度。
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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