水平井水力压裂裂缝扩展诱发垂直邻井光纤应变演化特征

Characteristics of fiber-optic strain evolution in vertical adjacent well induced by hydraulic fracture propagation in horizontal well

摘要

水力压裂过程中很难准确获取裂缝高度扩展信息,利用分布式光纤可准确评价裂缝扩展信息。采用有限元耦合内聚力单元方法,建立水平井水力压裂裂缝扩展诱发垂直邻井光纤应变的正演模型,进行垂直邻井光纤应变数值模拟,分析光纤应变演化特征;根据压裂施工参数及垂直邻井光纤布设位置,判定水力压裂裂缝的光纤有效监测范围;利用大型真三轴压裂实验与分布式光纤感测设备,进行光纤实时监测水平井水力压裂物理实验。结果表明:裂缝高度扩展诱发光纤应变演化分为应变增强、张应变扩展、应变直线状汇聚及应变弱化4个阶段,光纤应变演化特征表现为中间部分出现张应变汇聚带,两侧出现压应变汇聚带。当水力压裂裂缝在光纤有效监测范围内时,垂直邻井光纤可有效监测裂缝高度扩展情况。垂直邻井的光纤应变演化结果与光纤应变正演模计算结果验证正演模型的正确性。利用裂缝高度扩展诱发垂直邻井光纤应变演化特征可评价裂缝高度扩展状态,为油田压裂设计提供参考。

Abstract

It is difficult to accurately obtain the fracture height expansion information during the fracturing process, and the use of distributed optical fiber can accurately evaluate the fracture expansion information. Based on the finite element coupled cohesive force unit method, construct a forward model of fiber-optic strain induced in vertical adjacent wells due to the propagation of hydraulic fracturing fractures in horizontal wells, carry out numerical simulation of fiber-optic strain in vertical adjacent wells, and analyze the characteristics of fiber-optic strain evolution. Based on the fracturing construction parameters and the position of vertical adjacent well optical fiber deployment, it can be determined whether hydraulic fractures are within the effective monitoring range of the optical fiber. Utilizing large-scale true tri-axial fracturing experiments and distributed optical fiber sensing equipment to conduct real-time monitoring of hydraulic fracturing physical experiments in horizontal wells using optical fibers. The results show that the fiber-optic strain evolution induced by the fracture height expansion is divided into four stages: strain-enhancing, tensile-strain-expanding, strain-linear-converging and strain-weakening, and the fiber-optic strain evolution is characterized by the appearance of tensile strain convergence bands in the middle part and compressive strain convergence bands on both sides. When the fracture is within the effective monitoring range of the deployed fiber optic, the vertical adjacent well fiber optic can effectively monitor the height expansion of fractures. The evolution results of fiber-optic strain in vertical adjacent wells and the verification of the correctness of the forward model by fiber-optic strain forward modeling calculation results. The characteristics of the strain evolution induced by fracture height expansion observed by an adjacent optical fiber can help to evaluate the status of fracture height expansion, providing reference and guidance for oilfield fracturing design.

关键词

水平井 / 水力压裂 / 裂缝扩展 / 垂直邻井 / 光纤应变 / 演化特征 / 分布式光纤 / 裂缝识别 / 裂缝高度

Key words

horizontal well / hydraulic fracturing / fracture propagation / vertical adjacent well / fiber-optic strain / evolutionary characteristics / distributed optical fiber / identification of fracture / fracture height

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基金资助

国家自然科学基金项目(52334001)