致密储层CO₂驱动态裂缝网络水平井试井模型

Dynamic fracture network well-testing model for horizontal wells in tight reservoirs with CO₂ injection

摘要

为有效表征流体在致密储层 CO₂ 驱动态裂缝网络系统的分区闭合及动态储容效应，以及反演动态裂缝网络特征参数，建立一种动态裂缝网络水平井试井模型，采用半解析方法、Laplace 转换、动态裂缝特征函数、杜哈美原理和 Stehfest 数值反演求解试井模型，获得井底压力响应半解析解，绘制井底压力响应曲线，对动态裂缝闭合速度、井筒储集系数、动态裂缝网络半径和动态储容比进行敏感性分析。结果表明：考虑致密储层 CO₂ 驱动态裂缝网络的压力图版与常规压力图版存在显著差异；井底压力响应曲线呈异常尖峰和额外双水平线特征， ；动态裂缝闭合速度、动态裂缝网络半径及动态储容比对井底压力响应影响较大。动态裂缝网络水平井试井模型能有效定量表征致密储层长期注入 CO₂ 的动态裂缝网络行为及非稳态渗流规律，为 CO₂ 强化致密储层开发提供依据。

Abstract

In order to characterize the zonal closure and dynamic storativity effects of fluids in a dynamic fracture network system, and then invert the characteristic parameters of the dynamic fracture network, a dynamic fracture network well-testing model is established. The model is solved using semi-analytical method, Laplace transform, dynamic fracture conductivity function, dynamic storativity function, Duhamel's principle, and Stehfest numerical inversion theory to obtain a semi-analytical solution of the bot-tom-hole pressure response. The dynamic bottom-hole pressure response curve is plotted, and a sensitivity analysis is conducted on the dynamic fracture closure rate, wellbore storage coefficient, dynamic fracture network radius, and dynamic storage capacity ratio. Results show that the pressure plot considering the dynamic fracture network significantly differ from conventional pressure plots; the bottomhole transient pressure curve exhibits abnormal peaks and additional double-horizontal line features ( ). The dynamic fracture closure rate, dynamic fracture network radius, and dynamic storativity ratio significantly impact the bottom-hole pressure response. Numerical simulations and field case study validate the reliability and practicality of the proposed model. This model effectively quantifies the un-steady-state seepage behavior and dynamic pressure response characteristics of long-term CO2 injection in tight reservoirs, providing theoretical basis and technical support for the development of CO₂-enhanced tight reservoir.

关键词

致密储层 / CO₂ 驱 / 动态裂缝网络 / 分区闭合 / 动态储容 / 试井分析

Key words

tight reservoir / CO₂ flooding / dynamic fracture network / zonal closure / dynamic storativity / well testing analysis

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基金资助

国家自然科学基金项目(51974330)

国家自然科学基金青年项目(52004219)

陕西省自然科学基金项目(2020JQ-781)