摘要：

昭通示范区海坝区块浅层页岩气具有埋深浅、地层压力低、地层倾角变化大等特征，试气返排呈现见气时间长、见气返排率高、稳定试气产量低等规律。返排不当易出现井筒沉砂、积液以及裂缝体积损失等问题，需要优化返排制度以兼顾返排安全与排水采气效率。本文开展了系统性分析研究，基于区块内71口井试气返排数据，识别出纯排液、气相突破与稳定试气三阶段特征。结合裂缝压缩模型及产量不稳定分析方法，揭示不同返排制度下有效裂缝体积及有效裂缝半长变化规律：快速返排制度会导致有效裂缝体积不可逆损失达30%，而慢返排制度可将该损失降低至12%。为减少该不可逆损失，综合解决浅层页岩气返排关键问题，基于裂缝内有效应力求解，确定开井压力；建立井筒支撑剂沉降和裂缝支撑剂回流模型，分别得到井筒临界携砂流速和裂缝支撑剂回流临界流量；并基于井筒多相流原理确定最低排液井底压力和临界携液气速。据此提出了涵盖合理开井时机、井筒清砂、支撑剂回流防控、排液保障的综合优化方法，构建了试气返排制度优化图版。现场应用结果表明，该图版能够实现压裂效果保障与高效排采的协同优化，相似储层条件及改造措施下估算最终可采量增加20%。本研究实现了返排制度由经验化向定量化的转变，提出的关键临界判据和优化图版具有较强的普适性，可为其它非常规油气井的返排优化提供技术参考。

关键词: 浅层页岩气, 试气返排, 返排特征, 安全返排图版, 支撑剂回流

Abstract:

In the Haiba block of the Zhaotong demonstration area, shallow shale gas reservoirs are characterized by shallow burial depth, low formation pressure, and large variation in formation dip angle. The flowback process during well testing in these reservoirs is marked by a long gas breakthrough time, a high gas breakthrough flowback rate, and low stabilized gas testing rates. Improper flowback can lead to wellbore proppant settling, liquid loading, and loss of fracture volume, requiring an optimized flowback strategy to ensure safety and efficiency. This study presents a systematic analysis of flowback data from 71 wells in this block, identifying three distinct flowback stages: pure liquid flowback, gas breakthrough, and stabilized gas flowback. Using a fracture compression model and rate-transient analysis, the variations in effective fracture volume and fracture half-length under different flowback strategies were examined. The results show that a fast flowback strategy can cause an irreversible loss of up to 30% of the effective fracture volume, whereas a slow flowback strategy can reduce this loss to about 12%. To minimize this irreversible fracture loss, key flowback issues and controlling factors for these shallow shale gas wells were addressed. The well-opening pressure was determined by analyzing the effective stress within fractures. A wellbore proppant settling model and a fracture proppant flowback model were developed, yielding the critical flow rate in the wellbore required to carry proppant and the critical flow rate in fractures that triggers proppant flowback. Based on multiphase flow theory, the minimum bottomhole pressure for fluid unloading and the critical gas rate for liquid lifting were also determined. Accordingly, a comprehensive optimization strategy was proposed, encompassing appropriate well opening timing, wellbore sand cleanout, proppant flowback prevention, and assurance of fluid drainage, and the flowback optimization diagram was developed. Field application results indicate that this diagram enables a synergistic optimization of fracturing effectiveness and production efficiency: under similar reservoir conditions and stimulation measures, the estimated ultimate recovery increased by 20%. This study marks a transition of flowback management from an empirical approach to a quantitative one, and the proposed critical criteria and optimization diagram have broad applicability, providing a technical reference for flowback optimization in other unconventional oil and gas wells.

Key words: shallow shale gas, flowback, flowback characteristics, safety flowback diagram, proppant flowback

中图分类号: 

• TE37

• P618.13