李根生团队:青海共和盆地干热岩注采大尺度物理模拟实验

文摘   2024-08-10 07:53   湖北  

作者|赵鹏 朱海燕 李根生 陈作 陈世杰 上官拴通 齐晓飞

原题|青海共和盆地干热岩注采大尺度物理模拟实验

来源|石油勘探与开发

小编|阿热

这是"地热能在线"的第189篇文章

01


全文导读


中国干热岩资源量丰富,相当于860×10^12吨标准煤,约占全球资源量的1/6,开发潜力巨大。在能源消费结构中,地热能利用占比每提高1个百分点,相当于减排二氧化碳9400万吨。因此,高效开发干热岩资源,对改善中国能源结构、助力实现“双碳”目标具有重大战略意义。
干热岩渗透率低且发育有天然裂缝,利用水力压裂沟通天然裂缝在储层中形成具有足够换热面积和换热效率的高渗透裂缝网络体,是干热岩高效利用的技术关键。国内外学者通过建立干热岩注采多场耦合模型,开展了较为广泛的数值模拟研究,系统讨论了地质条件(天然裂缝间距、储层非均质性、温度梯度)和开采工艺(注入温度、注入速率、注采井间距)对干热岩采热性能的影响规律,并进行了采热性能综合评价。然而,尽管数值模拟方法能够体现干热岩长期注采的复杂物理过程及不同物理过程间的耦合关系,但是模型中通常进行较多的假设,例如假设流体流动符合达西定律、岩石和流体满足局部热平衡、裂缝形态和缝宽演化比较简单,因而获得的结果并不能真实反映干热岩注采取热过程。
为了研究裂缝内流体渗流换热过程,学者们利用劈开的小圆柱岩样开展了单裂隙实验,并得到了一些有意义的结论。然而,干热岩裂缝系统中的取热过程非常复杂。在长期注采过程中,裂缝网络动态演变,当注采井之间产生渗流优势通道时,缝网中会出现“热短路效应”,有效换热面积减小,大大降低取热效率。此外,干热岩天然裂缝发育,换热流体滤失也是导致干热岩取热效率低的重要原因。英国Rosemanowes项目和日本Ogachi项目运行后期的换热流体损失已达到70%以上。单裂隙渗流换热实验由于尺度小、裂缝通道简单,难以体现干热岩复杂的注采过程,亟需开展干热岩大尺度注采物理模拟实验。
因此,本文以青海共和盆地干热岩为研究对象,利用自主研制的真三轴多物理场原位注采大型物理模拟实验系统,开展干热岩多裂缝多井长期注采物理模拟实验。通过多井连通性实验初步分析了岩样内部天然裂缝系统的空间特征以及与井筒的连通情况。在此基础上开展了一注两采和一注一采实验,研究了开采温度、开采流量、采热速率和流体采收率随时间变化的特征,重点探讨了优势通道和换热流体滤失对采热性能的影响,为干热岩高效开发提供了理论依据和参考。
实验结果表明:一注两采阶段在热冲击、注入压力联合作用下裂缝导流能力增强,生产井开采温度表现为下降趋势且开采流量越大下降越快;当裂缝局部闭合区域逐渐激活产生新的换热面积后开采温度曲线升高或下降速率变慢;一注一采阶段生产井流量增加更大的裂缝闭合区域被激活开采温度再次升高之后保持稳定;由于滤失通道导流能力增加生产井流量逐渐降低开采温度呈现缓慢下降趋势。
采热速率主要由开采流量、注入和采出流体的温度差控制。对于注采井间导流能力强的5井采热速率前期受开采流量控制后期主要受开采温度影响;对于注采井间导流能力弱的3井采热速率主要由开采流量控制。5井流体采收率远高于3井决定了两井总采收率曲线变化特征;当滤失通道导流能力增强时生产井流体采收率快速下降距离注采区域越近监测井内温度受到的影响越大;当监测井和注采井之间的渗流通道被激活后少量高温流体流入监测井导致温度增加并出现波动变化。
长期注采过程中天然裂缝导流能力变化会影响干热岩开采温度的变化规律。优势通道和换热流体滤失对采热性能的影响机制不同前者限制换热面积后者影响采出流体流量二者都是影响干热岩长期高效开发的重要因素。


02


目录点睛

1
引言
PART ONE



2
青海共和盆地地质概况
PART TWO



3
干热岩多井长期注采实验系统
PART THREE



4
干热岩多井长期注采实验方案
PART FOUR

  • 实验岩样制备

  • 实验岩样温度设定

  • 多井注采实验方案

    主要包含:多井连通性实验多井注采实验


5
实验结果分析
PART FIVE

  • 干热岩多井连通性分析

  • 干热岩采热性能分析

    主要包含:开采流量和开采温度采热速率流体采收率监测井温度


6
讨论
PART SIX

  • 天然裂缝导流能力动态变化对开采温度的影响

  • 优势通道和流体滤失对采热性能的影响


7
结论
PART SEVEN



03


HIGHLIGHT图片


图1 青海共和盆地花岗岩露头

图2 干热岩多井长期注采实验系统

图3 干热岩多井长期注采实验岩样

图4 岩样井筒连通性和裂缝空间分布示意图

图5 注采过程中生产井流量(a)和温度(b)随时间变化

图6 注采过程中采热速率随时间变化曲线

图7 注采过程中流体采收率随时间变化曲线

图8 注采过程中监测井内温度随时间变化曲线


免责声明:本文仅用于学术交流和传播,不构成投资建议

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