数字岩心技术在致密气应力敏感研究中的应用

Application of digital core technology in the study of tight gas stress sensitivity

致密气储层基质中存在与缝网不连通的人工诱导缝和天然裂缝,研究裂缝发育的基质渗透率应力敏感对致密气藏开发具有重要意义。本文利用某盆地H组致密气藏的岩石,开展了渗透率应力敏感实验,结合电镜扫描、微米CT等实验方法,对不同类型岩样微观孔隙特征进行了描述,利用实验结果对现场产能进行了分析。实验中基质、层理和人工造缝致密储层表现为强应力敏感性,渗透率与有效应力呈负指数函数关系,应力敏感常数分别为0.078~0.153 MPa^(-1)、0.112~0.208 MPa^(-1)、0.073~0.079 MPa^(-1),人造缝岩样应力敏感程度整体相对较弱。微裂隙和裂缝的开启程度和分布特征对含裂缝岩心应力敏感性影响较大。通过建立的产能模型分析发现,随着生产压差增大产量下降幅度较大,最高为39%,因此致密气井要合理控制压差。

There are artificial induced fractures and natural fractures in the matrix of shale reservoir,which are not connected with fracture network.It is important to study the permeability stress sensitivity of matrix shale with fracture development for shale gas development.In this paper,the permeability stress sensitivity experiment is carried out by using the rock of group H in a basin.Combined with the experimental methods of scanning electron microscope and micro CT,the micro pore characteristics of different types of rock samples are described,and the field productivity is analyzed by using the experimental results.In the experiment,the matrix,bedding and artificial fracture shale show strong stress sensitivity.The permeability and effective stress show a negative exponential function.The stress sensitivity constants are 0.078~0.153 MPa^(-1),0.112~0.208 MPa^(-1) and 0.073~0.079 MPa^(-1),respectively.The overall stress sensitivity of artificial fracture rock is relatively weak.The opening degree and distribution characteristics of microcracks and fractures have great influence on the stress sensitivity of fractured core.Through the analysis of case data,it is found that with the increase of production pressure difference,the production decreases greatly,with the maximum of 39%.Therefore,shale gas wells should reasonably control the pressure difference.