Permeability Evolution at Various Pressure Gradients in Natural Gas Hydrate Reservoir at the Shenhu Area in the South China Sea
Permeability Evolution at Various Pressure Gradients in Natural Gas Hydrate Reservoir at the Shenhu Area in the South China Sea
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DOI：
10.3390/en12193688
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发表时间：
2019-09
期刊：
影响因子：
3.2
通讯作者：
Cheng Lu;Yuxuan Xia;Sun Xiaoxiao;H. Bian;Qiu Haijun;Hongfeng Lu;Wanjing Luo;J. Cai
中科院分区：
文献类型：
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作者：
Cheng Lu;Yuxuan Xia;Sun Xiaoxiao;H. Bian;Qiu Haijun;Hongfeng Lu;Wanjing Luo;J. Cai
神狐地区水合物藏沉积物主要为粘土质粉砂。其颗粒小、胶结性差的特点对产气过程中储层渗透率的定量提出了挑战。准确描述粘土粉砂储层渗流机制是南海天然气有效开发的基础，也是难点。本研究利用粘土粉砂储层沉积物进行了四组不同压力梯度下的渗水实验，其中第四组样品进行了计算机断层扫描（CT）。实验结果表明，随着压力梯度的增大，粘土粉砂储层孔隙结构受到压缩，渗透率降低。 CT 图像用于显示流体流动的孔隙空间的减少。当压力梯度小于3 MPa/米时，储层孔隙结构变化较小。当压力梯度大于该值时，储层孔隙结构将被快速压缩。这导致渗透率迅速下降，并且渗透率下降的过程是不可逆的。通过建立孔隙度变化的幂律模型，可以直接预测渗透率的降低。实验结果初步揭示了天然气水合物减压开采过程中粘土粉砂储层孔隙结构和渗透率的动态演化规律。不同压力梯度下渗透率演化规律为粘土粉砂天然气水合物减压采气产能控制体系提供了科学合理的依据。
The sediment of the hydrate reservoir in the Shenhu Area is mainly clayey silt. Its characteristic small particles and poor cementation challenge the quantification of the reservoir permeability during gas production. An accurate description of the seepage mechanism of the clayey-silt reservoir is the basis, and also a difficulty, of effective development of gas in the South China Sea. In this study, four sets of water seepage experiments under different pressure gradients are carried out using the clayey-silt reservoir sediments, in which the fourth sample was subjected to computed tomographic (CT) scans. The experimental results shows that the clayey-silt reservoir has a compression of the pore structure and decreasing permeability with the increasing pressure gradient. CT images are used to show the reduction of pore spaces for fluid flow. When the pressure gradient is less than 3 MPa per meter, the pore structure of the reservoir has minor changes. When the pressure gradient is greater than this value, the pore structure of the reservoir will be quickly compressed. This leads to a rapid decrease in permeability, and the process of permeability reduction is irreversible. The decrease of permeability can be predicted directly by establishing a power law model with the change of porosity. Our experimental results preliminarily reveal the dynamic evolution law of pore structure and permeability of clayey-silt reservoir in the process of gas hydrate exploitation via depressurization. The permeability evolution law at various pressure gradients provides a scientific and reasonable basis of a productivity control system for clayey-silt gas hydrate in depressurized gas production.