Study on the distribution laws and physical properties of the micro-infiltrated layer in the Jintan salt-cavern gas storage

In the process of storage construction in Maoxing field of Jintan gas storage, a micro-infiltrated layer is encountered, which has certain characteristics of filtration and is distributed extensively and continuously in the working area, so as to bring greater challenges to well deployment and later storage construction. In order to understand this micro-infiltrated layer further and reduce its adverse impact on storage construction, this paper studied its physical properties, including distribution characteristics, core characteristics, compositions and permeability. 3D seismic exploration and drilling construction show that this micro-infiltrated layer is located in the salt interval of cavity construction and it is distributed all over the working area. And its distance from the salt top averages about 20 m and its average thickness is 0.8 m. Sampling analysis results show that this micro-infiltrated layers is mainly composed of mudstone. There are a large number of micro-fractures, which are dominated by vertical micro-fractures. The fracture density is 10-20/m and the fracture length is 10-200 mm. The vertical micro-fractures are filled with salt and nitrate. And the fillings are in the state of uncompaction or undercompaction and the fractures are not completely filled with crystals, which are the main factors influencing the sealing capacity of the micro-infiltrated layer. The tested porosity of the micro-infiltrated layer is 7.52%-14.18%, averaging 11.74%, and its permeability is (0.11-21.2)×10⁻³ μm², averaging 8.155×10⁻³ μm², which are the main reasons for the filtration. The research results can provide the basic parameters and technical references for the later well deployment and completion structure optimization in this area.