Characteristics of the stratigraphic reservoirs and caprocks of the geothermal resources in the Northwestern Shandong region

The genetic relationships between the stratigraphic textures, thickness changes, burial depths, and the characteristics of the geothermal zoning of the Cenozoic in the northwestern Shandong region were analyzed in this study. Methods involving segmented water temperature measurements of geothermal well drilling, wellhead hydrological surveys, geothermal reservoirs, and caprock thickness measurements and statistics were adopted. The following findings were revealed in this study's research results: (1) The Paleogene and Neogene reservoir types in the northwestern Shandong region were determined to be mainly water-bearing fine sandstone and medium-fine sandstone pores, with thick layered, interbedded, and zoned stratigraphic structures. The layered and zoned geothermal reservoirs were found to be primarily distributed in a zonal manner on the bedding plane and characterized by good regional continuity. The fine sandstone and medium-fine sandstone sections with well-developed pores and high water content levels were geothermal reservoirs, while mudstone sections were geothermal barriers. The reservoirs and barriers were characterized by interlayer structures; (2) The boundary between the sag basin and the uplifting was taken as the dividing line of the geothermal fields, and the geothermal areas in the northwestern Shandong region were divided into different geothermal fields, all belonging to the sedimentary basin's conductive geothermal resources; (3) The major geothermal reservoirs included the lower members of the Neogene Minghuazhen Formation, Guantao Formation, and Dongying Formation. The Quaternary argillaceous sediment and the mudstone in the upper member of the Minghuazhen Formation formed the caprocks in the study area. In this study, the macroscopic distribution laws of geothermal resources in the northwestern Shandong region were proposed and were considered to have practical significance for further exploration and development.