Geothermal reservoir characteristics of SYYD-1 well and energy efficiency analysis after geothermal transformation

Abstract

SYYD-1 Well in Daqing, a shale oil parameter well, was implemented by the Shenyang Geological Survey Center of the China Geological Survey in 2019. The drilling depth and diameter are 2484.0 m and 139.7 mm, respectively. To satisfy the local demand for clean energy, cable transmission spiral perforation technology was applied to transform this well into a geothermal well. Based on a comprehensive understanding of the regional geothermal conditions, the geothermal reservoir characteristics of SYYD-1 Well were investigated through a detailed geophysical interpretation. Crucial energy efficiency parameters, such as the theoretical recoverable and annual available geothermal energies, were calculated using analytical methods after the transformation of the well. Subsequently, geothermal fluid quality and combustible gas composition were analyzed to provide technical guidance for the development and use of local clean energy. The results showed that the geothermal resource in SYYD-1 Wellis mid-deep hot groundwater. The primary geothermal reservoir consists of the sandstone strata of the second and third members of the Qingshankou and Quantou Formations, whereas the caprock is an extremely thick mudstone stratum of the Cretaceous Sifangtai, Nenjiang, and Yaojia Formations. The depths of the top and bottom of the geothermal reservoir are 1281.6 and 2464.4 m, respectively, where the temperatures were 44.08 and 84.20 °C, respectively; the average temperature was 64.14 °C. The wellhead water temperature remained stable at 44.0∼50.0 °C. The pH, total dissolved solids (TDS), and total hardness of the geothermal fluid were 8.29, 5536.0 mg/L, and 38.2 mg/L, respectively. This water could be classified as highly mineralized, alkaline, extremely soft water, of the hydrochemical Cl·HCO3-Na type. Methane was the main combustible gas in the wells, accounting for 97.8% of the total gas. The exploitable water quantity, theoretical recoverable geothermal energy, and annual available geothermal energy of the well were 163.68 m3/d, 362.07 KW, and 6.85 × 106 MJ, respectively. The geothermal resources of the well could be used for physiotherapy, bathing, and heating. The geothermal gradient of reservoir (1319.0∼2464.4 m) is 2.8 °C/100 m, which is suitable for development. The concentrations of Br−, I−, and F− in the geothermal fluid meet the requirements in the standard for natural medical value; substantial social, environmental, and economic benefits can be gained after the safe treatment of combustible wellhead gas and operational implementation.