Key geological factors greatly related to drilling design of karst geothermal reservoir in Xiong'an New Area

Abstract

Xiong'an New Area is a key area for the development and utilization of high-quality karst geothermal reservoirs in Bohai Bay Basin. Based on the regional geological background, 2-D seismic data and 131 well loggings, three key geological factors, including reservoir-caprock assemblage, caprock characteristics, and karst geothermal reservoir characteristics, were studied in detail, and comprehensive evaluation of favorable zones was carried out. The results showed that two reservoir-caprock assemblage patterns were identified, the Eogene-Jxw is distributed on the northern slope belt of the Niutuozhen Bulge, where the top surface burial depth of Jxw is below 1 500 m, and the Neocene-Jxw is distributed on the Niutuozhen Bulge and the Rongcheng Bulge, where the top surface burial depth of Jxw is above 1 500 m. The Neocene caprock has poor diagenesis and is unstable. As a result, borehole wall sloughing is more likely to occur in thick poorly-cemented sandstone intervals of the Niutuozhen Bulge and the Rongcheng Bulge, which is mainly developed in the depth range of 450-700 m and 800-1 000 m. The geothermal reservoir property is in the longitudinal and horizontal zonation. Burial-hill-type karstification controls the formation of high quality reservoirs of Jxw in Xiongan New Area, and first grade and second grade geothermal reservoirs mainly develope within a thickness of 350 m. The optimized thickness of production zone decreases from the Rongcheng Bulge to the northern slope belt of the Niutuozhen Bulge to the Niutuozhen Bulge, the results are 1 000 m, 880 m, and 500 m, respectively. The area of Rongcheng Bulge and Niutuozhen Bulge with top reservoir surface burial depth of 1 250~1 500 m is the most favorable exploration and development zone because of the moderate burial of the thermal reservoir, better reservoir property, stronger diagenesis, and less drilling risk. The results can provide guidance for the successful drilling of karst geothermal reservoirs and the effective development of geothermal resources in Xiongan New Area.