Studies on Development Regularity of Karst Fissure of the Ordovician Geothermal Reservoir in Tianjin

Abstract

In this paper, We make unified stratigraphic division based on the comprehensive analysis of drilling data and log data of 43 exposing Ordovician geothermal wells, then make statistic analysis of Type I and Type II fractures and original water yield of Ordovician of different tectonic units. The results show that the exposing buried depth of the Ordovician roof is 950m to 2720m, the bottom is 1218 m to 3450m. And the thickness of Ordovician system is 50.3m to 1050m,the formation thickness which contains Type I and Type II fractures is 14.5m to 140.1m, mainly is 40m to 80m. Thus we speculate that Type I fractures is distributed in Ordovician Majiagou, Liangjiashan and Yeli formation. And fracture development degree increase with the increase of buried depth and thickness of Strata. The fracture may also be affected by various overlay. The variation in thickness of fracture development segment which overlying Cenozoic is bigger while the buried depth of ordovician is minimum. The thickness of fracture development segment of Ordovician system which overlying Mesozoic is more thicker than which overlying Carboniferous in the geothermal well. Water inflow of single well increases with fracture development degree of geothermal reservoir. Water yield is larger in Shuangyao Salient,while smaller in Dacheng Salient and Baitangkou Depression.