Optimization Design of Well Spacing Pattern: A Case Study from Dongying Sag, Jiyang Depression, BBB, China

Abstract

The geothermal tail water should be reinjected back into the reservoir for the sustainable utilization of geothermal resources. It may cause temperature decrease in the production wells or pressure increase in the rejection well if the well pattern is unreasonable. The setting principle about the distance between production well and rejection well is that there should be no thermal breakthrough in the production well, meanwhile the distance should be small as far as possible to make up for the reservoir pressure decrease. The concept model and the parameters about geological condition and exploitation situation is derived from the Central Uplift geothermal field of Dongying Sag, Jiyang Depression, Bohai Bay Basin(BBB), China. The data of pumping tests and rejection tests from 4 projects is collected to determine the water production and rejection rate, and then the ratios of production well and rejection well is obtained. The production rate is 65-75 m3/h while the rejection rate is 30-40 m3/h, so the ratio of production well and rejection well should be 1:2. The change of temperature and pressure of the geothermal reservoir caused by the exploitation is mainly controlled by the reservoir characteristics and injection parameters. A series of hydro-thermal coupled simulation is carried out used the Petrasim-Tough2 Code to check the change of temperature field. The optimal distance between production well and rejection well is about 350 m.