Experimental Study on Reservoir Physical Properties and Formation Blockage Risk in Geothermal Water Reinjection in Xining Basin: Taking Well DR2018 as an Example

Abstract

The Xining Basin in Qinghai Province, China, is rich in mid–low temperature geothermal resources, but the reinjection of geothermal water has not yet started. In this paper, the physical properties of rocks sampled from the newly drilled geothermal well DR2018 were analyzed, and a series of core flooding experiments was conducted to assess the formation blockage risk during water reinjection. The experimental results show that the geothermal reservoir has a low porosity of 1.64–18.68% and a low permeability of 0.04–7.23 md. The rocks are weakly consolidated, and the movable clay and sand particles account for 0.18–23.42 wt %, which results in a significant rate and salinity sensitivity. Even at low water flow velocity of 0.31–1.64 cm/min, the core permeability will drop by 35–53% after 25-144PV injection. An obvious fluctuation and decline in core permeability can also be observed as the injected water salinity decreases. The blockage risk induced by the invasion of low-content scaling and suspended particles in injected water can be covered up by the migration of movable particles in cores. The particle migration and blockage in the near-wellbore formation will be the main reason to cause the decline in the well’s geothermal reinjection capacity.

Keywords

• geothermal water reinjection
• blockage mechanism
• risk assessment
• movable particles