Experimental and Numerical Investigation of the Hydromechanical Response of Low Permeable Rocks during Injection of supercritical CO2

摘要

In designing carbon capture and geological storage, the long-term behavior of stored CO2 in the underground geological formation is a crucial issue to be carefully considered. This is because of the fact that the injection of CO2 into the formation would impact rock formation integrity, reactivating pre-existing fractures and reopening seal that eventually lead to potential CO2 leakage to the underlying groundwater containing layers and the surface. Therefore, the deformation of the reservoir rock during injection of supercritical CO2 needs to be well understood and defined while designing the project. udIn this paper, we developed an experimental design using a newly developed flow pump permeability test to measure the change of strain and stress on the Ainoura sandstone cores under the injection of supercritical CO2. The experiment was set up to reproduce the similar condition of deep underground reservoir with 20 MPa confining pressure, 10 MPa pore pressure, 35??C temperature and 3 ??l/min CO2 injection rate. As CO2 was injected to the specimen, the hydraulic pressure increased and generated a stress alteration. The strain in the core was monitored. The injection was halted at 15.3 MPa hydraulic pressures over the period of 565.9 hours since the hydraulic pressure can reach the confining pressure applied on the core and this may break the silicon on the rubber sleeves covering the core. Therefore, in order to model the hydromechanical response of the core during the injection as well as to predict the strain propagated beyond the injection period measured in the experiment, a numerical investigation using coupling hydromechanical simulation was conducted. In this exercise, we employed a two phase flow reservoir simulator of TOUGH2 (ECO2N) coupled with rock mechanics computation of FLAC3D. A core specimen, with the rock properties and initial conditions similar to the experimental data, was generated and supercritical CO2 injection with a constant rate of 3.56??10-8 kg/s was simulated. It was observed that, the increased hydraulic pressure and strain shown in the numerical simulation have well agreement with the experimental result. The results also indicated that, during injection, the hydraulic pressure on the core increased transiently, and became constant at almost 60 MPa over the period of 5833 hours. The core specimen deformed elastically due to the increase of pore pressure caused by injection. The deformation of the specimen would not propagate failure even if the pore pressure exceeds the confining pressure applied on it. The results confirmed that the injection of supercritical CO2 into low permeable rocks has considerable effects on the integrity of low permeable rocks even at low flow rates.