Reformation Of Reservoir Sandstone With CO₂Fluid And Its Influencing Factors

Recently, a large number of emission of CO₂is generally considered one of theimportant reasons that cause global warming, so it is concerned by more and moregovernments, scientists and people around the world. CO₂from the fixed pointsource（such as power plants or similar industrial point source） could be collected andinjected into a relatively closed geological formations in order to prevent or reducethe anthropogenic emissions of CO₂into the atmosphere, so CO₂geological storage isconsidered to be one of the effective measures for reducing the CO₂emissions. In thispaper, the deep saline aquifers of Shihezi in the Ordos Basin northeast was regardedas the research object. Meanwhile, the transformation of the reservoir sandstone afterthe injection of CO₂and its influencing factors were studied by the componentanalysis of reservoir rock and the simulation experiment of CO₂-water-rockinteraction. Through the experimental study, the mechanism of CO₂geologicalstorage was further explored and it provided the theoretical basis for the storagecapacity of CO₂, security assessment and implementation of the project in the deepsaline aquifer of this Basin. Therefore, it had a very important significance for CO₂geological storage.When CO₂was injected into the target layer, it dissolved in water andstrengthened the acidity of saltwater in the high temperature and high pressure offormation environment. Then, the interaction between the CO₂-rich fluid and reservoirsandstones could change the mineral composition of the sandstone and generate newmineral carbon sequestration in order to achieve the geological storage of CO₂. In thereaction process, the soluble minerals were dissolved, such as feldspar and claydissolution. Meanwhile, the new minerals, including dawsonite, calcite, ankerite,kaolinite, and green claystone, are precipitated. Dawsonite, calcite and ankeritewere called carbon sequestration minerals and their generation showed that CO₂geological storage was feasible, stable and safe.In the same time, the paper also studied the effects of a number of geological factors on CO₂-water-rock interaction, the results showed that:1. When thetemperature risen, it could aggravate the dissolution of soluble minerals in thesandstone, promote the precipitation of ankerite and calcite and reduce the stability ofdawsonite.2. When the pressure risen, it could increase the concentration of CO₂insolution, which, on the one hand, promoted the dissolution of soluble minerals in thesandstone and other hand was conducive to the precipitation of dawsonite.3. Theincreasing of the salinity was conducive to maintaining the salt water in the acid-basebalance and accelerating the precipitation of carbonate minerals.4. After the additionof strong acid mixture, the acidity of salt water was enhanced significantly. Itaccelerated the dissolution of soluble minerals in the sandstone, but was notconducive to the formation of carbon sequestration mineral in a short time.