Experimental evaluation on EOR medium grading of shale in Jimusaer Oilfield

To evaluate the influence of the interaction between water, surfactant solution and CO₂ and reservoir on shale oil recovery factor, analyze the EOR effect of pressure difference and imbibition on shale oil in Jimusaer Oilfield, and study the influence of the action sequence of imbibition media on the recovery factor, centrifugal experiment was performed on the bottom hole cores saturated with reservoir oil, and then heavy water imbibition, surfactant solution imbibition and CO₂ huff-n-puff experiments were carried out. In addition, the oil volume in the pores of the cores was characterized by means of NMR technology, and the recovery factor was calculated. It is experimentally indicated that imbibition is the main driving force of shale oil production, and the recovery factor by heavy water imbibition, surfactant solution imbibition and CO₂ huff-n-puff are 30%-34%, 35%-40%, and 37%-50%, respectively. Pressure difference drive has less influence on shale oil production in Jimusaer, and the recovery factor by centrifugal is less than 3%. Based on the EOR capability in the experiment, three kinds of media are ranked from low to high as heavy water, surfactant solution and CO₂. The EOR media are graded based on oil recovery factor (called as grading). The contact sequence of medium with reservoir has great influence on ultimate recovery factor. The medium of the highest grading shall be firstly injected into the reservoir to contact it firstly, which is favorable for improving the ultimate recovery factor of shale oil well. As for new well fracturing in oilfield production, it is suggested to firstly use the medium of the highest EOR grading before prepad fluid instead of successive EOR, so as to ensure the contact of the medium of the highest EOR grading with the reservoir firstly and maximize the ultimate recovery factor. As for old wells, it is suggested to use the EOR medium whose grading is higher than that of the fluid in the well, so as to continue to produce oil by virtue of imbibition.