Study On The Transportation And Injection Technology Of CO_2 Subculture In Zhenglizhuang Oilfield

Zhenglizhuang Oilfield has abundant low-permeability reservoir resources, the proportion of which in newly proved reserves has been gradually increasing. For low-permeability reservoirs especially ultralow-permeability reservoirs, traditional water-flooding development requires excessively high water-flooding pressure, which causes great difficulty in development. However, CO2displacement is one of the major methods to increase the recovery ratio of low-permeability oilfields. Coal gasification devices in Qilu Second Chemical Plant produce a large amount of exhaust with high CO2content in the production process and directly discharge it into the atmosphere. Utilization of CO2in the discharged exhaust for displacement will not only protect the environment, but also increase the recovery ratio of crude oil.This paper first demonstrates the feasibility of the application of CO2displacement in Zhenglizhuang Oilfield, and determines the required ranges of temperature and pressure of CO2at the well bottom by experiments. On this basis, corresponding software for the prediction of wellbore temperature and pressure fields is developed based on the wellbore flow hydraulic and thermodynamic model, and combined with thermodynamic calculation of reservoir and physical data of CO2, and the wellhead ranges of CO2injection pressure and temperature are analyzed. In terms of pipeline transport, a scheme of CO2liquid transport with decentralized pressurization at distributed injection stations is determined in accordance with the locations of gas-injection wells and distribution of central injection stations. After verification of the compound economic model, the final CO2pipeline transport scheme is proposed. Specific contents are as follows:(1) Aiming at the geological characteristics of Zhenglizhuang Oilfield, the feasibility of the application of CO2displacement in Zhenglizhuang Oilfield is demonstrated through phase behavior study of reservoir oil and CO2, miscible experimental study of the long slim tube model, and displacement experiment of the long core model. The reservoir temperature and pressure system is analyzed, and the pressure maintenance level, injection timing, and single-well daily injection capacity are studied, thus laying a solid foundation for the ground injection scheme of CO2.(2) Based on the wellbore flow and heat-transfer model, and combined with thermodynamic calculation of reservoir and physical data of CO2, corresponding software for the prediction of wellbore temperature and pressure fields is developed. The prediction accuracy of the model is within5%after testing, which satisfies engineering demand. In addition, the wellhead temperature and pressure of a gas-injection well in Zhenglizhuang are predicted.(3) According to the predicted wellhead CO2temperature, pressure, single-well injection amount and other parameters, and combined with the actual situation on site, two CO2ground transport and injection schemes are designed, namely decentralized pressurization at distributed injection stations, and centralized pressurization at central injection stations with allocation at distributed injection stations. The injection scheme is preliminarily determined by comprehensively considering operation, management and other factors.(4) By investigating commonly used CO2transport and injection economic models at home and abroad, including Ogden, MIT, Ecofys, IEA GHG PH4/6, IEA GHG2005/2, IEA GHG2005/3, Parker and compound models, the several models are compared and analyzed, and the economic model most suitable for the situation of Zhenglizhuang Oilfield is selected. Then economic evaluation is further conducted on the two CO2transport and injection schemes, and finally the optimal scheme is determined.