| Application of hydrocarbon gas injection on exploring crude oil is a mature technology,which has unique advantages in the development of reservoirs with low permeability and ultra-low permeability.As the enrichment of supply of gas sources,the technology requirements for enhanced oil recovery,and the development of gas storage technology keep increasing,investigation of fundamental research contents,including phase behavior and constraint conditions of hydrocarbon gas-crude oil system and seepage and occurrence conditions of hydrocarbon gas-crude oil system in porous media,is demanded.To the best of our knowledge,there are few systematic investigations regarding oil-gas dynamic mass transfer mechanism,approaches of capability evaluation of miscibility and gas channeling identification and prediction,and phase behavior analysis of reservoir fluid during the integration construction of oil extraction and gas storage.Here lies in the purpose of this study.In this paper,laboratory experiments and numerical simulations were performed to study the mechanism of hydrocarbon gas-crude oil miscibility during mass transfer process,the approaches of evaluation and prediction of the minimum miscible pressure of hydrocarbon gas-crude oil system,the means of monitoring the gas drive front,and the oil-gas phase behavior during gas storage process.The following findings were obtained:（1）With the help of fluid phase characteristics analysis system,the multi-component dynamic mass transfer process of injected gas-reservoir oil system was studied.The mass transfer pattern of gas phase components under the non-equilibrium state of gas-oil system was defined.It was found that a hydrocarbon rich vaporizing layer was formed well above the oil-gas interface during the dynamic mass transfer process.This vaporizing layer is able to extract intermediate hydrocarbon components(C7-C15)significantly by comprehensive effect of extraction and condensation during mass transfer process.This study provides theoretical guidance for expanding the scale of miscible zone and facilitating immiscible flooding.（2）The high-definition infrared observation technology was introduced for the first time,and the high-temperature-high-pressure infrared full visual system of miscibility evaluation was designed.It realized the full visual observation of floating process of injected gas in the presence of reservoir oil.Based on the trajectory and velocity change of gas bubble floating in the crude oil,a series of methods for the minimum miscible pressure evaluation of injected gas-reservoir oil system was proposed:the qualitative evaluation method of initial floating trajectory（IFT）,the quantitative evaluation method of maximum floating velocity（MFV）,and turning floating velocity（TFV）.These methods can provide technical support for the fast and accurate evaluation of the feasibility of miscible flooding projects by injecting reservoir gas.（3）Based on the literature review and laboratory experiments,the influence of various factors on the minimum miscible pressure of gas-oil system was evaluated by artificial intelligence.The artificial intelligence model based on machine learning and deep learning and corresponding technique were introduced.The method of minimum miscible pressure prediction of domestic hydrocarbon gas flooding projects is established.BPNN-M9 model was used to predict minimum miscible pressure,where the AAD data was less than 3%.It provides technical support for screening and evaluation of miscible or immiscible flooding projects.（4）Combined with laboratory displacement experiments and numerical simulations,the changes of key parameters,including composition,viscosity,gas-oil ratio,and critical point of fluid in the miscible zone during gas flooding,were studied.The change pattern of phase characteristics of fluid in the miscible zone before and after gas breakthrough was unveiled.Phase-diagram-assisted gas channeling warning boundary and gas channeling boundary were proposed,and the method for gas channeling warning during miscible flooding was established,which can provide guidance for prediction and dynamic monitoring of gas channeling.（5）Taking a gas reservoir with oil ring as a typical example,the construction of a gas storage was divided into three stages:gas reservoir depletion production stage,storage capacity formation stage,and periodic injection-production stage.The change pattern of the key phase characteristics of the oil-gas system in the three stages was studied.Then,the phase characteristics and the corresponding effect of oil-gas system during the whole injection-production process of gas storage were proposed,and the influence of oil-gas phase behavior on the main design index of gas storage construction was analyzed,which provide theoretical support for the integration construction of oil extraction and gas storage.In this paper,dynamic hydrocarbon gas-reservoir oil mass transfer mechanism was first studied.Subsequently,a set of experimental measurement methods and theoretical calculation methods suitable for the capability evaluation of miscibility of injected gas-reservoir oil system was generated.Then,gas channeling warning method was established for hydrocarbon gas miscible flooding projects and the influencing mechanism of oil-gas phase behavior on the main design index of gas storage construction was analyzed.The prospective application of the research results was given in this paper.It provided theoretical and technical support for both the transformation design of development mode of near-depleted reservoirs and the development design for producing near-undeveloped reservoirs efficiently.Moreover,it can lay a foundation for the development of gas miscible flooding in unconventional reservoirs such as low permeable and ultra-low permeable reservoirs. |
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