Gas injection method and system for deep strong bottom water sandstone reservoir

A gas injection method for deep-layer strong bottom water sandstone reservoir, comprising:

• S1:
• providing a plurality of gas injection mediums for a present reservoir at issue, and analyzing a miscible feature of each gas injection medium in crude oil of the present reservoir to select a number of target gas injection mediums that are conducive to utilizing residual oil in the present reservoir from the plurality of gas injection mediums;
• S2:
• combining the number of target gas injection mediums with a well group simulation model corresponding to the present reservoir to analyze an exploitation rule of the residual oil, thus obtaining an optimal gas injection ratio between the target gas injection mediums;
• S3:
• performing, based on the optimal gas injection ratio and the well group simulation model, gas injection simulation for the present reservoir through a plurality of gas injection modes to obtain an increment in recovery efficiency corresponding to each gas injection mode, thereby determining an optimal gas injection mode;
• and
• S4:
• performing gas injection in the present reservoir through the optimal gas injection mode according to the optimal gas injection ratio,
• wherein, in S1, the step of analyzing the miscible feature of each gas injection medium in crude oil of the present reservoir comprises:
• S11:
• determining whether each gas injection medium has a minimum miscible pressure in the crude oil of the present reservoir to select a plurality of first gas injection mediums that are miscible;
• S12:
• selecting a plurality of second gas injection mediums compatible with an average formation pressure of the present reservoir from the plurality of first gas injection mediums according to a minimum miscible pressure of each first gas injection medium in combination with the average formation pressure of the present reservoir;
• and
• S13:
• determining the target gas injection mediums according to dissolution rule and density of each second gas injection medium in the present reservoir, which comprises:
• S131:
• obtaining, through a combination of indoor experiments and numerical simulation, a distribution feature and a miscible feature of each second gas injection medium in the present reservoir, a first target gas injection medium that is soluble in water and oil;
• and
• S132:
• determining a second gas injection medium with a smallest density as a second target gas injection medium,
• wherein S131 comprises:
• performing exploitation simulation for the present reservoir through seepage flow experiment and phase state experiment, thus obtaining changes in phase state of fluid in the present reservoir;
• configuring reservoir exploitation parameters, and calculating relevant parameters characterizing the changes in phase state of fluid in the present reservoir through numerical simulation to obtain a distribution rule of the residual oil;
• obtaining a dissolution feature of each second gas injection medium in formation water of the present reservoir through dissolution experiment to obtain dissolution, migration and distribution rules of each second gas injection medium in formation water of the present reservoir through numerical simulation;
• obtaining a diffusion feature of each second gas injection medium in single-phase oil, single-phase water and single-phase gas of the present reservoir through diffusion experiment to obtain the diffusion rule of each second gas injection medium in the present reservoir;
• configuring injection-production parameters to analyze, through numerical simulation, different displacement effect obtained by injecting each second gas injection medium into the present reservoir, in order to obtain an influence of each second gas injection medium on displacement effect with the dissolution and diffusion rules being taken into consideration;
• and
• combining the distribution feature and the miscible feature of each second gas injection medium in the present reservoir together to obtain a concentration distribution of each second gas injection medium in the present reservoir during early, middle and subsequent depletion exploitation stages of gas injection, respectively, so that the gas injection medium having a dissolution ratio that varies stably with injection time is taken as the first target gas injection medium that is soluble in oil and water.