Abstract
A gas–water two-phase fluid is present in a reservoir before a water-flooded sandstone gas reservoir is rebuilt. Therefore, in the process of injection and production of the rebuilt underground gas storage, the injected gas is easily blocked by the water in the pores, and the efficiency is low, resulting in a significant loss of gas. The study completely utilizes the geological data and dynamic operation monitoring data of a water-flooded sandstone underground gas storage and clarifies the rule of the gas–water three-phase seepage in a high-intensity injection–production process. Moreover, the main control factors of the low efficiency of this type of underground gas storage are clarified. The lost gas generated in the injection–production process is described from two aspects: microcosmic experiment and macroscopic law analysis. The type, mechanism, and occurrence state of the loss gas are clearly defined, its main type is “water trapped gas”, it formed when the gas rushing into the water area under high pressure and surrounded by water, and its occurrence of this kind of lost gas is mainly sporadic or continuous free gas. A gas–water two-phase mathematical model that can simulate the high-intensity injection–production process is set up according to the experimental result, this model is used to simulate the operation process of the Ban 876 underground gas storage. Based on the simulation results, the gas–water macroscopic movement rule and macroscopic accumulation mode of the lost gas are defined, and then the collection area of the lost gas is predicted and quantitatively described. The calculation results show that the lost gas in one cycle is about 775 × 104 m3, which are mainly concentrated in the inner of the gas-water transition zone. According to the numerical simulation result, six new wells have been designed to develop its internal lost gas, they all have good predictions, can increase the working gas volume of 3000 × 104 m3 and reduce the single cycle lost gas by 50%, which is only 326 × 104 m3. This provides guidance for the expansion and exploitation of the same type of water-flooded sandstone underground gas storage.
Highlights
In 1915, Canada built the first underground gas storage in the world
Statistics show that the filling reach up to 80%, whereas the charge rate of the original gas cap of a three-phase underground gas rate of the original gas cap of the gas–water two-phase underground gas storage can reach up to 80%, storage is less than 70%, and the filling rate of the oil ring is less than 50%, which is quite different whereas the charge rate of the original gas cap of a three-phase underground gas storage is less than (Figure 5)
The static parameters natural gas and reservoir are basic parameters for permeability numerical simulation, simulation is conducted in of different seepage zones using different relative curves to such as pressure, temperature, density and so on. These parameters determine the state of fluid and reflect the actual seepage characteristics of each area to improve the fitting rate of the gas–water control their seepage rules, the exact numeric value must be given according to the results of the movement rule in the underground gas storage (Figure 8)
Summary
In 1915, Canada built the first underground gas storage in the world. Until the 1940s, the number of underground gas storage sites slowly increased, and the technology of building libraries lagged [1]. They started studying the law of oil–gas–water relative seepage in the process of strong injection and intensive production By establishing their mathematical model, numerical simulation was performed to simulate the operation process of underground gas storage to improve its operation efficiency. By using an improved core clamping experimental equipment, the problem of pressure lag response in the gas production process was simulated, which explained why the lower limit of the pressure in a numerical simulation was higher than the actual gas production pressure These studies basically revealed the principle of gas–water seepage as nonlinear seepage in the high-intensity injection and production processes [8]. Based on the Warren–Root dual pore model, Fu established a mathematical model for underground gas storage considering the deformation of the medium, and used it to simulate the operation process of a depleted fractured reservoir rebuilt underground gas storage, and achieved good results [18]. It can provide guidance for the rational operation of the water flooded sandstone underground gas storage, and avoids the loss of gas
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