# Leak-tightness determination method for underground gas storage facilities with water drive operation mode

FIELD: oil and gas industry.

SUBSTANCE: stratum is impact cyclically, at that each cycle of impact includes gas injection to the stratum with further gas extraction. The stratum is impacted during 10 cycles at least. In each cycle current formation pressure as well as gas extraction (or injection) volume is measured simultaneously in gas- ^{th} measurement for the facility operation mode without gas losses and the function (Fy) for the facility operation mode with gas losses and when inequality Fy<F is satisfied the summary is made about available gas leaks in the storage facility.

EFFECT: simplifying control of gas leak-tightness, improving reliability and safety of the underground storage facilities made in the water-bearing strata.

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The invention relates to oil and gas industry and can be used to control the safe operation of underground gas storages (UGS) with water mode of operation.

Known hydrogeochemical method of determining inter-layer flows of gas in gas fields (Agishev A. P. Cross flows of gas at the development of gas fields. Moscow: Nedra, 1966, S. 79-88), which is in the exploration stage define constant hydrogeochemical background around the vertical incision. Then the accumulated data on the geochemical environment of the studied section intervals compare with the natural background of the field and identify emerging trends change on a particular area. The disadvantage of this method is the complexity of its implementation due to the need to study the initial hydrochemical background prior to injection of gas into storage. In addition, the application of the above method for UGS is associated with significant costs for the drilling of monitoring wells, because hydrogeochemical studies should be carried out in specially drilled test wells located in the path of the gas reservoir, and water samples should be selected in a well-isolated wells, retaining reservoir conditions (temperature and pressure), which leads to caribcan when determining the tightness of UGS.

The closest to the proposed method (prototype) is a method for studying dynamic processes gas environment UGS (RF patent No. 2167288, E21B 47/00, publ. 20.05.2001), including the introduction into the reservoir through different injection wells indicators in gas media, sampling of gas from the producing wells and the determination of concentrations of indicators over time in the production wells. In the period of maximum gas pressure chosen by the Central injection well, located in one or more operational levels, based on the location of production wells by area, using the indicators of multiple colors, and upload the indicator of the same color in the form of a gas-filled micro granules with the degree of dispersion of 0.5-0.6 μm, consisting of a mixture of polycondensation resins and organic luminescing substances in the estimated quantity. During the pressure reduction to the minimum weighted average by area size at the same time take samples of gas from wells located in one or more operational levels, and determine the time variation of the concentration of indicators of each color and volume rate of all gas production wells are the total number of the indicator of each color received in each production well, for the Anna formula. Build maps and largest share of migrating gas identify areas in-situ casting and cross flows and framing gazodinamichesky different zones. The disadvantage of this method is the need for identification of indicators by five parameters, which complicates the implementation of the method and reduces the reliability of the study of dynamic processes of the gas environment.

The task to be solved by the invention, is to develop a method for determining the integrity UGS created in the aquifer, the water mode of operation that enables to determine the leakage of gas from underground storage facilities during the entire period of operation.

The technical result, which directed the present invention is to simplify the control of the leak, which leads to increased reliability and safety of operation of UGS, created in aquifers.

This technical result is achieved due to the fact that in the proposed method of determining the tightness of UGS carry out cyclical effects on the reservoir, wherein each cycle includes a gas injection through wells into the reservoir until the value of the reservoir pressure not exceeding the maximum allowable design value, with subsequent OTB is rum gas until the value of the reservoir pressure is not below the minimum allowable design value.
The stimulation is carried out, at least for 10 cycles, with each cycle periodically simultaneously measure the current pressure in the gas_{t}). Then taking into account the measured parameters determine the design pressure in underground gas storage

where Ω_{o}- gas-saturated pore volume UGS,

P_{o}the initial reservoir pressure,

Z_{o}- the initial factor sverkhlineinoi gas

Z_{t}is the coefficient of sverkhlineinoi gas at time t,

q_{t}- volume injection (or selection) of gas at time t;

q_{in}- volume pushed (or established) produced water in the gas storage zone at time t, with

where C_{in}is the coefficient of proportionality pushed (or established) produced water in the gas storage zone;

and mode of operation of the store with gas leakage ratio

where C_{y}the proportionality coefficient of the gas leak.

Then define the function (F) as the average of the deviations of

where n is the number of measurements of reservoir pressure,

i - ordinal number of the measurement reservoir pressure;

and the function (F_{y}for operation mode store with gas leaks

and the execution of inequality Fy<F conclude that the presence of gas leaks in the repository.

During the operation of UGS gas leak mostly fixed in the later stage of their development, that is, when the manifestation of the gas to the surface and pollution control horizons, which further complicates the search for the specific cause of the gas leak, and can cause serious complications during the operation of UGS.

For UGS change the volume of the gas in the reservoir in time is determined from the equation:

where V_{t}the volume of gas in the reservoir at time t;

t - time;

q_{t}- volume selection (or injection) of gas per unit of time t.

Turning to the integral form, we obtain:

where V_{o}the volume of gas in the initial moment of time;

From the material balance equations (Zakirov S. N. "Design and development of gas fields". M.: Nedra, 1974, S. 28-35) it is known

where Ω_{t}- gas-saturated pore volume of the reservoir at time t;

P_{t}- formation gas pressure at time t;

Z_{t}is the coefficient of sverkhlineinoi gas at time t.

Equation (9) for storage in the aquifer with the water regime of exploitation takes the form

The coefficient of sverkhlineinoi (Z) depends on the gas composition, temperature, pressure, and is the reference index is (Trebinje F. A. "Natural gas production". M.: Nedra, 1976, S. 78-85). Z one can accurately be approximated by a polynomial of the form