INVESTIGATION OP THE SKIN FACTOR IN STEADY-STATE GAS FLOW OBEYING NONLINEAR FILTRATION LAW

Introduction. The productivity of the wells at gas and gas condensate fields along with the wells at underground gas storage facilities, depends on such parameters as thermodynamic conditions, properties of the produced fluid, method of opening and completion, filtration-volumetric and geometrical characteristics of the formation. To identify the factors affecting the flow rate of wells, the information obtained as a result of the interpretation of the data of systematically conducted gas well tests is used. The development of mathematical models for assessing the factors affecting the technological regime of gas wells' operation, followed by the formation of a list of candidate wells for wells intervention is an urgent approach for increasing the productivity of underground gas storage facilities. Materials and research methods. The processing of the results of gas well tests is based on the theoretical provisions of the iltration of luids in a porous medium obeying to linear and nonlinear laws. The results of well tests under steady-state filtration modes provide the most reliable estimate of the numerical values of the coefficients of filtration resistances A and B. The paper analyzes the reasons for the change in the coefficients A, B, and their main parameters by the example of underground gas storage wells. The definition of the turbulence coefficient p, which is included in the quadratic term of the equation of gas filtration obeying to the nonlinear law, has been substantiated. Since the largest pressure drop in the producing formation occurs in the immediate vicinity of the wellbore, the main factors affecting the iltration resistance in the bottomhole formation zone are the radius and degree of change in the permeability coefficient of the contaminated zone, as well as the radius of influence and the height of the sandclay plug. Research results and their discussion. To identify the parameters of the bottomhole formation zone, mathematical models have been developed for assessing the values of skin factors for the coefficients A and B, characterizing the linear and turbulent filtration resistance factors under the nonlinear law of gas filtration, respectively. The obtained formulas for calculating skin factors for cases of the presence of contamination of the bottomhole formation zone or sand-clay plug make it possible to determine the radius and permeability coeficient of the contaminated zone, as well as the radius of influence and height of the sand-clay plug. Mathematical models have been tested on synthetic wells of underground gas storage facilities. For these wells, the conditions for the change in the fiiltration resistance coefficients from the initial values A and B (without skin factors) to the current As and Bs (with regard to skin factors) are modeled. Conclusions. The paper presents the methodological foundations for assessing the main parameters of the bottomhole formation zone which affect the productivity of gas wells. The developed methodology can also be used to assess well interventions already performed to increase the productivity of gas wells.

nonlinear filtration law, filtration resistance coefficients, turbulent resistance coefficient, skin factor, radius and permeability coefficient of the changed formation zone, radius of influence and height of sand-clay plug

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