«Automation and Informatization of the fuel and energy complex»

Influence of the initial data uncertainty on the assessment of the possibility of hydrate formation in a reservoir during well operation

UDC: 622.279+519.6+510.644.4
DOI: 10.33285/0132-2222-2021-12(581)-35-42

Authors:

¹ National University of Oil and Gas "Gubkin University", Moscow, Russian Federation

Keywords: hydrate formation, bottomhole formation zone, uncertainty of initial data, robustness of simulation results, fuzzy set theory

Annotation:

The article deals with a problem of assessing the influence the initial data uncertainty when analyzing possibility of gas hydrates formation in a bottomhole formation zone. An assessment of a hydrate formation risk is based on modeling of a non-isothermal process of gas filtration and comparing the obtained data of temperature and pressure conditions in the bottomhole formation zone with the equilibrium conditions of hydrate formation. Mathematical model is a system of the partial differential equations based on the equations of continuity, energy balance, gas state and Darcy's law. The solution of equations system can be obtained by the finite-difference methods. The coefficients of the equations system include the parameters of the reservoir and gas: permeability, reservoir porosity, heat capacity and thermal conductivity of gas, coefficients of dynamic viscosity of gas, gas compressibility. Determination of their exact values presents significant difficulties. The description of the initial parameters uncertainty in terms of the theory of fuzzy sets is proposed. The article studies the model sensitivity to the error of methods for calculating the coefficient of gas compressibility. The graphs, revealing the changes in pressure and temperature values along the radial coordinate in the bottomhole zone taking into account the permissible error, when calculating gas compressibility coefficient, as well as the deviation that occurs when an iterative procedure for calculating the compressibility coefficient is replaced by a simplified correlation are shown. It is concluded that the method for calculating the compressibility factor has a rather weak effect on the results of pressure calculation, but as for temperature, this effect cannot be neglected.

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