Studying Thermophysical Processes during the Filtration of Paraffin Oil to a Horizontal Well

About the authors:

Anatoliy A. Kislitsin, Dr. Sci. (Phys.-Math.), Professor, Department of Applied and Technical Physics, University of Tyumen; a.a.kislicyn@utmn.ru; ORCID: 0000-0003-3863-0510

Sergey V. Kuznetsov, Cand. Sci. (Phys.-Math.), Project Coordinator, Gazprom Neft Science and Technology Center (Tyumen); kuznetsov72tmn@gmail.com

Aleksandr A. Podnebesnyh, Cand. Sci. (Geol.-Mineral.), Deputy Academic Director, SIAM Company, Integra; apodnebesnykh@integra.ru

Vitaliy O. Polyakov, Leading Specialist, LLC Novatek Science and Technology Centre

Abstract:

In this article, the authors have formulated a system of equations of filtration paraffin oil to a horizontal well in view of phase transitions (degassing oil, wax crystallization), the Joule–Thomson effect, as well as geometric features of the system. It relies on the assumption that local thermodynamic equilibrium is achieved for all phases at each point of the porous medium at each instant of time. The authors have developed an algorithm for calculating phase equilibrium three-phase multicomponent mixture, based on the use of the thermodynamic functions of fugacity and activity. They have substantiated quasi-one-dimensional approximation of the equations describing the flow of formation fluid. They have also accounted for the effect of reducing permeability effect in the bottom hole zone as a result of the crystallization of paraffin. Based on the formulated system of equations, the authors have created a software package that allows simulating the process of filtration of a three-phase multicomponent mixture in the bottom hole zone of a horizontal well with good accuracy. The paper has investigated the process of crystallization of paraffin oil and shown that its speed is heavily influenced by oil disintegration (gas allocation from oil when pressure is reduced). The simulation of bringing the well to the technological regime has established that the dynamics of the change in bottom hole pressure significantly affects the final productivity factor of the well. The authors show that a too rapid decrease of the bottom hole pressure can lead to a noticeable temperature decrease, paraffin crystallization, a decrease in dynamic porosity, and deterioration in permeability. In accordance with the proposed method, the paper presents the patterns of the decrease in productivity of the well depending on the intensity of the bottom hole pressure decrease. Numerical experiments have determined the optimum dynamics of the bottom hole pressure in the process of development of the well after drilling in order to achieve a maximum productivity index.

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