INVESTIGATION OF THERMAL FIELD IN A WELL UNDER FLUID MOVEMENT UNDER INDUCTION IMPACT

Abstract

Relevance. One of the promising methods of field geophysical studies of wells is active thermometry. The technology of conducting research by this method includes local induction heating of a metal casing, registration and analysis of changes in the temperature of the column. In case of poor-quality cementing of wells, a liquid flow may occur in the annular space between the casing and the cement ring (column overflow). Through the flow channel, water from unproductive reservoirs enters the well, which reduces the profitability of oil production. In this regard, timely detection and elimination of backwater flows is an important task of efficient well operation. During induction heating of the casing string in the liquid flow moving in the channel of the column overflow, due to heat exchange with the heated section of the column, a thermal disturbance occurs, which can be used to detect the presence of overflow. Object: a production well in which studies are carried out by the method of active thermometry using local induction heating of the casing string. Purpose of the research is to develop a mathematical model for calculating the thermal field caused by induction heating of a section of a metal casing string, taking into account liquid movement in the annular space between the casing string and the cement ring (column overflow); obtain analytical solutions for calculating the temperature of the casing string and liquid in the overflow channel; investigate the features of temperature field formation in the column and liquid in the overflow channel in induction heating, as well as the effect of fluid flow in the flow channel on the thermal field in the casing. Methods: method of the integral Laplace transformation in time and the numerical algorithm of Stefest in order to obtain analytical solutions for calculating the temperature field; comparison of the results of calculations based on an analytical model with the results of numerical modeling in the Ansys Fluent software package (ANSYS Academic Research CFD license, agreement with Bashkir State University dated 06/15/2020). Results. By the method of integral Laplace transformations, new analytical solutions were obtained for calculating the non-stationary temperature field in a well during induction heating of a section of a metal casing string, taking into account the fluid flow in the annular space between the column and the cement ring. The peculiarities of temperature field formation during heating and after switching off the inductor are investigated, it is shown that during 20 minutes of heating, temperature disturbances in the liquid moving in the overflow channel and the casing string propagate in the direction of flow at a distance of more than 2 m. It is shown that an increase in the column temperature at distances of about 1–2 m above the induction heating interval is associated with heat transfer from the heated fluid in the channel of the column flow. The criterion for increasing the temperature of the casing at distances of 1–2 m relative to the induction heating interval can be used as a sign of the column motion of the liquid. The influence of liquid velocity (flow rate) in the flow channel on column temperature formation nature during induction heating is investigated. It is shown that an increase in fluid flow in the overflow channel, other things being equal, leads to growth of temperature disturbance propagation rate in the casing body, as well as to a decrease in the heating value of the column due to an increase in the intensity of heat outflow from the inductor operation interval. The results of calculations based on the analytical model are compared with the results of modeling in the Ansys Fluent software package, it is found that the calculated temperatures of the column and liquid are somewhat overestimated compared to the numerical solution due to the use of simplifying assumptions within the analytical model.

Keywords

• active thermometry
• induction heating
• non-stationary temperature field
• laplace transforms
• stefest algorithm
• thermal mark
• temperature perturbation