OPTIMIZATION OF RHEOLOGICAL PROPERTIES OF DRILLING MUD INTENSIFYING TRANSPORTATION AND CLEANING OF HORIZONTAL WELLS FROM CUTTINGS

The relevance of this article is associated with the practical need for effective well cleaning in modern drilling especially in the case of extended horizontal sections, in which it is important to control dynamic pressure, which is very sensitive to changes in the rheological properties of drilling fluids described by complex deformation processes in viscous-plastic systems. For the most part, these are HerschelBulkley type fluids with three-constant parameters, each of which can significantly affect the pressure field drop and the ability of the solution to carry cuttings through the specific geometry of the eccentric annular space of horizontal wells. The study of the complex influence of the parameters of the rheological model is valuable and relevant for optimizing the cleaning process and preventing well control situations due to the danger of an excessive increase in pressure drop in the working units of the equipment. The purpose of the work is to determine the degree of influence of changes in the parameters of the Herschel-Bulkley model on the pressure field drop; to clarify the hydrodynamic features accompanying the internal flow of a rheologically complex medium; to issue practical recommendations for the improvement of cleaning and removal of cuttings from horizontal wells at minimum values of pressure drop, using the optimal combination of the range of changes in the rheological properties of the drilling fluid. The object of study is a well with a ten-meter horizontal eccentric section, in which the flow is carried out in conditions that are really close to the actual drilling parameters (in situ). Methodology is based on complex physical-mathematical and computer modeling of processes in the mechanics of homogeneous and heterogeneous continuums, widely tested on internal rheologically complex flows, as well as successfully validated and verified results under appropriate conditions and close to flow regimes, heat and mass transfer performed by other authors on the analysis of technological processes of drilling and cleaning wells. Results. Numerical modeling of the hydrodynamics of a laminar dispersed flow of a mixture of a non-Newtonian liquid with solid particles in an annular eccentric pipe has been performed. Within the framework of a real drilling process with characteristic conditions of a viscousinertial-gravitational incompressible isothermal flow of a viscous-plastic medium with spherical sand particles the authors carried out a detailed parametric analysis of the spatial effects that determine the intensity of mass transfer due to changes in the rheophysical, geometric and hydrodynamic properties of the flow and well sizes. The processes that determine and increase the efficiency of cleaning are studied by analyzing the fact: increase in the number of particles that left the geometry during the characteristic hydrodynamic time of the process; controlling the mechanisms of momentum and mass transfer in the mixture, as well as controlling the increase in pressure drop. Numerical modeling corresponded to scenarios of mixture flow with different parameters of geometry (lengths, diameters and eccentricity of pipes) and drilling fluid (non-Newtonian rheology). It was established that complete cleaning of the well when using solutions of the Herschel-Bulkley type in the drilling mode (in situ) in the laminar mode is impossible. In practice of applied research, recommendations are proposed for effective cleaning by correcting the rheophysical properties of the solution. It is shown that the most effective method for improving cleaning is the method of controlling the eccentricity of the annular space, as well as the method of controlling the geometric parameter, which is the ratio between the pipe diameters. Practical recommendations boil down to the need to control the eccentricity in the range of e<15 %. It was determined that from the parameters of the Herschel-Bulkley model, the flow index is the most important in terms of well cleanout management. It creates a high viscosity ''conveyor belt'' that is able to quickly transport cuttings particles through the geometry.