Dudych I. Improvement of directional well flushing technology

The thesis is devoted to the improvement of the technology for cleaning wells from cuttings in order to increase the efficiency of well flushing. To accomplish these tasks, the peculiarities of directional well flushing are analyzed and the main differences compared to vertical well flushing are highlighted. The reasons for ineffective wellbore cleaning and factors that may affect it are considered. The possibility of using pulse technologies in the drilling process is analyzed. It is established that the use of pulsed flow of drilling fluid has a positive effect on the process of rock destruction and its efficient transportation to the bottom surface. It has been found that the most common complications of the flushing process are the collapse and caving of well walls, which leads to the formation of additional rock particles and their ingress into the drilling fluid, complicating the process of cleaning wells from cuttings. The thesis analyzes the use of different types of drilling fluids to increase the stability of well walls, among which silicate inhibited drilling fluids are considered the most promising. A mathematical model of the process of cuttings removal from a well based on the classical results of Poiseuille flow is considered, as well as a model describing the perturbation of the zone in the annular space of the well due to the action of resonant and pre-resonant effects. Based on the principle of independence of motions, a mathematical model of oscillatory vibrations in the two-phase medium of the flow of drilling fluid with drilled rock along the axis of the wellbore was developed. To perform calculations in accordance with the analytical studies, a JavaScript program was developed to study changes in the natural vibration displacement of the two-phase medium over time. The program was used to study the effect of cuttings concentration and distance from the pulse source on the frequency and amplitude of pulsations. As a result it was found that with increasing distance, the pulse frequency decreases in a hyperbolic dependence due to their attenuation. Increasing the concentration of cuttingss in the drilling liquid reduces the amplitude of pulsations. Based on the provisions of the theory of similarity and dimensions, an experimental setup was designed to model the process of well flushing in laboratory conditions. Experimental plans for multifactorial assessment of the influence of the above factors on the transportation of cuttigs in the annular space based on the Taguchi and Latin squares methods were developed. Using a laboratory setup, a study was conducted to determine the significance of the influence of parameters and their range of change on the volume of cuttings deposited on the bottom wall of the wellbore: flow rate of driling fluid; eccentricity of the drill string in the well; plastic viscosity; rock particle diameter; pulsation frequency; drill string rotation; longitudinal movement of the drill string. Based on the results of experimental studies, the factors with the highest interdependence were identified, namely: pulsation frequency, drilling fluid flow rate, and plastic viscosity. The effectiveness of the use of pulsating flow on the carrying capacity of the drilling fluid along the horizontal section of the wellbore is investigated. It is established that the use of pulsations effectively reduces the volume of rock sedimentation in the annular section at small values of the fluid flow rate. The creation of pulsations with a frequency of 10-20 Hz reduces the volume of settled cuttings in the annular space by half at minimum fluid flow rates. The design of a downhole pressure pulsator was developed to create a pulsating flow of drilling fluid. The device is installed in the bottom of the drill string, thus creating fluid pressure pulsations at the bottom of the well with the possibility of propagation through the annular space. The design of the device allows to adjust the rotor speed of the power unit within technologically reasonable limits to ensure the frequency parameters of pressure pulses within (11÷15) Hz. To increase the stability of the well walls and prevent the formation of additional rock particles and their ingress into the drilling fluid, a clay-free biopolymer-silicate drilling fluid was developed, the basic recipe of which is protected by a Ukrainian patent. Based on the basic formulation and analysis of geological and technical conditions of drilling, the selection of the biopolymer-silicate drilling fluid formulation for drilling the interval 410-1550 m of the Hrabynska 9 well was carried out.