Experimental Study on the Suspension Amount of Invasion Gas in Drilling Fluid with Yield Stress

The gas suspension phenomenon caused by the yield stress of the drilling fluid affects the accurate calculation of wellbore pressure after gas invasion. At present, most studies on the bubble suspension in the yield stress fluid focus on the single-bubble suspension condition and there are few studies on the gas suspension concentration. This paper carried out the GSC (gas suspension concentration) experiment in the simulated drilling fluid, xanthan solution, with different gas invasion methods. The GSC in the drilling fluid under the conditions of diffuse gas invasion and differential pressure gas invasion was simulated by using two methods of stir-depressurization and continuous ventilation. The results showed that when the size of a single bubble satisfied the single-bubble suspension condition, multiple bubbles can be suspended at the same time. The GSC is affected by the average size of the suspended bubbles, the yield stress of the drilling fluid, and the gas invasion modes. For different gas invasion modes, the empirical models of critical GSC related to the dimensionless number Bi are established. Compared with the experimental data, the relative error of the critical GSC in diffuse gas invasion is less than 6% and the relative error of the critical GSC in differential pressure gas invasion is less than 10%. The results of this work can provide guiding significance for accurate calculation of wellbore pressure.

HEATING DEPTH OF GAS SUSPENSION FLOW BY COUNTER RADIATION

Выполнена аналитическая оценка отношения глубины прогрева газовзвеси излучением продуктов горения S к длине свободного пробега излучения в газовзвеси L. Использована одномерная модель стационарного распределения температуры в потоке взвешенных в воздухе монодисперсных инертных частиц, движущихся на равномерно нагретую абсолютно черную поверхность, имитирующую фронт пламени. Учитывается отражение и переизлучение тепловой энергии частицами. S / L >> 1 при низкой степени черноты и/или высокой конечной температуре частиц. It is accepted that the depth of heating of the gas suspension by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the gas suspension: SR ≈ LR. Numerical simulation of gas-air mixture combustion with the addition of inert particles, taking into account the re-emission of heat by heated particles of fresh suspension, shows the possibility of realizing the ratio SR >> LR (Ivanov M.F. et al, 2015). In this work, an analytical estimate of the SR/LR ratio is carried out within the framework of one-dimensional modeling of the temperature distribution in the flow of initially cold monodisperse inert particles suspended in air, moving to a uniformly heated absolutely black surface, permeable to air suspension and simulating a flame front. The following assumptions are used. The solution is stationary in the coordinate system associated with the emitting surface; radiation consists of two oppositely directed streams of electromagnetic energy; the interaction of particles and radiation is described in the approximation of geometric optics and takes into account both the processes of absorption and emission of thermal energy, and the process of reflection of radiation; the temperature inside the particle is the same. In contrast to the previously considered (Poletaev N.L., 2021) the simplified problem of the motion of particles in a vacuum or in the presence of a gas phase heated by particles but not experiencing thermal expansion, this work took into account both the presence of a gas phase heated by particles and expansion of the gas phase. The latter causes the acceleration and expansion of the air suspension as it approaches the radiating surface. The difference in the local values of temperatures and phase motion velocities of the air suspension was neglected. It is shown that the quasi-linear (in the above-mentioned coordinate system) temperature distribution function in the air suspension obtained in this work is qualitatively different from the quasi-exponential temperature distribution function obtained earlier by solving a simplified problem. At the same time, the ratio of the heating depth of the air suspension by thermal radiation and the free path of radiation in the layer of air suspension adjacent to the radiating plane turned out to be similar to that obtained for the simplified solution. Namely, SR/LR >> 1 at a low integral degree of emissivity of the particle material and / or at a high final temperature of the particles, comparable to the temperature of the emitting surface.

A Wellbore Pressure Calculation Method Considering Gas Suspension in Wellbore Shut-In Condition

In the oil industry, the drilling fluid is yield stress fluid. The gas invading the wellbore during the drilling process is distributed in the wellbore in the form of bubbles. When the buoyancy of the bubble is less than the resistance of the yield stress, the bubble will be suspended in the drilling fluid, which will lead to wellbore pressure inaccurately predicting and overflow. In this paper, the prediction model of gas limit suspension concentration under different yield stresses of drilling fluids is obtained by experiments, and the calculation method of wellbore pressure considering the influence of gas suspension under shut-in conditions is established. Based on the calculation of the basic data of a case well, the distribution of gas in different yield stress drilling fluids and the influence of gas suspension on the wellbore pressure are analyzed. The results show that with the increase of yield stress, the volume of suspended single bubbles increases, the gas suspension concentration increases, and the height at which the gas can rise is reduced. When the yield stress of drilling fluid is 2 Pa, the increment of wellhead pressure decreases by 37.1% compared with that without considering gas suspension, and when the yield stress of drilling fluid is 10Pa, the increment of wellhead pressure can decrease by 78.6%, which shows that when the yield stress of drilling fluid is different, the final stable wellhead pressure is quite different. This is of great significance for the optimization design of field overflow and kill parameters, and for the accurate calculation of wellbore pressure by considering the suspension effect of drilling fluid on the invasion gas through the shut in wellhead pressure.

Numerical determination of the combustion rate of a gas suspension of coal dust in a propane-air mixture

The results of the numerical solution of the problem of the combustion rate of a coal-propane-air mixture are presented. The physical and mathematical formulation of the problem is based on the approaches of the dynamics of multiphase reacting media. The method for solving the problem is based on the algorithm for the decay of an arbitrary discontinuity. The dependences of the visible and normal combustion rate of the coal-propane-air mixture on the radius and the volumetric content of propane in the gas are obtained.