Abstract
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.
Highlights
As oil and gas drilling continues to move towards deep fields and deep seas, complex formation conditions and temperature and pressure environments have brought great challenges to the accurate calculation and control of wellbore pressure [1, 2]
Most of the existing researches on suspended bubbles in yield stress fluids focus on the non-Newtonian rheology of wellbore fluids [8,9,10], the bubble slip velocity in yield stress fluid [11, 12], and the single-bubble suspension condition [13,14,15,16]
Based on the experimental results, we present the following conclusions: (1) The critical GSC of gas in the diffusion gas invasion increases with the increase of the dimensionless number Bi, until it reaches the peak value
Summary
As oil and gas drilling continues to move towards deep fields and deep seas, complex formation conditions and temperature and pressure environments have brought great challenges to the accurate calculation and control of wellbore pressure [1, 2]. The experimental data of Liu et al [13] and Samson et al [22] agreed with the results calculated by the model Due to their model results, the critical suspension conditions, Bic, are a function of yield stress, surface tension, and elastic modulus. When the distance between multiple suspended bubbles in the drilling fluid just satisfies the condition of simultaneous suspension after gas invasion, the corresponding GSC is the critical GSC. This paper intends to carry out experiments on the critical GSC under different gas invasion methods and establish a critical GSC prediction model considering the bubble size and distribution characteristics.
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