Miao He

Accurate prediction of the wellbore temperature field in deepwater drilling is essential for operational safety. A few existing studies have considered the coupled effects of swirling flow and drill-string vibration, making it difficult to accurately characterize the downhole thermal environment. Based on wellbore heat transfer and drill-string dynamics, with the coupled effects of drill-string rotation–vibration accounted for, a transient heat-transfer model for deepwater drilling was developed. The sensitivity of bottom-hole temperature (BHT) in deepwater drilling to various factors was evaluated using a Plackett–Burman (P–B) screening design, followed by the proposal of targeted cooling methods. Compared to DRILLBENCH and models ignoring coupling effects, this model predicts annular temperatures closer to actual conditions, with a relative error of 1.02%, demonstrating higher accuracy and improved stability. An optimal insulation coating thickness can reduce BHT by up to 23 °C. Additional methods, such as adjusting the drill string rotation–vibration coupling factor and increasing fluid displacement, can lower BHT by 5–7 °C. The effectiveness of surface cooling methods exhibits pronounced diminishing marginal returns, with cooling capacity becoming increasingly limited as depth increases. Given the limited efficacy of individual cooling strategies, an integrated approach that combines multiple methods is recommended to achieve effective wellbore temperature reduction. The efficiency of surface-based cooling exhibits pronounced diminishing marginal returns. As well depth increases, its cooling capacity becomes increasingly limited. Given the limited effect of a single method, it is recommended to integrate multiple cooling techniques to effectively reduce wellbore temperature. The research results provide practical guidance for predicting and controlling wellbore temperature in deepwater drilling.

Pressure waves possess many significant applications in the oil and gas drilling engineering field, such as mud pulse telemetry (MPT) and measurement while drilling (MWD). The focus of this research is to study the pressure wave propagation and attenuation characteristics of wellbore liquid-phase flow in managed pressure drilling (MPD) by fast switching throttle valve (FSTV). First, a mathematical model of transient pressure wave propagation along the wellbore in both upstream and downstream directions is proposed in MPD by FSTV based on the one-dimensional transient flow theory. The model considering the frictional shear effect between the pipe walls is solved by utilizing the method of characteristics. Meanwhile, boundary conditions at the drill string inlet and annulus outlet, at the throttle valve, at the junction of drill bit, and at the reducer are adequately taken into account according to the actual situation of fluid flow. Second, a laboratory experiment of excited pressure waves in a vertical wellbore is conducted to measure the variation of the pressure fluctuation with different pump rates by FSTV. Comparing with the measurement result, the calculation result is discovered that the overall change is consistent, where the maximum absolute relative error at the peak of the pressure wave is only 4.5%. Finally, it further analyzes influential factors affecting the propagation and attenuation behaviors of wellbore pressure waves in liquid-phase flow based on the model. The results indicate that pressure waveforms present sinusoidal wave propagation, and pump rates, pressure wave speed, excitation time, fluid type, mud density, fluid viscosity, and borehole size exert varying degrees of influence on downhole pressure fluctuations. The proposed model achieves accurate quantitative interpretation and analysis of downhole pressure wave in MPD by FSTV, which has important significance for the realization of safe and efficient drilling.

The application of fiber in the completion fluid can improve the rheological properties of the completion fluid and the plugging quality of the production layer by the completion fluid and reduce the damage of the filtrate to the reservoir formation. However, there are few studies on the influence of fibers on the rheological properties of completion fluids and the flow behavior in pores. In this paper, plant fiber, mineral fiber, and synthetic fiber are discussed. Carbon fiber, bamboo fiber, polypropylene fiber, and polyester fiber are selected as research objects. The dependence of the rheological property of polymer solution on fiber type, fiber concentration, temperature, and shear rate is evaluated. The evaluation is carried out by observing the microscopic state of the fiber through a microscope and a scanning electron microscope, testing the rheological property parameters of the fiber with an OFITE 900 rheological tester, and fitting with the Herschel–Bulkley model. The results show that polypropylene fiber and carbon fiber have the best dispersion in polymer solution. The higher the fiber content, the greater the influence of fiber on the rheological properties of the solution. Compared with the other three fibers, carbon fiber has the greatest influence on the rheological properties of polymer solution. When the temperature is lower than 70 °C, the influence of the fiber on the rheological properties of the solution is not affected by the temperature. When the temperature exceeds 70 °C, the carbon fiber and polypropylene fiber are affected by the temperature, and the viscosity of the polymer solution is increased. The flow behavior of fiber suspensions in pores varies with the flow factor n. Carbon fiber suspensions are most conducive to the transition of polymer solution to plate laminar flow, which can improve the bearing capacity of plugging materials.