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While exploring and developing oil and gas, well kick and overflow accidents are inevitable. In such an accident, if the drilling bit is not at the bottom of the well, the drilling tool is blocked, or the reservoir contains toxic gases such as hydrogen sulfide, the traditional technique for well control is no longer suitable, and the bullheading method must be adopted to kill the well. However, during bullheading, the flow patterns of gas and liquid are intricate, making gas velocity hard to predict. To solve these problems, a set of visual simulation experimental device for directional well bullheading was built to find out the effects of wellbore inclination, liquid viscosity, gas and liquid velocities, and bubble size on bubble migration characteristics in gas–liquid countercurrent (gas flowing in opposite direction to the liquid). Prediction models of bubble distribution coefficient and rising velocity considering liquid viscosity, bubble size, and wellbore inclination angle were worked out. The experimental results show that small bubbles are mainly located in the center of the wellbore and large bubbles tend to approach the wellbore wall in gas–liquid countercurrent. Increasing wellbore inclination, viscosity, and the velocity of the liquid flowing against the bubbles results in a gradual decrease in Taylor bubble migration speed, which promotes the bubbles' pressing-back, as inhibiting the upward movement of large bubbles is essential for effective bullheading operations. The prediction models of distribution coefficient and bubble migration velocity have an error of less than 10% and 9. 78%, respectively. [ABSTRACT FROM AUTHOR]

In order to further regulate equivalent circulating density (ECD), a novel downhole apparatus for reducing circulating pressure in high-temperature and high-pressure wells, the suction-type ECD reduction tool, was devised. The utilisation of this tool enables the bottomhole pressure of the equivalent circulating density to be attained in close proximity to its hydrostatic pressure, thereby facilitating the attainment of deeper drilling depths. The tool is composed primarily of a screw motor, scroll blades, annular seals, universal joints, and drilling columns. The tool operates by utilising the suction effect and hydraulic energy extracted from the circulating fluid by the screw motor, which is then converted into mechanical energy to create suction and enhance the flow energy of the drilling fluid within the annulus at the bottom of the well, thereby reducing the equivalent circulating density. Furthermore, based on ANSYS-FLUENT analysis simulations, the alteration of pressure drop characteristics in response to varying drilling fluid densities, displacements, and tool sizes was modelled. The simulation results demonstrate that the pressure drop effect is 1.0 MPa when the drilling fluid density is 1.2 g/cm3, 1.7 MPa when the drilling fluid density is 1.5 g/cm3, and 1.9 MPa when the drilling fluid density is 1.8 g/cm3. A pressure drop of approximately 2.3 MPa was observed when the drilling fluid density was 2.0 g/cm3. The maximum pressure drop is achievable with a flow rate ranging from 1500 to 2500 L/min. A maximum pressure drop of 2.3 MPa is observed when the flow rate is within the range of 1500 to 2500 L/min. Two distinct viscosity values (0.02 and 0.06 kg/(m·s)) were employed to assess the impact of viscosity on pressure drop characteristics in a suction-type ECD tool. The results demonstrated that the pressure drop remained largely unaltered, indicating that viscosity had minimal influence on this parameter. The flow rate emerged as the primary factor affecting pressure drop, with viscosity exerting a relatively minor effect. [ABSTRACT FROM AUTHOR]

The small difference between formation pressure and fracture pressure in offshore oil and gas reservoirs poses a huge challenge to drilling. Managed pressure drilling (MPD) technology, as a drilling technique that can accurately control bottomhole pressure, is an effective technique to solve this challenge. In MPD technology, the pressure wave propagation behavior and mechanism in the wellbore induced by wellhead backpressure are crucial for parameter design and efficient application. In this paper, pressure wave propagation characteristics and mechanism in gas-liquid flow were investigated with a new proposed pressure wave velocity model that considers inter-phase mass transfer effect. This new model and its solution algorithm were verified with experimental data in literature. The influence of gas invasion stage, drilling fluid type, drilling fluid density and backpressure on pressure wave propagation characteristics were investigated. Results show that the time for pressure wave induced by wellhead backpressure in the wellbore cannot be ignored in the design of the backpressure value during MPD. This propagation time increases with occurrence of gas invasion. Moreover, the propagation time in water-based drilling fluid is longer than that in oil-based drilling fluid, which is because the interphase mass transfer between invaded gas and oil-based drilling fluid. The influence mechanism of high drilling fluid density and wellhead backpressure on pressure wave propagation characteristics is due to the suppression of gas invasion process. These findings could be used as guides in parameters design and optimization in MPD. [ABSTRACT FROM AUTHOR]

Harvesting and converting solar energy is a promising strategy for addressing energy and environmental crises. To achieve this strategy, numerous semiconductors and heterojunctions have been explored and developed. However, the low utilization rates of light and low charge separation efficiency are still major drawbacks limiting its development. The structure and electron transfer paths of semiconductor heterojunctions are important for solar energy harvesting and conversion. A one-dimensional hollow structure has excellent light scattering and reflection effects that can improve the harvesting and conversion of solar energy. Furthermore, S-scheme has recently become a hot topic of research because of its ability to weed out useless photoelectrons and holes while retaining powerful ones. In this study, a hollow Ni2P/TiO2 S-scheme heterojunction was designed to harvest solar energy and enhance the photoelectric effect. The Ni2P/TiO2 heterojunction has excellent photoelectric separation effects, which are confirmed by photoelectrochemical characterization results and density functional theory (DFT) calculations. Consequently, the hollow Ni2P/TiO2 heterojunction provides good photocathodic protection under visible light irradiation, and the surface potential of 304ss coupled with the Ni2P/TiO2 heterojunction decreases to −0.83 V in a 3.5% NaCl solution. Laser scanning confocal microscopy (LSCM) shows that the 3D morphology and roughness of the 304ss surface changes slightly with the photocathodic protection of the Ni2P/TiO2 composite. Based on the band matching and electron spin resonance (ESR) experimental results, the S-scheme interfacial charge transfer path was confirmed. This study demonstrates the potential of the Ni2P/TiO2 S-scheme heterojunction for photocathodic protection and can inspire future exploration of the S-scheme heterojunction for photocathodic protection. [ABSTRACT FROM AUTHOR]

Uncontrollable blowout is a great drilling accident. For gas kick during drilling, in order to prevent uncontrollble blowout, the gas-liquild two-phase flow model is established, considering the kick characteristics in well kick and well killing process, and it is solved with finite difference method, given initial values in different periods. The results indicated that a one-to-one correspondence was established between standpipe pressure and kick rate and height while drilling, and another one-to-one correspondence was also established between casing pressure and kick rate and height while well killing. Based on the findings above, the standpipe pressure method and casing pressure method were proposed to detect kick, and the related coefficient method was used to judge the kick rate and height during drilling and killing. Meanwhile, a computer system was developed to judge kick velocity and height automatically, which provided a theoretical basis for kick parameter judgement. [ABSTRACT FROM AUTHOR]

In the process of penetrating the reservoir by underbalanced drilling, with the increase of the penetrated reservoir thickness, the volume of gas kicking into the wellbore increases, which causes the drastic change of wellhead void fraction, leading to the bottom-hole pressure out of control. The changing of void fractions in different well depths are calculated during underbalanced drilling, and the influence of different air intake flow and wellhead back pressure on wellbore void fractions is analyzed. In consideration of wellhead pressure adding value on bottom hole pressure, the computing method of wellhead pressure of constant air intake flow is obtained for penetrating the reservoir by underbalanced drilling. The results show that gas rapidly expands when it reaches the surface, and the wellhead back pressure have a enormous effect on the void fractions at wellhead while have a little influence on the void fraction under 500 meters. Keeping the air intake flow constant, with the increase of the penetrated reservoir thickness, the wellhead pressure increases. The smaller the air intake flow, the bigger the wellhead pressure needs to load. [ABSTRACT FROM AUTHOR]