In the drilling of horizontal wells, the drill cuttings tend to settle down on the low side of the annulus due to gravity and form a stationary bed, which results in hole cleaning problems. In this paper, a novel type of drillpipe with an elliptical shape was proposed to alleviate inadequate hole cleaning during the drilling of horizontal wells. A three-dimensional computational fluid dynamic (CFD) Eulerian-Eulerian approach with the Realizable k-ɛ turbulence model was developed to predict the solid–liquid two-phase flow in the annular space. Numerical examples were given to investigate the influence of different parameters on cuttings’ transport behavior, and the elliptical drillpipe was compared with the circular drillpipe. The annular cuttings concentration, annular pressure drop, and hole cleaning efficiency were evaluated. The numerical results clarify the potential of the elliptical drillpipe to enhance the hole cleaning efficiency without significantly increasing the annular pressure drop. Due to the swirl flow and secondary flow caused by the rotation of the curvature wall, the swaying phenomenon of drill cuttings’ distribution along the rotation direction of drillpipe was observed and enhanced the cuttings transport ability. Using the elliptical drillpipe as a joint-type tool can improve hole cleaning performance. Under the optimum conditions applied in this study, the hole cleaning efficiency increased by nearly 18%.

In the late stage of the steam flooding development of heavy oil reservoirs, the contradiction between layers is prominent, which makes the development of the reservoir difficult. To obtain a profile control agent suitable for steam flooding in heavy oil reservoirs, the modification technology was used to improve the temperature resistance of the traditional NH-1 main agent, as the conjugation effect may enhance the stability of the molecular structure. Thus, we obtained the modified NH-1 main agent, which was used in combination with graphite particles. To explore the oil displacement effect of the profile control system, the single-variable method was used to optimize the profile control system and evaluate its performance. Moreover, the multimedium steam flooding experiment was carried out to further verify the profile control capability of the profile control system. The results show that the formula of the graphite particle–gel compounding system is 0.03% coagulant BK-A05 + 2.2% cross-linking agent I + 1.8% cross-linking agent II + 6% modified NH-1 main agent (prepared by reacting NH-1 main agent with 65% concentrated nitric acid at a solid–liquid ratio of 1:6) + 0.7% graphite particles (10 000 meshes) + 0.3% suspending agent CMC. The gel viscosity of the profile control system can reach 2 × 10 6 mPa·s, the gel temperature range is wide (160–280 °C), and the temperature resistance is 300 °C. The profile control system has good injection performance, plugging effect, washing resistance, and thermal stability and is significantly better than the gel system alone. The experiment results also show that the profile control system has a strong profile control capability and expands the swept volume. The crude oil recovery increases by 8.89%, and it can be effectively applied to the profile control operation of heavy oil multimedium steam flooding.

The drag coefficient CD plays an important role in studying the interaction forces between individual particles and fluid. Due to the irregular particle shape of natural sands, studying the sedimentation characteristics and drag coefficient model of irregular particles is of great significance in explaining natural phenomena, predicting the sedimentation process, and calculating the interphase forces between individual particles and fluid. In this paper, firstly, an experimental system for measuring the settling velocity was built, the settling velocity of 67 tests of spheres with different particle Reynolds number Res in the Newtonian fluid were obtained, and the CD–Res correlation of sphere settling in the Newtonian fluid was established. The proposed CD–Res correlation was in good agreement with the existing classical CD–Res correlations, which proves the reliability of the experimental system and data processing method. Existing literature shows that the previous models are only suitable for irregular-shaped particles with three-dimensional shape-described parameters. However, the three-dimensional shape information of sand particles can only be obtained through accurate laboratory measurements, and it is often impossible to calculate accurately. By introducing the two-dimensional shape-described parameter (circularity c), using image analysis technology, the two-dimensional shape information of natural sands was obtained. The settling velocity of 221 tests of natural sands in the Newtonian fluid was obtained experimentally. It is found that the sand particles’ drag force exerted by the fluid is more significant than its equivalent sphere. With the increase in the particle Reynolds number, the shape irregularity’s influence on sand particle drag coefficient is more significant, and the CD–Res correlation of natural sand was proposed by fitting. The established CD–Res correlation has good prediction accuracy and can better predict the drag coefficient and terminal settling velocity of natural sand with irregular shapes.

The application of hole cleaning devices can effectively solve the hole cleaning problem during the drilling of horizontal wells. Improving the hole cleaning performance is directly related to subsequent drilling time and cost. In this paper, the solid–liquid two-phase hydrodynamic characteristics under the action of the V-shaped hole cleaning device for drilling horizontal wells were studied experimentally and numerically. The decay law of spiral flow induced by the V-shaped hole cleaning device was obtained numerically using the commercial CFD code “Fluent” by changing the blade rotational speed, blade helix angle, and consistency coefficient of drilling fluid. The helix angle will cause the flow direction of local fluid to deflect. The swirl intensity of spiral flow increases significantly with an increase in rotational speed. The hole cleaning performance was better when the helix angle was from about 10 to 20 degrees. Increasing the fluid consistency coefficient will rapidly make the spiral flow decay, resulting in a shorter effective action distance and a worse hole cleaning effect. The simulation results were validated against the experimental results of the flow loop. Both experimental and simulation results showed that the hole cleaning performance was improved by using the V-shaped hole cleaning device. The very good agreement achieved between the results has presented an opportunity to study the hole cleaning effect of a hole cleaning device in unsteady state conditions. The results will provide theoretical guidance for efficient hole cleaning using V-shaped hole cleaning devices for horizontal well drilling.

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