Ruihe Wang

Determination of rock-breaking performance of high-pressure supercritical carbon dioxide jet

In this study, a well-designed experimental setup is used to determine the rock-breaking performance of a high-pressure supercritical carbon dioxide (SC-CO2) jet. Its rock-breaking performance is first compared with that of a high-pressure water jet under the same operation conditions. The effects of five major factors that affect the rock-breaking performance of the high-pressure SC-CO2 jet, i.e., the nozzle diameter, the standoff distance, the jet pressure, the rock compressive strength and the jet temperature are experimentally determined. The experimental results indicate that the rock-breaking performance of the SC-CO2 jet is significantly improved over the high-pressure water jet. It is also found that the rock-breaking performance of the SC-CO2 jet is improved with the increase of the nozzle diameter or the standoff distance, until the nozzle diameter or the standoff distance reaches a certain critical value and after that it begins to deteriorate. The rock-breaking performance of the SC-CO2 jet improves monotonically with the increase of the jet pressure, while it shows a monotonic deterioration with the increase of the rock compressive strength. In addition, it is found that, under the same working conditions, the SC-CO2 jet can always provide a better rock-breaking performance than the subcritical liquid CO2 jet.

Numerical simulation of transient cuttings transport with foam fluid in horizontal wellbore

With considering the interlayer mass transfer and fluid influx from the reservoir, a one-dimensional two-layer hydraulic model was established to describe the mechanism of transient cuttings transport with foam fluid in horizontal well section. The model was numerically calculated based on the modified SIMPLE algorithm, and the height of cuttings bed was predicted by the trial-and-error method. Sensitivity analysis was conducted on the affecting factors on the cuttings transport performance. Results show that cuttings deposition moves along the horizontal wellbore from the drilling bit, and finally achieves a steady state with dynamic balance. Dimensionless cuttings bed height decreases with the increase of foam quality or foam flow rate, but increases with the increase of drillpipe eccentricity, cuttings size or drilling rate. The influx of water and gas from the reservoir is helpful to improve the cuttings transport efficiency with foam. The proposed model offers theoretical guidelines for hydraulic parameter design and hole cleaning control in foamed horizontal drilling.

Experimental and numerical simulations of bottom hole temperature and pressure distributions of supercritical CO2 jet for well-drilling

The supercritical carbon dioxide (Sc-Co2) drilling is a novel drilling technique developed in recent years. A detailed study of temperature and pressure distributions of the Sc-Co2 jet on the bottom of a well is essensial to the Sc-Co2 drilling. In this paper, the distributions of pressure and temperature on the bottom of the hole during the Sc-Co2 jet drilling are simulated experimentally and numerically, and the impacts of the nozzle diameter, the jet length, and the inlet pressure of the Sc-Co2 jet are analyzed. It is shown that, the bottom hole temperature and pressure increase with the increase of the nozzle diameter, and the bottom hole temperature reduces and the pressure increases first and then decreases with the increase of the jet length, indicating that the jet length has an optimum value. The increase of the inlet pressure can increase the temperature and pressure on the bottom, which has a positive effect on the drilling rate.

Dynamical analysis of high-pressure supercritical carbon dioxide jet in well drilling

This paper presents the design of an experimental setup and mathematical and physical models to determine the dynamical characteristics of the high-pressure supercritical carbon dioxide (SC-C2) jet with a highly potential applications in the well drilling. The effects of three major factors on the wellbore dynamical characteristics of the high-pressure SC-CO2 jet, i.e., the nozzle diameter, the standoff distance and the jet pressure are determined. It is indicated that the pressure of CO2 reduces severely in the SC-CO2 jet impact process. It is also found that the bottom-hole pressure and the temperature increase as the nozzle diameter increases but decrease with the increase of the standoff distance. The higher the jet pressure at the wellbore inlet is, the higher the pressure and the lower the temperature at the bottom-hole will be.

A Three-Segment Hydraulic Model for Annular Cuttings Transport With Foam in Horizontal Drilling

Through mechanical analysis, an improved hydraulic model for annular cuttings transport with foam was established for horizontal drilling. Based on the two critical inclination angles, the entire well was divided into three segments. The Bagnold stress, generalized power law rheological model and modified hindered particle settling velocity in foam fluid were adopted in the model to improve the simulation accuracy. The proposed model allows more precise prediction of cuttings transport property in the whole range of well inclination angle. Model performance was examined via case study and experimental data. Simulation results given by the propulsion iteration and trial-and-error method agree well with in-situ horizontal well drilling practice for the case study, and the comparison between the model prediction and Capo’s experimental data shows satisfactory agreement.

HYDRODYNAMIC ANALYSIS OF SUCK-IN PULSED JET IN WELL DRILLING

The development of new drilling methods is important for the exploration and production of oil fields. The pulsed jet is a drilling technology of high potentiality. This article proposes a new concept of suck-in pulsed jet with self-excited oscillation, by which a full use of the hydraulic power can be made in the annular space. A hydrodynamic analysis of suck-in pulsed jet with self-excited oscillation is carried out by numerical simulations and rock-breaking experiments. It is shown that with the jet, a negative pressure zone will be formed in the oscillation cavity to ensure automatic sucking of enough annular fluids and the formation of an efficient pulsed jet. The rock-breaking and pressure testing results have verified the reliability of the numerical simulation. The research provides a basis for the development of the pulsed jet drilling technology.

Pressure controlling method for managed pressure drilling with supercritical carbon dioxide as the circulation fluid

Abstract Heat transfer along the wellbore was analyzed, and then a closed mathematical model, which fully couples the hydrostatic pressure, temperature, physical properties of CO2 and friction, was established to keep bottom-hole pressure constant during drilling process. Based on the pressure profile in wellbore achieved for a certain surface back pressure, a pressure controlling method for managed pressure drilling with supercritical carbon dioxide was presented. The influences of mass flow rate, well depth and inlet temperature on the annulus pressure profile and surface back pressure were investigated. The results show that, the pressure profile is almost in linear correlation with well depth in the annulus, which provides convenience for well control. The needed back pressure (applied by surface choke) decreases with increasing mass flow rate and decreasing well depth. The impact of inlet temperature on the annulus pressure profile, surface back pressure and flow friction is negligible. It also shows that the density of CO2 increases significantly and abruptly at a critical pressure. It is suggested that the storage pressure of CO2 in surface tank be larger than the critical pressure for a certain temperature.

An Experimental Study on the Synergetic Effects of Kinetic and Thermodynamic Gas Hydrate Inhibitors

Gas hydrate can be inhibited by using hydrate inhibitors, such as thermodynamic inhibitors (e.g., methanol and salts) and kinetic inhibitors (KHIs; polymer based). The study of kinetic hydrate inhibitors is paid growing attention in recent years because of its low dosage and environment friendly features, but its application is restricted at high sub-cooling conditions. In this study, the combination of kinetic hydrate inhibitor (polyvinylcaprolactam based) and thermodynamic inhibitors (methanol and NaCl) was investigated in terms of the synergetic effect of the two types of hydrate inhibitors and the effects of pressure and sub-cooling time on the kinetic inhibition effect. The results show that the combined system has a good synergetic effect, which can make the KHIs to stand at higher sub-cooling conditions. The performance of polyvinylcaprolactam and methanol is better than that of polyvinylcaprolactam and NaCl, and the combined system can be also greatly affected by high pressure and long sub-cooling time.

Research on the Mechanism of In-Plane Vibration on Friction Reduction

A modified model for predicting the friction force between drill-string and borehole wall under in-plane vibrations was developed. It was found that the frictional coefficient in sliding direction decreased significantly after applying in-plane vibration on the bottom specimen. The friction reduction is due to the direction change of friction force, elastic deformation of surface asperities and the change of frictional coefficient. Normal load, surface topography, vibration direction, velocity ratio and interfacial shear factor are the main influence factors of friction force in sliding direction. Lower driving force can be realized for a pair of determinate rubbing surfaces under constant normal load by setting the driving direction along the minimum arithmetic average attack angle direction, and applying intense longitudinal vibration on the rubbing pair. The modified model can significantly improve the accuracy in predicting frictional coefficient under vibrating conditions, especially under the condition of lower velocity ratio. The results provide a theoretical gist for friction reduction technology by vibrating drill-string, and provide a reference for determination of frictional coefficient during petroleum drilling process, which has great significance for realizing digitized and intelligent drilling.

Euler/Euler theory and application of fluid-particle two-phase jet

High Pressure abrasive waterjet is a typical fluid-particle two-phase jet, it is widely used in many industries. In this paper, abrasive particle phase is treated as a continuum, both fluid phase and particle phase are handled in Eulerian framework, numerical simulation of submerged flow field outside a convergent nozzle is performed and the flow field characteristics are studied. Numerical results are compared with experimental results, and good agreements are achieved.