Effects of Rock/Cutter Friction on PDC Bit Drilling Performance: An Experimental and Theoretical Study.

A new mechanistic drilling model for PDC bits was derived from the balance of forces acting at the PDC cutter. The model combined the torque and the drilling rate equations, cutter\u27s geometry and rock properties. A new understanding of frictionally generated heat between rock and PDC cutter is introduced. The numerical analysis revealed that neglecting the heat generated at the cutting surface area results in underestimation of the actual wearflat temperature by 10% to 530%, depending upon bit dull and downhole hydraulics. The example bit performance comparison made by calculating the MBP curves showed 18% reduction of drilling rate when the new and more rigorous temperature limitation is used. A new PDC bit wear model was derived and used for bit performance prediction. The model relates bit life with temperature, weight on bit, rotary speed, and cutter geometry. The predictions showed that the effect of the friction dominates bit life, and this effect is greater than the effect of convective cooling. A new laboratory instrument was constructed and succesfully used to measure friction forces between sliding surface of a PDC cutter and the rock surface. Results showed that friction coefficient did not change considerably within the range of tested rock and fluid types. The concept of maximum bit performance (MBP) curve was introduced. The curves represented the maximum values of average drilling rates for various pre-assumed footage values. A new method for preparing a multi-bit drilling program, the dynamic drilling strategy, was developed. The dynamic drilling strategy provided the best combination of PDC bit runs to achieve the minimum drilling cost for a long borehole interval. The method was numerically compared to the conventional drilling optimization and to the field practices. Considerable savings of 25% and 60% were estimated, respectively. Based on the drilling model, a new method was developed for the insitu measurements of the PDC bit condition and lithology change detection. The technique was verified by comparing the predicted and measured PDC bit wear and by showing the correlation between rapid formation changes and discontinuities in the diagnostic plots

Advanced Cuttings Transport Study: Final Technical Report

The Advanced Cuttings Transport Study (ACTS) was a 5-year JIP project undertaken at the University of Tulsa (TU). The project was sponsored by the U.S. Department of Energy (DOE) and JIP member companies. The objectives of the project were: (1) to develop and construct a new research facility that would allow three-phase (gas, liquid and cuttings) flow experiments under ambient and EPET (elevated pressure and temperature) conditions, and at different angle of inclinations and drill pipe rotation speeds; (2) to conduct experiments and develop a data base for the industry and academia; and (3) to develop mechanistic models for optimization of drilling hydraulics and cuttings transport. This project consisted of research studies, flow loop construction and instrumentation development. Following a one-year period for basic flow loop construction, a proposal was submitted by TU to the DOE for a five-year project that was organized in such a manner as to provide a logical progression of research experiments as well as additions to the basic flow loop. The flow loop additions and improvements included: (1) elevated temperature capability; (2) two-phase (gas and liquid, foam etc.) capability; (3) cuttings injection and removal system; (4) drill pipe rotation system; and (5) drilling section elevation system. In parallel with the flow loop construction, hydraulics and cuttings transport studies were preformed using drilling foams and aerated muds. In addition, hydraulics and rheology of synthetic drilling fluids were investigated. The studies were performed under ambient and EPET conditions. The effects of temperature and pressure on the hydraulics and cuttings transport were investigated. Mechanistic models were developed to predict frictional pressure loss and cuttings transport in horizontal and near-horizontal configurations. Model predictions were compared with the measured data. Predominantly, model predictions show satisfactory agreements with the measured data. As a part of this project, instrumentation was developed to monitor cuttings beds and characterize foams in the flow loop. An ultrasonic-based monitoring system was developed to measure cuttings bed thickness in the flow loop. Data acquisition software controls the system and processes the data. Two foam generating devices were designed and developed to produce foams with specified quality and texture. The devices are equipped with a bubble recognition system and an in-line viscometer to measure bubble size distribution and foam rheology, respectively. The 5-year project is completed. Future research activities will be under the umbrella of Tulsa University Drilling Research Projects. Currently the flow loop is being used for testing cuttings transport capacity of aqueous and polymer-based foams under elevated pressure and temperature conditions. Subsequently, the effect of viscous sweeps on cuttings transport under elevated pressure and temperature conditions will be investigated using the flow loop. Other projects will follow now that the ''steady state'' phase of the project has been achieved

Experimental investigation of solids transport in horizontal concentric annuli using water and drag reducing polymer-based fluids

When drilling long horizontal wells, drilled solids tend to settle down on the low side of the welibore and form a stationary bed. Presence of stationary cuttings bed causes operational difficulties such as pack-off, excessive torque and drag, slow drilling rate, and in severe cases, stuck pipe, lost circulation, and even loss of the well control. Despite significant progress made in drilling fluids, tools, and field practices, along with more than 50 years of university and industry research, field experience indicates that cuttings transport is still a major problem in most horizontal wells

A Numerical Simulation Study of the Impact of Microchannels on Fluid Flow through the Cement–Rock Interface

Microchannels located at the cement–rock interface can form potential pathways for formation fluid leakage in oil and gas wells. The effects of geometric shape, quantity, and the inclination angle of microchannels on the flow through cemented rock samples were explored. Finite element 3D models were established based on modified micro-CT images obtained from physical samples. The volume flow rate through different sections of cemented rock samples was extracted after the fluid flow simulations. The numerical results showed that with the presence of a single microchannel, the total volume flow rate could be higher than that of the base case by as much as 9%. Microchannel contact and cross-sectional areas were found to be the two most important factors affecting the total volume flow rate. The overall volume flow rate increased with the increasing cross-sectional area, contact area, and inclination angle of the microchannel. The total volume flow rate for the cases with microchannels having the same cross-sectional area but different shapes increased with the decreasing number of sides of the shape (from circular to triangular) due to the increased contact area. The simulation results also revealed that the relative magnitude of the rock permeability may influence the volume flow rate through each section

A Numerical Simulation Study of the Impact of Microchannels on Fluid Flow through the Cement–Rock Interface

Microchannels located at the cement–rock interface can form potential pathways for formation fluid leakage in oil and gas wells. The effects of geometric shape, quantity, and the inclination angle of microchannels on the flow through cemented rock samples were explored. Finite element 3D models were established based on modified micro-CT images obtained from physical samples. The volume flow rate through different sections of cemented rock samples was extracted after the fluid flow simulations. The numerical results showed that with the presence of a single microchannel, the total volume flow rate could be higher than that of the base case by as much as 9%. Microchannel contact and cross-sectional areas were found to be the two most important factors affecting the total volume flow rate. The overall volume flow rate increased with the increasing cross-sectional area, contact area, and inclination angle of the microchannel. The total volume flow rate for the cases with microchannels having the same cross-sectional area but different shapes increased with the decreasing number of sides of the shape (from circular to triangular) due to the increased contact area. The simulation results also revealed that the relative magnitude of the rock permeability may influence the volume flow rate through each section

Effect of the Particle Size on the Near-Wall Turbulence Characteristics of the Polymer Fluid Flow and the Critical Velocity Required for Particle Removal from the Sand Bed Deposited in Horizontal Wells

Water-based polymer drilling fluids are commonly used for drilling long horizontal wells where eliminating the drilling fluid-related formation damage and minimizing the environmental impact of the drilling fluids are the main concerns. An experimental study was conducted to investigate the turbulent flow of a polymer fluid over a stationary sand bed deposited in a horizontal pipeline. The main objectives of the study were to determine the effects of sand particle size on the critical velocity required for the onset of the bed erosion and the near-wall turbulence characteristics of the polymer fluid flow over the sand bed. Industrial sand particles having three different size ranges (20/40, 30/50, 40/70) were used for the experiments. The particle image velocimetry (PIV) technique was used to determine instantaneous local velocity distributions and near-wall turbulence characteristics (such as Reynolds stress, axial and turbulence intensity profiles) of the polymer fluid flow over the stationary sand bed under turbulent flow conditions. The critical velocity for the onset of the particle removal from a stationary sand bed using a polymer fluid flow was affected by the sand particle size. The critical velocity required for the particle removal from the bed deposits did not change monotonously with the changing particle size. When polymer fluids were used for hole cleaning, the particle size effect on the critical velocity varied (i.e., critical velocity increased or decreased) depending on the relative comparison of the sand particle size with respect to the thickness of the viscous sublayer under turbulent flow condition