Modeling PDC cutter rock interaction

Optimizing the drilling performance in high pressure high temperature (HPHT) operations is crucial to successful, economic mineral extraction, and is one of the major goals behind the Department of Energy\u27s (DOE) Deep Trek program and the primary goal of the Ultra-Deep Drilling Simulator (UDS) laboratory currently being designed and constructed at National Energy Technology Laboratory (DOE-NETL).;To best leverage the valuable unique data from experiments in the UDS, a three-dimensional FLAC model of a single cutter interacting with the rock specimen (as tested in the UDS) has been developed. This cutter-rock model was developed using parameters so that various aspects of the model could be easily changed in subsequent runs.;This study will present the development of the cutter-rock model and the results of the initial numerical tests investigating the effect of various geologic and drilling parameters such as: rock strength, pore pressure, stress fields and cutting depth. Also, the results of the comparison/calibration of the model with single cutter laboratory tests will be presented.;Three basic initial models were run. First, two different rock types (a sandstone and a shale) with three different cutting depths are modeled to investigate the effect of rock strength and cutting depth on cutter loads. Second, The effect of various confining stress levels on the single cutter tests are analyzed by applying three different hydrostatic confinements (0 MPa, 25 MPa, and 50 MPa) to the core. Third, to incorporate the effects of fluid (both drilling mud and internal fluid) on the drilling process, pore pressure is included in the cutter/rock model. Results of these models showed that initial cutter/rock model is working properly.;The calibration of the 3D numerical model with the laboratory single cutter tests was primarily accomplished by matching the average vertical and horizontal loads on the cutter between the model and the laboratory tests. A FLAC 3D model was developed to back analyze the linear cutter test data published by Glowka (1989). The model eventually calculated the cutter loads pretty close to the test results. It is found that the different failure modes in the cutter/rock model, shear (crushing) and tensile (chipping), are highly dependent on the depth of cut and the tensile strength of the rock and greatly affect the cutting loads

New Abutment Angle Concept for Underground Coal Mining

In the Analysis of Retreat Mining Pillar Stability (ARMPS), Analysis of Longwall Pillar Stability (ALPS) and LaModel programs, the magnitude of the abutment loading adjacent to a gob area is calculated using an abutment angle concept, and the extent of the abutment loading is determined as solely a function of depth from an empirically derived equation. However, the latest in-situ stress measurements of abutment loading performed in the United States and Australia have shown that there can be significant deviations in the measured abutment magnitude and extent as compared to the predicted values from the empirical formulas used in ARMPS, ALPS and LaModel.;In this dissertation, stress measurements from U.S. and Australian mines were back analyzed by using analytical and numerical methods to investigate the measured abutment extent and loading. Ultimately, it was determined that the original empirical abutment extent formula in conjunction with the original ALPS square-decay stress distribution function was supported by the case histories reviewed in this dissertation. Also, for depths less than 900 ft, the average 21° abutment angle was supported by the case histories; however, at depths greater than 900 ft, the abutment angle was found to be significantly less than 21° and should be calculated with a new proposed equation

Using LaModel to analyze coal bumps

Coal bumps have long been a safety hazard in coal mines, and even after decades of research, the exact mechanics that cause coal bumps are still not well understood. Therefore, coal bumps are still difficult to predict and control. The LaModel program has a long history of being used to effectively analyze displace- ments and stresses in coal mines, and with the recent addition of energy release and local mine stiffness calculations, the LaModel program now has greatly increased capabilities for evaluating coal bump potential. This paper presents three recent case histories where coal stress, pillar safety factor, energy release rate and local mine stiffness calculations in LaModel were used to evaluate the pillar plan and cut sequencing that were associated with a number of bumps. The first case history is a longwall mine where a simple stress analysis was used to help determine the limiting depth for safely mining in bump-prone ground. The second case history is a room-and-pillar retreat mine where the LaModel anal- ysis is used to help optimize the pillar extraction sequencing in order to minimize the frequent pillar line bumps. The third case history is the Crandall Canyon mine where an initial bump and then a massive pillar collapse/bump which killed 6 miners is extensively back-analyzed. In these case histories, the cal- culation tools in LaModel are ultimately shown to be very effective for analyzing various aspects of the bump problem, and in the conclusions, a number of critical insights into the practical calculation of mine failure and stability developed as a result of this research are presented

Deep cover bleeder entry performance and support loading: A case study

Several questions have emerged in relation to deep cover bleeder entry performance and support loading: how well do current modeling procedures calculate the rear abutment extent and loading? Does an improved understanding of the rear abutment extent warrant a change in standing support in bleeder entries? To help answer these questions and to determine the current utilization of standing support in bleeder entries, four bleeder entries at varying distances from the startup room were instrumented, observed, and numerically modeled. This paper details observations made by NIOSH researchers in the bleeder entries of a deep cover longwall panel—specifically data collected from instrumented pumpable cribs, observations of the conditions of the entries, and numerical modeling of the bleeder entries during longwall extraction. The primary focus was on the extent and magnitude of the abutment loading expe- rienced by the standing support. As expected, the instrumentation of the standing supports showed very little loading relative to the capacity of the standing supports—less than 23 Mg load and 2.54 cm conver- gence. The Flac3D program was used to evaluate these four bleeder entries using previously defined mod- eling and input parameter estimation procedures. The results indicated only a minor increase in load during the extraction of the longwall panel. The model showed a much greater increase in stress due to the development of the gateroad and bleeder entries, with about 80% of the increase associated with development and 20% with longwall extraction. The Flac3D model showed very good correlation between expected gateroad loading during panel extraction and that expected based on previous studies. The results of this study showed that the rear abutment stress experienced by this bleeder entry design was minimal. The farther away from the startup room, the lower the applied load and smaller the con- vergence in the entry if all else is held constant. Finally, the numerical modeling method used in this study was capable of replicating the expected and measured results near seam