Laboratory data are presented on the changes in the densities of 11-18 lb/gal oil and water base drilling fluids in the temperature and pressure ranges of 70°-400°F and 0-14,000 psig. Results indicate that the change in density of a given type of drilling fluid appear to be independent of the initial density of the fluid, and as oil base drilling fluids are subjected to high temperatures and pressures, they become more dense than water base drilling fluids. The test apparatus and calibration are also described.
Introduction The viscosity of oil-base muds can be determined over a wide range of temperature and pressure using the BHC Viscometer. This instrument consists of two concentric cylinders mounted in a 20,000-psig autoclave that has an upper operating-temperature limit of 650 degrees F. The inner cylinder, or rotor, is connected by a magnetic couple to a Haake Rotovisko. A detailed description of the instrument has been published previously. In operating the BHC Viscometer, the autoclave is completely filled with mud and sealed. The rotor is rotated at a constant rate and the sample is allowed to reach an equilibrium temperature. The pressure is then adjusted with an auxiliary pump and the shear stress is recorded for each shear rate. The instrument was calibrated by first calculating the shear rates from the viscometer dimensions. This method gave shear rates of 11, 21, 32, 64, 96, 191, 286, 573, and 860 sec-1. The mean shear-stress constant was then determined experimentally to be 8.1 dynes/cm2/scale part (1.6 lb/100 ft2/scale part). Discussion The best mathematical description of the viscosity of an oil-base mud at constant temperature and pressure is the power-law model. The linear form of this model is power-law model. The linear form of this model is(1)ln = ln K + n ln y However, two sets of constants are required, one set for use at shear rates below ~ 200 sec and the other set for the higher shear rates. The analysis of the pressure and temperature effects shows that the logarithm of the shear stress is directly proportional to the pressure and inversely proportional to proportional to the pressure and inversely proportional to the temperature. These relationships can be expressed by the following equations:(2)ln p, JPT P. 884
Full-scale laboratory testing was conducted under a joint industry and Department of Energy program titled "Optimization of Deep Drilling Performance; Development and Benchmark Testing of Advanced Diamond Product Drill Bits and HP/HT Fluids to Significantly Improve Rates of Penetration." In total, seven bits and twelve different drilling fluids were tested in three different rocks at a variety of drilling parameters. Phase 1 results have been reported in a previous paper (Arnis Judzeis et al., 2007). This paper presents the results from Phase 2 of the study. The goal of Phase 2 testing was to evaluate bit features and mud additives that might enhance ROP under high-pressure conditions. The test protocols developed in Phase 1 to simulate Arbuckle play and Tuscaloosa trend drilling at pressures in excess of 10,000 psi were employed to evaluate these features. Significant findings of Phase 2 include the following:Mud additives can substantially enhance ROPs in high-pressure conditions and may play a larger role than bit design features.A 16-ppg cesium formate brine increased ROPs 100% as compared to 16-ppg oil-based mud in Carthage marble and Mancos shale.The cesium formate improved ROPs by increasing both the efficiency and the aggressiveness of the bit.A 16-ppg oil-based mud weighted with fine particle size (D50 ˜ 1–3 microns) manganese tetroxide increased ROPs in Crab Orchard sandstone 100% as compared to a similar mud weighted with conventional barite. The manganese tetroxide improved ROPs by increasing the efficiency of the bit, but did not have a measurable effect on bit aggressiveness.Phase 2 tests continue to support the conclusion of Phase 1 that specific energy consumed while drilling is substantially higher than the confined compressive strength (CCS) of the rock. Introduction An important factor in future gas reserve recovery is the cost to drill a well. This cost is dominated by the rate of ROP that becomes increasingly important with increasing depth. The object of this study is to improve the economics of deep exploration and development. In September 2002, the U.S. Department of Energy's National Energy Technology Laboratory awarded funding to the Deep Trek program to assist in its goal "…to develop technologies that make it economically feasible to produce deep oil and gas reserves…" and "…focus on increasing the overall rates of penetration in deep drilling." The researcher's proposal was to test drill bits and advanced fluids under high-pressure conditions. Phase 1 of the proposal was to establish a baseline of performance and provide data upon which to make design improvements. Phase 2 was to establish improvements in design.
Compaction characteristics of granular materials subjected to axial loading are investigated for both sphere and non-sphere granular assemblies. The computational study is based on the discrete element method (DEM). The compressive stress–strain relation obtained from three-dimensional DEM simulations is compared with that of an idealized two-dimensional plane-strain compression test and physical experiments using a bronze sphere assembly. We observed good agreement between the experimental and three-dimensional DEM simulation results, while two-dimensional simulations significantly underestimate the stiffness of particulate bed, particularly at large strains. This demonstrates that two-dimensional analysis is generally inadequate to model the compaction characteristics of granular systems. We performed a detailed analysis on the force–transmission characteristics of granular materials at microscopic level and present a connection between the directional orientation of force-networks and the invariants of the macroscopic stress tensor: the non-sphere systems were able to build up a strongly anisotropic network of heavily loaded contacts. Several complex phenomena, both geometric and kinematic, that are operative in sphere and non-sphere assemblies due to inter-particle interactions during compression are presented here. It is often assumed that the ratio of invariants of the stress tensor is uniform and constant in uni-axial compression tests. Our results show that the ratio of invariants of the stress tensor is non-uniform and non-constant even when the granular assemblies are subjected to the so-called uni-axial compressive loading, which is in agreement with other recent studies (e.g. Gu et al 2001 Int. J. Plasticity 17 147) performed using the finite element method. The non-homogeneous characteristics that are reported at the particulate scale need to be accounted in considering possible continuum models for the granular systems.
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