Analysis of Geomechanical Properties in Well Design and Well Optimization
Main aspect in wellbore instability is the selection of an appropriate rock failure criterion. This criterion involves only the maximum and minimum principal stresses 1  and 3  and therefore assumes that the intermediate stress 2  has no influence on the rock strength. When Mohr-Coulomb criterion was developed it justified by experimental evidence from conventional triaxial test ( 1  > 3 2    ). Based on triaxal failure machine the Mohr-Coulomb criterion has been extensively used to represent rock failure under the polyaxial stress state ( 1  > 3 2    ). In contrast to the prediction of redistribution Mohr-Coulomb much evidence has been accumulating to suggest that 2  thus indeed have a strengthening effect. This research shown that Mohr-Coulomb failure criterion only represent, that triaxial stress state ( 1  = 1 2 3     or ) which only occasionally encountered in-situ.The linear failure criterion has been justified by experimental evidence from triaxial tests as well as polyaxial test. It is natural extension of the classical Mohr-Coulomb criterion into three dimensions. As the Mohr-Coulomb criterion only represents rock failure under triaxial stress state, it is expected to be conservative in predicting well bore instability. The 3D analytical model employed by MogiCoulomb has been achieved by using linear elasticity theory to calculate the stresses. A model was developed used in analyzing shale intrusion, at depth 6100ft the well bore pressure of the formation is found to be 0.9180psi/ft and decreases to 0.420psi/ft at depth 7300ft. The membrane efficiency of the formation increases from 0.698 to 0.719 at the depth considered above.
Evaluation of Spotting Fluids in a Full-Scale Differential Pressure Sticking Apparatus
This paper reports that a full-scale differential-pressure simulator was used to evaluate spotting fluids in the laboratory. Tests at elevated temperature and pressure identified a variety of unweighted and weighted, oil and nonoil fluids that are able to free differentially stuck pipe. Some low-toxicity, water-based spotting fluids are effective and acceptable substitutes for the traditional oil-based systems.
Removal of urea in a wearable dialysis device: a reappraisal of electro-oxidation.
A major challenge for a wearable dialysis device is removal of urea, as urea is difficult to adsorb while daily production is very high. Electro-oxidation (EO) seems attractive because electrodes are durable, small, and inexpensive. We studied the efficacy of urea oxidation, generation of chlorine by-products, and their removal by activated carbon (AC). EO units were designed. Three electrode materials (platinum, ruthenium oxide, and graphite) were compared in single pass experiments using urea in saline solution. Chlorine removal by AC in series with EO by graphite electrodes was tested. Finally, urea-spiked bovine blood was dialyzed and dialysate was recirculated in a dialysate circuit with AC in series with an EO unit containing graphite electrodes. Platinum electrodes degraded more urea (21 ± 2 mmol/h) than ruthenium oxide (13 ± 2 mmol/h) or graphite electrodes (13 ± 1 mmol/h). Chlorine generation was much lower with graphite (13 ± 4 mg/h) than with platinum (231 ± 22 mg/h) or ruthenium oxide electrodes (129 ± 12 mg/h). Platinum and ruthenium oxide electrodes released platinum (4.1 [3.9-8.1] umol/h) and ruthenium (83 [77-107] nmol/h), respectively. AC potently reduced dialysate chlorine levels to < 0.10 mg/L. Urea was removed from blood by EO at constant rate (9.5 ± 1.0 mmol/h). EO by graphite electrodes combined with AC shows promising urea removal and chlorine release complying with Association for the Advancement of Medical Instrumentation standards, and may be worth further exploring for dialysate regeneration in a wearable system.