Simplified HTHA Evaluation Using Larson Miller Parameter Concepts

Researchers have been developing mechanistic approaches describing High Temperature Hydrogen Attack (HTHA) damage for quite some time. Although there are a variety of approaches, all of them make use of describing HTHA as a time and temperature dependent phenomena that is sensitive to methane pressure. HTHA research shows the damage process is a phenomenon that is very similar to creep damage which has an exponential relationship to the applied stress and temperature. Based on these observations, the authors propose an HTHA damage assessment procedure that uses the familiar Larson Miller Parameter (LMP) approach and employs the well-known Linear Life Fraction Rule for evaluating operating condition variations in hydrogen partial pressure and temperature.

Numerical Simulation Research on Hydraulic Fracturing Promoting Coalbed Methane Extraction

Although hydraulic fracturing technology has been comprehensively investigated, few scholars have studied the influence of hydraulic fracturing on the effect of coalbed methane (CBM) extraction, and few considered the interaction between water and CBM in the research process, which is not conducive to guiding the engineering design of hydraulic fracturing wells. In this work, a hydraulic-mechanical-thermal coupled model for CBM extraction in hydraulic fracturing well is established; it combines gas-liquid two-phase infiltration, where nonisothermal adsorption is also considered. The COMSOL Multiphysics software is used to carry out the numerical simulation study of the CBM extraction process in hydraulic fracturing well and analyze the influence of coalbed permeability, initial methane pressure, and fracture length on CBM extraction in hydraulic fracturing well, and the results show that the hydraulic-mechanical-thermal coupled model for CBM extraction can be used for CBM extraction research in hydraulic fracturing well. The initial coalbed permeability, initial gas pressure, and fracture length all affect the migration speed of CBM to surface well in different ways and have a greater impact on the CBM production rate of hydraulic fracturing well. The greater the initial coalbed permeability and methane pressure are, the longer the fracture length is and the greater the CMB production rate of hydraulic fracturing well is. The change trend of coalbed permeability during the extraction process of surface fracturing well is directly related to the state of the reservoir. The factors of stress, temperature, and CBM desorption jointly determine the increase or decrease of coal seam permeability.

Environmental justification of the distribution of pressure drop in a dead-end low-pressure gas network

The gas supply system is determined by the classes of the elements of the gas transmission network associated with the pressure of the pumped natural gas. Laying gas pipelines in urban areas requires sufficient space around the pipes as a safety zone. The gas pipelines of the first level include gas communications in which the methane pressure is high or medium. To eliminate dead-end sections, gas pipelines are backed up (duplicating individual segments or ringing). The creation of a dead-end network is allowed only in small settlements. Dead-end network is a gas pipeline branching in various directions to gas consumers. Each section of the branched network has a one-way power supply.

Experimental Investigation on Permeability and Mechanical Deformation of Coal Containing Gas under Load

Coalbed effective permeability is widely used as a primary index to evaluate gas-drainage effect in CBM exploitation field. However, it seems to be difficult to obtain by the reason of dynamic change in close relationship with crustal stress, methane pressure, porosity, and adsorption. Due to their dissimilar adsorption properties and tectonic deformation degrees, different types of coal containing gas have various stress-strain and gas seepage curves. The paper presents the experimental investigations of the dynamic relationship between coal permeability and deformation under load. In this work, stress-strain and permeability investigations were performed using anthracite lump with a vitrinite reflectance of about 3.24% at various pressures and temperatures. The permeability (including the initial, minimum, and maximum) decreased with increasing temperature. At a constant confining pressure, the strains in different directions almost all increased with increasing axial stress and decreased with increasing pore methane pressure during the prefracture stage. At a constant pore pressure, the compression strength of the coal specimens increased approximately linearly during the prefracture stage and sharply decreased during the postfracture stage, while the permeability decreased rapidly and then increased slowly during the prefracture and remained stable during the postfracture stage. The permeability of the coal specimens mainly depended on the inner fissures. The permeability was greater during the postfracture than that during the prefracture stage. At the same temperature, the gas seepage curve of each coal specimen could be divided into three sections: decreasing, increasing, and constant sections. The necessary time for the permeability to reach a steady state increased as the confining and pore pressures increased. At high confining pressures (i.e., 6 MPa and 8 MPa), no significant differences between the methane seepage velocities of the specimens were evident, and their seepage curves were similar to prefracture. However, clear differences were observable at the postfracture stage. The seepage abilities of the coal specimens were more sensitive to stress than temperature in the same condition.

A Fluid-Solid Coupling Mathematical Model of Methane Driven by Water in Porous Coal

The existence of the water-driven-methane effect in gassy coal has been verified by field tests and laboratory experiments. However, a water-driven-methane mathematical model that considers methane adsorption and desorption has not yet been established. Based on the water-driven-methane process, a fluid-solid coupling mathematical model of methane driven by water is established. The model’s reliability is verified by the results of a water-driven-methane physical experiment and by using a solution of the COMSOL Multiphysics software. The space-time distribution regularities of the pore pressure, water-methane two-phase saturation, and pore pressure gradient in the water-driven-methane process are analysed. The results reveal the following. (1) The water-driven-methane fluid-solid coupling mathematical model for porous coal is reliable. (2) In the water-driven-methane process, there is an increasing zone and a decreasing zone of pore pressure in the coal sample. The increasing zone of pore pressure is closest to the side of the water inlet, and its area gradually decreases. The decreasing zone of pore pressure is closest to the side of the methane outlet, and its area gradually increases. Over time, the methane pressure in the increasing zone of pore pressure first increases and then decreases, and the methane pressure in the decreasing zone of pore pressure continuously decreases. The change (increase or decrease) rate of the methane pressure gradually decreases from both ends towards the middle of the coal sample. (3) The curve of the water saturation over time changes from a lower concave curve to a straight line, while the curve of the methane saturation with time changes from an upper convex curve to a straight line. The methane saturation in the decreasing zone of pore pressure is greater than that in the increasing zone of pore pressure. Over time, the water saturation of a specific point in space continuously increases while its methane saturation continuously decreases. Both of the increase rate of the water saturation and the decrease rate of the methane saturation gradually reduce over time. (4) The pore pressure gradient along the driving direction first decreases and then increases. The decreasing zone of the pore pressure gradient is located in the increasing zone of pore pressure, and the increasing zone of the pore pressure gradient is located in the decreasing zone of pore pressure. Over time, the pore pressure gradient at the side of the water inlet increases, and its increase rate decreases. The pore pressure gradient at the side of the methane outlet decreases, and its decrease rate decreases. The rate of increase in the pore pressure gradient at the side of the water inlet is greater than the rate of decrease in the pore pressure gradient at the side of the methane outlet.

Effect of Hydrogen on Creep Behavior of a Vanadium-Modified CRMO Steel and its Continuum Damage Analysis

Creep properties both in hot hydrogen and in air of a vanadium-modified CrMo steel 2.25Cr1Mo0.25V, widely used in hydroprocessing reactors in petrochemical industry, were investigated to determine the effect of hydrogen on high-temperature creep behavior of the low-alloy ferritic steel. The minimum creep strain rate in hydrogen is higher than that in air, whereas the creep strain at failure in hydrogen is relatively smaller. Many tiny spherical cavities are dispersively distributed in the ruptured specimen under hydrogen, which has relatively higher Vickers hardness. Based on the thermodynamics theory, the pressure of methane generated by the so-called “methane reaction” in the vanadium-modified CrMo steel can be calculated by using corresponding thermodynamic data, assuming that methane can reach its equilibrium state during cavitation. Meanwhile, a creep constitutive model based on continuum damage mechanics (CDM) was proposed, taking methane pressure into consideration. The results show that methane pressure increases nonlinearly with increase of hydrogen pressure while it decreases gradually with increase of temperature. The constitutive model considering the damage induced by methane pressure can be used to predict the effect of hydrogen pressure and temperature on creep life, indicating that the influence of hydrogen at elevated temperatures becomes smaller when increasing temperature or decreasing hydrogen pressure.

Pressure sensitivity of ANME-3 predominant anaerobic methane oxidizing community from coastal marine Lake Grevelingen sediment

Anaerobic oxidation of methane (AOM) coupled to sulfate reduction is mediated by, respectively, anaerobic methanotrophic archaea (ANME) and sulfate reducing bacteria (SRB). When a microbial community from coastal marine Lake Grevelingen sediment, containing ANME-3 as the most abundant type of ANME, was incubated under a pressure gradient (0.1-40 MPa) for 77 days, ANME-3 was more pressure sensitive than the SRB. ANME-3 activity was higher at lower (0.1, 0.45 MPa) over higher (10, 20 and 40 MPa) CH4total pressures. Moreover, the sulfur metabolism was shifted upon changing the incubation pressure: only at 0.1 MPa elemental sulfur was detected in a considerable amount and SRB of theDesulfobacteralesorder were more enriched at elevated pressures than theDesulfubulbaceae. This study provides evidence that ANME-3 can be constrained at shallow environments, despite the scarce bioavailable energy, because of its pressure sensitivity. Besides, the association between ANME-3 and SRB can be steered by changing solely the incubation pressure.ImportanceAnaerobic oxidation of methane (AOM) coupled to sulfate reduction is a biological process largely occurring in marine sediments, which contributes to the removal of almost 90% of sedimentary methane, thereby controlling methane emission to the atmosphere. AOM is mediated by slow growing archaea, anaerobic methanotrophs (ANME) and sulfate reducing bacteria. The enrichment of these microorganisms has been challenging, especially considering the low solubility of methane at ambient temperature and pressure. Previous studies showed strong positive correlations between the growth of ANME and the methane pressure, since the higher the pressure the more methane is dissolved. In this research, a shallow marine sediment was incubated under methane pressure gradients. The investigated effect of pressure on the AOM-SR activity, the formation sulfur intermediates and the microbial community structure is important to understand the pressure influence on the processes and the activity of the microorganisms involved to further understand their metabolism and physiology.