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Fetkovich or Blasingame type rate decline analysis is a common and practical method to obtain reservoir parameters and evaluate well productivity. Pseudo-steady-state constant is an indispensable parameter for establishing these new type rate decline curves and works as a bridge linking conventional productivity and new type productivity. Refracturing is widely used to enhance tight oil wells’ productivity and improve their economic benefits, the pseudo-steady-state constant of refracturing horizontal wells has been presented in our previous research, but an in-depth discussion on the definition, accuracy, sensitivity, and application of this constant has not been conducted. It results in the insufficient understanding of the physical meaning, characteristics, and functions of pseudo-steady-state constant at present. In this study, taking the derived pseudo-steady-state constant for refracturing horizontal wells with fracture reorientation as an example, its accuracy was verified by an equivalent model presented in the literature, and the sensitivity of relevant key parameters on this constant was investigated. For the refracturing horizontal well defined in this study, pseudo-steady-state constant is independent of time, and related to fracture conductivity, fracture face damage, reorientation fracture number and permeability anisotropy. Results show that this constant decreases with the increase of fracture conductivity, but tends to remain unchanged when fracture conductivity increases to a certain extent. Meanwhile, this constant shows a positive correlation with fracture face damage and permeability anisotropy, but an inverse correlation with reorientation fracture number. Blasingame type rate decline curves of refracturing horizontal wells with fracture reorientation were also established, regarding as a practical application of this pseudo-steady-state constant and a concrete manifestation of its bridge-linking function. These type curves are directly conducive to the inversion of reservoir properties and fracturing parameters and the prediction of future productivity for refracturing horizontal wells. More importantly, this study is helpful to understand and strengthen the role and importance of pseudo-steady-state constant, and also beneficial to the establishment of new type rate decline curves of other similar models.

Abstract The paper reports the cellobiose hydrothermal decomposition at 200–250 °C under non-catalytic (with an initial pH close to 7) and weakly acidic conditions (with an initial pH of 4–6). It was found cellobiose decomposition under both non-catalytic and weakly acidic conditions follows similar primary decomposition pathways, i.e., isomerization and hydrolysis reactions being the main primary reactions. However, cellobiose decomposition under acidic conditions decreases the selectivities of isomerization reactions but increases the selectivity of hydrolysis reaction. While the rate constants of isomerization reactions under various pH conditions are found to be similar, that of hydrolysis reaction increases significantly with reducing the initial pH of the solution. Therefore, the acceleration of cellobiose decomposition under acidic conditions is mainly due to the increased contribution of hydrolysis reaction. Further analysis suggests that the rate constant of hydrolysis reaction is dependent on the hydrogen ion concentration of the solution at reaction temperature. A kinetic model was then developed, considering the isomerization and hydrolysis reactions. The model can well predict the cellobiose hydrothermal decomposition under various initial pH conditions at low temperatures (i.e.,

Abstract An analysis of the integration of a Ca-looping process into a cement plant is presented. The capture process, based on selective absorption of CO2 by calcium oxide, has two interconnected reactors where the carbonator captures CO2 from the preheater flue gases and the calciner regenerates the CaCO3 into CaO by oxy-combustion. The study also considers the purge rate of part of the circulating CaO, given the tendency of the material to sinter and reduce its capture capacity. Fresh CaCO3 is added to maintain reactivity in the carbonator, while the purged sorbents are utilised as a cement kiln feed. The detailed carbonator model has been implemented using Matlab and incorporated into Unisim to provide a full flowsheet simulation for an exemplary dry-feed cement plant as a user-defined operation. The effect of molar flowrate ratio of lime make-up to feed CO2 ( F 0 / F CO 2 ) between two operational limits has been investigated. This process configuration is capable of achieving over 90% CO2 capture with additional fuel consumption of 2.5–3.0 GJth/ton CO2 avoided which depends on the F 0 / F CO 2 ratio. It is found that a proper heat recovery system supplementary to the Ca-looping process makes the Ca-looping process more competitive than the traditional low temperature absorption process based on amine solvents.

AbstractThis paper will present results of a numerical modelling study on CO2 migration through abandoned wells. Leakage of CO2 through plugged and abandoned wellbores is one of the major concerns for long-term safety and effectiveness of geologic CO2 sequestration. For risk assessment and mitigation, it is not only important to understand and characterize the potential for CO2 leakage through wellbores but also subsequent CO2 migration beyond the primary sequestration reservoir. Subsequent to the leak, CO2 may take a direct path towards the accessible environment or it may migrate in an indirect stair-stepping manner through wellbores/fractures across multiple, shallow permeable strata. In the later case, identification of leak source and application of mitigation strategies may become a challenge.For this study we use data from a site in Alberta, Canada which has reported natural gas leak at surface. Investigations on origin of the gas and potential gas migration path from the original source to the surface at the analog site show that the gas could be moving through multiple wells and across multiple formations. There are multiple wells at the site which were drilled and abandoned without production casing and are completely open between two hydrocarbon bearing zones creating cross-flow across zones through open wellbores. Our study focuses on the deeper formations and potential for leakage for CO2 injected in deeper formation. A complex numerical fluid-flow model is developed for the site in FEHM, LANL’s porous media fluid-flow simulator. The model explicitly accounts for wellbore details such as abandonment plugs, casing, annulus cement, etc. The model was used to perform long-term simulations of CO2 injection and potential migration through abandoned wells. Numerical simulation results show limited migration of CO2 through abandoned wells. Such detailed simulation would be valuable to develop effective abandonment practices as well as mitigation strategies at CO2 sequestration sites.

Deep water shallow natural gas hydrate (NGH) is a kind of clean energy and has entered the commercial exploitation stage. However, it produces a lot of seabed sediment in the process of large-scale mining, which not only easily causes undersea natural hazards, but also leads to pipeline equipment blockage and high energy consumption in the mining process. A downhole solid–liquid separator can effectively separate natural gas hydrate from sand and backfill sand in situ, which can effectively solve this problem. In this paper, the safety of a downhole solid–liquid separator desander under torsion conditions is determined by a test method. A numerical simulation method was used to simulate the tension and pressure of the downhole solid–liquid separator, and a modal simulation analysis and erosion analysis of the downhole solid–liquid separator were carried out. The experiments showed that the downhole solid–liquid separator could withstand 30 KN/m of torque, and a numerical simulation analysis showed that it could withstand 30 MPa of pressure and 50 KN of tension. The results show that the maximum stress is 116.56 MPa, and the maximum allowable stress is 235 MPa. The modal analysis showed that the downhole solid–liquid separator produces resonance at a frequency of about 93 Hz, resulting in large deformation, which should be avoided as far as possible. Through the erosion analysis, the life of the downhole solid–liquid separator was determined to be about 2.3 years. Numerical simulation and experimental results show that the designed downhole solid–liquid separator for natural gas hydrate can ensure safety.

In the present paper, we analyze numerically the disproportionate permeability reduction (DPR) water-shutoff (WSO) treatments in oil production well, i.e., the ability to reduce relative permeability (RP) to water more than to oil. The technique consists of bullhead injection of polymer solutions (gelant) into the near-wellbore formation without zone isolation. By assuming the low dissolution of polymer in oil and the low mobility of the gel in porous medium, we reduced the compositional model of the process to a simple two-phase model, with RP and capillary pressure (PC) dependent on the water and gel saturation. We proposed the extension of the LET correlations used to calculate RP and PC for the case of three phases (oil–water–gel). The problem is divided into two stages: the polymer injection and the post-treatment production. Both of these processes are described by the same formal mathematical model, which results from incompressible two-phase flow equations formulated in terms of normalized saturation and global pressure. The thermal effects caused by the injection of a relatively cold aqueous solution are taken into account. The numerical solution shows favorable results for the DPR WSO treatments. Other techniques, such as the creation of impermeable barrier and downhole water sink (DWS) technology, are also tested in order to check the validity of the developed numerical model with experimental data.

Abstract Membrane contactors offer a promising alternative to conventional CO2 absorption processes using columns. In a membrane contactor the advantages of absorption technology and membrane technology are combined as direct contact of the solution and gas feed stream is avoided by membrane barrier. In this study, the possibility of employing the enzyme carbonic anhydrase (CA) for the acceleration of CO2 reaction in MDEA and MEA solution in combination with the use of a membrane contactor was investigated in a lab scale module. The membranes employed in this study were microporous and specifically chosen to have both hydrophobic (bulk) and hydrophilic (surface) properties in order to avoid wetting of solution and reduce fouling by the enzymes simultaneously. By adding the enzyme carbonic anhydrase (CA), a significant improvement of CO2 absorption rate was observed in MDEA solution while a negative effect was observed in MEA solution. Meanwhile the porous hydrophobic membranes were coated with a highly selective poly(ionic liquids) layer increasing the affinity of CO2 towards the interfacial area and hence also the driving force. The concept may initially appear counter intuitive, as the dense membrane layer introduces an added resistance, however the active membrane material gave promising results and was observed to accelerate CO2 transport in MDEA solution. The combination of both enzyme and PILs resulted in synergies, which significantly improved CO2 absorption in MDEA solution.

AbstractThe transportation of hydrogen is a weak link in the large‐scale development of the hydrogen energy industry. Injecting hydrogen into the natural gas pipeline network for transportation is an efficient way to achieve the large‐scale, long‐distance, and low‐cost transportation of hydrogen. Hydrogen can lead to hydrogen embrittlement in natural gas pipelines and cause safety incidents if hydrogen and natural gas are not mixed uniformly. Therefore, it is necessary to study the blending process and blending uniformity of hydrogen and natural gas. In this study, a three‐dimensional model of the hydrogen‐injected natural gas pipeline was constructed. The effects of hydrogen injection inlet and turbulator configuration on the mixing process of hydrogen and natural gas were investigated using a computational fluid dynamics approach. The results show that increasing the number of hydrogen injection inlets shortens the distance L98% of uniform mixing of hydrogen and natural gas. Increasing the radial distance r from the initial hydrogen mixing positions to the center of the pipeline will shorten the distance for uniform gas mixing in the pipeline. The addition of turbulator configurations in the pipeline significantly reduces the distance to uniform gas mixing. Changing the distance Lturb from the turbulator to the initial mixing position further shortens the distance between hydrogen and natural gas mixing uniformly. The results of this study provide a reference for the structural design of the hydrogen–natural gas mixing pipeline and the gas distribution state during the mixing process.

Summary This paper describes the application of a genetic algorithm to the development of a solvent-additive SAGD process. A review of related field projects and key simulation studies is provided, together with a discussion of the pros and cons of potential alkane solvents. Economics and the impact of dynamic and ultimate retention are discussed. A general conclusion drawn from literature is that optimal solvent application to SAGD will likely involve time variations in both rate and composition of the solvent. This results in an optimization problem that has a large number of dimensions, and is nonlinear. We have found genetic algorithms, which mimic biological evolution, have been found to be extremely effective in addressing such problems. The general methodology of application to solvent additives by Laricina Energy Ltd. is described. A key product of this effort, optimized for a simple clastic reservoir, is presented. The genetic algorithm produced an operable process, which could be described as a new combination of preexisting concepts. The process offers material improvements in thermal bitumen supply costs, as well as recovery factor. Major reductions in the physical steam/oil ratio (SOR), (and therefore) capital intensity and carbon emissions, are indicated.