Analytical Investigation of Gas Production from Methane Hydrates upon Thermal Stimulation

In this study, analytical models are developed to investigate methane hydrate dissociation in porous media upon thermal stimulation employing wellbore heating. This work investigates how the wellbore’s external and internal structure affect the dissociation process. The models are based on both Radial (2D) and Cartesian coordinates (1D) to couple the wellbore heating process and the associated methane response in the hydrate dissociation in the reservoir. Different types of heat-sources are studied: i) a flat heat-source in the 1D cases with a constant temperature; ii) line heat-source in radial cases with a constant temperature; iii) wellbore heat-source in radial cases, employing both a constant temperature and a coaxial wellbore. Wellbore’s external layers consist of casing, gravel, and cement. In the coaxial wellbore heat-source, both conduction and convection heat transfers are considered. It consists of an inner tube and an outer structure (casing, gravel, and cement layers). The analytical solution employed a similarity solution, in which a moving boundary to separate the dissociated (containing produced gas and water) and undissociated (containing only methane hydrate) zones is assumed, to model the dissociation in the reservoir. Two different operating schemes have been studied for water inlet of the coaxial wellbore heat-source: i) inner tube; and ii) annulus section of the wellbore. The results of temperature distribution along the wellbore (for the coaxial heat-source), temperature and pressure distributions in the reservoir, hydrate dissociation rate, and energy efficiency considering various initial and boundary conditions and reservoir properties are presented and compared with those of the previous studies. Direct heat transfer from the heat source to the reservoir in the case with a line heat-source higher dissociation rate and gas production compared to those of the wellbore-heat-source models, considering the heat conduction in the wellbore thickness causes. Decreasing the heat-source pressure and increasing its temperature increases the dissociation rate and gas production. Employing them simultaneously also increases gas production but reduces energy efficiency. The wellbore thickness affects the energy efficiency of the process negatively. The two different operating schemes affect the process in almost the same way with slightly higher gas production in the case with annulus hot-water inlet because the annulus is in direct contact with the reservoir. Increasing the inlet water temperature and decreasing the wellbore pressure simultaneously results in a greater gas production and energy efficiency. Porosity, thermal diffusivity, thermal conductivity, and thickness of the reservoir have direct relation with the dissociation rate, but the permeability and gas viscosity of reservoir almost do not impact the process. The wellbore parameters, such as water flow rate, inlet temperature, and wellbore radius except the inner tube radius, directly impact the wellbore mean temperature and the dissociation process. The findings of this study make a major contribution to research on methane hydrate dissociation upon thermal stimulation with wellbore heating by analytically demonstrating, for the first time, how the wellbore structure affect the process

4-Cycle Free Spatially Coupled LDPC Codes with an Explicit Construction

Spatially coupled low-density parity-check (SC-LDPC) codes are a class of capacity approaching LDPC codes with low message recovery latency when a sliding window decoding is used. In this paper, we first present a new method for the construction of a class of SC-LDPC codes by the incidence matrices of a given non-negative integer matrix $E$, and then the relationship of 4-cycles between matrix $E$ and the corresponding SC-LDPC code are investigated. Finally, by defining a new class of integer finite sequences, called {\it good sequences}, for the first time, we give an explicit method for the construction of a class of 4-cycle free SC-LDPC codes that can achieve (in most cases) the minimum coupling width

An Experimental Investigation of Different Formation Waters and Injection Water Incompatibility to Obtain the Optimum Water Mixing Ratio in Injection Processes

Scale formation and well plugging due to the incompatibility of injected waters is a critical field problem in oil recovery. A water injection process was successfully performed when the identification of the source of water, water quality considerations, and laboratory compatibility tests were considered. When different waters are mixed, it is necessary to evaluate their compatibility prior to the injection into oil wells. Jar test is conventionally performed in the laboratory to estimate formation damage by scale formation in the wellbore and facility. The individual waters may be quite stable under all system conditions and present no scale problems. However, once they are mixed, the reaction between ions dissolved in the individual waters may form insoluble products that cause permeability damage in the vicinity of the wellbore. The obtained results from the jar test for different mixtures of waters can be used to know the type of scale in the reservoir. This work was undertaken to experimentally identify the composition of mineral scales that occur in a raw water and different volume mixings. The formation of CaSO4, SrSO4, and CaCO3 during the sampling of production waters, including different reservoir layers and mixing of their different volumes with K sample have been proved by scanning electron microscopy micrographs and X-ray diffraction. The results of jar tests for the mixing of different waters indicated that the main constituents of the scale were strontium sulfate and calcium carbonate. The results showed that mixing ratio of 75 to 25% of K water to different produced waters were the most suitable ones

Reviewing the use of resilience concepts in forest sciences

Purpose of the review Resilience is a key concept to deal with an uncertain future in forestry. In recent years, it has received increasing attention from both research and practice. However, a common understanding of what resilience means in a forestry context, and how to operationalise it is lacking. Here, we conducted a systematic review of the recent forest science literature on resilience in the forestry context, synthesising how resilience is defined and assessed. Recent findings Based on a detailed review of 255 studies, we analysed how the concepts of engineering resilience, ecological resilience, and social-ecological resilience are used in forest sciences. A clear majority of the studies applied the concept of engineering resilience, quantifying resilience as the recovery time after a disturbance. The two most used indicators for engineering resilience were basal area increment and vegetation cover, whereas ecological resilience studies frequently focus on vegetation cover and tree density. In contrast, important social-ecological resilience indicators used in the literature are socio-economic diversity and stock of natural resources. In the context of global change, we expected an increase in studies adopting the more holistic social-ecological resilience concept, but this was not the observed trend. Summary Our analysis points to the nestedness of these three resilience concepts, suggesting that they are complementary rather than contradictory. It also means that the variety of resilience approaches does not need to be an obstacle for operationalisation of the concept. We provide guidance for choosing the most suitable resilience concept and indicators based on the management, disturbance and application context

Design and analysis of a coherent memory sub-system for FPGA-based embedded systems

Cache coherence and memory consistency are of the most decisive and challenging issues in the design of shared-memory multi-core systems that influence both the correctness and performance of parallel programs. In this thesis, we identify and analyze the problem of designing a coherent/consistent memory subsystem in general and then focus on FPGA-based multi-core embedded systems containing general purpose CPUs and dedicated hardware accelerators. We narrow down the range of the problem by targeting only the stream-based applications and developing dedicated application-specific solutions. A flexible Windowed-FIFO communication pattern is proposed to be used by the parallel programs being run on the multi-core system. The software APIs for the FPGA platform are implemented and tested, a customized streaming cache memory is designed, implemented and tested based on the proposed communication pattern and in the end, example embedded systems are developed and tested on the FPGA platform to prove the correct functionality of the APIs, the cache memory and the coherent data communication between the cores. All the tests are done on a Xilinx Spartan3dsp development board and all the hardware and software aspects of the FPGA platform are studied and their influence on the memory system is analyzed. The simulations and analyses show that the developed solution has less complexity and more scalability and portability comparing to existing solutions while it provides a flexible range of functionality that different streaming parallel applications can benefit from.Embedded systemsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc

Cesarean Scar Pregnancy: A Case Report

Introduction: Due to a significant increase in cesarean section, cesarean scar pregnancy has increased dramatically which can endanger the life of the mother if early diagnose and treatment is not timely performed. Severe vaginal bleeding can be mentioned as one of the symptoms which its definite diagnosis could be made by ultrasound. Case report: The patient was a 36-year-old woman with a history of a normal vaginal delivery and a caesarean section at 10 weeks and 5 days of gestational age who was admitted with chief complaints of severe vaginal bleeding. Ultrasound examination detected no fetal heart rate, and then serum of the oxytocin was infused. After two episodes of bleeding, the patient was transferred to the operating room for curettage. During performing curettage, a notch was observed in inferior anterior part of uterus simultaneously with much vaginal bleeding so as the patient was regarded hemodynamically unstable, and thus the hysterectomy was taken. After the uterine incision in the Department of Pathology, pregnancy in previous cesarean scar was detected. Two days later, the patient was discharged with good general condition receiving some medication advice and necessary recommendations. Conclusion: Previous cesarean scar pregnancy if not detected early can be associated with high morbidity and mortality. Therefore, the possibility of this pregnancy should be considered in pregnant women with uterine bleeding, abdominal pain as well as a history of cesarean section. It should be noted that after previous cesarean scar pregnancy was definitely diagnosed via ultrasound examination, treatment necessitates to be started utilizing methotrexate to ensure the future fertility of the mother

The Effects of Plant Age and Harvesting Time on Chicoric and Caftaric Acids Content of E. purpurea (L.) Moench: Chicoric and caftaric acids content of E. purpurea

Plants of Asteraceae are used in traditional medicine and phytotherapy. The two main caffeic acid derivatives, chicoric and caftaric acid which are found in many genus of Asteraceae including Echinacea exhibit important biological activities. The level of these acids in E. purpurea is affected by many factors such as growing situations, extraction methods, storage conditions and plant age. In this investigation,chicoric acid and caftaric acid content in aerial parts and roots of E. purpurea harvested in spring and summer from 1-, 2- and 3-years old plants cultivated in Iran were determined by using HPLC method. The results revealed that maximum level of chicoric acid achieved in aerial parts of 1- and 2-years old plants beside 2-years old roots collected in spring. Aerial parts of 1- and 2-years old plants harvested inspring had maximum content of caftaric acid as well. It is concluded that total parts of 2-years old E. purpurea harvested in spring can be a good source of caffeic acid derivatives and used for preparation of the plant products

The Effects of Hypericum Extract on Blood Factors in Diabetic Rats

Diabetes mellitus comprises a heterogeneous group of metabolic diseases characterized by chronic hyperglycemia and impaired metabolism of carbohydrates, lipids and proteins caused by defects in insulin secretion or function. It is said to be the sixth factor of mortality and its complications, if untreated, include: atherosclerosis, nephropathy, neuropathy, foot ulcers, disability and death. To treat diabetes either insulin is administrated or some chemicals that lower blood sugar levels are prescribed. However, due to their various complications, the use of medicinal herbs has been increasingly taken into consideration. In this study, the effects of Hypericum extract on blood parameters in diabetic rats-male Wistar rats-were studied.Methods: In this study, male rats (n =36) were randomly divided into six groups: control, 21 day treated control, 28 day treated control, diabetic, 21 day treated diabetic rats, and 28 day treated diabetic rats. To induce diabetes, streptozotocin was used intraperitoneally at a single dose of 60 mg per 1kg body weight. The treated groups were gavaged with the extract at a dose of 60 mg per kg body weight in a period of 3-4 weeks. After this period, blood serum parameters were measured and the data were analyzed using multivariate analyze of varianceResults: The results showed that there is a significant difference between the six groups in parameters FBS, Total P, and Na in blood, and PU, FBSU, KU in urine.Conclusion: The administration of Hypericum extract in the experimental models of diabetes mellitus has improved the biochemical parameters in diabetic rats.Â