This paper presents material and energy process-step models of hydrogen production via concentrated solar energy using Aspen Plus®. The paper provides a thorough comparison of solar cracking and solar reforming of methane processes against conventional steam methane reforming. The material and energy balances show that solar cracking is the most environmentally friendly hydrogen production technique. Some of the primary advantages of solar cracking include (1) elimination of CO2 emission, (2) elimination of costs associated with CO2 sequestration, transportation, and storage, and (3) generation of two commercially viable products, namely carbon black and hydrogen which can be used both as a fuel and a commodity. Considering the hydrogen shortage for different hydrogenation and fuel upgrading processes that the petrochemical industry is facing today, hydrogen production from solar cracking may offer an alternative solution. Therefore, it is important to find less energy intensive and more environmentally friendly hydrogen production techniques to meet the demand of industry. The results show that solar cracking is a more environmentally friendly and commercially competitive process compared to solar reforming and steam reforming considering that it produces virtually no carbon dioxide, but produces the commercially viable carbon black as a by-product.
The stability of asphaltene molecules is tied to the changes induced by temperature, pressure or composition. Therefore, the precipitation of these molecules is expected during various operations and at different stages of well life. While the deposition and remediation of asphaltenes in wellbores and pipelines are well-addressed, the deposition phenomena in reservoir rock and its impact on rock characteristics and fluid dynamics is still not well-developed. We have developed an experimental workflow to create a uniform deposit of asphaltene inside the core sample. The results show that injecting oil or a heptane/oil mixture results in a non-uniform deposition of Asphaltene, which was quantified using the TOC and density measurements. Uniform exposure to crude oil and deposition was obtained through vacuum saturation of the cores. However, permeability impairment is evident in both cases; whether the deposition is developed using vacuum-saturation or injection. Interestingly, the absolute permeability damage could be mitigated by reversing the injection flow direction which suggest that pore throat plugging is the main damage mechanism, while deposition onto the rock surface is the secondary damage mechanism for absolute permeability.
With the declining access to ‘easy oil’ and an increase in energy demand, oil and gas producers are increasingly focusing on producing from more challenging unconventional reserves. This can especially be seen from the widespread proliferation of fracturing operations, during which a production well is purposely hydraulically fractured by injecting fracturing fluids at elevated pressures. However, in many operations, especially in deep reservoirs, casing deformations or cement layer integrity failures are observed. Therefore, it is necessary to thoroughly understand wellbore integrity issues for ensuring safe fracturing operation. A decay in the mechanical properties of steel and cement is expected after exposure to different operations, pressures, temperatures and fluids over time, which can significantly degrade the thickness and burst pressures ratings of the casing string. In this study, the degree of casing wear developed due to routine operations as well as corrosion and erosion in existing conventional wells is calculated using drilling and completion program datasets. Casing wear depends on several factors such as rate of penetration, rotary speed, wellbore orientation, as well as wellbore wear constants. These parameters are used in various models to calculate the wear volume, which is then correlated to an average percentage reduction in thickness of the casing string. This is then used as an input parameter for a finite-element analysis of casing-cement interaction under different scenarios, especially focusing on stresses in the connections. Analyses show that long term wellbore integrity does indeed depend on the quality of the casing program, cementing job as well as the minimization of human errors. The design of fracture treatments should therefore consider weak points around the casing and the cementing layer, especially those arising due to casing wear. Based on calculations, casing wear losses of over 40% of the initial volume can occur during the operational life cycle of a well, leading to a considerable decrease in thickness and burst ratings of the casing string. Finite element simulations show that varying stress concentrations in the steel and cement components can lead to fatigue and failure through tension and compression. Depending on the extent of casing wear, stresses above the unconfined compressive strength of common cement formulations are observed. If not accounted for, these lapses can lead to cement integrity issues and a critical well integrity failure. The results of this work can be used as a simpler field evaluation to determine actual casing and cement properties over the operational lifespan of a well and provide a methodology to assess the effects of wear on the casing, connections and the cement layer. This should be correlated to the integrity of the wellbore under different conditions before starting fracturing operations.
Oilfield cements have been an integral part of any drilling operation and forms the primary barrier when it comes to ensuring wellbore integrity. The strength of the cement layer is one of the primary factors that confirms the success of the drilling job and ensures the well remains productive and without issues throughout its productive years. The type of cements used in any oilfield operation depends on several factors including, but not limited to lithology, type of formation, pressures and temperatures, type of formation fluids and the overall purpose of the cement job. This requires customized cement jobs and recipes specific to the well and the section being drilled, and this is ensured by the use of specialized additives to the base cement mixtures to control its properties. Due to major differences in lithology, standardization, and properties of hydrocarbon reservoirs in the Middle East and the rest of the world, several customized recipes and formulations are used which are specific to the region. This paper is aimed at aggregating available information from common cement recipes in the Middle East and North America, and evaluating properties based on laboratory results available from representative experiments done as part of developing a cement database. The differences in geology have resulted in fundamental variations in cement formulations used in Middle East and North America. Literature from the Middle East region overwhelmingly indicated that API Class G is more commonly used, while Class H cement is more commonly favored in North America and the rest of the world. The differences further extend to the type of additives used as well. Formations in the Middle East have a higher occurrence of vugs and fractures, as well as gaseous hydrocarbons and/or H2S needing the use of LCM and other additives. Cement recipes vary from well to well, as does the use of sea water versus fresh water. Additives such as accelerators, retarders, defoamers, as well as fluid-loss control agents, are also commonly used. All these impact the properties of the cement, especially when monitored over time, and when accounting for ageing effects. Several teams have conducted stand-alone evaluations of various cement formulations, and documented their properties, though the presence of a comprehensive database of literature and laboratory-based results are lacking. Documenting such variations in the cement formulations and comparing the differences can help in better understanding the functionalities and efficiencies of cements used. Integrating these into a comprehensive database with laboratory-tested results can help in creating a knowledge base which could be utilized by the industry to better understand the performance of these cement mixtures over time and identify potential wellbore integrity issues.
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