For more than 30 years, the design of platform and jackup conductors has been based on Stahl and Baur's famous hypothesis that internal string loads do not contribute to buckling (Stahl and Baur 1983). It is a vital result, allowing significant weight and cost savings. However, no derivation was ever given, and the result has remained a folk theorem: widely used, but never proved. The industry has, therefore, been at risk should the result prove to be a severe approximation, or to have unduly restrictive assumptions and/or limitations. This paper provides a rigorous proof of the hypothesis. It shows that it is an approximation, though an acceptable one, and gives a thorough exposition of its meaning, assumptions, and limitations. Finally, it derives the exact counterpart of Stahl and Baurs' result. The improved result gives minor weight and cost savings.
The two hydraulic-diagnostic methods detailed in this paper can monitor the "health" of a subsea hydraulic-control system, diagnose or predict a system problem (particularly leaking or clogging problems), and locate its source by using readily available valve-signature data.
The methods were tested in a laboratory environment using a hydraulic system with simulated clogging and leaking mechanisms. Leak detection was performed using both signature-matching and mass-balance methods. The results showed a mean accuracy of 93% for mass-balance method and 82% for the signature-matching method. Clog detection by signature matching showed high accuracy in the controlled laboratory condition. The difference between the simulated and actual clogging is within 1%.
The methods provide a monitoring tool for detecting and locating potential leaks, blockages, and other system changes or anomalies, which could be used to estimate the potential high cost of intervention, possible downtime, and lost revenue.
While remote parts of the world are awash with hundreds of trillions of cubic feet (Tcf) of natural gas, the industrialized West and emerging economies of the East cannot get enough of the clean-burning, environmentally friendly fuel. The problem is transporting this compressible fluid long distances and across major bodies of water. For markets more than 1,500 miles distant, liquefied natural gas (LNG) has proved to be the most economic option. By refrigerating natural gas (primarily methane) to 260°F (162°C), thereby shrinking its volume by 600:1, natural gas in the form of LNG can be transported in large insulated cryogenic tankers at reasonable cost.
Natural-gas liquefaction is a series of refrigeration systems similar to home air-conditioning (AC) systems, consisting of a compressor, condenser, and evaporator to chill and condense the gas. The difference is in the scale and magnitude of the refrigeration. A typical single-train LNG plant may cost USD 1.5 billion and consume 6 to 8% of the inlet gas as fuel. Because many of the impurities (e.g., water vapor, carbon dioxide, hydrogen sulfide) and heavier hydrocarbon compounds in natural gas would freeze at LNG temperatures, they must first be removed and disposed of or marketed as separate products.
This paper will provide an overview of LNG liquefaction facilities, from inlet gas receiving to LNG storage and loading. However, the focus is on the liquefaction process and equipment. Differences among the commercially available liquefaction processes (e.g., cascade, single mixed refrigerant, propane precooled mixed refrigerant, double-mixed refrigerant, nitrogen) will be discussed. The aim is to provide SPE members with a clear understanding of the technologies, equipment, and process choices required for a successful LNG project.
Carbon dioxide (CO2) sequestration in saline aquifers has been proposed as one of the most practical options for reducing CO2 emissions into the atmosphere. Massive CO2 injection into an aquifer would alter the geochemical equilibrium between the rock-forming minerals and the formation water. In this work, a novel and simple predictive tool is presented to estimate the formation of calcium carbonate (CaCO3) scaling as a function of pH, temperature, ionic strength of the solution, calcium cation concentration, bicarbonate anion concentration, and CO2 mole fraction when the water mixture is saturated with a gas containing CO2 to evaluate the effect of solution conditions on the tendency and extent of precipitation. The proposed simple method covers concentrations of calcium cation or bicarbonate anion in the range of 10 to 10 000 mg/L, with temperature ranging between 5 and 90°C, total ionic strength ranging between 0.1 and 3.6, and pH values ranging between 5.5 and 8. The predicted values are found to be in good agreement with the reported data, with average absolute deviations being less than 2.6%. The proposed tool is superior because of its accuracy and clear numerical background based on the Vandermonde matrix, wherein the relevant coefficients can be retuned quickly if more data become available in the future. The simple predictive tool proposed in the paper can be of immense practical value for engineers and researchers to have a quick check on the formation of calcium carbonate scaling when the water mixture is saturated with a gas containing CO2 at various conditions without opting for any experimental measurements. In particular, process engineers would find the proposed method to be user friendly, involving no complex expressions and presenting transparent calculations.
Carbon emitted on account of our continued use of fossil fuel can be offset using carbon capture and storage (CCS). The technology for this exists, but the economics of it is context dependent, and CCS has shown itself to be not very cost effective in oil sands. Committing to the large-scale sequestration projects needed without properly considering alternatives can prove costly at both the economic and social levels. Charcoal sequestration, discussed earlier by Gupta, provides a few advantages, such as being less costly and lacking any post-operation liabilities. Above all, it is reversible, allowing flexibility of policy and operation and avoiding long-term or large-scale commitments.
The economics of the charcoal approach mainly depends on two factors--the cost of the feed biomass and the cost of processing. The first of these is addressed by using municipal waste as feedstock, which can be available free of charge. Expectedly, the cost of processing, the second factor, depends on the apparatus and the scale of operation.
In this paper, the authors discuss the benefits and drawbacks of prominent traditional and modern apparatus used for conversion of biomass to charcoal and describe a simple and pragmatic apparatus that could be assembled relatively easily for a small-scale operation such as processing industrial-camp-generated solid organic waste.
Offsetting carbon in this manner obviously can be a good way to initiate demonstration projects for the charcoal-sequestration approach because it also helps with waste management. These demonstration projects in turn will help evaluate various aspects of this novel method of sequestration and enhance public awareness on the subject, which in turn will help society make an informed choice to embark on a correct course of action for atmospheric carbon abatement. Additionally, in light of the growing per capita waste worldwide, use of municipal waste as feedstock for charcoal sequestration can be a significant measure of carbon offset at global scale in its own right.
Libre, Jean-Marie (Total E&P) | Tripathi, Amita (Fluidyn-Transoft) | Le Guellec, Malo (Fluidyn-Transoft) | Mailliard, Thibault (Fluidyn-Transoft) | Guérin, Stéphanie (Total E&P) | Souprayen, Claude (Fluidyn-Transoft) | Castellari, Aldo (Total E&P)
The knowledge in real time of the concentration fields resulting from the accidental release of a hazardous substance would be extremely valuable information as support for emergency actions and for impact evaluation on the industrial site itself and its vicinity. For that purpose, a modeling platform is being developed and applied to simulate in real time the atmospheric dispersion of a hazardous substance at the scale of the industrial site and also of its surroundings. The industrial site of Lacq (France) has been chosen as a pilot, and the key hazardous substance considered in this study is hydrogen sulfide (H2S). A 3D computational-fluid-dynamic (CFD) model (Fluidyn-Panepr) has been chosen to simulate the 3D wind-field pattern on the industrial site, taking into account the details of the installations. This approach enables a simulation as close as possible of the turbulence and flow around the buildings that could not be achieved with a standard Gaussian approach. For that purpose, a detailed numerical model of the Lacq installation was built on the basis of a thorough review of the existing installations and an evaluation of their size and "porosity." Wind fields were calculated for a set of predefined boundary conditions based on the climatology of the site. Investigations were carried out to ensure that site information systems could deliver the information available from the H2S sensors and on-site meteorological station in real time. The real-time approach is made possible by the use of a complete wind-field precalculated database automatically selected in case of accidental release by comparison with real-time wind-direction and -speed measurements from the meteorological station located on the industrial site. The location and intensity of the source term are determined using a probabilistic approach (Bayesian inference), making use of both real-time measurements and precalculated concentration responses from unitary emissions (puffs) on sensors. This approach was validated successfully using a limited number of sensors and sources but with the complex structure and flow patterns expected on the site. The activation of the simulation platform is triggered by the detection of threshold concentrations at the sensors. The estimated source term is then used in forward dispersion mode to simulate the dispersion in (fast) Lagrangian puff mode. The modeling platform will be validated through measurement campaigns with a neutral species in 2010.
Popli, Sahil (The Petroleum Institute) | Rodgers, Peter (The Petroleum Institute) | Eveloy, Valerie (The Petroleum Institute) | Al Hashimi, Saleh (The Petroleum Institute) | Radermacher, Reinhard (University of Maryland) | Hwang, Yunho (University of Maryland)
The oil and gas industry is under increasing pressure to improve the efficiency of its energy-intensive oil- and gas-processing operations through improved energy use and waste-heat recovery. This paper explores the use of waste-heat-powered absorption cooling to boost the efficiency of natural-gas (NG) processing, enhance hydrocarbon recovery, and reduce utility cost in an NG plant. A thermodynamic analysis of a gas turbine waste-heat-powered double-effect water/lithium bromide (H2O/LiBr) absorption chiller in an integrated NG plant is presented.It is found that waste heat recovered from turbine exhaust gases could be used to provide enhanced process cooling capacity to the NG plant through absorption cooling. The results suggest that adouble-effect LiBr absorption chiller utilizing 34.6 MW of gas-turbine exhaust heat could provide 45 MW of cooling at 5°C.This could save approximately 9 MW of electric energy required by a typical compression chiller, while providing an equivalent amount of cooling.The associated annual savings are estimated to be approximately USD 7.8 million/yr, with a payback period of 2 years.
Ultrasonic gas-leak detection (UGLD) is gaining broader acceptance in the oil and gas industry as a means for detecting combustible-gas leaks. UGLD responds to high-pressure leaks by measuring the airborne ultrasound emitted, which when detected by the sensor provides a measure that is proportional to the leak rate. Principal advantages of the technology are that it does not require gas to be transported to the detector and it provides coverage for a relatively large area, up to 20 m in radius, suggesting that UGLD is suitable for detecting gas releases in open, well-ventilated sections of offshore platforms.
Despite such advantages, the location criteria and commissioning and routine-maintenance procedures for UGLD are not as well understood as those for conventional gas detectors. A reason might be that UGLD requires the establishment of an ambient ultrasonic background-noise level to decide the alarm level and assist with selection of optimal location, a requirement that has no parallel with point IR or catalytic sensors. Location of ultrasonic gas-leak detectors is also based on identifying the potential sources of leaks and taking into account acoustic reflections and interferences caused by continuous or short-time-scale background ultrasonic noise.
Such newness might be enough to give some would-be users pause. They may believe that UGLD is for people with high technical competence or that mapping, commissioning, and maintenance are best left to UGLD-equipment manufacturers. Experience by one of the authors of this monograph suggests the contrary. UGLD, for its reliance on ultrasound as a proxy for a gas leak, is a simple concept to understand. Over the course of more than 3,000 installations during the last 10 years, offshore-platform personnel have developed best practices that reduce the time and cost required for installing and commissioning ultrasonic gas monitors and that ease the burden on maintenance. In this report, we examine several of these procedures and highlight the simplicity of installation and maintenance of this method of gas detection.
Acrolein (2-propenal) is a highly effective microbiocide and sulfide scavenger that has been commercially available since 1960 and has been used widely in the oil- and gas-production industry. Acrolein is a liquid product supplied in and applied from specialized containers, eliminating potential releases from transfers between tanks. The acrolein containers are built to comply with international transportation regulations. This paper will cover the development of a safety-management program and standardization of application equipment that allow the usage of acrolein for applications with a risk comparable to, or in some cases lower than, that for conventional chemical products.
Standardized operating procedures, closed-system application equipment [verified by industrial hygiene (IH) monitoring], and redundant safety devices are built into the system to prevent chemical exposures or misapplications. Applications are performed by trained and certified personnel who have completed a specific competency evaluation under field conditions. A detailed and customized safety-management program is completed and implemented for each application with extensive client participation.
This paper will cover the core of the safety-management program, which focuses on developing site-specific elements, including process safety information, process hazard analysis, operating procedures, employee and contractor training, applicator competency and field evaluation, prestartup safety reviews, management of change, and emergency planning and response procedures.
A safety audit program is also implemented to ensure that the completed safety management program complies with each element. Audits are conducted at the actual location during the course of the chemical application. A strong safety-management program and standardized application system have been shown to reduce personnel and environmental risks by lowering the potential for misapplications or equipment failures. These systems have allowed successful treatment programs on numerous global production assets. To validate this, a series of case histories will be presented that highlight the best practices that enable the safe application of acrolein.
Removing mercaptans from sour natural gas has always been considered a challenge. This is becoming an even more important issue with the global trend toward more-stringent specifications for commercial gases.
Amines have been used extensively because of their ability to meet the most severe H2S and CO2 specifications and their very high acid-gas selectivity over hydrocarbons, but they present very limited mercaptans-removal performances. They require an additional treatment step to achieve the total sulfur-content specification in the exported gas. Hybrid solvents are more efficient in removing mercaptans but have the disadvantage of poor acid-gas selectivity over hydrocarbons, resulting in hydrocarbon losses with the separated acid gases.
Total, taking advantage of its extensive knowledge and experience in acid-gas removal with amine mixtures, has developed a new proprietary hybrid-solvent formulation allowing simultaneous absorption of acid gases and of mercaptans, with limited coabsorption of hydrocarbons. (The new hybrid solvent process is Total's proprietary process known as the HySWEET® process, which is a registered trademark.) The solvent was selected at the laboratory scale, with a particular attention given to operation-related constraints (e.g., cost, corrosion, foaming, degradation). The new solvent's acid-gas- and mercaptans-removal performances were then validated on a pilot rig.
The performance of the process has been assessed for several field applications and compared with the performances of conventional amine processes. This allowed evaluating the potential gain achievable by the implementation of the new hybrid solvent. The study identifies the application cases for which the new hybrid solvent will allow an economic and complete mercaptan removal without any additional treatment and identifies the perspective reduction of these additional treatments for the other cases. Besides an economical mercaptan removal, the new hybrid solvent allows a significant reduction in the energy consumption.
The results of the technoeconomic evaluation of the process have been confirmed during the first successful industrial application at the Lacq sour-gas plant in 2008. Half of the gas production is now treated with the hybrid solvent, allowing the plant to achieve high global mercaptans removal.
These results are fully documented in the paper, demonstrating that the newly developed process is a good contender for the development of new sour-gas fields to achieve the increasingly stringent commercial gas specifications.