Measuring and testing – Fluid pressure gauge – With pressure and/or temperature compensation
Reexamination Certificate
2000-07-05
2004-02-10
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Fluid pressure gauge
With pressure and/or temperature compensation
Reexamination Certificate
active
06688180
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a multi-test assembly for evaluating, detecting and monitoring processes at elevated pressure, and uses of the mufti-test assembly. Further, the present invention relates to a system for fast, systematic and effective testing and detection of solids formation such as those used for testing and optimizing of chemicals for controlling gas hydrates.
BACKGROUND OF THE INVENTION
One of the most challenging problems in oil and gas exploration is the presence of natural gas hydrates in transport pipelines and equipment. Natural gas hydrate is an ice-like compound consisting of light hydrocarbon molecules encapsulated in an otherwise unstable water crystal structure. These hydrates form at high pressures and low temperatures wherever a suitable gas and free water are present. Gas hydrate crystals can become deposited on pipeline walls and in equipment, and in the worst case, lead to complete plugging of the system. Costly and time-consuming procedures may be needed to restore flow again. In addition to the economic consequences, there are also numerous hazards connected to hydrate formation and removal. Although gas hydrates are generally thought of as a problem mostly in connection with gas production, they are also a significant problem for condensate and oil production systems.
To control gas hydrates, the usual approach has been to take steps to avoid any hydrate formation at all. This can be achieved by keeping pressure low (often not possible from flow or operational considerations), keeping temperature high (usually by insulating), removing the water completely (costly equipment and difficult), or by adding chemicals that suppress hydrate formation thermodynamically or kinetically. Insulation is very often used, but is not sufficient alone. Adding chemicals, specifically methanol (MeOH) or ethylene glycol (EG), is therefore the most widespread hydrate control mechanism in the industry today (E. D. Sloan Jr., Clathrate Hydrates of Natural Gases, Marcel Dekker, Inc., New York, 1998, pp. 164-170). These antifreezes ,expand the pressure-temperature-area of safe operation, but are needed in large quantities—50% of the water liquid fraction is not unusual in water-rich production. The use of MeOH in the North Sea may approach 3 kg per 1000 Sm3 of gas extracted. The need for such large amounts of antifreeze places severe demands on logistics of transportation, storage and injection in offshore facilities with a deficiency of space.
Inhibitor chemicals of different types are not only used in pipeline transport and processing areas, but also extensively in drilling operations and wells.
Mainly due to the huge amounts and large costs involved in using traditional inhibitors like MeOH, there has ver the last decade been extensive efforts devoted to finding chemicals which may be effective at controlling hydrates at much lower concentrations.
Many oil companies and research institutes have contributed to this effort, and at present, the results are divided into three main categories; kinetic inhibitors, dispersants, and modificators. Kinetic inhibitors have: an affinity for the crystal surface, and thereby can be used to prevent hydrate crystal growth. Dispersants act as emulsifiers, dispersing water as small droplets in the hydrocarbon liquid phase. This limits the possibilities for hydrate particles to grow large or to accumulate. The modifiers act as a combination of the two other methods, attaching to the crystal surface, the hydrate is dispersed as small particles in the hydrocarbon liquid phase.
Dispersant and modifiers are generally dedicated for condensate and oil production systems.
The development of low dosage chemicals for hydrate control has been somewhat successful, although there are practical and environmental drawbacks to most of them.
One principal reason for the limited success has been the lack of a method and a system for fast systematic and effective testing of large test matrixes for new chemicals. Most of these chemicals work efficiently only in blends. Further, the blends have to be suited to each field fluid which may contain other field chemicals such as corrosion, wax, and scale inhibitors.
The present invention will also definitely affect testing and optimizing of other field chemicals (e.g. corrosion, wax and scale inhibitors). Not necessarily used in the same amount per volume unit pipe as the hydrate inhibitors, the total amount of chemicals (sometimes with environmentally highly adverse effects) are huge, as they are used in such a great number of pipelines.
The present invention provides a method for fast, systematic and effective detection and monitoring of phase transformation or solids formation such as those used for multi-testing of chemicals for controlling gas hydrates.
Many compounds, such as, for example, gas hydrates, are formed in liquids, or in mixtures of liquids and gases under elevated pressures. For testing and studying their formation, it is necessary to use pressure vessels. The pressure vessel has to be designed such that the handling of it does not represent any unnecessary hazard, provided it is used according to working instructions.
Pressure cells used for testing of gas hydrate formation are described in E. D. Sloan Jr., Clathrate Hydrates of Natural Gases, Marcel Dekker, Inc., New York, 1998, pp. 292-300. A test cell (15-300 cc) usually consists of a sight glass for visual confirmation of hydrate formation and disappearance. Normally only up to 50 per cent of the cell volume is liquids, with the remainder being gas and hydrate. The cell is enclosed in a thermostated bath with thermocouples in the cell interior to measure the thermal lag between the cell and the bath. The pressure in the cell is usually measured via Bourdon tube gages or transducers. Mixing in the cell may be provided by mechanical or magnetic agitators, by rotating or rocking the cell, by bubbling gas through the liquids, or by ultrasonic agitation. Hydrate formation is normally tested in one of three modes: isothermal (constant temperature), isobaric (constant pressure) or isochoric (constant volume). The hydrate is observed visually or detected through measurements of temperature and pressure in the cell, gas consumption, or apparent liquid viscosity.
Common to all test cells mentioned, and for all other known methods for testing of gas hydrate formation on laboratory scale, is that each pressure vessel can only perform one test mixture at the time. When a pressure vessel weights up to 8 kg, handling more than a small number of vessels at the time is difficult. This makes each test a very resource intensive process, and there is consequently a great need for more efficiency, rationalization, downscaling and automation.
Common to all the test procedures mentioned and for all other known test procedures for the testing of gas hydrate formation on laboratory scale with the purpose of discovering new inhibitors or to optimize existing inhibitors, is that these are performed in a cumbersome and expensive manner by having to separately prepare each reaction mixture, which typically consists of 4-7 reagents, and by adding the reagents one by one. Furthermore, each reaction mixture is typically prepared in batches of 5 to 100 g and tested in expensive and heavy pressure vessels with internal volumes often in the range of 25 to 250 ml and with weights of up to 8 kg per pressure vessel, causing considerable expense due to a large consumption of often expensive reagents and due to the fact that the handling of the heavy pressure vessels often makes it difficult to handle more than one pressure vessel at the time. The combination of all these elements are, according to state of the art technology, making each inhibitor test a very resource intensive process. Consequently there is a great need for greater efficiency, rationalization, down-scaling and automation.
In recent years new, automated methods for systematic preparation of new compounds, so-called “combinational techniques”, have been developed. In WO 9512608-A1
Akporiaye Duncan E.
Dahl Ivar Martin
Hjarbo Kai W.
Karlsson Arne
Lund Are
Davis Octavia
Lefkowitz Edward
Sinvent AS
Wenderoth , Lind & Ponack, L.L.P.
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