Wells – Processes – Assembling well part
Patent
1996-11-20
1999-01-26
Tsay, Frank S.
Wells
Processes
Assembling well part
166 57, 285 47, E21B 1916, F16L 1112
Patent
active
058628665
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to double walled insulated tubing and to a method of installing such tubing in a well, such as a geothermal or oil well.
There is requirement to provide excellent thermal insulation properties in a tubular pipe string where it is required to bring warm or hot liquids to the surface from a deep depth. In other words, it is required to keep the liquid cooling on its traverse from the bottom of the well to the top of the well to a minimum, even though the temperature of the surrounding formations may drop by an average of3.degree. C. per 100 meters. Such applications are as follows: low flow rates where the thermal water would otherwise cool a considerable amount on the traverse to the surface, thereby losing thermal energy available to surface consumers. is commonly water, is pumped down to the bottom of a well in an annular space formed between a cemented casing string and a tubing string while drawing thermal energy from the surrounding formations and subsequently transporting the thermal energy to the surface through the tubing string. Without an efficient thermal insulation, the oil in the tubing string cools considerably as the oil flows towards the surface installation. Once the temperature drops below a level which is specific to the type of oil, bitumen or paraffin starts to change to the solid state and adhere to the internal wall of the tubing string. As a result, flow resistance increases due to the decreased cross-section of the tubing so that sucker rods may become stuck and break. To pump cool and, therefore, highly viscous oil through the pipeline sections close to the well head requires an unnecessary high amount of energy. bearing formation where hot steam is pressed into the formation around the well bore to heat up the viscous oil and, thus, improve its flow behaviour. Heat losses on the way to the surface are required to be low so as not to cause any unnecessary flow pressure drop in the production tubing string.
(2) Description of the Related Art
Pipe strings that are covered with glass or stone wool and then wrapped with foils or strips of thin steel sheets to shield the insulating layer against water are frequently used for surface applications. However, water may enter the insulating material through small holes or cracks that may occur in the surrounding cover and reduce the insulating properties of such a string. Therefore, this known method cannot be used to thermally insulate production tubing strings exposed to high pressure liquids in the annular space between the tubing string and a deep wells' casing.
Pipe made from fibreglass has a lower thermal conductivity than steel and is usually used for pipelines or tubing strings for corrosive media rather than for the purpose of thermal insulation because the thermal properties are usually insufficient. Temperature limits and lower strengths further reduce the possible range of applications of pipe made from such material. Fibreglass material is also considerably more expensive than steel pipe of the same diameter and cannot be used in oil wells equipped with reciprocating sucker rods. Also, inventory costs would rise if fibreglass tubing has to be kept in stock in addition to the standard steel tubing that is generally used in oil field operations.
Hitherto, thermally insulated injection and production tubing strings have sometimes been used to complete steam injection wells to obtain increased thermal efficiency of the system. The strings, which often have a length exceeding 1,000 meters, are constructed from individual lengths of double wall pipe, each of which usually has a length of about 9 meters--that is equivalent to range 2 API tubing joints--to be run and retrieved by oil field rigs in the same way as single wall strings.
The most common version of such a string is shown in the Composite Catalogue of Oil Field Equipment, Volume 1, page 988H, 35th revision, 1982-83, published by Gulf Publishing in the U.S.A. The prior art tubing string will now be
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Roxwell International Limited
Tsay Frank S.
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