Wells – Expansible anchor or casing – Liner hanger
Patent
1991-10-22
1993-07-20
Melius, Terry Lee
Wells
Expansible anchor or casing
Liner hanger
166304, 166902, E21B 3706
Patent
active
052285090
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new concept of well completion using a steel support casing associated with a composite material injection or production string, with free annular space.
The invention applies in particular to the construction of geothermal wells for combatting the effects of the corrosive and scale-forming thermochemistry of the geothermal fluid and preserving the long-life of the structures. These problems are particularly well known, for example, in the Paris basin where numerous geothermal "doublets" (assembly formed of a production well for collecting the hot water of the reservoir and an injection well used for re-injecting fluid into the reservoir after heat has been extracted) have been realized from the 1970s.
In these installations, the geothermal fluid--hot water whose temperature is between 50.degree. C. and 85.degree. C. and with high salinity (15 to 25 g/l)--comprises a dissolved gas phase enriched with C02 and H2S which confer thereon a slight acidity (pH of 6 to 6.4). This aggressiveness results, in certain zones of the harnessed reservoir, in repeated and accelerated damage to the structures because of the corrosion and deposits affecting the casings and clogging affecting the collection zone of the reservoir.
The damage mechanism may be summed up as follows: the injection structure; formation of iron sulphides; casing without protection thereof (continuation of the corrosion kinetics under the deposits); and clogging of the heat exchangers, deposits/scaling of the injection casing and accumulation on the bottom and on the walls of the reservoir collection zone; loop and clogging of the structures and surface equipment.
The curative and preventive means for, if not eradicating, at least reducing such damage are of three kinds: rotation and mud flow, of conventional cable and rod fittings, well known to specialists; specific products for reducing the costs of such trouble-shooting have been provided; the French patent 2 631 708 describes one of these devices based on a coiled tubing system; of corrosion inhibiting/deposit agents with respectively film-forming (corrosion) and dispersant (deposits) functions. Such injection is carried out using an auxiliary injection tube (AIT), the positioning and resistance in time of which are also subject to caution; the French patents 2 463 197 and 2 502 239 describe respectively an inhibiting method by injecting aliphatic amines and a well bottom injection device; either resistant materials or, preferably, materials which are electro-chemically inert with respect to corrosion in the H2O--CO2--H2S system. The choice of noble alloys (Cr, Mo, Ni, etc. . . . ), of a high cost, have moreover the drawback of making the solid structure fragile in the presence of dissolved H2S, in a low concentration, which does not exist with the carbon steels usually used. The composite materials are passive from the corrosion point of view; positioning thereof in the borehole, however, is not without risk because of the mechanical characteristics of the material used. For the same reason, this risk of damage exists at the time of interventions during working. The simple friction of a cable, used for lowering electric well-logging tools, may create at points a hole in the thickness of the casing.
This reveals the fact that the use of conventional solutions for overcoming well damage problems due to the aggressiveness of the geothermal fluid, comprise non negligible risks.
The invention according to the present application, forms another alternative combining the possibilities of chemical preventive means and material alternatives without having the drawbacks thereof.
The invention and its advantages will be better understood from the description of one embodiment illustrated by the accompanying figures in which:
FIG. 1 shows one example of a geothermal production well completion according to the invention;
FIGS. 2, 3 and 4, relative to the prior art, show certain risks inherent in the conventional solutions and avoided in the solution forming the object of t
REFERENCES:
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patent: 4424862 (1984-01-01), Munari et al.
patent: 4494607 (1985-01-01), Ford et al.
patent: 4615387 (1987-10-01), Johnson et al.
patent: 5048603 (1991-09-01), Bell et al.
patent: 5103914 (1992-04-01), LaHaye
Turon Roland
Ungemach Pierre
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