Wells – Above ground apparatus – Moving tubing or cable into an existing well
Patent
1991-10-22
1993-08-17
Dang, Hoang C.
Wells
Above ground apparatus
Moving tubing or cable into an existing well
138139, 138153, 138174, 166242, E21B 1720, E21B 1922
Patent
active
052360369
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a new concept of "auxiliary injection tube", called hereafter AIT for injecting a fluid containing corrosion and/or deposit inhibiting agents into a well, continuously from the surface without stopping working.
The invention is more particularly applicable to 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 well known 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 reinjecting the 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 CO2 and H2O 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; geothermal loop and clogging of the structures and surface equipment.
To reduce, in the absence of eradicating, such damage different curative and preventive means may be used. Chemical preventive means are among the most widely employed. Based on the injection at the well bottom of corrosion/deposit inhibiting agents with respectively film-forming (corrosion) and dispersant (deposit) functions, these methods have not demonstrated all the required reliability in their geothermal applications, because in particular of the AIT resistance. 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 connected to the end of an auxiliary injection tube.
The very object of a well is to extract the highest possible flow; the space occupied by the AIT in the production string must then be minimum so as to limit the pressure losses. The usual 1" or 1"1/4 carbon steel tubings are rapidly corroded in contact with the geothermal fluid. Recourse to 1" glass fibre "macaronis" regularly gives rise to operating troubles because of the mechanical characteristics of the material which is too weak.
The choice of noble alloys (Cr, Mo, Ni, etc. . . ), of a high cost, have the further drawback of making the solid structure fragile in the presence of dissolved H2S in a low concentration.
The invention, forming the subject matter of the present application, palliates the drawbacks of present day systems by using a metal web or core offering the mechanical characteristics required for this application, coated with a material which is inert with respect to the geothermal fluid, while remaining of a limited diameter.
Understanding of the invention and its advantages will be facilitated by the description of one embodiment illustrated by the accompanying figures, in which:
FIG. 1 is one example of auxiliary injection tube application in a production well equipped with an immersed pump;
FIG. 2 is a section of an auxiliary injection tube formed in accordance with the present invention;
FIGS. 3a-3d show a sectional view of different particular embodiments of an auxiliary injection tube in accordance with the object of the present invention.
The geothermal fluid, in FIG. 1, is driven by pump 1 through the production casing 2 and, after passing through the master valve 3 of the well head 4, is fed into the surface network 5 towards the exc
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Lucet Raymond
Turon Roland
Ungemach Pierre
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