Wells – Processes – Heating – cooling or insulating
Reexamination Certificate
1999-06-11
2001-09-04
Nueder, William (Department: 3672)
Wells
Processes
Heating, cooling or insulating
C166S057000, C166S309000, C166S901000
Reexamination Certificate
active
06283215
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of tubings used for carrying fluids, and more particularly to tubings placed in wellbores. These tubings are placed in a hydrocarbon producing borehole and they serve either as fluid delivery lines by means of a borehole pump or directly as production lines in the case of eruptive reservoirs, or as injection lines for injecting fluids into a reservoir.
More generally, the present invention relates to tubings for carrying fluids placed in a pipe.
BACKGROUND OF THE INVENTION
The fluids conveyed by these tubings can be of very different kinds, and most often these tubings will be used for oil extraction. It is often interesting to transport oil at its bottomhole temperature, thus avoiding a certain number of drawbacks generated by heat exchanges with the outside. These drawbacks are for example paraffin, asphaltene, hydrate or viscous crude deposits under surface conditions, condensation or instability phenomena, productivity losses. These drawbacks can generate phenomena referred to as self-killing phenomena and lead to premature well or even field abandonment.
A known solution consists of thermally insulating the production tubing so as to minimize heat losses as the fluids flow therethrough, with the aim of keeping the thermal conductivity of these insulated tubings in the 0.05-0.2 watt/m/° C. range.
Various thermal insulation methods for tubings exist and have already been applied in production fields. A distinction can be made between complete tubing insulation processes using various fluids, for example gas, oils, aqueous or organic gels. molten sulfur, and processes for insulating the outer wall of the production tubing, for example lining using insulating materials, aluminium-based insulating paints, rigid foams and polysilicate foams generated in situ.
All these techniques are either expensive or not very effective, or hardly reversible. Using fluids whose reversibility would not be total furthermore presents risks of damage to certain producing formations as weakly soluble products are brought into contact. The reversibility of the systems used thus appears to be essential.
SUMMARY OF THE INVENTION
The present invention relates to a process for thermally insulating reversibly a string comprising at least one tubing placed in a pipe and in which a fluid circulates, the insulant being a non-rigid foam produced from a liquid solution and a gas, said foam is situated in the annular space defined by the outside of the tubing string and the walls of the pipe in which these tubings are placed.
According to a variant, the pipe is a wellbore; this wellbore is preferably cased with a steel pipe.
The main advantages of the process according to the present invention are as follows: on account of its low density, the non-rigid foam has a very low thermal conductivity in relation to the dense materials generally used, its insulating properties are therefore enhanced. Without referring to any theory, one may think that the no generation of a foam in the annular space allows this space to be partitioned. The gas contained in this space will therefore be less inclined to circulate in said space, and convection phenomena will be limited.
This foam generally has a density ranging between 0.01 and 0.8 and preferably less than 0.3; the nature of this foam also allows to add anticorrosion additives whose function is to protect the metallic surfaces of the production tubing and of the casing string of the well. The nature of this foam also reversibly allows to return to the state preceding the formation of said foam; this property can be interesting if servicing operations have to be carried out in the annular space defined by the outside of the tubing string and the walls of the pipe in which these tubings are placed, for example if one of the tubings has to be replaced. Furthermore, these solutions comprising one or more additives that contribute to foaming the carrier fluid and contain mainly water and/or an organic liquid are economically interesting.
The non-rigid foam used in the insulation process according to the invention is produced by introducing at least one foaming agent selected from the group made up of the systems of foaming agents for aqueous foams and the systems of foaming agents for foams based on an organic liquid into at least one liquid phase selected from the group made up of water and organic liquids.
One or more additives can also be added to the foaming agent. These additives are generally foam formation promoting additives, foam stability promoting additives, anticorrosion agents heat-stabilizing agents, viscosifiers, liquid phase thickeners.
To produce aqueous foams, one can use at least one foaming agent selected from the group made up of anionic, non-ionic, cationic or amphoteric surfactants, or combinations of these various surfactants according to whether the temperature stability, the resistance to possible contaminations (water, salts, hydrocarbons, . . . ), wall adherence, compatibility with the carrier fluid and the possible thickening and/or weighting agents is favoured.
To produce oil-based foams, one can use, as the case may be, at least one foaming agent selected from the group made up of the foaming agents obtained from gas oil, kerosine, oils or derivatives of vegetable origin, linear alkanes possibly substituted such as, for example, fluorinated surfactants, esters, antines, aluminium complexes. All kinds of liposoluble surfactants or crudes with high foaming properties can also be used.
Concerning the liquid phase thickening or stabilizing agents, they are generally high-molecular polymers, for example hydrosoluble polymers such as polyacrylamides, ethylene polyoxides, carboxymethylcellulose, hydroxyethylcellulose, liposoluble polymers such as polyolefins, polymethacrylates. The thickening agent can also be an aqueous or organic gel, or mineral particles dispersed in an aqueous or organic medium such as bentonites for example, or treated bentonites for use in organic media.
Non-toxic and/or biodegradable oils and systems of foaming and gelling agents will be advantageously used.
Setting the foam in the annulus defined by the outside of the tubing string and the walls of the well in which these tubings are placed is generally performed according to one of the procedures described below.
The foam is generated at the surface and pumped into the annulus or the tubing provided with bottom valves allowing circulation with the annulus.
The solution containing the foaming agent can also be injected into the annulus and the foam is then formed in situ by injecting gas at the base of the column of fluid, by means of a tube preferably placed in the annulus. In this case, the annulus can be kept open at the surface or controlled by a shutting valve or a choke.
The gases used for producing the foam or the gel are air, nitrogen, natural gases, exhaust gases, carbon dioxide (CO
2
) and mixtures thereof.
In any case, it may be useful to maintain, by a suitable means, a minimum continuous flow of gas injected in the lower part of the annulus throughout the period of use of the foam.
When the invention relates to wellbores, two fluids are referred to. A distinction thus has to be made between the<<fluid to be extracted>>from the producing rock and the<<liquid and/or gaseous fluid>>corresponding to the foam generated before or in situ.
The present invention also relates to a system for working a fluid producing well comprising at least one tubing placed in the wellbore and in which said fluid to be extracted circulates. The working system also comprises a non-rigid insulating foam situated in the annulus defined by the outside of the tubing string and the walls of the well in which these tubings are placed, and at least injection means whose outlets are situated in said annulus.
These means allow injection of either a previously formed foam or of a gas intended to cause the constituents of a foam placed in the annulus to foam. These injection means can comprise a valve placed a
Argillier Jean-Francois
Jarrin Jacques
Kohler Norbert
Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Nueder William
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