Wells – With heating – refrigerating or heat insulating means – Heater surrounding production tube
Patent
1992-11-04
1994-02-15
Bui, Thuy M.
Wells
With heating, refrigerating or heat insulating means
Heater surrounding production tube
166302, E21B 3600
Patent
active
052858464
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention relates to the extraction of minerals, for example oil or sulphur, from underground formations.
When the viscosity of a well effluent being recovered or extracted from an underground formation falls, as because of decreasing temperature, the rate of production flow can be adversely affected, possibly to such an extent that production from the well becomes impractical or impossible. Furthermore, the well effluent tends to deposit solids, for example, paraffin or free sulphur in the flow piping and production equipment, so as to obstruct perhaps completely half production. When these conditions occur, it may be necessary to abandon the well or to maintain production only at the cost and trouble of employing heat treatment operations calculated to increase the temperature and thus lower the viscosity of the well effluent, so as to facilitate its flow and thus permit continued production.
For example, sulphur is commonly mined by injecting heated water into a sulphur bearing formation for the purpose of melting the sulphur and permitting it to flow to the surface. A special solvent can be injected into the well to increase the solubility of the sulphur and prevent the deposition of elemental sulphur, as this tends to form a hard, adherent scale which can eventually plug the well and also the associated surface production equipment.
Paraffin blockages can occur in the production of oil and one of the methods for treating this condition is to inject hot oil into the formation. Hot water, steam and heated gases may be injected similarly for re-starting production from petroleum bearing formations.
However, a definite limitation is experienced as to the depth at which formations can be treated with heated fluids, because of heat loss from the fluids as they flow downwardly from the surface to the formation to be heated. Because of this cooling effect, it is generally not considered feasible to produce sulphur by existing heat transfer methods at depths below about 460-610 m. (1500-2000 ft.). Similarly, efforts to treat oil bearing formations at depths greater than this range with heated fluids such as oil or gas are generally not considered economical. In general, such prior art heat treatment methods for the thermal extraction of oil or other minerals have been expensive, labour intensive and more or less complicated in operation. They are moreover often attended by an undesired contact between the injected heating fluid and the well effluent itself.
The present invention is accordingly concerned with the thermal recovery or extraction of oil, sulphur and other subsurface minerals by means which at least partially overcome the difficulties encountered with previous thermal and solvent injection recovery methods.
The invention accordingly provides a method of and apparatus for thermal extraction of minerals from an underground formation, in which heat is generated in and/or supplied to an assembly of spaced tubing extending downwardly from a surface installation into a well hole and arranged to guide the extracted mineral from the formation to the surface installation.
The apparatus of the invention can readily be constructed as a complete production system, providing all the facilities appropriate to such a system.
The tubing assembly can comprise electrical heating elements, which can have the form of tubular electrical conductors, extending lengthwise within the space between inner and outer tubing, or inner and outer tubing can be connected together at their lower ends or at an appropriate downhole position in series with an electric supply source so that heat is generated resistively in the tubing itself. Appropriate insulation is provided and in the second instance this can comprise a dielectric barrier fluid between the inner and outer tubing, which can be circulated through a downhole pump unit included in the apparatus where artificial lift is required for the mineral to be extracted.
The electrical heating elements can be constituted, additionally or instead, as one or more he
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Bui Thuy M.
Framo Developments (UK) Limited
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