US 4,790,375 AGranted

Mineral well heating systems

AssigneeORS Development Corporation

InventorsJack E. Bridges, Guggilam C. Sresty, Vincent R. Young, Homer L. Spencer

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Abstract

Heating systems for mineral wells (e.g. oil wells) employ electrical power sources, sometimes operating at relatively high frequencies, that are connected to the well casing and production tubing so as to provide a coaxial line electrical heater projecting down into the well. The heating pattern of the coaxial line is effectively controlled so that most of the power is dissipated as heat, primarily in the tubing, above a depth D above which paraffins or other condensible constituents would tend to condense or otherwise impair the flow of mineral fluid up through the production tubing. The applied electrical power is controlled so that the fluid is kept approximately at or only somewhat above the flow impairment temperature for constituents of the fluid. In some embodiments the system is extended to provide heating of a portion of the deposit formation adjacent to the well.

Claims56

Dependent claims

A well heating system for a mineral well of the kind in which a flow of a mineral fluid moving upwardly above a predetermined subsurface depth D is subject to impairment due to condensation of paraffin or other condensible constituents from the fluid flow or to increasing viscosity of that fluid, caused by temperature reduction, the well comprising a well bore projecting downwardly from a surface to a fluid reservoir and having an outer wall that is electrically conductive, and an electrically conductive production tubing extending down into the well bore in physically spaced and electrically insulated relation to the well bore wall, the heating system comprising:

an electrical power source;
connection means for electrically connecting the power source to the tubing and to the electrically conductive wall so that the tubing and wall conjointly afford a two-conductor heating apparatus projecting downwardly into the well bore, which heating apparatus functions electrically approximately as a coaxial line;
means for effectively terminating the coaxial line so that most of the electrical power supplied to the coaxial line from the power source is dissipated within the well above the depth D;
and control means for controlling the electrical power supplied to the coaxial line from the power source to maintain the mineral fluid flowing in the tubing approximately at or above a flow impairment temperature for the fluid without substantially exceeding a predetermined upper limit temperature for the fluid in more than a minor fractional part of the well from depth D to the surface,
in which the temperature limits are:
______________________________________ content of flow impairment upper limit mineral fluid temperature temperature ______________________________________ paraffin cloud point paraffin melting point sulfur sulfur 300.degree. F. precipitation point hydrates crystal precipitation 300.degree. F. point heavy, viscous no-flow pour point five centipoise oil temperature ______________________________________

3 more elements

A well heating system for a mineral well of the kind in which a flow of a mineral fluid moving upwardly to a ground surface from a subterranean reservoir is subject to flow impairment due to condensation of paraffin or other condensible constituents from the fluid flow or to increasing viscosity of that fluid, caused by temperature reduction, the well comprising a well bore projecting downwardly from the ground surface to the fluid reservoir and an electrically conductive production tubing extending down into the well bore in physically spaced and electrically insulated relation to the well bore, the heating system comprising:

an alternating current electrical power source of given frequency f;
connection means for electrically connecting the power source to the tubing so that the tubing constitutes a part of a heating apparatus projecting downwardly through the well bore;
downhole connector means for electrically connecting a downhole portion of the tubing to the mineral fluid in the portion of the reservoir immediately encompassing the well bore;
and control means for controlling the electrical power supplied to the tubing from the power source to maintain the mineral fluid flowing in the tubing approximately at or above the flow impairment temperature for the fluid without substantially exceeding a predetermined upper limit temperature for the fluid in more than a minor fractional part of the tubing,
in which the temperature limits are:
______________________________________ content of flow impairment upper limit mineral fluid temperature temperature ______________________________________ paraffin cloud point paraffin melting point sulfur sulfur 300.degree. F. precipitation point hydrates crystal precipitation 300.degree. F. point heavy, viscous no-flow pour point five centipoise oil temperature ______________________________________

3 more elements

A well heating system for a mineral well of the kind in which a flow of a mineral fluid moving upwardly through the well is subject to impairment due to condensation of paraffin or other condensible constituents from the fluid flow or to increasing viscosity of that fluid, caused by temperature reduction, the well comprising a well bore projecting downwardly from a surface to a fluid reservoir and having an outer wall that is electrically conductive, and an electrically conductive production tubing extending down into the well bore in physically spaced and electrically insulated relation to the well bore wall, the heating system comprising:

a first electrical power source, comprising an alternating current source having a given frequency f;
a second electrical power source having a frequency much lower than f, down to D.C.;
connection means for electrically connecting both of the power sources to the tubing and to the electrically conductive wall so that the tubing and wall conjointly afford a two-conductor heating apparatus projecting downwardly into the well bore, which heating apparatus functions electrically approximately as a coaxial line, for both power sources;
and control means for controlling the electrical power supplied to the coaxial line from each of the power sources to maintain the mineral fluid flowing in the tubing approximately at or above the flow impairment temperature for the fluid without substantially exceeding a predetermined upper limit temperature for the fluid in more than a minor fractional part of the well;
whereby electrical power from the first source primiarly heats the upper part of the well whereas electrical power from the second source primarily heats the downhole portion of the well;
in which the temperature limits are:
______________________________________ content of flow impairment upper limit mineral fluid temperature temperature ______________________________________ paraffin cloud point paraffin melting point sulfur sulfur 300.degree. F. precipitation point hydrates crystal precipitation 300.degree. F. point heavy, viscous no-flow pour point five centipoise oil temperature ______________________________________

4 more elements

Dependencies are inferred from the claim text.