Corrosion inhibition apparatus for downhole electrical heating

Claim 2

In an electromagnetic heating system for an oil well or other mineral fluid well, including a main heating electrode located downhole in the well at a level adjacent a mineral fluid deposit, and a return electrode located such that an electrical current between the electrodes passes through and heats a portion of the mineral fluid deposit, an electrical energizing apparatus including an A.C. power source for generating a high amplitude A.C. heating current, of at least fifty amperes, a D.C. bias source for generating a low amplitude D.C. bias current having a given polarity such as to inhibit corrosion at the main electrode, and connection means for applying both the A.C. heating current and the D.C. bias current to the electrodes of the well heating system, the improvement in which the D.C. bias source comprises a bias circuit, connected to a heating circuit that includes the A.C. power source, the bias circuit including at least one semiconductor device and developing a net D.C. voltage differential of the given polarity in response to the A.C. heating current.

Claim 3

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the bias circuit further includes amplitude adjusting means for maintaining the bias current below a given amplitude.

Claim 4

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 2, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which the amplitude adjusting means is actuated by the D.C. sensor means, and maintains the D.C. bias current below a given amplitude of about one ampere.

Claim 5

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the bias circuit includes a pair of semiconductor devices connected in parallel with each other but with reversed polarities, the devices having different forward voltage drops.

Claim 6

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 4, in which the bias circuit further includes amplitude adjusting means for maintaining the bias current below a given amplitude.

Claim 7

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 5, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which the amplitude adjusting means is actuated by the D.C. sensor means, and maintains the D.C. bias current below a given amplitude of about one ampere.

Claim 8

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the bias circuit includes a semiconductor device connected in parallel with a resistor.

Claim 9

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 7, in which the bias circuit further includes amplitude adjusting means for maintaining the bias current below a given amplitude.

Claim 10

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 8, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which the amplitude adjusting means is actuated by the D.C. sensor means, and maintains the D.C. bias current below a given amplitude of about one ampere.

Claim 11

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the bias circuit includes two parallel-connected branch circuits, each including at least one semiconductor device, the sum of the work functions for the semiconductor devices in one branch circuit being substantially different from the sum of the work functions for the semiconductor devices in the other branch circuit.

Claim 12

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 10, in which one branch of the bias circuit further includes amplitude adjusting means for maintaining the bias current below a given amplitude.

Claim 13

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 11, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which the amplitude adjusting means is actuated by the D.C. sensor means, and maintains the D.C. bias current below a given amplitude of about one ampere.

Claim 14

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the D.C. bias source comprises a plurality of bias circuits connected in series with each other and connected to a heating circuit that includes the A.C. power source, each bias circuit including at least one semiconductor device and developing a net D.C. voltage differential of the given polarity in response to the A.C. heating current.

Claim 15

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 13, in which each bias circuit further includes amplitude adjusting means for maintaining the bias current below a given amplitude.

Claim 16

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 14, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which each of the amplitude adjusting means is actuatable by the D.C. sensor means, so that the bias source maintains the D.C. bias current below a given amplitude of about one ampere.

Claim 17

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the bias circuit includes a first plurality of semiconductor devices that are connected in series with each other and in parallel with a second plurality of semiconductor devices that are in series with each other.

Claim 18

Electrical energizing apparatus for A.C. heating and corrosion inhibition in a mineral fluid well, according to claim 16, in which the bias circuit further includes a plurality of control switches for individually bypassing selected ones of the semiconductor devices.

Claim 19

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 17, in a heating system including D.C. sensor means for sensing the D.C. bias current, in which the control switches are actuated by the D.C. sensor means to maintain the D.C. bias current below a given amplitude of about one ampere.

Claim 20

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the frequency of the A.C. heating current is in the range of about 0.01 to 35 Hz.

Claim 21

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 1, in which the connection means comprises an output transformer, and the D.C. bias source is connected to the secondary of the output transformer.

Claim 22

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 20, in a heating system including D.C. sensor means for sensing the D. C. bias current, in which the D.C. bias circuit further comprises amplitude adjusting means, actuated by the D.C. sensor means, for maintaining the D.C. bias current below a given amplitude of about one ampere.

Claim 23

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 21, in which the frequency of the A.C. heating current is in the range of about 0.01 to 35 Hz.

Claim 24

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 22, in which the semiconductor devices are diodes.

Claim 25

In an electromagnetic heating system for an oil well or other mineral fluid well, including a main heating electrode located downhole in the well at a level adjacent a mineral fluid deposit, and a return electrode at a location remote from the main electrode such that an electrical current between the electrodes passes through and heats a portion of the mineral fluid deposit, an electrical energizing apparatus including an A.C. power source for generating a high amplitude A.C. heating current, of at least one hundred amperes, a D.C. bias source for generating a low amplitude D.C. bias current having a polarity such as to inhibit corrosion at the main electrode, connection means for applying both the A.C. heating current and the D.C. bias current to the electrodes of the well heating system, and D.C. sensor means for sensing the D.C. bias current, the improvement in which the D.C. bias source comprises: a bias circuit including a pair of semiconductor devices connected in parallel with each other but with reversed polarities, the devices having different work functions; and amplitude adjusting means, actuated by the D.C. sensor means, for maintaining the D.C. bias current below a given amplitude of about one ampere.

Claim 26

In an electromagnetic heating system for an oil well or other mineral fluid well, including a main heating electrode located downhole in the well at a level adjacent a mineral fluid deposit, and a return electrode at a location remote from the main electrode such that an electrical current between the electrodes passes through and heats a portion of the mineral fluid deposit, an electrical energizing apparatus including an A.C. power source for generating a high amplitude A.C. heating current, of at least one hundred amperes, a D.C. bias source for generating a low amplitude D.C. bias current having a polarity such as to inhibit corrosion at the main electrode, connection means for applying both the A.C. heating current and the D.C. bias current to the electrodes of the well heating system, and D.C. sensor means for sensing the D.C. bias current, the improvement in which the D.C. bias source comprises: a bias circuit including a pair of semiconductor devices connected in parallel with each other but with reversed polarities, the devices having different work functions; and amplitude adjusting means, actuated by the D.C. sensor means, for maintaining the D.C. bias current below a given amplitude of about one ampere.

Claim 27

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 24, in which the amplitude adjusting means comprises a variable impedance connected in series with one of the semiconductor devices.

Claim 28

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 25, in which the semiconductor devices are diodes.

Claim 29

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 26, in which the frequency of the A.C. heating current is in the range of 0.01 to 35 Hz.

Claim 30

Electrical energizing apparatus for A.C. heating and D.C. corrosion inhibition in a mineral fluid well, according to claim 24, in which the amplitude adjusting means comprises a variable impedance semiconductor device connected in parallel with the bias circuit.