Current feed-through wireline release tool and method

1. A wireline release tool for downhole intervention, the tool comprising:

a housing having an electrical input and an electrical output;

a pass-through switch located inside the housing and electrically connected between the electrical input and the electrical output, the pass-through switch including two enhancement mode transistors; and

a current limiter device located inside the housing and electrically connected between the electrical input and the electrical output, the current limiter device including two depletion mode transistors,

wherein the pass-through switch is connected in parallel to the current limiter device, between the electrical input and the electrical output, and

wherein the two enhancement mode transistors are configured to be OFF when a gate-source voltage is zero and the two depletion mode transistors are configured to be ON when the gate-source is zero.

2. The wireline release tool of claim 1 , wherein the current limiter device allows a test electrical current, smaller than a threshold current, to pass while the pass-through switch does not allow the test electrical current to pass.

3. The wireline release tool of claim 2 , wherein the current limiter device limits a current from increasing past the threshold current.

4. The wireline release tool of claim 2 , wherein the pass-through switch is open while the test electrical current passes through the current limiter device.

5. The wireline release tool of claim 4 , wherein the threshold current is 20 mA and the test electrical current is smaller than 3 mA.

6. The wireline release tool of claim 2 , wherein the threshold current times a resistance of the current limiter device equals a voltage that is smaller than a voltage that closes the pass-through circuit.

7. The wireline release tool of claim 1 , wherein the current limiter device comprises:

the two depletion mode transistors and a resistor.

8. The wireline release tool of claim 7 , wherein the two transistors are N-channel mosfet transistors.

9. The wireline release tool of claim 7 , wherein the resistor is the only resistor in the device.

10. The wireline release tool of claim 7 , wherein there are no other electrical components of the current limiter device.

11. The wireline release tool of claim 7 , wherein a drain of the first transistor is connected to the electrical input, a source of the first transistor is connected to a first side of the resistor, and a gate of the first transistor is connected to a second side of the resistor.

12. The wireline release tool of claim 11 , wherein a drain of the second transistor is connected to ground, a source of the second transistor is connected to the second side of the resistor, and a gate of the second transistor is connected to the first side of the resistor.

13. The wireline release tool of claim 1 , wherein the housing has a first end that is attached to a wireline and a second end that is attached to a casing locator.

14. A method for ohmic testing a gun string assembly in a well, the method comprising:

connecting a wireline release tool to a gun string;

lowering the assembly into the well;

applying with a current source a test current to the wireline release tool, the test current being smaller than a threshold current, so that the test current passes a current limiter device, but does not pass a pass-through switch, which is electrically connected in parallel to the current limiter device;

measuring a test voltage associated with the test current; and

determining a status of the gun string,

wherein the pass-through switch includes two enhancement mode transistors and the current limiter device includes two depletion mode transistors, and

wherein the two enhancement mode transistors are configured to be OFF when a gate-source voltage is zero and the two depletion mode transistors are configured to be ON when the gate-source is zero.

15. The method of claim 14 , further comprising:

applying with a voltage source a voltage larger than a threshold voltage to close the pass-through switch.