Apparatus and methods for controlling and communicating with downhole devices
Apparatus and methods for controlling and communicating with one or more tools in a downhole tool string including a tractor, an auxiliary tractor tool, a logging tool, a safety sub, a release mechanism, a unit containing sensors for monitoring downhole conditions, a setting tool, and a perforating gun. Also provided are apparatus and methods for controlling and communicating with one or more perforating guns, release devices, and explosive devices in a string to be lowered into a wellbore. Control and communication are accomplished by sending signals from the surface to control switches in the control units on the tool, with redundant switches for safety, to state machines in the respective control units, “each state machine returning a signal verifying switch status to the surface. Control and power functions are accomplished with voltage of different polarities for safety.
1. A method of communicating with a switch unit located on a perforating gun, release device, or explosive device for lowering into a wellbore comprising the steps of:
sending a command to the switch unit;
identifying the status of a switch with a state machine within the switch unit;
identifying one or more valid commands for the status of the switch with the state machine;
determining whether the command is valid for the status of the switch with the state machine;
if the command is invalid, returning a signal comprising an error message from the switch unit at a current level in the range of from about 4 milliamps to about 15 milliamps;
if the command is valid, controlling the position of the switch; and
if the command is valid, returning a signal validating switch status from the switch unit at a current level in the range of from about 4 milliamps to about 15 milliamps.
2. The method of claim 1 wherein the return signal further comprises the status of the switch.
3. The method of claim 1 wherein the return signal further comprises an identifier for the switch unit.
4. The method of claim 1 additionally comprising the step of lowering the perforating gun, release device, or explosive device into the wellbore and returning a signal from the switch unit at a current level in the range of from about 10 milliamperes to about 100 milliamperes.
5. A method of switching between a safe mode for tractoring and a perforating mode for perforating in a tool string including a tractor and a perforating gun for lowering into a wellbore on a wireline comprising the steps of:
sending a signal to a control unit on the tractor from the surface;
identifying the status of a switch with a state machine within the switch unit;
identifying one or more valid commands for the status of the switch with the state machine;
determining whether the command is valid for the status of the switch with the state machine;
if the command is invalid, returning a signal comprising an error message from the control unit;
if the command is valid, controlling the position of the switch to connect the wireline to either the tractor motor or a through wire connecting to the perforating gun while blocking negative voltage below a predetermined threshold through the wireline; and
if the command is valid, returning a signal validating switch status to the surface.
6. The method of claim 5 wherein the tool string additionally includes a safety sub between the tractor and the perforating gun and negative voltage is blocked at the output of the safety sub.
7. The method of claim 5 wherein the return signal comprises an identifier for the control unit.
8. The method of claim 5 wherein the return signal comprises the status of the switch.