Method and apparatus for controlling the permeability of mineral bearing earth formations

A method of electrotreating an earth formation to affect changes in the permeability of the earth formation, comprising the steps of:

• providing a pulsed voltage power supply having electrodes and an output for applying voltage pulses of selectable pulse durations to the electrodes;
• electrically connecting the electrodes to a zone of the earth formation;
• selecting an amplitude for the voltage pulses applied to the electrodes to cause an electric treatment current to flow within the zone at a desired current density which will cause irreversible changes in the permeability of the formation;
• selecting the pulse durations of the voltage pulses applied to the electrodes to correspond to maximum values for the conductivity of the formation;
• wherein the pulse durations which correspond to the maximum values for the conductivity of the formation are determined for various treatment time intervals during treatment of the formation zone;
• wherein the step of selecting the pulse durations includes the steps of varying the pulse durations to determine a saturation current and a critical value of the pulse duration which corresponds to a treatment current which is proportionate to the saturation current, selecting a value of the pulse duration to be proportionate to the critical value of the pulse duration, and, after the treatment time intervals, repeating the steps of varying the pulse durations and selecting the value of the pulse duration until a final saturation current is detected.

A method of electrotreating an earth formation to effect changes in the fluid flow characteristics of the formation, comprising the steps of:

• providing a pulsed voltage power supply having electrodes and a selectable output for applying voltage pulses of selectable amplitudes, pulse durations and periods to the electrodes, and a current sensor for determining an amplitude value of current passing through one of the electrodes;
• electrically connecting the electrodes to a zone of the earth formation;
• determining a desired current flow within the zone according to selected characteristics of the earth formation;
• selecting a value for the amplitude of the voltage pulses to apply the desired current flow within the zone;
• initially applying an initial substantially continuous sequence of the voltage pulses to the zone, with an initial pulse duration and an initial period;
• determining an amplitude value of the current passing through the one of the electrodes;
• varying the pulse duration and the period of the voltage pulses until an initial saturation current is detected;
• setting the pulse duration and the period to a first set point, such that the amplitude value of the current passing through the one of the electrodes is proportionate to the amplitude of the initial saturation current;
• applying a first substantially continuous sequence of the voltage pulses to the formation at the first set point for the pulse duration and the period, for a selected time duration;
• and
• after the first selected time duration, repeating the steps of varying, setting and applying, to determine further saturation currents, to set the pulse duration and the period at further set points and then to applying further substantially continuous sequences of the voltage pulses at further set points for the pulse duration and the period for further time durations according to values detected for the saturation currents, until a final value for the saturation current is detected.

A method for changing the permeability of an earth formation by applying pulsed current to a zone of the formation, comprising the steps of:

• determining a critical value (j*) of a pulsed current density which corresponds to a level of current density at which irreversible changes in the fluid flow characteristics of the formation zone occur, taking into account a particular type of rock which characterizes the formation, the structure of voids in the formation and parameters of a saturating liquid of within the formation;
• selecting a preliminarily value of the pulsed current density (j) applied to the zone of the formation which is not substantially less than a critical value (j*) of the pulsed current density;
• periodically determining critical values of pulse duration (tp*) which correspond to saturation points of the current flow within the formation zone during the treatment;
• periodically selecting pulse durations (tp) which are proportionate to the periodically determined critical values of the pulse durations (tp*), according to the formula tp=Btp*, where B is selected within a range of 0.5 to 5;
• and
• wherein the periods (T) of pulses of the pulsed current applied to the formation are periodically set such that an on-off time ratio of the pulse periods (T) to corresponding ones of the pulse durations (tp) are not substantially greater than 10.

An apparatus for selectively operating to change the permeability of a zone of an earth formation, comprising:

• means for applying pulsed electric currents to the formation zone, said means for applying having a power control unit for operatively controlling time parameters of said pulsed electric current;
• means for setting said time parameters of said pulsed currents, said means for setting said time parameters being connected to said power control unit for controlling said time parameters, said time parameters including the durations of said pulses and the periods of said pulses;
• a current sensor which detects said pulsed currents applied to the formation zone;
• and
• said means for setting said time parameters being connected to an output of said current sensor and being operated to periodically vary said time parameters to determine values of saturation currents applied to the formation zone, and to adjust said time parameters of said pulsed currents according to corresponding ones of said determined saturation currents.

An apparatus for electrotreating an earth formation to effect changes in the fluid flow characteristics of the formation, comprising:

• a pulsed voltage power supply having a power control unit for selectively determining pulse durations and pulse periods of voltage pulses and electrodes for electrically connecting to the formation for applying said voltage pulses to the formation;
• a current sensor for detecting values of electric currents passing through at least one of the electrodes;
• a programmable controller connected to an output of said current sensor and said power control unit, such that said pulse durations and said pulse periods of said voltage pulses are selected according to detected values of said electric current passing through said one of the electrodes;
• and
• said programmable controller periodically varying said pulse durations and said pulse periods to determine saturation currents corresponding to critical values for said pulse durations during various treatment time intervals, and then selecting set points for said pulse durations and said pulse periods during said treatment time intervals which correspond to respective ones of said saturation currents.