In a pair of electrode wells to be developed for injection and production wells for the electrothermal process for recovering heavy hydrocarbons, the electrodes are formed by inserting a heating device in each borehole and heating the surrounding formation to a temperature at which the hydrocarbon-containing material undergoes thermal cracking, resulting in a coke-like residue surrounding the heater. This conductive and permeable material serves as an electrode, for each well, by which the formation is heated. The heavy hydrocarbon material, such as bitumen found in tar sands, becomes mobile and can be recovered.
There is provided a well completion for electrical alternating current power transmission that minimizes power losses and related corrosion problems. Casing is used both as the electrode and conductor. Most of the conductor portion is made of nonmagnetic metal, for example aluminum, and is electrically insulated both exteriorly and interiorly. The insulation extends below the point where the nonmagnetic metal ends. Tubing is used to produce or inject fluids. The upper end of the conductor-electrode may be surrounded by a nonmagnetic surface string which is also electrically insulated.
Corrosion in well tubing strings, pipe and similar conduits may be determined by a circuit which includes a current sensitive meter and a known voltage source which is placed at selected intervals in the tubing string to make current flow measurements and voltage drop measurements between spaced apart contactors engaged with the tubing string at the selected intervals. The current flow measurements from the known source are used to determine resistance of the measured interval and voltage drop from a second source imposed on the tubing string at the surface is measured at the selected intervals to determine current flow from the second source. The differences in current flow at the selected intervals at a first measurement are compared with the differences in current flow at the same intervals at a later time to indicate any changes in current flow which may be related to corrosion in the tubing string between the intervals of measurement. The circuits may be placed in gas lift valve assemblies at spaced apart gas lift mandrels in the tubing string and signals related to current flow and voltage transmitted to the surface by stress wave telemetry or electromagnetic waves transmitted through the earth, for example. The circuits may also be interposed in selected sections of tubing spaced apart in the tubing string or on an instrument carrier apparatus which may be selectively positioned in the tubing string by a coiled tubing conveyed or wire line conveyed running tool.
The invention involves combining a plurality of vertical wells, each having a power conditioning unit located on the surface and an electrode in electrical contact with the reservoir, with a horizontal well extending through the reservoir in spaced relation to the vertical wells. The liner and tubing of the horizontal well function as the common return means for the circuit. Low frequency current is supplied to flow between the vertical and horizontal wells at adequate levels so as to cause heating in the near-wellbore regions of all the wells. Oil is produced, at the same time as electrical heating, at enhanced rates as a result.
Methods are provided that include the steps of providing wells in a formation, establishing one or more fractures (12) in the formation, such that each fracture intersects at least one of the wells (16, 18), placing electrically conductive material in the fractures, and generating electric current through the fractures and through the material such that sufficient heat (10) is generated by electrical resistivity within the material to pyrolyze organic matter in the formation into producible hydrocarbons.
A method and apparatus are provided for electrically treating an earth formation to cause changes in the permeability of the formation. An electric treatment unit includes a power supply and a power section which together supply voltage pulses of an amplitude which will cause a critical current density to flow within the formation, at which irreversible changes in formation permeability occur. A power control unit controls the pulse duration and the pulse period of the voltage pulses. The voltage pulses are applied to the formation by two electrodes which are preferably connected to respective ones of the conductive casing strings of two different wells which pass through the formation. A current sensor detects the pulsed current being applied to the formation. A programmable controller operates the power control unit such that the durations and the periods of the voltage pulses are varied during different treatment time intervals to correspond to maximum values of conductivity of a zone of the formation. The maximum values of conductivity are determined for respective ones of the time intervals by detecting values of the pulse durations and the pulse periods at which saturation currents occur within the formation, and then setting the pulse durations and the pulse periods during the time intervals to provide treatment currents which are proportionate to respective ones of the saturation currents.
