System and method for extraction of hydrocarbons by in-situ radio frequency heating of carbon bearing geological formations

Abstract

A method of producing liquid hydrocarbons from a hydrocarbon-bearing rock in situ in a geological formation begins with exploring the formation by drilling a plurality of boreholes into the formation and taking core samples of the hydrocarbon-bearing rock and at least one overburden layer. Electrical parameters of the hydrocarbon-bearing rock and the overburden layer are determined, as well as a roughness of a boundary between the hydrocarbon-bearing rock and the at least one overburden layer. These electrical parameters are used to construct a computer model of a portion of the hydrocarbon-bearing rock and at least one overburden layer, the computer model based upon modeling the formation as a rough-walled waveguide. This computer model is used to simulate propagation of radio frequency energy within the hydrocarbon-bearing rock, including simulation of radio frequency wave confinement within the hydrocarbon-bearing rock, at several frequencies and temperatures. A frequency for retorting is selected based upon simulation results. Radio frequency couplers are installed into at least one borehole in the hydrocarbon-bearing rock and driven with radio frequency energy to heat the hydrocarbon-bearing rock. As the rock heats, it releases carbon compounds and these are collected.

1 . A method of producing liquid hydrocarbons from a hydrocarbon-bearing rock in situ in a geological formation comprising:
 drilling a plurality of boreholes into the formation and taking core samples of the hydrocarbon-bearing rock and at least one overburden layer therefrom;   determining electrical parameters of the hydrocarbon-bearing rock and the overburden layer;   performing a seismic study to determine a roughness of a boundary between the hydrocarbon-bearing rock and the at least one overburden layer;   constructing a computer model of electromagnetic properties of a portion of the hydrocarbon-bearing rock and at least one overburden layer, the computer model based upon modeling the formation as a rough-walled waveguide;   using the computer model to simulate propagation of radio frequency energy within the hydrocarbon-bearing rock, including simulation of radio frequency wave confinement within the hydrocarbon-bearing rock, at a plurality of frequencies;   selecting a frequency of the plurality of frequencies;   placing a first radio frequency coupling apparatus into at least one borehole in the hydrocarbon-bearing rock;   driving the first radio frequency coupling apparatus with radio frequency energy to heat the hydrocarbon-bearing rock; and   collecting carbon compounds released from the rock.   
   
   
       2 . The method of  claim 1 , wherein the hydrocarbon-bearing rock is oil shale. 
   
   
       3 . The method of  claim 2 , further comprising:
 electromagnetically logging the boreholes to determine electrical parameters of the hydrocarbon-bearing rock and the at least one overburden layer;   and wherein determining electrical parameters of the hydrocarbon-bearing rock comprises analysis of data from the step of electromagnetically logging and data from studies of core samples at a plurality of temperatures to determine temperature dependence of the electrical parameters.   
   
   
       4 . The method of  claim 1  further comprising determining electrical characteristics of at least one underlying layer. 
   
   
       5 . The method of  claim 1  further comprising observing the formation for changes in the electrical parameters of the hydrocarbon-bearing rock, and when changes occur in the electrical parameters adjusting a parameter selected from the group consisting of a phase shift between two couplers, a frequency of the radio frequency energy, a parameter of the impedance matching circuitry, and a dimension of the radio frequency coupling apparatus in response thereto. 
   
   
       6 . The method of  claim 5  further comprising adjusting parameters of the computer model to match the changed electrical parameters and re-simulating to verify continued confinement of applied radio frequency energy within the hydrocarbon-bearing rock. 
   
   
       7 . The method of  claim 1  wherein there is a second radio frequency coupling apparatus in a second borehole in the hydrocarbon-bearing rock, and wherein the radio frequency energy applied to the second radio frequency coupling apparatus is applied at a phase offset from a phase of the radio frequency energy applied to the first radio frequency coupling apparatus; the phase offset determined to direct radio frequency energy towards a production zone of the hydrocarbon-bearing rock. 
   
   
       8 . The method of  claim 7 , wherein the phase offset is also determined to direct controlling wave direction to direct the radio frequency energy away from a freeze wall. 
   
   
       9 . The method of  claim 1 , wherein the first radio frequency coupling apparatus comprises a first and a second dipole coupling element, and wherein the first and the second dipole coupling element are driven to produce a pattern of radiation into the hydrocarbon-bearing rock that is vertically narrower than a pattern produced by a dipole such that electromagnetic radiation strikes the boundary between the hydrocarbon-bearing rock and the layer of overburden primarily at an angle where it will be reflected back into the formation. 
   
   
       10 . The method of  claim 1 , wherein the first radio frequency coupling apparatus comprises a radiator rod coupled to the center conductor of a coaxial transmission line, and a plurality of radial groundplane rods coupled to the outer conductor of the coaxial transmission line. 
   
   
       11 . A system for extracting marketable hydrocarbons from a carboniferous formation covered by an overburden layer, comprising:
 at least one radio frequency source;   at least one coupler for coupling radio frequency energy from the radio frequency source into a heated zone of the carboniferous formation;   wherein the radio frequency source operates at a frequency chosen to provide deep penetration of radio frequency energy into the carboniferous formation and chosen such that a high percentage of radio frequency energy striking a boundary between the carboniferous formation and the overburden layer is reflected back into the carboniferous formation.   
   
   
       12 . The system of  claim 11  wherein the frequency is further chosen by:
 determining electrical properties of the carboniferous formation at various temperatures;   using the electrical properties of the carboniferous formation in a cole-cole model of absorption to model penetration of the radio frequency energy into the carboniferous formation, and choosing the frequency such that adequate penetration is obtained.   
   
   
       13 . The system of  claim 12 , wherein the frequency is further chosen by:
 determining electrical properties of the overburden layer;   using the electrical properties of the overburden layer and the carboniferous formation in a model of a boundary of the overburden layer and the carboniferous formation, the model of the boundary modeling the boundary as a rough-walled waveguide and being used to choose a frequency where a majority of radio frequency energy from the carboniferous formation that strikes the boundary is reflected back into the carboniferous formation.   
   
   
       14 . The system of  claim 11 , wherein the coupler comprises a plurality of groundplane rods driven radially outwards into a boundary between the overburden layer and the carboniferous formation, and a coupling rod. 
   
   
       15 . The system of  claim 11 , wherein the coupler comprises a colinear plurality of center-fed, half-wave, dipoles. 
   
   
       16 . The system of  claim 11 , further comprising a freeze-wall surrounding the heated zone of the carboniferous formation. 
   
   
       17 . The system of  claim 16 , wherein there are a plurality of couplers and wherein a first coupler of the plurality of couplers is driven with radio frequency energy at a phase offset from a second coupler of the plurality of couplers to direct radio frequency energy into a heated zone and away from the freeze wall. 
   
   
       18 . The system of  claim 11 , further comprising means for selectively allocating power from the RF source to a plurality of discrete zones in the carboniferous formation.