Wind-heated molten salt as a thermal buffer for producing oil from unconventional resources

Abstract

Embodiments of the present invention relate to heat transfer fluids (e.g. molten-salt) as a thermal buffer for heating, by thermal energy derived from wind-generated electricity, at least one of (i) a subsurface hydrocarbon-containing formation or (ii) a bed of hydrocarbon-containing rocks. During times when wind is plentiful, wind electricity is used to heat the heat transfer fluid—e.g. by means of an electrically resistive heater immersed in the heat transfer fluid. At any time, thermal energy from the wind electricity may be transferred to the hydrocarbon-containing rocks or subsurface formation by the heat transfer fluid. In some embodiments, the fluid is heated both by wind-generated electricity and by solar radiation. Some embodiments relate to a subsurface molten salt heater (e.g. powered by wind-generated electricity) having a non-thermally insulation portion through which molten salt flows. The heater is configured to maintain a temperature of the circulating molten salt, throughout the substantially non-thermally-insulated portion, at a temperature significantly above a melt temperature of the molten salt.

What is claimed is: 
     
         1 . A system for heating a subsurface formation comprising:
 a. an insulated storage tank and a quantity of heat transfer fluid disposed therein, at least one electrically resistive heater(s) situated within the storage tank and immersed within the heat transfer fluid;   b. a source of wind electricity configured to supply electrical power to the immersed resistive heater(s) so as to heat the heat transfer fluid within the storage tank; and   c. a flow system configured to force the wind-electricity-heated heat transfer fluid received from the storage tank: (i) to flow within subsurface conduits situated within the formation so as to heat the formation and; and (ii) to return to the storage tank for reheating.   
     
     
         2 . The system of  claim 1 , further comprising a fuel-burning furnace configured to further heat the heat transfer fluid as it flows from the storage tank to the subsurface conduits. 
     
     
         3 . The system of any of  claims 1 - 2  wherein the heat transfer fluid is molten salt. 
     
     
         4 . The system of any of  claims 1 - 2  wherein the heat transfer fluid is synthetic oil. 
     
     
         5 . The system of any of  claims 1 - 2  wherein the heat transfer fluid is a supercritical fluid. 
     
     
         6 . A system for production of hydrocarbon fluids comprising:
 a. an insulated storage tank and a quantity of heat transfer fluid disposed therein, at least one electrically resistive heater(s) situated within the storage tank and immersed within the heat transfer fluid;   b. a bed of hydrocarbon-containing rocks situated within an enclosure, the storage tank being located outside of the enclosure;   c. a source of wind electricity configured to supply electrical power to the immersed resistive heater(s) so as to heat the heat transfer fluid within the storage tank; and   d. a flow system configured to force the wind-electricity-heated heat transfer fluid received from the storage tank: (i) to flow within conduits in thermal communication with the rocks of the bed so as to heat the rocks; and (ii) to return to the storage tank for reheating.   
     
     
         7 . The system of  claim 6  wherein the conduits pass through rocks of the rock-bed. 
     
     
         8 . The system of any of  claims 6 - 7  wherein the conduits are embedded within a wall or floor of the enclosure. 
     
     
         9 . The system of any of  claims 6 - 8  wherein the enclosure is an excavated enclosure. 
     
     
         10 . The system of  claim 9  the excavated enclosure is a pit or an impoundment. 
     
     
         11 . The system of any of  claims 6 - 10 , further comprising a fuel-burning furnace configured to further heat the heat transfer fluid as it flows from the storage tank to the subsurface conduits. 
     
     
         12 . The system of any of  claims 6 - 11  wherein the heat transfer fluid is molten salt. 
     
     
         13 . The system of any of  claims 6 - 11  wherein the heat transfer fluid is synthetic oil. 
     
     
         14 . The system of any of  claims 6 - 11  wherein the heat transfer fluid is a supercritical fluid. 
     
     
         15 . The system of any of  claims 5 - 14 , further comprising a fuel-burning furnace configured to further heat the heat transfer fluid as it flows from the storage tank to the conduits in thermal communication conduits in thermal communication with the rocks of the bed. 
     
     
         16 . The system of any previous claim further comprising a solar furnace, the flow system and the solar furnace being configured so that heat transfer fluid received directly or indirectly from the storage tank is (i) directly or indirectly heated by the solar furnace and (ii) forced to directly or indirectly return to the storage tank. 
     
     
         17 . A solar-wind integrated system for heating hydrocarbon-containing matter, the system comprising:
 a. a flow system configured to force a heat transfer fluid to flow through subsurface conduits that are (i) located within and in thennal communication with a hydrocarbon-containing subsurface formation or (ii) in thermal communication with a bed of hydrocarbon-containing rocks situated within an enclosure;   b. a solar furnace configured to configured re-direct concentrated solar radiation onto the heat-transfer fluid or onto an auxiliary fluid in thermal communication therewith so that at least some energy of the solar radiation is transferred to the subsurface or to the hydrocarbon-containing rocks by the heated, flowing heat-transfer fluid; and   c. a wind-electricity heating apparatus configured to resistively heat the heat-transfer fluid by wind energy so that at least some energy of wind energy is transferred to the subsurface by the heated, flowing heat-transfer fluid   
     
     
         18 . The system of  claim 17  wherein the wind-electricity heating apparatus comprises (i) an electrically-conductive element(s) in thermal communication with the heat transfer fluid; and (ii) a source of wind-electricity configured such that electrical current received therefrom is forced through the electrically-conductive element and converted into thermal energy which is transferred to the heat transfer fluid. 
     
     
         19 . The system of any of  claims 17 - 18  wherein the heat transfer fluid is molten salt. 
     
     
         20 . The system of any of  claims 17 - 18  wherein the heat transfer fluid is synthetic oil. 
     
     
         21 . The system of any of  claims 17 - 18  wherein the heat transfer fluid is a supercritical fluid. 
     
     
         22 . The system of any of  claims 16 - 21  wherein the solar furnace includes a solar receiver located or a near the top of a centralized tower through which the heat transfer fluid or the auxiliary fluid flows and a plurality of heliostats aimed at the centralized tower. 
     
     
         23 . The system of any of  claims 16 - 21  wherein the solar thermal heating system includes at least one of a solar parabolic trough and a solar parabolic dish. 
     
     
         24 . The system of any preceding claim wherein the source of wind electricity includes one or more wind turbine(s). 
     
     
         25 . The system of any previous claim wherein the flow system includes one or more pump(s). 
     
     
         26 . Use of the system of any of preceding claim to produce hydrocarbon fluids by pyrolyzing kerogen or bitumen or by mobilizing bitumen. 
     
     
         27 . A method of allocating wind electricity to an integrated wind-solar thermal apparatus for heating a subsurface formation, the method comprising:
 a. heating a heat transfer fluid by solar thermal means;   b. convectively heating a subsurface formation by circulating solar-thermal heated heat transfer fluid in a closed-loop through the formation; and   c. resistively heating, by locally-generated wind electricity, an electrically conductive material(s) in thermal communication with the subsurface formation and/or with the heat transfer fluid so as to heat the subsurface formation.   
     
     
         28 . The method of  claim 27  further comprising:
 c. monitoring respective power-level indicators of local generation of wind electricity and of the solar-thermal-heating of the heat transfer fluid; and 
 d. responsive to the monitoring, allocating a first portion of locally-available wind electricity to the resistive heating of the electrically conductive material and a second portion of the locally-available wind electricity for remote power transmission. 
 
     
     
         29 . An integrated wind-solar thermal system for heating a subsurface formation, the system comprising:
 a. a solar thermal apparatus operative to heat a heat transfer fluid;   b. a heat transfer fluid circulation apparatus configured to force the solar-thermal-apparatus-heater heat transfer fluid to flow through a closed loop embedded in the subsurface formation;   c. a source of locally generated wind electricity operative to resistively heat an electrically conductive element(s) so as to supply thermal energy to the subsurface formation directly and/or indirectly via the flowing heat transfer fluid;   d. a controller operative to allocate at least a first portion of the locally generated wind electricity to the resistive heating and to remotely transmit a second portion of the locally generated wind electricity, the controller being further operative to:
 i. monitor respective power-level indicators of local generation of wind electricity and of the solar-thermal-heating of the heat transfer fluid; 
 ii. responsive to the monitoring, modifying relative fractions of the locally-generated wind electricity that are allocated to the resistive heating and to the remote transmission. 
   
     
     
         30 . An apparatus for heating a subsurface formation, the apparatus comprising:
 a. a subsurface molten salt heater including a substantially non-thermally-insulated portion within the subsurface formation through which molten salt flows so as to heat the subsurface formation primarily by convective heat transfer,   b. a molten salt circulation system configured to supply molten salt to and to receive returning molten salt from the subsurface molten heater so as to form a closed flow loop; and   c. an electrical power source configured to electrically-resistively heat an electrically conductive element(s) arranged within the subsurface molten salt heater to indirectly heat the circulating molten salt,   the electrical power source and the electrically conductive element being configured to maintain a temperature of the circulating molten salt, throughout the substantially non-thermally-insulated portion, at a temperature significantly above a melt temperature of the circulating molten salt.   
     
     
         31 . An apparatus for heating a subsurface formation, the apparatus comprising:
 a. a subsurface molten salt heater including a substantially non-thermally-insulated portion within the subsurface formation through which molten salt flows so as to heat the subsurface formation primarily by convective heat transfer;   b. a molten salt circulation system configured to supply molten salt to and to receive returning molten salt from the subsurface molten heater so as to form a closed flow loop; and   c. an alternating current electrical power source configured to electrically-resistively heat an electrically conductive element(s) arranged within the subsurface molten salt heater to indirectly heat the circulating molten salt;   the electrical power source and the electrically conductive element being configured to maintain a temperature of the circulating molten salt, throughout a majority of the substantially non-thermally-insulated portion, within a substantially constant set-point temperature range having a lower bond that is significantly above a melt temperature of the circulating molten salt.   
     
     
         32 . An apparatus for heating a subsurface formation, the apparatus comprising:
 a. a subsurface molten salt heater including a substantially non-thermally-insulated portion within the subsurface formation through which molten salt flows so as to heat the subsurface formation primarily by convective heat transfer,   b. a molten salt circulation system configured to supply molten salt to and to receive returning molten salt from the subsurface molten heater so as to form a closed flow loop; and   c. an alternating current electrical power source configured to electrically-resistively heat an electrically conductive element(s) arranged within the subsurface molten salt heater to indirectly heat the circulating molten salt;   the electrical power source and the electrically conductive element being configured to maintain a temperature of the circulating molten salt, throughout a majority of the substantially non-thermally-insulated portion, within a substantially constant set-point temperature range having a lower bond that is significantly above a melt temperature of the circulating molten salt.   
     
     
         33 . An apparatus for heating a subsurface formation, the apparatus comprising:
 a. a subsurface molten salt heater configured to heat the subsurface formation primarily by convective heat transfer from molten salt circulating therein to the subsurface formation,   b. a molten salt circulation system configured to supply molten salt to and to receive returning molten salt from the subsurface molten heater so as to form a closed flow loop; and   c. an electrical power source configured to electrically-resistively heat an electrically conductive element(s) arranged within the subsurface molten salt heater to indirectly heat the circulating molten salt,   the apparatus being configured such that:
 i. the circulation system provides a sufficient molten salt flow rate so that, in the absence of the resistive heating, a temperature difference between molten salt at upstream and downstream subsurface heater locations due to the convective heat transfer from the circulating molten salt to the formation is significant; 
 ii. the electrical power source and the electrically conductive element are configured to deliver sufficient thermal energy to the circulating molten salt so as to maintain the upstream, downstream and a majority of intervening locations at substantially the same set-point temperature. 
   
     
     
         34 . The apparatus of any of  claims 30 - 33  wherein:
 i. the apparatus is configured to heat the subsurface formation such that first and
 second thermal energy fractions are respectively delivered to the subsurface formation from the circulating molten salt by enthalpy of the supplied molten salt entering the subsurface molten salt heater and by the resistive heating of the molten salt within the subsurface heater; and 
 
 ii. each of the first and second fractions exceeds 0.1. 
 
     
     
         35 . The apparatus of any of  claims 30 - 33  wherein the substantially constant set-point temperature exceeds the melt temperature by at least 150 degrees Celsius. 
     
     
         36 . The apparatus of any of  claims 30 - 35  wherein the system is configured such that:
 i. an amount of thermal energy convectively transferred to the subsurface formation by circulating molten salt en route from an upstream location to a downstream location equals at least 20% of the liquid-phase enthalpy of the molten salt at the upstream location; 
 ii. the electrical power source and the electrically conductive elements are operative to maintain the molten salt for a majority of locations between the upstream and downstream location, substantially at the set-point temperature. 
 
     
     
         37 . The apparatus of any of  claims 30 - 36  wherein the subsurface heater is an L-shaped heater, a U-shaped heater, a horizontally-oriented heater, a vertically-oriented heater and/or a slant-oriented heater. 
     
     
         38 . The apparatus of any of  claims 30 - 36  wherein the electrically conductive element includes a ferromagnetic material having a Curie temperature substantially equal to the set-point temperature and/or significantly exceeding the molten salt melt temperature. 
     
     
         39 . The apparatus of any of  claims 30 - 38  wherein the subsurface heater has a conduit-in-conduit structure defining nested inner and outer flow regions such that:
 i. in the inner flow region, molten salt longitudinally flows in a first direction; 
 ii. in the annular-shaped outer region, molten salt longitudinally flows in the opposite direction. 
 
     
     
         40 . The apparatus of any of  claims 30 - 39  wherein the subsurface molten salt heater is configured to heat at least a portion of the subsurface formation by at least 100 degrees Celsius.