Heating tar sands formations to visbreaking temperatures
Methods for treating a tar sands formation are described herein. Methods may include heating at least a section of a hydrocarbon layer in the formation from a plurality of heaters located in the formation. The heat may be controlled so that at least a majority of the section reaches an average temperature of between 200° C. and 240° C., which results in visbreaking of at least some hydrocarbons in the section. At least some visbroken hydrocarbon fluids may be produced from the formation.
1. A method for treating a tar sands formation, comprising:
heating at least a section of a hydrocarbon layer in the formation from a plurality of heaters located in the formation;
controlling the heating so that at least a majority of the section reaches an average temperature of between about 200° C. and about 240° C. resulting in visbreaking of at least some hydrocarbons in the section;
maintaining a pressure in the section below a fracture pressure of the section and within about 1 MPa of the fracture pressure of the section; and
producing at least some visbroken hydrocarbon fluids from the formation.
2. The method of claim 1 , wherein the average temperature is between about 205° C. and about 230° C.
3. The method of claim 1 , wherein the fracture pressure of the section is between about 2000 kPa and about 15000 kPa.
4. The method of claim 1 , wherein maintaining a pressure in the section comprises removing at least some fluids from the section.
5. The method of claim 1 , further comprising operating the heaters at substantially full power until the portion of the formation reaches the average temperature of between about 200° C. and about 240° C.
6. The method of claim 1 , wherein the liquid hydrocarbon portion of the produced fluids has a viscosity of at most about 350 cp, the viscosity being measured at 1 atm and 5° C.
7. The method of claim 1 , wherein the liquid hydrocarbon portion of the produced fluids has an API gravity between 7° and 19°.
8. The method of claim 1 , wherein the liquid hydrocarbon portion of the produced fluids has an API gravity of at least 15°, a viscosity of at most 350 cp wherein viscosity is measured at 1 atm and 5° C., a P-value of at least 1.1, wherein P-value is determined by ASTM Method D7060, and a bromine number of at most 2%, wherein bromine number is determined by ASTM Method D1159 on a hydrocarbon portion of the produced fluids having a boiling point below 246° C.
9. The method of claim 1 , further comprising varying the amount of mobilized hydrocarbons and/or visbroken hydrocarbons produced from the formation to vary a quality of the fluids produced from the formation and/or to vary the total recovery of hydrocarbons from the formation.
10. The method of claim 1 , further comprising controlling the temperature and the pressure in at least a portion of the section such that (a) at least a majority of the hydrocarbons in the section are visbroken, (b) the pressure is below the fracture pressure of the portion of the section, and (c) at least some hydrocarbons in the portion of the section form a fluid comprising visbroken hydrocarbons that can be produced through a production well.
11. The method of claim 1 , wherein superposition of heat from the plurality of heaters heats a majority of the section.