1. A method for heating a subsurface formation, comprising:
applying an electrical current to an elongated heater such that the heater provides an electrically resistive heat output, wherein the elongated heater comprises two or more portions along the length of the heater that have different power outputs, at least one portion of the elongated heater comprising at least one temperature limited portion with at least one selected temperature at which the portion provides a reduced heat output;
providing heat to the formation with the different power outputs such that the heater heats one or more portions of the formation at one or more selected heating rates; and
allowing the heat to transfer to a section of the formation.
2. The method of claim 1, further comprising providing time-varying electrical current to the elongated heater such that the heater operates as a temperature limited heater.
3. The method of claim 1, further comprising providing heat to the formation with the different power outputs such that at least two of the portions of the formation reach a selected temperature at approximately the same time.
4. The method of claim 1, wherein the subsurface formation comprises hydrocarbons, the method further comprising allowing the heat to transfer to the formation such that at least some hydrocarbons are pyrolyzed in the formation.
5. The method of claim 1, further comprising producing a fluid from the formation.
6. The method of claim 5, wherein the fluid comprises hydrocarbons.
7. The method of claim 6, further comprising producing transportation fuel from at least a portion of the hydrocarbons.
8. The method of claim 1, wherein the elongated heater is at least 30 m in length.
9. The method of claim 1, wherein two or more portions of the elongated heater comprise different mechanical properties such that the heater has sufficient mechanical strength to support the weight of the heater at the operating temperature of the heater.
10. The method of claim 1, wherein at least one temperature limited portion of the elongated heater comprises:
a ferromagnetic conductor; and
an outer electrical conductor electrically coupled to the ferromagnetic conductor, the outer electrical conductor at least partially surrounding the ferromagnetic conductor, wherein the outer electrical conductor provides a majority of a resistive heat output of the heater at temperatures up to approximately the selected temperature of the ferromagnetic conductor.
11. The method of claim 1, wherein the portions of the elongated heater comprise temperature limited heaters with different selected temperatures.
12. The method of claim 1, wherein the portions of the elongated heater comprise different electrical resistivities.
13. The method of claim 1, further comprising varying dimensions of the portions of the elongated heater to provide the different power outputs.
14. The method of claim 1, further comprising varying materials in the portions of the heater to provide the different power outputs.
15. The method of claim 1, wherein the portions of the formation comprise different thermal properties andor different richnesses.
16. The method of claim 1, further comprising heating at least two of the portions of the formation such that the portions reach a selected temperature at approximately the same time.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A write power adjustment method that is used to test-write a signal onto an information recording medium at a plurality of different power levels and adjust write power in accordance with read signal quality of the signal when the information recording medium is irradiated with light to write information onto the information recording medium andor read information from the information recording medium, the write power adjustment method comprising the steps of:
determining a modulation Mm from a read signal amplitude of the signal that is test-written at the plurality of different levels of write power Pwm;
setting a write power compensated value Pcn;
determining an evaluated value Smn=Mm\xd7(Pwm\u2212Pcn) from the modulation Mm and compensated write power (Pwm\u2212Pcn), which is obtained from the write power compensated value Pcn and the write power Pwm;
determining an optimum write power compensated value PcO in accordance with the relationship between the compensated write power (Pwm\u2212Pcn) and the evaluated value Smn;
determining compensated write power PthO that provides an evaluated value SmO of zero when the relationship between compensated write power (Pwm\u2212PcO) for the optimum write power compensated value PcO and the evaluated value SmO is subjected to linear approximation;
determining a write power threshold Pth by using the compensated write power PthO and the optimum write power compensated value PcO; and
determining optimum write power Popt in accordance with the write power threshold Pth.
2. The write power adjustment method according to claim 1, wherein the step of determining the optimum write power compensated value PcO includes the steps of:
determining the relationship between the compensated write power (Pwm\u2212Pcn) and the evaluated value Smn; and
determining the write power compensated value Pcn that maximizes the linearity of the relationship, as an optimum write compensated value PcO.
3. The write power adjustment method according to claim 1, wherein the step of determining the optimum write power Popt includes the step of:
calculating the optimum write power Popt by using the write power threshold Pth and the ratio \u03b1 which is set for each information recording medium between the optimum write power Popt and the write power threshold Pth.
4. The write power adjustment method according to claim 3, wherein the ratio \u03b1 between the optimum write power Popt and the write power threshold Pth is derived from control information that is written on an information recording medium.
5. A write power adjustment method that is used to test-write a signal onto an information recording medium at a plurality of different power levels and adjust write power in accordance with read signal quality of the signal when the information recording medium is irradiated with light to write information onto the information recording medium andor read information from the information recording medium, the write power adjustment method comprising the steps of:
determining an optimum write power compensated value PcO by using write power Pwm, a write power compensated value Pcn, and an evaluated value Smn derived from a modulation Mm;
determining a write power threshold Pth from the relationship to current compensated write power PthO; and
determining the optimum write power Popt by using the ratio \u03b1 written on the information recording medium between optimum write power Popt and the write power threshold Pth.
6. The write power adjustment method according to claim 5, wherein the relationship between compensated write power (Pwm\u2212Pcn), which is the difference between the write power Pwm and the write power compensated value Pcn, and the evaluated value Smn is examined to determine the optimum write power compensated value PcO from the write power compensated value Pcn that maximizes the linearity of the relationship.
7. The write power adjustment method according to claim 5, wherein the ratio \u03b1 between the optimum write power Popt and the write power threshold Pth is set for each information recording medium and prerecorded on each information recording medium.
8. The write power adjustment method according to claim 5, wherein the ratio \u03b1 between the optimum write power Popt and the write power threshold Pth is used as a predetermined value without regard to the information recording medium.
9. An optical readwrite apparatus that irradiates an information recording medium with light to write information onto the information recording medium andor read information from the information recording medium, the optical readwrite apparatus comprising:
a write power adjustment section configured to adjust write power that is used when information is to be written onto at least the information recording medium,
wherein the write power adjustment section includes
a section configured to determine a modulation Mm from a read signal amplitude of a signal that is test-written at a plurality of different levels of write power Pwm,
a section configured to determine an evaluated value Smn=Mm\xd7(Pwm\u2212Pcn) from the modulation Mm and compensated write power (Pwm\u2212Pcn), which is obtained from the write power compensated value Pcn and the write power Pwm,
a section configured to determine an optimum write power compensated value PcO in accordance with the relationship between the compensated write power (Pwm\u2212Pcn) and the evaluated value Smn,
a section configured to determine compensated write power PthO that provides an evaluated value SmO of zero when the relationship between compensated write power (Pwm\u2212PcO) for the optimum write power compensated value PcO and the evaluated value SmO is subjected to linear approximation,
a section configured to determine a write power threshold Pth by using the compensated write power PthO and the optimum write power compensated value PcO, and
a section configured to determine optimum write power Popt in accordance with the write power threshold Pth.
10. The optical readwrite apparatus according to claim 9, wherein the section configured to determine the optimum write power compensated value PcO includes:
a section configured to determine the relationship between the compensated write power (Pwm\u2212Pcn) and the evaluated value Smn; and
a section configured to determine the write power compensated value Pcn that maximizes the linearity of the relationship, as an optimum write compensated value PcO.
11. The optical readwrite apparatus according to claim 9, wherein the section configured to determine the optimum write power Popt includes:
a section configured to determine the write power threshold Pth and the ratio \u03b1 between the write power threshold Pth and the optimum write power Popt, which is set for each information recording medium.
12. The optical readwrite apparatus according to claim 11, wherein the section configured to determine the optimum write power Popt determines the optimum write power Popt from \u03b1\xd7Pth by using the ratio \u03b1 determined by the section configured to determine the ratio \u03b1.
13. The optical readwrite apparatus according to claim 12, wherein the ratio \u03b1 between the optimum write power Popt and the write power threshold Pth is determined by acquiring control information that is written on an information recording medium.
14. The optical readwrite apparatus according to claim 11, wherein the section configured to determine the ratio \u03b1 determines the ratio \u03b1 by selecting a desired ratio from a plurality of ratios related to a plurality of information recording media.
15. The optical readwrite apparatus according to claim 14, wherein the plurality of ratios are preset.