Active cable for wellbore heating and distributed temperature sensing

A wellbore heating apparatus comprising:

• a cable comprising one or more loops of electrical conductor running the length of the cable;
• control equipment for controlling heating of the wellbore by supplying a designed range of currents to the loops of electrical conductor, the currents creating heat within the loops of electrical conductor, the heat being dissipated into the surrounding wellbore structure and into the surrounding formations along the length of the cable;
• an upper section wherein the electrical conductors are sized, insulated and applied at a lay angle such that they dissipate a low amount of heat when a designed range of current is applied;
• and
• a lower section wherein the electrical conductors are sized, insulated and applied at a lay angle that is higher than the lay angle of the conductors in the upper section such that they dissipate a large amount of heat compared with the upper section when the designed range of current is applied, wherein the electrical conductors in the lower section have an electrical resistivity of between 10 and 100 times greater than the electrical resistivity of the electrical conductors in the upper section.

A wellbore heating apparatus comprising:

• a cable comprising one or more loops of electrical conductor running the length of the cable;
• and
• control equipment for controlling heating of the wellbore by supplying a designed range of currents to the loops of electrical conductor, the currents creating heat within the loops of electrical conductor, the heat being dissipated into the surrounding wellbore structure and into the surrounding formations along the length of the cable, wherein the one or more loops of electrical conductors comprises:
• an outer layer of electrical conductors for carrying an electrical current down the cable;
• and
• an inner layer of electrical conductors for carrying the current up the cable, said inner layer of electrical conductors being sized, insulated and applied at a lay angle such that they dissipate a low amount of heat when a designed range of current is applied.