Abstract

A major challenge to production and stimulation is to send heat from the surface to the reservoir to reduce the oil viscosity. While steam injection is recognized as an efficient way to do so, to meet this expectation, Majus has developed the TOR technology. The aim is to improve the productivity of a well and to increase the recoverable reserves by sending heat into the reservoir by conduction with limited energy consumption and limited CAPEX. This is made possible with the use of a highly insulated coiled tubing which links the surface equipments to the downhole production drain.

The usual fluid to convey energy is water heated and sent in the reservoir as steam to heat by convection. As mentioned in many papers, the technologies such as Huff‘n’Puff and SAGD show generally good results but there are some issues related to these technologies. Amongst them, the quantity of energy and water required and the need to treat the liquid produced. These are alleviated with this new system. The paper will present the innovative completion design, the fabrication process, the installation phase and the first results when applied on a horizontal well on a field in the Sultanate of Oman where the production increased more than threefold to reach 300 b/d. In a second part we will try to identify the typical wells where the process should give the same positive results.

Thermal considerations

In order to help the heavy oil flowing, the industry usually chooses to heat the reservoir. The advantages and problems of the different existing heating methods are well known.

Heating the reservoir the way the electrical heaters do has the following main benefits:

  • Possibility of designing light units amenable on any heavy oil field

  • No water required

  • No extra water separation required

  • Most efficient way of using the energy being next to the wellbore

  • Possibility of combining the technology with other technologies to enhance heavy oil productions

However, for an effective conduction heating, a good order of magnitude for the power input is in the range of 100W/m of horizontal perforated drain length and heating up the production drain at about 200°C. With the relatively small velocities in the production conduits, the heat exchange coefficient between the oil and the conduits is lower than 5 W/m²/K and the exchange surfaces are in the range of 0.2 m²/m, therefore if a heating element is introduced in the productive drain, its temperature must have a temperature differential with the drain of at least 150°C which means bringing the heating element at about 250°C which is already quite high for an electrical element especially on a long term basis.

On top of that, knowing accurately the thermal resistance of the ground is quite unpredictable and can generate very high temperatures for the heating elements. If the resistance is longitudinally homogeneous, the power dissipated linearly is quite constant too, therefore if the thermal resistance of the ground changes sharply along the drain length, the temperature temperature differential between the heating element and the ground will change with the same ratio. This could imply extremely high temperatures.

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