Patent Application
20120012319
There are a number of techniques used to stimulate or enhance production of hydrocarbons from wells by increasing the permeability of the formation outside the wellbore. The most well-known and widely used approach is hydraulic fracturing of the formation to increase permeability. In-situ heating of hydrocarbon bearing formations has also been used to address production problems relating to fluids in the reservoir rock and the production equipment, such as deposition of wax and asphaltene materials, creation of water and oil emulsion, fluid invasion resulting in clay swelling and fines migration. However, thermal stimulation of a formation can also be used to fracture the formation through thermal expansion of materials comprising the formation, as well as to improve fluid flow characteristics of near-wellbore porous regions by reducing the viscosity of the oil, preventing or removing waxes or asphaltenes build-up in the wellbore and near-wellbore region, preventing formation of hydrates and dehydrating clay.
The invention pertains, generally, to stimulating production of hydrocarbons from a well by lowering a downhole tool into a wellbore to generate microwave radiation for heating.
A first, exemplary embodiment of a downhole tool comprises a microwave generator positioned for generating microwave radiation and a transmission line for carrying microwave electromagnetic energy from the generator towards a microwave absorbable material disposed within a head portion of the tool. After the tool is lowered into the borehole using jointed pipe or coiled tubing, electric energy is supplied to the microwave generator, causing microwave radiation to be generated. This radiation is directed to, and absorbed by, the microwave absorbable material causing it to heat. The thermal energy is transferred to fluids in the borehole through thermal conduction, and then to the adjoining formation.
A second, exemplary embodiment of such a downhole tool comprises a microwave generator and a transmission line that carries the microwave electromagnetic energy from the generator toward a head, at least a portion of which is made from microwave transparent material. The microwave radiation travels through the head and then is radiated from an antenna so that microwave absorbable materials within fluids within the wellbore and/or surrounding hydrocarbon-bearing formation absorb the microwave radiation. The microwave radiation absorbed by the well fluid and/or the microwave absorbable material within the rock formation results in heating of the rock formation. The head may optionally include a reflecting element for directing or focusing the radiation, or for scattering the radiation.
According a method for using the tool, the tool is lowered into the borehole to the desired position, and the microwave generator is turned on to generate microwave electromagnetic energy that is transmitted toward the head of the tool. Optionally, drilling fluid to which microwave absorbable material has been added is circulated into the wellbore so that the microwave radiation heats the microwave absorbable material. Depending on the formation and how the downhole is used, the heating stimulates flow of hydrocarbons by either reducing its viscosity or causing thermal expansion that leads to fracturing of the formation.
In the following description, like features or elements are marked throughout the specification and drawings with the same reference numerals, respectively.
Referring to
A controller 114 controls operation of the tool. One example of a controller comprises a circuit that turns power to the tool on or off, or that changes the voltage and/or current of the electricity being supplied to the tool. Another example is a circuit that generates and transmits to the downhole tool control signals understood by a controller within the downhole tool, which in turn causes the tool to operate or to stop operation, or to change an operational characteristic. The signals can be transmitted, for example, over cable 110, another wire that runs to the downhole tool from the surface, the continuous tubing or jointed pipe that lowers the tool into the hole, or using RF communication methods. The controller may also include logic implemented using just hardware or a combination of hardware and software (for example a specially programmed processor) for performing one or more predetermined or programmed control processes.
Drilling fluid from a source 116 on the surface supplies fluid containing microwave absorbable compounds. The fluid can be drilling fluid to which such compounds have been added. The fluid can be pumped down continuous tubing or joined pipe inserted into the bore hole prior to the tool 100 being lowered into the bore hole, or while the tool is in the bore hole by, for example, pumping fluid through the tubing or pipe to which the tool is connected and having the fluid exit openings into the bore hole above or in the tool.
Enclosed within the body is at least one microwave generator 206 and a waveguide 208 for transmitting microwaves from the generator to head 210 (for the embodiment of
The microwave generator may take the form of, for example, a magnetron, a klystron or a travelling tube. It could, alternatively, utilize solid state devices rather than vacuum tubes. The generator 206 that is schematically illustrated includes additional elements such as a power supply for rectifying and stepping up voltage, an adaptor for coupling the generator to the waveguide, an isolator for preventing reflected microwave energy from entering the generator, and a controller and other instrumentation for controlling and/or monitoring the operation of the generator. The body can also house other auxiliary equipment, such as instrumentation for reporting the temperature of various parts of the generator and the head. The generator may be tuned to operate at standard frequencies set aside for industrial application or scientific applications, such as 915 MHz, 2.45 GHz, 5.8 GHz and 22.125 GHz. However, it could be tuned to a frequency within the microwave range of 300 MHz to 300 GHz. The frequency being chosen depending at least in part on the material that is intended to be heated by the microwave energy from the generator.
In the embodiment of
Referring only to
In the example of
Microwave energy transmitted from the waveguide 208 is coupled to the microwave absorbable elements 214 by an applicator, which is generally indicated by reference number 216. Although the illustrated applicator comprises a feed horn, it is intended only to be representative. Other types of applicators could be utilized, including resonant, travelling-wave and near-field applicators. Near-field applicators include open-ended waveguides, slotted waveguides and antennas. An applicator may extend into the head, depending on the type of applicator utilized. In the case of a resonant applicator, a resonant cavity can be, for example, formed within the head 210 and coupled with the waveguide. The cavity could resonate in a single mode or a multi-mode.
Referring to
The foregoing description is of an exemplary and preferred embodiments employing at least in part certain teachings of the invention. The invention, as defined by the appended claims, is not limited to the described embodiments. Alterations and modifications to the disclosed embodiments may be made without departing from the invention. The meaning of the terms used in this specification are, unless expressly stated otherwise, intended to have ordinary and customary meaning and are not intended to be limited to the details of the illustrated structures or the disclosed embodiments.
