Patent Application
20150267522
The present invention is directed to Steam Assisted Gravity Drainage (SAGD) in general, and, more particularly, to the use of electrical heating elements to both reduce the start-up time of a SAGD operation and control the amount of heat (thermal energy) used in start-up based on the particular characteristics of a SAGD reservoir. The electrical heating elements may be retained in the injection well after start-up is complete and during normal SAGD operations.
Alberta, Canada has some of the world's largest deposits of oils sands. Oil sands are a mixture of sand, water and bitumen, a type of heavy oil that is very thick and thus difficult to flow on its own. Bitumen can be extracted from oil sand by mining oil sands and extracting the bitumen with either hot water or solvents. However, over 80% of oil sands deposits in reservoirs contain oil that is deeper than 75 meters below the earth's surface, making it very difficult to mine.
Thus, a number of in situ methods for extracting bitumen from oil sands have been developed. One of these methods, Steam Assisted Gravity Drainage (SAGD) has proven to be very reliable. Generally, SAGD involves drilling two horizontal, parallel wells (well pairs), a top injector well for injecting steam for reducing the viscosity of the bitumen and a bottom producer well to collect the reduced viscosity bitumen which is lifted to the surface. Start-up generally involves a pre-heating stage, wherein steam is injected into the injector well, or circulated through both the injector well and the producer well, with the aim of establishing thermal communication between the well pair.
However, the pre-heating stage can take several months before thermal communication is established between the well pair and the production of bitumen can begin. Thus, there is a need in the industry for a method to reduce the pre-heating time necessary to establish thermal communication between the SAGD well pair.
Furthermore, there may be some instances where there exists permeability barriers in sections of the formation surrounding either the injector well, the producer well, or both. Establishing a desireable thermal communication profile between the well pair may be difficult due to the presence of these permeability barriers. In these instances, the pre-heating time may be even greater, as it will take more energy (steam) and time to establish the micro-channels in these permeability barriers which are necessary for fluid to flow during the steam injection and production processes. Thus, there is a need in the industry for a method to also be able to control the amount of heat (thermal energy) used in given areas of the wells in order to also conserve on the energy used during pre-heating of a SAGD well pair.
The current application is directed to a method for decreasing the start-up time for a SAGD well pair, with the added flexibility of being able to control the amount of heat (thermal energy) used in start-up by controlling the amount of heat used to heat up a given area of the SAGD wells in order to conserve on the energy. It was discovered that by conducting the method of the present invention, one or more of the following benefits may be realized:
(1) Less time is needed to establish initial thermal communication between a pair of SAGD wells.
(2) Less energy in the form of steam is required to establish initial thermal communication between a pair of SAGD wells.
(3) The pre-heating process could be accompanied by fluid injection for enhancing the heat transfer efficiency.
(4) The material of the electro-thermal heating element used in the present invention may be selected for proper heat-capacity and thermal conductivity so that increasing and decreasing temperature (heating and cooling processes) occurs in a timely manner as required.
(5) The electro-thermal heating element can comprise one or more individually controllable heating sections which sections can be placed in either the injector well, producer well, or both, at sectors of the well where it is difficult for the steam to reach, e.g., a permeability barrier or localized water pocket.
(6) The electro-thermal heating element can comprise one or more individually controllable heating sections which sections can be placed in either the injector well, producer well, or both, to preferentially heat the higher bitumen-saturation zones and to preferentially avoid heating the lower bitumen-saturated zones.
(7) The electro-thermal heating element can comprise a plurality of individually controllable heating sections, whereby the temperature of each section can be separately controlled and may be switched on/off so that a desired pre-heating temperature profile in the reservoir can be achieved.
(8) The present invention can be used together with a solvent, a surfactant or other additive which changes the wettability or reduces the viscosity of the bitumen present in the oil sand reservoir.
Thus, in one aspect, a method for pre-heating a SAGD operation is provided, comprising:
It is understood that proper casing and well-completion is adopted to accommodate the high temperature source of the present invention. In one embodiment, the at least one individually controllable heating section is positioned at the toe of the injector well, the producer well, or both. In another embodiment, the at least one individually controllable heating section is positioned at or near the middle of the injector well, the producer well, or both. In one embodiment, steam is also circulated through the injector well, the producer well, or both.
Following the pre-heating stage, the electro-thermal heating element that is placed in or near the injector well may be left down hole. Thus, when the steam injection into the injector well commences during the steam assisted gravity drainage process, the electro-thermal heating element can assist in controlling the quality of steam in the injector well. For example, steam often condenses at the toe of the well. Thus, the electro-thermal heating element may comprise an individually controllable heating section that is positioned at the toe of the well. It is understood, however, that, in most instances, it is generally undesirable to leave an electro-thermal heating element in the producer well and, hence, the element should be removed prior to commencing the SAGD process. Thus, it is understood that in one embodiment, the electro-thermal heating elements are removable.
In one embodiment, the electro-thermal heating element comprises a plurality of individually controllable heating sections so that more heat can be provided to one or more specific sections of either the injector well, the producer well, or both, for example, those sections having poor permeability issues or other undesirable reservoir conditions, than other sections of either the injector well, the producer well, or both. In one embodiment, the electro-thermal heating element can be wrapped around the outside of the injector tubing, or liner, of the injector well, the producer tubing of the producer well, or both. Thus, depending on thermal properties of the formation, i.e., heat capacity, thermal conductivity, thermal expansion, and coefficient, an electro-thermal heating element comprising individually controllable heating sections of varying temperatures may be deployed along the injection well, the production well or both to achieve the desired (e.g., uniform) thermal pattern.
In one embodiment, the electro-thermal heating elements can be controlled from surface of the SAGD and each individually controllable heating section can be separately controlled by controlling or adjusting the current passing through the element and to the individual controllable heating section. In one embodiment, each individually controllable heating section of the electro-thermal heating element has its own thermocouple, DTS sensor, or similar, for measuring the temperature and adjusting the temperature of each section accordingly.
It is further contemplated to use this technique for infill wells between the SAGD well pairs. The invention will allow for the faster communication of the infill well to steam chambers so that production of the infill well can begin sooner than would be possible without this technique.
In one embodiment, a solvent, a surfactant or other additive which changes the wettability or reduces the viscosity of bitumen is added to either the injector well, the producer well, or both, either prior to or during pre-heating. By being able to control the temperature of individual sectors of a well, one can also control how much solvent or other wettability additive will diffuse into the formation at a particular sector. Useful solvents can be hydrocarbon solvents such as naphtha, butane, propane and the like. It is understood, however, that non-hydrocarbon solvents could also be used.
Surfactants that could be used in this process could be either non-ionic surfactants such as some alcohols (e.g., fatty, cetyl, stearyl) or ionic surfactants such as sulfates, sulfonates, phosphates or carboxylates. Generally, many ionic surfactants are not preferable, due to potential implications downstream in the refining process, but bitumen does have some natural carboxylates that could be enhanced biologically, using the same microbes that are used to help clean up oil spills. In another embodiment, depending on reservoir conditions, surfactants having cationic head groups such as primary, secondary and tertiary amines, which are pH dependent, or quaternary ammonium cations can be used. The mineral characteristics of the reservoir should be taken into account in all cases when choosing a surfactant.
Thus, the present invention reduces the circulation time of steam in traditional SAGD operations by reducing the start-up time from a few months to a few weeks. In particular, a midpoint temperature between the injector well and the producer well of 70-195° C. may be reached within 60 days or less. In one embodiment, the electro-thermal heating element comprises an electrical cable, such as an ESP cable, at least one temperature gauge and the at least one heating section comprises an electro-thermal heating cable. In another embodiment, the heating sections are spaced along the electrical cable.
Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
In conventional SAGD, the injector well 20 injects steam to heat the space between and above the two wells and establish thermal communication between the two wells. With continuous injection of steam, hydrocarbon (e.g., bitumen) present in the pay zone 14 is heated, mobilized and collected in producer well 22.
In the embodiment of
A power supply and control system 50 can control the temperature of each individually controllable heating section 40, 42 by increasing/decreasing the amount of current through electrical cables 46, 48, respectively. For example, the sector of the pay zone surrounding the individually controllable heating section 40 may be a sector of the well where it is difficult for the steam to reach, e.g., it is near a permeability barrier. Therefore, while individually controllable heating section 40 will eventually heat up the entire area surrounding the horizontal leg 26, the majority of the heat is initially focused on the area within the permeability barrier. In this way, energy can be used in the most efficient way possible to form the thermal communication between the two wells.
In the embodiment of
By way of example, in the injector well 220, three of the individually controllable heating sections 240a, 240b and 240c (i.e., closest to the toe 228) may be operated at a much higher temperature than the two individually controllable heating sections 240d and 240e. This would be due to the fact that the sectors of pay zone 214 surrounding horizontal section 226 has a variable geological profile along its width, with the right half having a lower permeability than the left half. However, with respect to the producer well 222, the pay zone 214 surrounding the horizontal section 234 is much more uniform. Thus, individually controllable heating sections 242a, 242b, 242c, 242d and 242e are all operated at the same temperature, albeit at a higher temperature that the two left individually controllable heating sections 240d and 240e of injector well 220, as the permeability is lower in the area surround the horizontal section 234 of the producer well 222 than that surrounding the left half of the horizontal section 226 of the injector well 220.
Thus, with the embodiment shown in
With reference now to
Electrical elements of approximately 100 m were installed at the toe of the injector only or at the toes of both injector and producer of a SAGD well pair. Generally, circulation start up involves establishing inter well communication by circulating steam through the injector and producer, The steam would flow through the tubing string to the toe of each well. The rate of heat transfer and fluid convection into the reservoir formation determine how communication is established along the length of the well pair. In this example, an electrical cable is located at the toe of injector or both the injector/producer, at a maximum temperature of 350° C.; steam is also injected into both the injector and producer.
When steam is added, it was discovered through simulation, that the electric cable can heat the condensed steam at the toe of the well and further transfer the heat generated to the mid section of the well, reducing the start up time and creating uniform steam chamber development along the entire well length. The minimum temperature at the midpoint between the two wells of 70 to 100° C. is used as an indicator for terminating steam circulation and switching to SAGD production mode.
Simulation results indicate that having electrical heaters at the toe of the well can improve the heat transfer, which can lead to a favorable development of uniform temperature between the well pairs and faster start up.
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention. However, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.
| Number | Date | Country | |
|---|---|---|---|
| 61969731 | Mar 2014 | US |
