CA2883967C - Method and system for enabling fluid communication between wells in a bitumen reserve - Google Patents

Abstract

A system and method are provided for establishing fluid communication between a pair of wells positioned in a pay region of a bitumen reserve. The method operates to achieve fluid communication by applying rapid heat to an inter-well region between the pair of wells using at least one heat source and in the absence of fluid injection, the heat sufficient to cause dilation of pores in the inter-well region via thermal expansion of connate fluid present in the pores.

Description

METHOD AND SYSTEM FOR ENABLING FLUID COMMUNICATION BETWEEN WELLS IN
A BITUMEN RESERVE
TECHNICAL FIELD
[0001] The following relates to systems and methods for enabling fluid communication between wells in a bitumen reserve.
DESCRIPTION OF THE RELATED ART

[0002] Bitumen is known to be considerably viscous and does not flow like conventional crude oil, and can be present in an oil sand reservoir. As such, bitumen is recovered using what are considered non-conventional methods. For example, bitumen reserves are typically extracted from a geographical area using either surface mining techniques, wherein overburden is removed to access the underlying pay (e.g., oil sand ore-containing bitumen) and transported to an extraction facility; or using in situ techniques, wherein subsurface formations (containing the pay) are heated such that the bitumen is caused to flow into one or more wells drilled into the pay while leaving formation rock in the reservoir in place. Both surface mining and in situ processes produce a bitumen product that is subsequently sent to an upgrading and refining facility, to be refined into one or more petroleum products, such as gasoline and jet fuel.

[0003] Bitumen reserves that are too deep to feasibly permit bitumen recovery by mining techniques are typically accessed by drilling wellbores into the hydrocarbon bearing formation (i.e. the pay) and implementing an in situ technology. There are various in situ technologies available, such as steam driven based techniques. These include, for example, Steam Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS). In a typical implementation of the SAGD method, a pair of horizontally oriented wells are drilled into the bitumen reserve, such that the pair of horizontal wells are vertically aligned with respect to each other and separated by a relatively small distance, typically in the order of several meters. The well installed closer to the surface and above the other well is generally referred to as an injector well, and the well positioned below the injector well is referred to as a producer well. The injector well and the producer well are then connected to various equipment installed at a surface site.

[0004] Prior to extracting bitumen from the reserve using the SAGD method, "start-up" of the wells is generally required. As used herein, "start-up" generally refers to the step of achieving or enabling fluid communication between two or more wells situated in a bitumen reserve. In a typical SAGD implementation, start-up is conventionally achieved by injecting and 22690332.1 circulating steam through both the injector well and the producer well. The steam is circulated through both wells until the region between the injector well and the producer well (i.e. the inter-well region) has been sufficiently heated to mobilize the bitumen and therefore allow fluid communication between the wells. Once start-up has been achieved, production can begin.
During production, steam is typically introduced into the bitumen reserve through the injector well which, in the process of condensing, further heats up the surrounding bitumen to lower its viscosity. The heated bitumen and the condensate then flows towards the producer well due to gravity, and are then pumped to the surface through the producer well.

[0005] However, achieving start-up using the conventional method of steam circulation can be inefficient and/or impractical for some bitumen reserves. For example, steam has been found to not effectively penetrate the cold bitumen surrounding the wells in low permeability formations or reserves (e.g. inclined heterolithic strata units). This can result in long start-up time and relatively high cost in achieving start-up if steam is employed as the primary heat source during the start-up phase of such low permeability reserves. Furthermore, the conventional start-up method of steam circulation requires additional surface equipment to be installed on-site for steam generation, which can unfavourably delay start-up in some cases.
SUMMARY

[0006] In one aspect, there is provided a method for establishing fluid communication between a pair of wells positioned in a pay region of a bitumen reserve, the method comprising:
applying rapid heat to an inter-well region between the pair of wells using at least one heat source and in the absence of fluid injection, the heat sufficient to cause dilation of pores in the inter-well region via thermal expansion of connate fluid in the pores.

[0007] In an implementation of the method, the rapid heat is provided by an electromagnetic heat source, the electromagnetic heat source being configured to direct radio frequency radiation towards the inter-well region.

[0008] In another aspect, there is provided a system for establishing fluid communication between a pair of wells positioned in a pay region of a bitumen reserve, the system comprising:
at least one heat source configured to apply rapid heat to an inter-well region between the pair of wells using at least one heat source and in the absence of fluid injection, to cause dilation of pores in the formation in the inter-well region by thermal expansion of connate fluid in the pores.

22690332.1 BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Various aspects and implementations will now be described by way of example only with reference to the appended drawings wherein:

[0010] FIG. 1 is a cross-sectional elevation view of an in situ gravity drainage system deployed in a bitumen reserve;

[0011] FIG. 2A is a schematic cross-sectional enlarged view illustrating a portion of an inter-well region in an implementation wherein a rapid heat source is installed in both the injector well and the producer well;

[0012] FIG. 2B is a schematic cross-sectional enlarged view illustrating the rapid heat sources radiating electromagnetic radiation in the implementation of FIG. 2A;

[0013] FIGs. 3A and 3B illustrate the dilation of pores containing connate water in the inter-well region due to rapid heating;

[0014] FIG. 4 is a schematic cross-sectional enlarged view illustrating an implementation wherein the rapid heat source is installed inside the injector well;

[0015] FIG. 5 is a schematic cross-sectional enlarged view illustrating an implementation wherein the rapid heat source is installed inside the producer well;

[0016] FIG. 6 is a schematic diagram illustrating a configuration for powering a pair of electromagnetic antennas in one implementation;

[0017] FIG. 7 is a schematic diagram illustrating a configuration for powering an electromagnetic antenna in one implementation;

[0018] FIG. 8 is a schematic diagram illustrating a configuration for powering an electromagnetic antenna in another implementation;

[0019] FIG. 9 is a schematic diagram illustrating a configuration for powering a pair of electromagnetic antennas in another implementation;

[0020] FIG. 10 is a diagram illustrating the various stages of a conventional SAGD
process;

[0021] FIGs. 11A-11C are diagrams illustrating the rapid heat source being installed inside the injector well and/or producer well in various configurations;

22690332.1

[0022] FIG. 12 is a diagram illustrating the pore dilation effect caused due to rapid heating;

[0023] FIG. 13A is a chart showing the variation of the incremental thermal pressurization of pure water in an exemplary formation;

[0024] FIG. 13B is a chart showing the variation of the incremental thermal pressurization of steam in drained condition in an exemplary formation;

[0025] FIG. 130 is a chart showing the variation of parameters for incremental thermal pressurization of vaporized steam in undrained condition in an exemplary formation;

[0026] FIG. 13D is a chart showing the variation of the incremental thermal pressurization of vaporized steam in undrained condition in an exemplary formation;

[0027] FIG. 14A is a chart showing the pressure of water after thermal-pressurization at reservoir temperature of 5 C;

[0028] FIG. 14B is a chart showing the pressure of vaporized steam after thermal-pressurization at reservoir temperature of 5 C;

[0029] FIG. 15 is a chart showing the pressure caused by thermal pressurization in shale and sand formations before pressure leak-off at reservoir temperature of 5 C;

[0030] FIG. 16 is a chart showing the pressure caused by thermal pressurization before and after flashing in two exemplary formations at reservoir temperature of 5 C;

[0031] FIG. 17A is a phase diagram of water;

[0032] FIG. 17B is a chart of thermal-pressurization factor for water, steam and vaporized steam under various conditions;

[0033] FIG. 18 is a chart showing the temperature change in a formation with respect to distance from the rapid heat source operating at various power levels;

[0034] FIG. 19 is a chart showing the pressure change in a formation with respect to distance from the rapid heat source operating at various power levels; and

[0035] FIG. 20 is a chart showing the change in thermal expansion components with respect to porosity at various temperatures.
DETAILED DESCRIPTION

22690332.1

[0036] In the following, there is provided a system and method for establishing fluid communication between a plurality of wells extending through a pay region of a bitumen reserve. The system and method operate to achieve fluid communication (i.e.
start-up) by applying rapid heat to an inter-well region to cause dilation of the pores in the inter-well region via thermal expansion of connate fluid present in the pores.

[0037] As used herein, the term "inter-well region" will be understood to refer to a region between two or more wells positioned in a formation. In particular, it will be appreciated that in a typical SAGD-type well configuration, the inter-well region would generally include at least the portion of the pay which lay between the injector well and the producer well.

[0038] In an implementation of the system and method, the rapid heat is applied in the absence of fluid injection. In some implementations, the rapid heat can be provided by an electromagnetic heat source. The electromagnetic heat source can be configured to direct radio frequency radiation towards the inter-well region. The power of the electromagnetic heat source required to achieve dilation, can be greater than about 10 kilowatts per meter of well length (kW/m). For example, the power output of the electromagnetic heat source can be between 10 kW/m and 50 kW/m according to the compressibility of the rock in the formation. The electromagnetic heat source can be located in at least one of the plurality of wells.

[0039] In one implementation, the plurality of wells includes an injector well and a producer well, and the electromagnetic heat source is located at least inside the injector well for rapidly heating the inter-well region. In another implementation, the electromagnetic heat source is located inside both the injector well and the producer well.

[0040] Turning now to the figures, FIG. 1 illustrates an example of a SAGD
production site 30 at a surface location 10 in a particular geographical region. The SAGD
production site 30 is positioned to allow one or more SAGD well-pairs 40 to be drilled from the surface location 10 towards a bitumen reserve (i.e., the pay 20). In the illustrated example, the one or more SAGD
well-pairs 40 include an injector well 42 positioned above a producer well 44.
As will be appreciated, the injector well 42 is configured to inject steam into the pay 20 and the producer well 44 is configured to recover a bitumen-containing fluid that has been mobilized by the injected steam during the typical SAGD production stage. The injector well 42 is typically located about 4 to 6 meters above the producer well 44 to define an inter-well region 22 therebetween, however, other relative distances between the wells are possible. The one or 22690332.1 more SAGD well-pairs 40 are drilled vertically into the overburden 15 towards and into the underlying pay 20, and as they are drilled become oriented substantially horizontal, such that the producer well 44 is above but near the formation 25 underlying the pay 20 (hereinafter the "underlying formation 25"). The one or more SAGD well pairs 40 are operated using a surface equipment 60.

[0041] To prepare the SAGD production site 30, the location where the one or more SAGD
well-pairs 40 will be located is determined, for example, by conducting typical computer simulations using geological and reservoir data. The corresponding locations of the production site 30 are then prepared for drilling, including providing infrastructure for water and electricity, as is known in the art. A drilling rig is then installed at the location and drilling commences subject to requisite inspections.

[0042] After drilling the wells 42, 44, the surface production equipment 60 is installed for operating the SAGD well pair 40. The wells 42, 44 are then completed according to steps which are generally known in the art.

[0043] Once the wells 42, 44 have been completed, one or more rapid heat sources can be installed within the injector well 42 and/or the producer well 44 for initiating the start-up phase.
In one implementation illustrated in FIG. 2A, a first rapid heat source 72a is installed inside the injector well 42 and a second rapid heat source 72b is installed inside the producer well 44. In the illustrated implementation, the first rapid heat source 72a and the second rapid heat source 72b are electromagnetic antennas. As will be explained, the electromagnetic antennas can be connected to a radio frequency (RF) transmitter and a controller located at the surface location 10.

[0044] FIG. 2B schematically illustrates the first and second rapid heat sources 72a, 72b being used to achieve start-up, and thus establish fluid communication between the wells 42, 44. In the implementation illustrated in FIG. 2B, the first and second rapid heat sources 72a, 72b are electromagnetic antennas configured to emit RF radiation 80 directed at least towards the inter-well region 22 of the pay 20.

[0045] As is well known in the art, many bitumen reserves contain pores which hold connate fluids. As used herein, the term "connate fluids" will be understood to refer to fluids which are trapped within the reserve and the formation. Typically, connate fluids primarily consist of water 22690332.1 =
and dissolved minerals. Accordingly, the term "connate water" will be used interchangeably with the term "connate fluids" herein.

[0046] FIG. 3A illustrates the pores 100 containing connate water in the inter-well region 22 of the reserve prior to initiating start-up in the implementation illustrated in FIGs. 2A and 2B. As illustrated in FIG. 3A, the pores 100 have an average diameter of 0 before the inter-well region 22 is subjected to RF radiation. However, when the inter-well region 22 is subjected to rapid heat in the form of RF radiation, the pores dilate as illustrated in FIG. 3B.
Specifically, in FIG.
3B, the dilated pores 100' are illustrated as having an average diameter of 0', which is greater than 0. The size of the pores 100 prior to dilation is illustrated using dotted lines in FIG. 3B for reference. The dilation of the pores increases the porosity and the permeability of the pay 20 in the inter-well region 22, and over time, fluid communication can be established between the injector well 42 and the producer well 44, thus completing the start-up phase.

[0047] This pore dilation effect is further illustrated in FIG. 12, which also takes into account a relatively small pressure leak (i.e. pressure leak << AP) which can occur in thermo-hydromechanical pressurization. It will be understood that, for example, an operator can check to see if fluid communication has been established between the wells by applying fluid pressure to the injector well and seeing if a response (i.e. pressure change) is detected in the producer well.

[0048] It has been determined that dilation of the pores can be caused by the thermal expansion of the connate water. More specifically, when the connate water trapped within the pores 100 is rapidly heated by RF radiation, the connate water thermally expands, thereby exerting pressure against the formation surrounding the pores 100. As the connate water continues to be heated, the pressure inside the pores builds until sufficient pressure has been reached to cause dilation. The pressure necessary to cause dilation can depend on a number of factors including, but not limited to, the volume of connate water present in the pores, and the type of bitumen formation surrounding the pores. Reaching such a pressure via rapid heating can be affected by the power and frequency of the RF radiation. If connate water is sufficiently heated such that it is vaporized, the generation of steam can further increase the pressure within the pores to cause dilation. For example, this is apparent from the chart of FIG. 17B, which provides the thermal-pressurization factor of water, steam, and vaporized steam under 22690332.1 various conditions. Specifically, under the conditions in which vaporized steam typically form, the thermal-pressurization factor of the vaporized steam is higher than that of water. As discussed below, higher thermal-pressurization factor of the fluid trapped inside the pores can result in greater dilation. For greater clarity, it is noted that vaporized steam is understood to refer to steam which is created as a result of the connate water flashing into vapor.

[0049] Returning to FIG. 2B, the inter-well region 22 is subjected to RF
radiation 80 until the permeability in the inter-well region 22 has been sufficiently increased by dilation of the pores to enable fluid communication between the injector well 42 and the producer well 44. The enhanced permeability in the inter-well region 22 is illustrated by a series of arrows pointing towards the producer well 44 in FIG. 2B.

[0050] Various RF radiation antenna configurations are illustrated in FIGs.
11A-11C.
Specifically, in FIG. 11A, RF antenna is provided in each of the injector well and the producer well. In FIG. 11B, an RF antenna is provided in the producer well only, and in FIG. 11C, an RF
antenna is provided in the injector well.

[0051] Shallow reservoirs (i.e. reservoirs with thin overburden) can be relatively easily fractured when dilation is caused by injection of fluids (e.g. cold water or steam) into the reservoir during the start-up phase. It can be considered undesirable to fracture the formation during start-up, since fracturing can create "high mobility highways" which can direct steam injected during the production stage away from the desired area. Furthermore, fracturing can result in sand production, which can prevent fluid propagation into the reservoir. As such, in the present method, the pores are dilated using RF radiation 80 in the absence of fluid injection into the pay 20 or the reservoir. For example, in a SAGD operation, the injection of steam can be delayed until after start-up has been achieved using the method described herein (i.e. by way of RF radiation). It can be particularly advantageous to achieve start-up in this way for shallow reservoirs, since the likelihood of fracturing the formation is reduced due to the absence of fluid injection during start-up.

[0052] In another implementation illustrated in FIG. 4, the rapid heat source 72 in the form of an electromagnetic antenna is only provided within the injector well 42. In the illustrated implementation of FIG. 4, it will be appreciated that RF radiation 80 emitted by the rapid heat source 72 will be directed at least towards the producer well 44, thereby causing dilation of the pores in the inter-well region 22 as explained above. In yet another implementation illustrated in 22690332.1 , FIG. 5, the rapid heat source 72 in the form of an electromagnetic antenna is illustrated as being present only within the producer well 44.

[0053] As described above, the electromagnetic antenna 72 can function as a rapid heat applicator in some implementations. It will be understood that the electromagnetic antenna 72 as used herein refers to a passive device that converts applied alternating electrical current into oscillating electromagnetic radiation, which can then be directed at least towards the inter-well region 22. For example, the electromagnetic antenna 72 can comprise a directional antenna and/or an omnidirectional antenna. The frequency of the electromagnetic radiation emitted by the antenna will generally be in the radio frequency range (i.e. approximately between 3 kHz and 300 GHz), which includes the microwave frequency range (i.e. approximately 3 to 30 GHz).
Accordingly, rapid heating of the connate water is primarily achieved through dielectric heating.
It will be understood that, where applicable, the antenna can be configured to operate within specific frequency ranges which are preserved for industrial or scientific purposes. For example, the antenna can be configured to emit electromagnetic radiation in the frequency ranges falling under the industrial, scientific and medical (ISM) radio bands (e.g. 6.78 MHz 15 kHz).

[0054] As is well known in the art, dielectric heating occurs when materials containing polar molecules are subjected to rapidly changing or oscillating electromagnetic fields. More specifically, such materials are generally heated by the friction generated from the polar molecules continuously re-aligning themselves with the oscillating electromagnetic field. In comparison to other forms of heating such as resistive heating or steam circulation, dielectric heating can be particularly advantageous for rapidly heating the connate water trapped in the pores, since it does not rely on diffusion of heat or mobility of fluids within the reservoir. Rather, polar molecules such as water molecules trapped in the formation can be selectively heated by dielectric heating, since hydrocarbons and sand surrounding the water molecules are generally non-polar and are therefore not susceptible to dielectric heating. For this reason, dielectric heating generally has superior penetration and heating rate compared to conductive heating in hydrocarbon formations. Dielectric heating can also have properties of thermal regulation because steam is not susceptible to dielectric heating. In other words, once the water is heated sufficiently to vaporize using dielectric heating, its permittivity decreases substantially such that it is not further heated by continued application of electromagnetic radiation.

22690332.1 ,

[0055] In order to rapidly heat the connate water trapped in the formation using RF radiation as described above, RF radiation will generally need to possess sufficient power. In one implementation, the output of the electromagnetic antenna is greater than about 10 kW per meter of well length. For example, the output can be approximately 10 to 50 kW
per meter of well length. As will be appreciated, if the output power of the RF radiation is insufficient for rapidly heating the connate water trapped in the pores, dilation of the pores cannot be achieved due to slow build up and leakage of the pressure from the pores. It will also be appreciated that the level of power output required to cause pore dilation would depend on a number of factors, such as the compressibility and permeability of the formation being treated.

[0056] The simulated effects of applying RF radiation to an oil sand formation at various power levels are illustrated by the charts of FIGs. 18 and 19. Specifically, FIG. 18 shows the temperature in the region surrounding the RF antenna after RF radiation has been applied for 6 minutes. In FIG. 18, simulated temperature results for RF power output of 1 kW
per meter of well length (kW/m) is indicated by reference numeral 310, and similar results for power output of kW/m, 10 kW/m, 50 kW/m, and 100 kW/m are indicated using reference numerals 320, 330, 340, and 350, respectively.

[0057] FIG. 19 shows the induced pressure (i.e. due to thermal pressurization) in the region surrounding the RF antenna after RF radiation has been applied to an oil sand formation for 6 minutes. In FIG. 19, simulated pressure results for RF power output of 1 kW
per meter of well length (kW/m) is indicated by reference numeral 410, and similar results for power output of 5 kW/m, 10 kW/m, 50 kW/m, and 100 kW/m are indicated using reference numerals 420, 430, 440, and 450, respectively.

[0058] The electromagnetic antenna 72 can be powered using various configurations.
FIG. 6 illustrates one configuration in which a pair of electromagnetic antennas 72a, 72b is powered by an RF transmitter 210. As will be appreciated, the RF transmitted 210 can be located on the surface as part of the surface equipment 60. In the implementation illustrated in FIG. 6, the RF transmitter 210 is configured to operate both electromagnetic antennas 72a, 72b.
For example, as illustrated in the implementation of FIGs. 2A and 2B, the electromagnetic antennas 72a, 72b can be installed inside the injector well 42 and the producer well 44, respectively. The RF transmitter 210 can be connected to a controller 220, which is configured to control the RF transmitter 210. For example, the controller 220 can be configured to control 22690332.1 the power and frequency of the current being outputted by the RF transmitter 210. As will be understood, controlling the parameters such as the power and frequency of the current being generated by the RF transmitter 210 would effectively modulate the RF
radiation 80 generated by the electromagnetic antennas 72a, 72b.

[0059] Other configurations of powering the electromagnetic antenna 72 are illustrated in FIGs. 7 and 8. In the implementation illustrated in FIG. 7, the electromagnetic antenna 72 can be installed inside the injector well 42, and in the implementation illustrated in FIG. 8, the electromagnetic antenna 72 can be installed inside the producer well 44. In both of these implementations, the electromagnetic antenna 72 is powered by a dedicated RF
transmitter 210. As with the implementation of FIG. 6, the RF transmitter 210 can be connected to a controller 220 for controlling various parameters of the current outputted by the RF transmitter 210.

[0060] FIG. 9 illustrates yet another configuration in which each electromagnetic antenna 72a, 72b is connected to a dedicated RF transmitter 210a, 210b. More specifically, a first electromagnetic antenna 72a is illustrated as being connected to a first RF
transmitter 210a and a second electromagnetic antenna 72b is illustrated as being connected to a second RF
transmitter 210b. As discussed above, the first electromagnetic antenna 72a can be installed inside the injector well 42 and the second electromagnetic antenna 72b can be installed inside the producer well 44. In the illustrated configuration, both the first transmitter 210a and the second transmitter 210b are controlled by the controller 220. However, it will be understood that the system can also be configured such that each transmitter 210a, 210b is connected to a dedicated controller.

[0061] In another implementation, rapid heating may be achieved using inductive heating in some formations. For example, inductive heating can be applied by generating an electromagnetic field in the range of 1 kHz to 200 kHz to cause an eddy current to be generated within the reservoir, which in turn heats the reservoir to cause pore dilation. As will be understood, the electromagnetic field can be generated using a solenoidal coil, also known as an inductor, placed within the pay and connected to appropriate power source(s), which can be located on the surface. For example, inductive heating can be applied in some low permeability formations, such as shale formations.

22690332.1

[0062] Once start-up has been achieved between the injector well 42 and the producer well 44 in accordance with the method described herein, production can begin. For example, in a typical SAGD operation, steam is introduced into the pay 20 through the injector well 42 to heat up the bitumen surrounding the injector well 42 to lower its viscosity, thereby allowing the heated bitumen and steam condensate to flow into the producer well 44 to be pumped to the surface 10.

[0063] During production, the rapid heat source 72 can be removed from the injector and/or producer wells. Alternatively, the rapid heat source 72 can be left inside the injector and/or producer wells during production. For example, the rapid heat source 72 can be kept inside the wells to continue heating the interwell region during production.

[0064] In one implementation, the rapid heat source 72 can be kept inside the injector and/or producer wells after start-up has been achieved, and steam may be injected (e.g. bull-heading) or circulated through the wells. In such implementation, applying RF
radiation simultaneously with steam injection or circulation can enhance the permeability of the formation and therefore assist production.

[0065] In another implementation, once start-up has been achieved, an electromagnetic steam-assisted gravity drainage (EM-SAGD) process can be implemented on the wells. For example, in such implementation, electromagnetic inductive heating can be applied simultaneously with steam injection or circulation. As explained above, inductive heating can be applied by generating an electromagnetic field in the range of 1 kHz to 200 kHz using a solenoidal coil placed within the pay, at a lower power than that used to apply rapid heating.

[0066] In addition to or as an alternative to using the typical SAGD method for producing the bitumen, solvent can be injected into the pay 10 once start-up has been achieved. For example, the Enhanced Solvent Extraction Incorporating Electromagnetic Heating (ESEIEH) advanced oil recovery technique as described in U.S. Patent No. 8,616,273, can be used to produce bitumen from the pay 10. As will be appreciated, solvent can be used to mobile the bitumen at lower temperatures than, for example, steam-based heating techniques.

[0067] In an implementation where the ESEIEH process is used during production, RF
heating can be used to heat the pay 10 prior to solvent injection. When the pay 10 reaches the desired temperature within a desired region, an appropriate solvent can be injected into the pay 10. The solvent partially mixes with the bitumen and further reduces its viscosity and partially 22690332.1 displaces the hot-diluted bitumen towards the producer well 44. The choice of solvent can be similar to existing solvent injection processes. As described above, rapid heating can be used during start-up to establish fluid communication between the injector well 42 and the producer well 44. The flow pathway thus created is then used as the primary conduit to inject a solvent from an appropriate well (e.g. the injector well 42).

[0068] The effects of pore dilation caused by electromagnetic radiation will now be described with reference to various equations below.

[0069] When the connate water trapped inside the pores is rapidly heated, such as by RF
radiation, the leakage of pressure from the pores is negligible, especially in formations with low permeability. In other words, the hydraulic permeability is effective zero in such formations, and therefore a closed boundary system (i.e. undrained system) can be used to simulate the pressure change in such formations. Specifically, the change in fluid pressure per unit change in the temperature in a bulk porous medium maintaining a constant volume in such systems can be given by:
aP 4) f + + 0)Ys Ysf = (Equation 1) aT (1)13f ¨ (1 ¨ (1)13saBio, Psf in which 4) is the porosity of the caprock, yf is the volumetric coefficient of thermal expansion of the pore fluid (1/ C), ysf is the volumetric coefficient of thermal expansion of the porous medium (1/ C), Pf is the compressibility of the fluid in pore space (1/Pa), 13s is the compressibility of solid grains (1/Pa), f3sf is the compressibility of porous medium (1/Pa), and abiot is the Biot-Willis coefficient. It is noted that apiaT can also be referred to as the thermal-pressurization factor (A), and therefore the above equation can also be written as:
Of 4- (2 HOY, ¨ Ysf A = (Equation 2) (I) Pf + (1¨ (I) )PsaBiof + Psf It is also noted that for water saturated formations, the thermal-pressurization factor can be determined based on the chart of FIG. 13A.

[0070] As illustrated in FIG. 20 which compares the thermal expansion of the fluid portion (i.e. 4) yf ) and the thermal expansion of the solid-matrix portion (i.e. (2-1)) Vs - '1s0, the factor associated with the thermal expansion of the solid-matrix portion is negligible in comparison to 22690332.1 =
the factor associated with the thermal expansion of the fluid portion for formations with porosities greater than 8% and temperatures above 25 C. This can be expressed as:
4)Yf >>(2¨ ()y,¨ Ysf >0.082 .... (Equation 3)

[0071] Table 1 provided below lists the values of the properties used to generate a comparison between the thermal expansion of the fluid portion and the thermal expansion of the solid-matrix portion in Equation 3.
Table 1: Table of parameters for Clearwater caprock (or shale) formation Parameter Value Caprock Thermal Expansion Properties:
Shale porous medium thermal expansion, (ysf),1PC 0.1 x 10-4 A
Shale solid thermal expansion, (y,),1/ C (0.2-0.3) x 104 AB
Pore Fluid Thermal Expansion Properties:
Water thermal expansion (y),1/ C
at 25 C 3.49 x 104 at 100 C 7.73 x 104 at 200 C 12.28 x 10-4 at 300 C 15.29 x 10-4 A Given in Mase, C. W., Smith, L., 1987. Effects of Frictional Heating on the Thermal, Hydrologic, and Mechanical Response of a Fault, Journal of Geophysical Research, 92(B7), pp. 6249-6272.
B Given in Wong, R.C.K., Samieh, A.M., 2000. Geomechanical Response of the Shale in the Colorado Group Near a Cased Wellbore Due to Heating, Journal of Canadian Petroleum Technology, Vol.
39, No. 8, pp. 30-33.

[0072] It has been found that for media with appreciable porosity, such as Clearwater shale formation, the Biot's coefficient (abiot) is approximately equal to 1.
Although it is possible to measure the Biot's coefficient in a lab using a core sample obtained from a formation, this test is rarely performed and therefore experimental value for the Biot's coefficient of formations such as Clearwater shale and Colorado shale are generally not readily available.

[0073] By assuming that the Biot's coefficient (abo) is 1 and neglecting both the thermal expansion of the solid-matrix portion (i.e. (2- 4)) Vs - ysf) and the solid grains compressibility (13), Equation 2 can be simplified as:
4YY f A ¨ (Equation 4) (1)13f Psf 22690332.1

[0074] Further, for cases in which the porous medium compressibility (NO is much greater than the fluid compressibility (13f), such as in the case for water-saturated shale formations, Equation 4 can be further simplified as:
A ,z, 4)7 f (Equation 5) since ii sf ,i)pf and it is assumed that:
13sf>> fly; Orf >>(2-4)7s---isf However, it is noted that in cases where steam is introduced to the medium either from vaporization or from diffusion from the steam chamber into the caprock, the fluid compressibility would be taken into account in Equation 4.

[0075] In contrast to the above, for cases in which the porous medium compressibility (13sf) is much less than the fluid compressibility (I3f), the thermal pressurization factor (A) equation of Equation 4 can be simplified as:
A ,,z-,' -.) - - = = (Equation 6) R f since of 13,f and it is assumed that:
13sf<<
It is noted that the above assumption is not valid for water-saturated shale formations, but that assumption can be valid for steam-saturated caprocks at low temperatures such as in the case of shallow caprocks. Using Equation 6 and substituting fluid thermal expansion and compressibility with known properties of water, the thermal pressurization factor for stiff caprocks saturated with water can be given by the following:
A = ¨aP\ = ________________________ l'w = - - = (Equation 7) ( aTip 13,, in which 7w is the thermal expansion of water and 13 w is the compressibility of the water.
Variation of the incremental thermal pressurization (or thermal pressurization coefficient) of 22690332.1 water is calculated based on Equation 7 and presented in FIG. 13A for a stiff caprock (i.e., 13.0 =0-

[0076] Similarly, using Equation 6 and substituting the fluid thermal expansion and compressibility with known properties of steam, the thermal pressurization factor for stiff caprocks saturated with steam can be given by the following:
A = (¨al) = 1st = = = (Equation 8) Pst in which Yst is the thermal expansion of steam and Rt is the compressibility of the steam.

[0077] Variation of the incremental thermal pressurization (or thermal pressurization coefficient) of steam for drained conditions is calculated based on Equation 8 and presented in FIG. 13B for a stiff caprock (i.e., põ .0). Variation of other important parameters for incremental thermal pressurization of vaporized steam in undrained condition is shown in the chart of FIG.
13C, and variation in the incremental thermal pressurization of vaporized steam in undrained condition vs. injection temperature and pressure is shown in the chart of FIG.
13D.

[0078] Neglecting the condensate convection and temperature independent thermal conductivity, the partial differential equation governing the thermal transport in RF heating can be expressed as:
a21" 1T 1 __ x 2 2 ( r a)] = 1 1'1 ....
F exp[ zA
(Equation 9) ar2 r or K x 2nr L oRF ntenna Antenn "RF KThermal ) in which K is the oil sand thermal conductivity (W/m- C), L is the length of antenna, 6RF is the penetration depth of RF radiation (m), -15174F is the total RF power radiated across the radius (J/sec=m3), ZAntenna is the vertical distance from antenna center (m), rAntenna is the mean radius of the RF antenna (m), [(Thermal is the thermal diffusivity (m2/sec).

[0079] For medium with low conductivity (i.e. non-metallic) and/or relative permeability of approximately one, such as typical oil sands at high frequencies, the penetration depth (5RF) of RF radiation can be determined based on the following equation:
8õ 0.0053 piTE7 = 0.0053 r .............. l CT/WCoer (Equation 10) a 22690332.1 in which Er is the relative permittivity, which is also known as the dielectric constant of the medium, and a is the electric conductivity.

[0080] As previously described, the connate water can be rapidly heated using RF radiation in absence of any fluid injection. In such an implementation, the dissipation of heat generated by RF heating is negligible and therefore the conductive term can be neglected to simplify Equation 9 as follows:

___________ X __ 2 exp [ RF at 2 (Z Antenna ) ¨aT
(Equation 11) 6 Antenna r Antenna -27crL pr cpr oRF
in which Pr is the bulk density of the oil sand (kg/m3), and cpr is the specific heat capacity of the medium (J/kg= C).

[0081] Solution for Equation 11 is given by:

- Tres = __________________ !IF exp [- R2 (zAntenna -rAntenna)] t (Equation 12) n Pr Cpr6RFzAntenn L "RF
in which Tres is the initial reservoir temperature and Tz is the temperature of the reservoir at a distance of z meters from the antenna.

[0082] Based on the above, the pressure induced in the formation by RF
heating can be expressed as:
APRF =
-F(2-4)'y s -7sf 1 ____________ (ZAntenna rAntenna ) ........ t (Equation 13) (1)13f (1¨ 4)13sa5l0t Psf n Pr CprkFzAntenn L RF exp[- "RFii

[0083] For "stiff" formations in which the porous medium compressibility (I3g) is much less than the fluid compressibility (I3f), it can be seen that 413r >> f3sr, and therefore the change in pressure can be expressed as:

APRF ={ YwRFexp(zAntenna rntenna) t =CRF exp Ar ntenna t = = = (Equation 14) 13 ¨A
I3w it Pr Cpr6RFZAntenn "RF \ "RF
in which:

CRF eXP ¨ ¨2ZAntenna = = = = (Equation 15) 13w TCPr Cpr8RFzAntenn SRF

22690332.1

[0084] The pressure of water and vaporized steam after thermal-pressurization at reservoir temperature of 5 C is shown in FIGs. 14A and 14B. Similar data for thermal pressurization in oil sand and clay and other known formations are shown in FIGs. 15 and 16.

[0085] Assuming radial flow into a well opened over entire thickness, single phase, slightly compressible fluid, constant viscosity, ignoring the gravity, constant permeability and porosity, the governing equation for pressure distribution including pressure rise due to RF-heating is as follows:
a2p ap 1 (ap) 2+ APRF = = = = = (Equation 16) ¨ar1j¨tar KHydraulic at in which KHydraulic is the hydraulic diffusivity (m2/sec).

[0086] Substituting Equation 14 into Equation 16, the following is obtained:
a2p 1P 2 1 ¨+--+CRF exp ______________ rAntenna t = = ' ' = ' (Equation 17) ar2 r ar \,61iF ) KHydraulic

[0087] For Equation 17, boundary conditions can be given as follows:
P( rw)=13,,, P(co) =
and the initial condition can be as follows:
P(t=0)=P,

[0088] Additional details relating to the mathematical equations discussed above are provided in the following references, which are incorporated herein by reference in their entirety:
- Ghannadi, S., Irani, M., Chalaturnyk, R., 2014a. Evaluation of Induced Thermal Pressurization in Clearwater Shale Caprock in Electromagnetic Steam-Assisted Gravity-Drainage Projects, SPEJ, 19(03): 443-462.;
- Ghannadi, S., Irani, M., Chalaturnyk, R., 2014b. Induction and Radio Frequency Heating Strategies for Steam-Assisted Gravity Drainage Start-Up Phase, SPE Heavy Oil Conference-Canada, 10-12 June, Alberta, Canada.

22690332.1 - Ghannadi, S., Irani, M., Chalaturnyk, R., 2014c. Understanding the Thermo-Hydromechanical Pressurization in Two-Phase (Steam/Water) Flow and its Application in Low-Permeability Caprock Formations in Steam-Assisted-Gravity-Drainage Projects, SPEJ.

[0089] Various charts related to properties of water, steam, and vaporized steam are shown in FIG. 17.

[0090] It will be appreciated that although various aspects and embodiments of the present method and system have been described in relation to SAGD-type well configurations, the method and system can be similarly implemented in other types of well configurations, and in particular, other gravity drainage well configurations. It will also be appreciated that while various aspects and embodiments of the present method and system have been described with reference to a pair of wells (i.e. the injector well 42 and the producer well 44), the present method and system can be similarly implemented in other well configurations in which there are lesser or greater number of wells drilled into the reservoir.

[0091] It will be appreciated that any module or component exemplified herein that executes instructions can include or otherwise have access to computer readable media such as storage media, computer storage media, or data storage devices (removable and/or non-removable) such as, for example, magnetic disks, optical disks, or tape.
Computer storage media can include volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Examples of computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by an application, module, or both. Any such computer storage media can be part of the controller 220, RF transmitters 210, or any component of or related thereto, or accessible or connectable thereto. Any application or module herein described can be implemented using computer readable/executable instructions that can be stored or otherwise held by such computer readable media.

[0092] For simplicity and clarity of illustration, where considered appropriate, reference numerals can be repeated among the figures to indicate corresponding or analogous elements.

22690332.1 In addition, numerous specific details are set forth in order to provide a thorough understanding of the examples described herein. However, it will be understood by those of ordinary skill in the art that the examples described herein can be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the examples described herein. Also, the description is not to be considered as limiting the scope of the examples described herein.

[0093] The examples and corresponding diagrams used herein are for illustrative purposes only. Different configurations and terminology can be used without departing from the principles expressed herein. For instance, components and modules can be added, deleted, modified, or arranged with differing connections without departing from these principles.

[0094] The steps or operations in the flow charts and diagrams described herein are just for example. There can be many variations to these steps or operations without departing from the principles discussed above. For instance, the steps can be performed in a differing order, or steps can be added, deleted, or modified.

[0095] Although the above principles have been described with reference to certain specific examples, various modifications thereof will be apparent to those skilled in the art as outlined in the appended claims.
22690332.1

Claims (24)

Claims:

1. A method for establishing fluid communication between a pair of wells positioned in a pay region of a bitumen reserve, the method comprising:
determining one or more control parameters for at least one heat source to achieve thermal expansion of connate fluid in the pores, according to compressibility and permeability of the formation in the pay region and volume of the connate fluid present in the pores; and applying heat to an inter-well region between the pair of wells in the pay region using the at least one heat source and in the absence of fluid injection, by operating the at least one heat source using the one or more control parameters, the application of the heat according to the one or more control parameters being sufficient to cause dilation of pores in the inter-well region via the thermal expansion of connate fluid in the pores during the heating.

2. The method of claim 1, wherein the heat is provided by an electromagnetic heat source, the electromagnetic heat source being configured to direct radio frequency radiation towards the inter-well region.

3. The method of claim 2, wherein the power of the electromagnetic heat source is greater than about 10 kilowatts per meter of well length.

4. The method of claim 3, wherein the power of the electromagnetic heat source is between about 10 kilowatts per meter of well length and about 50 kilowatts per meter of well length.

5. The method of any one of claims 1 to 3, wherein the electromagnetic heat source is located in at least one of the pair of wells.

6. The method of claim 5, wherein the pair of wells comprises an injector well and a producer well, and wherein a first electromagnetic heat source is located in the injector well.

7. The method of claim 6, wherein a second electromagnetic heat source is located in the producer well.

8. The method of claim 5, wherein the pair of wells comprises an injector well and a producer well, and wherein the electromagnetic heat source is located in the producer well.

9. The method of any one of claims 1 to 8, wherein the heat is applied using a controller.

10. The method of claim 9, wherein the controller is located at surface.

11. The method according to any one of claims 1 to 10, further comprising:
producing bitumen from the pay region using a production well after establishing the fluid communication between the pair of wells.

12. The method of claim 11, wherein the at least one heat source is utilized while producing bitumen by operating the at least one heat source at a lower power than used for heating.

13. A system for establishing fluid communication between a pair of wells positioned in a pay region of a bitumen reserve, the system comprising:
at least one heat source configured to apply heat to an inter-well region between the pair of wells in the pay region using at least one heat source and in the absence of fluid injection;
and one or more control parameters for the at least one heat source to achieve thermal expansion of connate fluid in the pores, the one or more control parameters having been determined according to compressibility and permeability of the formation in the pay region and volume of connate fluid present in the pores, the heat applied according to the one or more control parameters being sufficient to cause dilation of pores in the formation in the inter-well region by the thermal expansion of connate fluid in the pores during the heating.

14. The system of claim 13, wherein the heat is provided by an electromagnetic heat source, the electromagnetic heat source being configured to direct radio frequency radiation towards the inter-well region.

15. The system of claim 14, wherein the power of the electromagnetic heat source is greater than about 10 kilowatts per meter of well length.

16. The system of claim 15, wherein the power of the electromagnetic heat source is between about 10 kilowatts per meter of well length and about 50 kilowatts per meter of well length.

17. The system of any one of claims 13 to 16, wherein the electromagnetic heat source is located in at least one of the pair of wells.

18. The system of claim 17, wherein the pair of wells comprises an injector well and a producer well, and wherein a first electromagnetic heat source is located in the injector well.

19. The system of claim 18, wherein a second electromagnetic heat source is located in the producer well.

20. The system of claim 17, wherein the pair of wells comprises an injector well and a producer well, and wherein the electromagnetic heat source is located in the producer well.

21. The system of any one of claims 13 to 20, further comprising a controller for controlling application of the heat.

22. The system of claim 21, wherein the controller is located at surface.

23. The system according to any one of claims 13 to 22, further comprising:
a production well for producing bitumen from the pay region after establishing the fluid communication between the pair of wells.

24. The system of claim 23, wherein the at least one heat source is utilized while producing bitumen by operating the at least one heat source at a lower power than used for heating.