CA2832626A1

CA2832626A1 - Downhole pressure pulse and pressurized chemical treatment for sagd startup

Info

Publication number: CA2832626A1
Application number: CA2832626A
Authority: CA
Inventors: Adel Nabhan; Thomas W. De Haas; Gilles Chalier
Original assignee: Suncor Energy Inc
Current assignee: Suncor Energy Inc
Priority date: 2013-11-05
Filing date: 2013-11-05
Publication date: 2015-05-05
Anticipated expiration: 2033-11-05
Also published as: CA2832626C

Abstract

A startup process for a Steam-Assisted Gravity Drainage (SAGD) operation may include pressure pulsing from within a horizontal section of one or both SADG wells, the pulsing source being within a startup fluid such that pressure pulses propagate into a treatment zone of the interwell region between the SAGD wells, thereby providing micro-fracturing and/or dilation in the treatment zone. The process may also include providing a penetration pressure on the startup fluid such that a portion of the startup fluid penetrates into the treatment zone to increase fluid mobility. The process may be implemented in shallow reservoirs, plastic reservoirs, and operations having a low maximum operating pressure (MOP) limit, for example.

Description

DOWNHOLE PRESSURE PULSE AND PRESSURIZED CHEMICAL TREATMENT FOR
SAGD STARTUP
TECHNICAL FIELD
The general technical field relates to in situ hydrocarbon recovery operations, and more particularly to reservoir treatments for enhancing startup of hydrocarbon recovery operations.
BACKGROUND
There are a number of in situ techniques for recovering hydrocarbons from subsurface reservoirs. One technique, called Steam-Assisted Gravity Drainage (SAGD), involves well pairs each of which consists of two horizontal wells drilled in the reservoir and aligned in spaced relation one on top of the other. The upper well is a steam injection well and the lower well is a production well, separated by an interwell region. The injected steam forms a steam chamber that grows upward and outward within the formation, heating the bitumen or heavy oil sufficiently to reduce its viscosity and allow it to flow under the force of gravity toward the producer well along with condensed water.
Once a SAGD well pair is drilled and completed, the first phase of SAGD
operations is the so-called startup phase. In the startup phase, fluid communication is established between the injection and production wells of a given well pair. Startup procedures typically involve circulating steam through the injection well and sometimes the production well. Steam circulation is continued to establish fluid communication between the injection and production wells.
In some situations, steam circulation can provide slow or inefficient results in terms of heating the interwell region sufficiently to establish fluid communication.
Steam circulation inefficiencies can be due to low permeability of the interwell region, geological barriers within the interwell region, and/or limitations on the steam pressure that can be used.
Solvent injection can also be used in the context of SAGD startup operations.
The efficiency of the solvent-assisted startup also depends on a variety of factors, such as the reservoir properties.

2 Determining reservoir properties is also challenging in the context of enhancing SAGD
startup and normal operations.
Various challenges still exist in the area of SAGD startup operations.
SUMMARY
In some implementations, there is provided a startup process for a Steam-Assisted Gravity Drainage (SAGD) operation for increasing fluid mobility between a SAGD
injection well and a SAGD production well having horizontal sections separated by an interwell region, the process comprising: pressure pulsing from a pulsing source located within a horizontal section of at least one pulsing well selected from the SAGD injection well and/or the SAGD
production well, the pulsing source being within a startup fluid such that pressure pulses propagate from the pulsing source via the startup fluid and into a treatment zone of the interwell region, thereby providing micro-fracturing and/or dilation in the treatment zone; and providing a penetration pressure on the startup fluid such that a portion of the startup fluid penetrates into the treatment zone to increase fluid mobility in the treatment zone.
In some implementations, the startup fluid comprises a hydrocarbon solvent for dissolving bitumen within the interwell region.
In some implementations, the hydrocarbon solvent comprises at least one of toluene, xylene, diesel, butane, pentane, hexane, heptane and naphtha.
In some implementations, the startup fluid comprises an aqueous solution including a bitumen emulsifier for emulsifying bitumen within the interwell region.
In some implementations, the startup fluid is a substantially incompressible liquid having a low viscosity within the horizontal section.
In some implementations, the penetration pressure is provided such that the startup fluid is in liquid phase within the horizontal section.
In some implementations, the penetration pressure is below the fracturing pressure of the reservoir.
I

3 In some implementations, the penetration pressure is above the fracturing pressure of the reservoir.
In some implementations, the process also includes introducing the startup fluid in order to substantially fill at least the horizontal section of the pulsing well.
In some implementations, the process also includes pre-heating the startup fluid prior to introducing the startup fluid into the pulsing well.
In some implementations, the process also includes providing a soak period for the startup fluid within the interwell region.
In some implementations, the process also includes displacing the pulsing source along the horizontal section of the pulsing well.
In some implementations, the pulsing source is displaced along substantially an entire length of a slotted liner within the horizontal section.
In some implementations, the pressure pulses comprise shockwaves.
In some implementations, the pressure pulses are generated by ultrasonic pulses, electric sparks, gas expansion, mechanical release of pressurized fluid or exploded solid.
In some implementations, the process also includes inserting a pressure pulse generating device into the pulsing well to act as the pulsing source; and controlling the pressure pulse generating device to generate the pressure pulses.
In some implementations, the pulsing well is the SAGD injection well.
In some implementations, the pulsing well is a first pulsing well that is the SAGD injection well, and the process comprises providing a second pulsing well that is the SAGD
production well.
In some implementations, the process also includes operating the SAGD
production well to provide a pressure sink.
. i i

4 In some implementations, the process also includes providing steam circulation or bullheading via the SAGD injection well; determining that fluid communication has not been established between the SAGD injection well and a SAGD production well;
ceasing the steam circulation or bullheading; introducing the startup fluid into the SAGD
injection well;
and commencing the pressure pulsing and providing a penetration pressure on the startup fluid.
In some implementations, the interwell region is part of a generally plastic formation, such that the pressure pulsing provides dilation and fracturing in the treatment zone.
In some implementations, the interwell region is part of a generally elastic formation, such that the pressure pulsing provides micro-fracturing in the treatment zone.
In some implementations, the SAGD operation is in a shallow reservoir.
In some implementations, the SAGD operation is in a reservoir having a low maximum operating pressure (MOP) limitation.
In some implementations, there is provided a method for enhancing Steam-Assisted Gravity Drainage (SAGD) startup of a SAGD well pair, comprising simultaneously generating pressure pulses from within a horizontal section of a SAGD well of the SAGD
well pair to provide micro-fracturing and/or dilation in an interwell region between the SAGD well pair and pressurizing a startup fluid within the SAGD well to penetrate the interwell region.
In some implementations, there is provided a process for producing hydrocarbons from a reservoir in a Steam-Assisted Gravity Drainage (SAGD) operation, comprising:
drilling a production wellbore and an injection wellbore into the reservoir, the wellbores having respective horizontal sections separated by an interwell region; providing a slotted liner within the injection wellbore, thereby providing a lined injection well;
introducing a startup fluid into the lined injection well so as to provide a startup fluid-filled horizontal section;
pressure pulsing from a pulsing source located within the startup fluid-filled horizontal section, such that pressure pulses propagate from the pulsing source via the startup fluid and into the interwell region, thereby providing micro-fracturing and/or dilation therein;
providing a penetration pressure on the startup fluid such that a portion of the startup fluid i penetrates into the interwell region to increase the fluid mobility therein;
completing the wells to provide a SAGD injection well and a SAGD production well; providing steam circulation or bullheading via the SAGD injection well to heat the interwell region and achieve fluid communication between the SAGD injection well and the SAGD
production well; and producing hydrocarbons from the SAGD production well while injecting steam through the SAGD injection well.
In some implementations, the process also includes, prior to the step of completing the wells to provide the SAGD production well, the steps of providing a second slotted liner within the production wellbore, thereby providing a lined production well;
introducing a second startup fluid into the lined production well so as to provide a second startup fluid-filled horizontal section; pressure pulsing from a second pulsing source located within the second startup fluid-filled horizontal section, such that pressure pulses propagate from the second pulsing source via the second startup fluid and into the interwell region, thereby providing micro-fracturing and/or dilation therein; providing a second penetration pressure on the second startup fluid such that a portion of the second startup fluid penetrates into the interwell region to increase the fluid mobility therein.
In some implementations, the first and second startup fluids are the same.
In some implementations, the first and second pulsing sources utilize a same mechanism to generate the pressure pulses.
In some implementations, the interwell region is part of a generally plastic formation, such that the pressure pulsing provides dilation and fracturing in the treatment zone.
In some implementations, the interwell region is part of a generally elastic formation, such that the pressure pulsing provides micro-fracturing in the treatment zone.
In some implementations, there is provided a startup process for a horizontal well in a hydrocarbon recovery operation for increasing fluid mobility in a near-wellbore region adjacent to the horiztonal well, the process comprising: pressure pulsing from a pulsing source located within the horizontal well, the pulsing source being within a startup fluid such that pressure pulses propagate from the pulsing source via the startup fluid and into a , treatment zone of the near-wellbore region, thereby providing micro-fracturing and/or dilation in the treatment zone; and providing a penetration pressure on the startup fluid such that a portion of the startup fluid penetrates into the treatment zone to increase fluid mobility in the treatment zone. In some implementations, the hydrocarbon recovery operation is in a shallow reservoir. In some implementations, the hydrocarbon recovery operation is in a reservoir having a low maximum operating pressure (MOP) limitation. In some implementations, the hydrocarbon recovery operation is SAGD.
BRIEF DESCRIPTION OF DRAWINGS
Fig 1 is a detailed side cut view schematic of a SAGD well pair with pressure pulsing.
Fig 2 is a side cut view schematic of a SAGD well pair with pressure pulsing.
Fig 3 is a front cut view schematic of a SAGD operation, including infill and step-out wells.
Fig 4 is a front cut view schematic of a SAGD operation with pressure pulsing.
Fig 5 is a front partial perspective view schematic of a SAGD well pair and an adjacent well with pressure pulsing.
Fig 6 is a top plan view schematic of two arrays of SAGD well pairs, including an infill well and pressure pulsing.
Fig 7 is a front cut view schematic of a SAGD operation including an infill well with pressure pulsing.
Fig 8 is a cut view schematic showing an array of SAGD well pairs in front view and another well in side view with pressure pulsing.
DETAILED DESCRIPTION
Various techniques are described for pressure pulse assisted SAGD startup.
SAGD startup processes may include a pressure pulse treatment of the interwell region defined between the injection and production wells, in the presence of a startup fluid to induce micro-fracturing and/or dilation around the wellbore, which includes an interwell region, and allow õ

penetration of the startup fluid. The startup fluid thus propagates the pressure pulses originating from within the well and is pressurized into the reservoir rock to enhance penetration into the interwell region, in order to increase its mobility.
In some implementations, the penetration pressure exerted on the startup fluid from the surface is below the fracture pressure of the reservoir yet sufficient to force the startup fluid to penetrate micro-fractured and/or dilated zones of the interwell region resulting from the pressure pulses. Thus, while localised in situ pressure pulses of high amplitude induce micro-fracturing and/or dilation in the interwell region, a more constant penetration pressure enhances penetration of the startup fluid.
1.0 In some implementations, the process includes pressure pulses stimulation of a wellbore or SAGD well pair by injecting the startup fluid and using a pressure pulse generating device to micro-fracture and/or dilate the near-wellbore region and improve startup fluid penetration. Multiple locations along the wellbore may be pulsed using the pressure pulse generating device, and the well is pressurized to keep the micro-fractures open, for example until steam circulation is initiated.
Steam quantity, steam circulation time during SAGD startup, and overall startup times may thus be reduced. In some scenarios, improved conformance and lower operating expenses can be achieved compared to steam circulation alone.
The pressure pulsing techniques may be particularly advantageous in shallow SAGD
20 reservoirs, in particular in reservoirs that may be are too shallow to achieve high enough steam pressure and temperature to enable fluid communication between the injection and production wells in a reasonable time.
In some implementations, the pressure pulsing techniques may be coupled with other startup operations, such as steam circulation and chemical treatments of the reservoir rock and fluids. The pressure pulsing technique may be performed in order to pre-treat and increase the mobility of the interwell region prior to a subsequent stage of the startup operation. The subsequent stage of the startup operation may be one or more of steam circulation, bullheading, hot water circulation, steam injection, solvent injection, surfactant and alkaline treatment, and so on. In some implementations, the pre-treatment can enhance the mobility so as to increase the performance and/or efficiency of the subsequent stage of the startup operation.
SAGD startup pulsing implementations Referring to Fig 1, a SAGD well pair may include an injection well 10 and an underlying production well 12, the horizontal sections of which are separated by an interwell region 14.
In terms of well construction, injection and production wellbores are first drilled into the reservoir, and then certain well completion components are introduced. Well completion may include casings, as well as an injection slotted liner 16 and a production slotted liner 18 introduced within the respective wellbores. The slotted liners are typically introduced into the horizontal sections of the wellbores without substantial delay after drilling, since the wellbores can have a tendency to close up if the wellbore walls are not structurally supported. The slotted liners also allow fluids and steam to go through their slots. Various well completion components and methods may be used for SAGD wells, some of which are discussed further below.
Still referring to Fig 1, a pressure pulse generating device 20 may be introduced within the injection well 10 via a cable 22, such that the pressure pulse generating device 20 is positioned within the injection liner 16. The pressure pulse generating device 20 is configured to generate pressure pulses 24 from within the lined injection well. One or more pressure pulse generating devices may be provided in the injection well 10, the production well 12, or both. The well in which the pressure pulse generating device 24 is located may be referred to as a "pulsing well".
In some implementations, a startup fluid 26 is also introduced into the injection well 10. As shown in Fig 1, the startup fluid 26 may be introduced using a startup fluid pump 28 in fluid communication with a startup fluid holding tank 30 located at the surface 32.
The injection well 10 may be fully or partially filled with the startup fluid 26, such that the pressure pulse generating device 20 is within the startup fluid and the pressure pulses 24 propagate through the startup fluid. The pressure pulses 24 propagate via the startup fluid into part of the interwell region 14 that is proximate to the source of the pressure pulses 24. In this regard, liners are equipped with slots, which may have various slot densities, patterns, aperture and internal geometries. The pressure pulses 24 can propagate through the slots and into the surrounding zone of the reservoir, thereby enabling micro-fracturing and/or dilation in the interwell region 14. The micro-fracturing and/or dilation are schematically illustrated and represented as characters 34 and 35 in Fig 1. The pressure pulses 24 also generate seismic waves 36 that propagate through the reservoir and can be detected, which will be further described below.
In some implementations, the startup fluid 26 is pressurized within the injection well to a penetration pressure to facilitate the startup fluid 26 to penetrate into the micro-fractures 34 to aid in dissolving, interacting with, and/or mobilizing bitumen in the interwell region 14.
The penetration pressure exerted on the startup fluid may depend on the nature of the fluid and properties of the interwell region such as permeability, degree of micro-fracturing, and so on. The penetration pressure may be below a fracturing pressure of the reservoir, such that the pressure of the startup fluid itself induces little or no fracturing of the reservoir, allowing the pressure pulse treatment to enable the micro-fracturing.
The pressure pulse generating device 20 may be progressively moved along the injection well 10 to generate micro-fractures and/or dilation along part of the entire length of the interwell region. The displacement of the pressure pulse generating device 20 along the well may be done in a generally continuous manner or step-wise for pulsing certain intervals one at a time.
Once the pressure pulse and startup fluid penetration have been completed, the startup fluid may be allowed to soak within the interwell region 14. The pressure pulse generating device 20 may be removed or can remain within the well during part of the soaking period or used to squeeze a second chemical or solvent. The soaking time may depend on a number of factors, such as the type of startup fluid, initial and post-pulsing properties of the interwell region, and logistics related to the SAGD operations. Soaking may be advantageous for hydrocarbon solvent startup fluids that dissolve the bitumen to enhance mobility.
Referring still to Fig 1, when the production well 12 may be operated in production mode during the pulsing and penetration of the startup fluid, in order to create a pressure sink to i 1 promote pressure drive of the startup fluid from the injection well toward the production well.
This pressure sink approach may be used when prolonged soaking is not used.
The pressure sink may be provided by operating a suitable production pump 38, which is run inside a production string 70 within the casing of the well.
As illustrated on Fig 1, the pressure pulse generating device 20 may be coupled to a controller 39, which may be configured to send signals from the surface 32 to the device 20 to trigger the pulses. The controller 39 may be automated or manually operated, and may be configured to receive information (e.g., seismic information) acquired from the reservoir in order to adapt the pulsing. The controller 39 may be a generator/receiver for sending and 10 receiving signals and/or information via appropriate wiring or other equipment within the suspension cable 22.
Startup fluids The startup fluid is a fluid that can (i) propagate pressure pulses in order to enable micro-fracturing and/or dilation in the interwell region, (ii) penetrate into the pulsed interwell region under the penetration pressure, and (iii) increase the mobility within the interwell region.
The mobilization may be effected by dissolution, emulsification and/or viscosity reduction by heating, depending on the type and state of the startup fluid and other startup process operating conditions.
Hydrocarbon solvents In some implementations, the startup fluid includes or is a hydrocarbon solvent for dissolving bitumen within the near-wellbore zone of the reservoir including the interwell region. The hydrocarbon solvent may include an aromatic solvent, an aliphatic solvent or a mixture thereof. For example, the hydrocarbon solvent may be at least one of toluene, xylene, diesel, butane, pentane, hexane, heptane and naphtha. The hydrocarbon solvent may be purchased from the market or derived from a stream of a bitumen or heavy hydrocarbon extraction operation. Hydrocarbon solvents may be provided at ambient temperatures or may be pre-heated. Pre-heated hydrocarbon solvent may increase the bitumen dissolution rate. Hydrocarbon solvents may also be selected in order to be in liquid form within the injection well, such that the pressure pulses propagate through a , , i 1 substantially incompressible liquid. The penetration pressure and the solvent temperature may also be provided such that the hydrocarbon solvent is substantially liquid within the injection well.
Aqueous solution with emulsifier In some implementations, the startup fluid may include an aqueous solution including a bitumen emulsifier for emulsifying bitumen within the interwell region. The bitumen emulsifier may include a surfactant in an amount sufficient to cause bitumen droplets to enter the aqueous phase within the residence time of the startup fluid within the interwell region. The aqueous startup solution may be pre-heated to a temperature that is higher than some hydrocarbon solvents with lower boiling points.
The concentration of the surfactant may depend on various factors, such as the anticipated soaking time, temperature of the startup fluid, and properties of the interwell region.
Additives In some implementations, the startup fluid may also include other additives such as co-surfactants, alkali agents to induce in situ production of natural surfactants in the interwell region, and so on.
For some reservoir applications, the startup fluid may include proppant to further prop open the micro-fractures.
Startup fluid temperature and pressure In some implementations, the startup fluid is provided at ambient temperatures. The startup fluid may also be heated so as to be present at a temperature of at least about 30 C, 40 C, 50 C, 60 C or 70 C, for example, or as high as possible while remaining liquid and respecting the temperature tolerance of the pressure pulse generating device.
The startup fluid may be at a temperature above reservoir temperature and below a boiling temperature of the startup fluid. In some scenarios, the startup fluid may be at a temperature above its boiling temperature resulting in cavitation effects.
, i The temperature of the startup fluid may also be provided depending on the nature of the startup fluid and the operating conditions of the startup operation. For example, for a short residence time of the startup fluid within the interwell region, the startup fluid may be pre-heated to accelerate mobilization of the bitumen, whereas for longer residence times where prolonged soaking is performed, the startup fluid may be provided at ambient temperatures if the benefit of the heat may be reduced or lost to the reservoir over the soaking time.
The penetration pressure exerted on the startup fluid may be provided by the startup fluid pump 28. The penetration pressure may be selected according to various factors, so as to ensure the startup fluid is in liquid phase within the horizontal section of the well and to facilitate penetration into the micro-fractures of the interwell region. The penetration pressure may be substantially constant or may be varied. For example, the penetration pressure may be modified in the event the mobility of the interwell region increases over time. In addition, the penetration pressure may be modulated in a pulsed manner.
In some implementations, the startup fluid is pressurized to at or near the maximum operating pressure (MOP) of the well.
In some implementations, the penetration pressure is provided such that the startup fluid keeps the micro-fractures open until subsequent steam circulation is initiated.
Startup fluid quantities In some implementations, the amount of startup fluid introduced into the injection well is sufficient to substantially fill at least the horizontal section of the well.
In some scenarios, the injection well is filled with the startup fluid and is continuously replenished as the startup fluid penetrates the interwell region and other adjacent parts of the reservoir. The amount of additional startup fluid that is required can be used as an estimate of the amount of startup fluid that has penetrated the pulsed interwell region, particularly at early stages of the process.
In some implementations, a section of the injection well may be isolated with packers or other isolation equipment, and thus the volume of the startup fluid may be reduced to exclude the parts beyond the isolated section. In some scenarios, isolation may be 1 i performed at intervals along the well pair such that the pulsing treatment is performed interval-by-interval along the length of the interwell region.
In some implementations, the startup fluid may be injected to occupy part or all of the horizontal section of the injection well, while the remainder of the well (i.e., dogleg and vertical sections) can be filed with another liquid. This method may be used to reduce the total amount of startup fluid that is introduced into the well.
Pressure pulse treatments Referring to Fig 1, in some implementations the pressure pulses 24 are generated in situ by the pressure pulse generating device 20 that is inserted within the liner of the well. Various different pressure pulse generating devices 20 may be used to generate different kinds of pulses. For example, the pressure pulses may be vibrational or shockmves emanating from the pressure pulse generating device 20. In some implementations, the pressure pulse generating device 20 may generate pressure pulses by various mechanisms including ultrasound, electric spark, gas expansion, mechanical release of pressurized fluid, exploding solid mechanisms. In some scenarios, ultrasound or electric spark sources may be advantageous in terms of simplicity, controllability and reliability. In some implementations, the pressure pulses are shockwaves.
In some implementations, the pressure pulse generating device may be a wire-line tool available from Blue Spark Energy-5A, which has been used for wellbore stimulation and converts standard electrical power into repeatable, high power hydraulic impulses. This shockwave tool has been shown to achieve hydraulic pulses of up to 10,000 psi.
Another example of a pressure pulse generating device is associated with Pulsonix TFA
tool based on fluidic oscillator technology which enables alternating bursts of fluid generating pulsating pressure. A further example of a pressure pulse generating device may be referred to as an AST-1 TM (Advanced Sparker Tool) available from Avalon Sciences Ltd. A
device such as a Hydro-lmpactTM tool supplied by Applied Seismic Research may also be used. It should be understood that various other devices may be used. The pressure pulses may be provided by releasing energy stored in capacitors, where the energy is released in micro-seconds.
, , In some implementations, the pressure pulses have a limited micro-fracturing or dilation radius such that the micro-fractures extend from the source a limited distance into the reservoir. The micro-fracturing or dilation radius will depend on local reservoir properties and operating conditions of the startup process. As the horizontal sections of SAGD wells often extend many hundred meters, the pressure pulse treatment may be performed along the length of the interwell region by displacing the pressure pulse source along the well at intervals. The intervals may be relatively close (e.g., less than a meter) or may be farther apart (e.g., a distance such that two adjacent micro-fracturing or dilation radii meet). The intervals may be regular or, in some cases, irregular when certain zones along the interwell region are targeted for pulsing (e.g., low permeability zones) while other zones are not subjected to pulsing (e.g., higher permeability zones). The intervals may be pre-determined in accordance with various parameters or may be determined based on monitoring or measurements obtained during the startup operation.
Typically, there is a single pressure pulse source per SAGD well pair that is in operation and that is displaced along the well to pre-treat the interwell region. In some implementations, two or more pressure pulse sources may be provided in a single well. In addition, in some scenarios, a first pressure pulse source may be operated in the SAGD
injection well while a second pressure pulse source is operated in the underlying SAGD
production well. The first and second pressure pulse sources can be operated to treat in the same or different regions of the interwell region.
Reservoir implementations While the startup techniques can be used in a variety of reservoirs to enhance SAGD
startup operations, some reservoirs may be particularly suitable. For example, shallow reservoirs or reservoirs having a relatively low maximum operating pressure (MOP) limitation can benefit from the startup technique which can be performed at lower pressures and thus high-pressure steam circulation can be avoided.
In some scenarios, such as in shallow reservoirs, typical startup methods involving steam circulation are limited to lower steam pressures. Steam circulation at lower steam pressures can lead to slower SAGD startup. Since raising the steam pressure is not an option for some shallow reservoirs, the pressure pulse technique with startup fluid penetration may be employed to accelerate fluid communication between the well pair.
Referring to Fig 2, in some scenarios the interwell region 14 between the SAGD
well pair may include a hydraulic barrier 40 that limits the fluid communication between the wells.
The pressure pulse treatment may enable to provide fractures in the hydraulic barrier 40 in order to facilitate fluid flow and enhance conformance along the well pair.
The pressure pulses may also generate seismic waves that can be used to detect such hydraulic barriers 40 and thereby target those areas for pressure pulse treatments.
In addition, bitumen-containing formations may display "plastic" behavior, such that the 10 material may tend to bend and dilate rather than break and fracture.
Bitumens may be considered to be plastic materials, while limestones and sandstones are examples of naturally-occurring "elastic" rocks. In this context, a "plastic" material is one that behaves in between a solid and a liquid, tending to bend and dilate when pressure is exerted. When the pressure pulsing treatment is implemented in bitumen-containing formations displaying "plastic" behavior, dilation of the near-wellbore reservoir zones may be the dominant mechanism rather than micro-fracturing depending upon the quality of the bitumen and the reservoir conditions. It should also be noted that the properties of the formation may change with factors such as temperature, such that a pre-heated bitumen formation would have greater plastic behaviour compared to the bitumen formation at initial conditions. In some scenarios, a formation may have a combination of elastic and plastic properties, such that both micro-fracturing and dilation occur in response to the pressure pulse treatment. For example, different areas of the reservoir may have different plastic/elastic properties, and/or the plastic/elastic properties of the reservoir may change over time in response to heating which may occur if pre-heated startup fluid is used. Both the pressure pulsing and the penetration pressure may be implemented, controlled or adjusted in accordance with the plastic/elastic properties of the reservoir.
In some implementations, the process is implemented in a generally elastic reservoir such that the pressure pulsing generates micro-fractures in the near-wellbore region. The elastic reservoir may be composed of various minerals and may include various hydrocarbons for recovery. The process may be implemented while the elastic reservoir is at initial reservoir conditions such that the elasticity of the reservoir is greater than at elevated temperatures.
Well completion and steam circulation implementations In some scenarios, an existing SAGD well pair undergoing steam circulation startup may be adapted for implementing the pressure pulse startup process. In such cases, steam circulation is stopped; the completion is removed from the injection well, the lined well is filled with the startup fluid, and the pressure pulse generating device is introduced into the startup fluid-filled injection well.
In the event a SAGD well pair is experiencing difficulty establishing fluid communication under steam circulation, the pressure pulse techniques may be implemented.
This may be particularly advantageous in shallow reservoirs where steam pressure is limited. After the pressure pulse treatment, during which startup fluid has been forced into the micro-fractures and/or dilations, the pressure pulse generating device can be removed, the completion can be re-installed, and the well is pressurised (e.g., at or near MOP) to help keep the micro-fractures open. The treated well can remain pressurized until the surface facilities are available to begin steam circulation. Once steam circulation is ready to begin, the startup fluid remaining in the well can be removed. The completed well can then undergo steam circulation to establish the desired level of fluid communication between the injection and production wells.
In some scenarios, the pressure pulse treatment is performed before any steam circulation is attempted. In this case, the well is only provided with a slotted liner and not completed with additional pipes. After the pressure pulse treatment, the pressure pulse generating device can be removed and the well is pressurised (e.g., at or near MOP) to help keep the micro-fractures open. The treated well can remain pressurized until the surface facilities are available to begin steam circulation. Once steam circulation is ready to begin, the completion can be installed and the startup fluid remaining in the well can be removed. The completed well can then undergo steam circulation to establish the desired level of fluid communication between the injection and production wells.

It is noted that drilling operations are typically conducted in batches when the ground is solid. A series of wellbores are drilled and for elastic reservoirs, such as oil sands bitumen-bearing reservoirs, the wellbores are equipped with liners. In other reservoirs having more consolidated rock defining the wellbore rocks, liner may not be required for the startup process. Once the wellbores are equipped with liners, steam circulation may not be performed for several months for logistical reasons. During this time period, the wells can be subjected to the pressure pulse treatment and then soaked until the steam circulation operation is ready to be implemented.
In fill well and step-out well implementations Various pressure pulse techniques can also be used for infill well or step-out well startup.
Referring to Fig 3, an infill well 44 may be provided in between two SAGD well pairs having respective steam chambers 46 extending from the injection wells 10. A step-out well 48 can also be provided adjacent to one of the SAGD well pairs. Startup fluid and pressure pulse generating devices 20 may be introduced into the infill well 44 and/or the step-out well 48.
Referring to Fig 4, in some scenarios an array 50 of SAGD well pairs with corresponding steam chambers can have infill wells 44 drilled in between each adjacent pair.
For some infill wells, the heat in the surrounding zone may be sufficient to produce hydrocarbons or to enable efficient steam circulation startup. Other infill wells may benefit more from the pressure pulse treatment. In addition, the pressure pulse generating device may be provided into one or more of the infill wells while still at lower temperatures, to generate seismic waves 36. The other wells in the array may be equipped with seismic detection devices, such as distributed acoustic system (DAS) optical fibers, for performing seismic imaging in the area of the SAGD well array 10.
Seismic monitoring implementations In SAGD operations, there are various challenges associated with obtaining information regarding the reservoir characteristics in between wells, whether the interwell region between a given well pair or between adjacent well pairs. Reservoir heterogeneity tends to reduce conformance, and detection of heterogeneity could enable modified operations to improve conformance. There are various seismic techniques that enable detection and mapping of reservoir properties.
Pressure pulse seismic and DAS systems Referring to Fig 1, interwell seismic techniques can enable both generation and detection of seismic waves between wells. In some scenarios, the seismic source may be the pressure pulse generating device 20 that produces seismic waves 36 that propagate through the reservoir. The pressure pulse generating device 20 may be provided within a seismic source well (e.g., the SAGD injection well 10 in Fig 1), while a seismic detection device may be provided in another well (e.g., the underlying SAGD production well 12 in Fig 1) or in the same well. In some scenarios, DAS can be implemented in the same well as the pressure pulse generating device 20.
In some implementations, the seismic detection device may include a distributed acoustic sensing (DAS) system 52 that includes at least one optical fiber 54 coupled to an interrogator 56. The interrogator 56 may be provided at the surface and the optical fibers 54 extend down and along the horizontal sections of the wells 10, 12. The optical fibers 54 can be exposed to the elevated temperature and pressure conditions of SAGD, as the optical fibers can have a temperature rating of about 300 C.
The DAS interrogator 56 is connected to the optical fibers 54 to inject light into the optical fibers 54 and receive return light therefrom. The return light can be analysed to obtain information on one or more seismic event experienced along the length of the optical fiber 54. In some implementations, the DAS system 52 may be a Rayleigh scattering based sensor, where the DAS interrogator 56 launches optical pulses along the optical fibers 54, and the backscattered return light is analysed along selected section(s) of the entire length of the optical fibers 54, to detect and analyze seismic events. In other scenarios, other optical schemes may be used.
The DAS interrogator 56 may include components for generating, controlling or detecting light. In some implementations the detected return light is converted to an electrical or digital signal for processing and analysis.

Referring now to Fig 5, the pressure pulse generating device 20 may be provided in a well that is spaced away from a SAGD well pair 58 equipped with a DAS system. Both the SAGD injection well 10 and the SAGD production well 12 may be equipped with corresponding optical fibers 54 for sensing the seismic waves 36 generated by the pressure pulse generating device 20. In this scenario, the pulsing well may be an infill well 44 or another type of well provided adjacent to the SAGD well pair 58 or sufficiently close such that the seismic waves can be sensed by the optical fibers 54. !nthl wells are often drilled after the adjacent SAGD well pairs have been operating for several years and are relatively hot (e.g., about 270 C). Initially, the infill wells 44 are at a lower temperature and can thus accommodate pressure pulse generating devices having lower temperature tolerance. The lower temperature of the infill wells can thus be leveraged in order to use pressure pulse generating devices for interwell seismic mapping. The infill well and other wells that are part of the SAGD operation can then be operated in accordance with the seismic information.
Fig 6 is a top plan view of first and second arrays 60, 62 of SAGD well pairs 64 extending from corresponding well pads 66. The first well array 60 is older and has been in normal SAGD operation for some time, while the second array 62 includes recently drilled well pairs 64. Thus the first SAGD well array 60 is at elevated operational temperatures (e.g., approximately 270 C), while the second SAGD well array 62 is near reservoir conditions. In some scenarios, a pressure pulse generating device 20 may be introduced into one or more wells of the second SAGD well array 62 in order to generate seismic waves 36.
The seismic waves may be detected by a DAS system that includes optical fibers within one or more of the wells of the first SAGD well array 60 and/or the second SAGD well array 62. In some scenarios, an infill well 44 may be provided in the first SAGD well array 60 and equipped with a pressure pulse generating device 20 for generating seismic waves that can be detected by optical fibers within one or more of the wells of the first SAGD
well array 60 and/or the second SAGD well array 62. Information regarding the reservoir obtained via the DAS system may be used to regulate normal or wind-down operations of the wells in the first SAGD well array 60, and also to regulate startup operations of the wells of the second array 62. It should also be noted that the pressure pulse generating device 20 can be provided in an observation well instead of an infill well 44 as shown in Fig 6.
I

1 i Referring now to Fig 7, the pressure pulse generating device 20 may be provided in an infill well 44 while still below the temperature tolerance of the device 20, to generate seismic waves 36 that may be detected by DAS optical fibers 54 in adjacent wells. The information gathered by the DAS system may be used to detect hydraulic barriers 40 that may potentially cause problems for new wells to be drilled, such that the drilling can be adjusted.
For example, if part of a hydraulic barrier 40 extends substantially into the interwell region of SAGD wells to be drilled, the drilling of the new wells can be performed to avoid the hydraulic barrier 40.
Fig 8 is illustrates another example where an array 50 of SAGD well pairs is shown in front 10 view and a low-lying well 68 is shown in side view, the low-lying well 68 having a horizontal section positioned beneath the SAGD well pairs. The low-lying well 68 may be provided with the pressure pulse generating device 20 and the SAGD well pairs may be equipped with DAS optical fibers for detecting seismic waves.
Various other implementations of using the pressure pulse generating device and the DAS
systems in SAGD operations are also possible. As the DAS can be interrogated at any location along the optical fiber and at any time during the life of the well, the combination of DAS and an downhole seismic source can be used to determine changes in the formation structure during start-up, production, and wind-down, and to provide information for drilling of new well pairs and infill wells.
20 DAS system implementations in SAGD
In addition, DAS systems may be used in SAGD operations without necessarily using a pressure pulse generating device to generate the seismic waves. DAS optical fibers can record various wellbore-related seismic events (e.g., liner failures, gas leaks, etc.) and also detect naturally occurring seismic events (e.g., micro-seismic events) around the wellbore.
Various methods for seismic assessment of a reservoir containing a series of SAGD well pairs may employ a DAS system, in which one or more optical fibers are positioned along the length of one or more SAGD wells. The optical fibers can be arranged on the outside of corresponding casings (in direct contact with the reservoir) or may be located within the wells. Each point along each optical fiber can be interrogated independently to obtain , , i various information (e.g., temperature, pressure, etc.) for any location along the well at any time.
DAS optical fiber can also act as an infinite number of geophones, and can be interrogated and filtered appropriately in time and space to provide seismic data. As the DAS optical fiber can remain in a well throughout the life of the well, seismic data can be gathered at any time without the need to deploy sensors downhole.
In SAGD reservoir environments, local impermeable barriers between injection and production wells can delay the steam circulation process and decrease overall recovery factor. Understanding the location and extension of these barriers can help enhance performance of SAGD operations. Interwell seismic employing DAS optical fibers as temperature resistant geophones can be used to scan the reservoir volume between SAGD
wells for reservoir heterogeneity and to provide guidance to regulate SAGD
production conditions and to conduct new drilling operations. Extending the fi optical fibers along SAGD wells can provide a virtually infinite number of geophones capable of acquiring seismic waves generated from adjacent wells (e.g., operating SAGD injection or production well, newly drilled SAGD injection or production well, infill well, observation well, etc.).
In some implementations, each SAGD well pair in an array of parallel well pairs is equipped with at least one optical fiber running substantially the entire length of the injection well and/or the production well, to provide an array of DAS optical fibers. Seismic waves propagating through the reservoir can be received by the array of DAS optical fibers. The information is transmitted through the optical fibers to a central interrogator or another type of receiver module, which is configured to process the signal information.
Signal processing may include mathematical filters to exclude unnecessary wellbore noise, as well as background and naturally occurring seismic events.
In some scenarios, a method for seismic mapping of a reservoir to be subjected to a SAGD
operation, including: generating seismic waves from a pressure pulse generating device located within a first SAGD well, the pressure pulse generating device having a temperature tolerance and being operated prior to the first SAGD well exceeding the temperature tolerance; detecting the seismic waves via a distributed acoustic sensing (DAS) optical fiber provided within an second SAGD well that is operating above the temperature tolerance of the pressure pulse generating device, to generate a signal; determining reservoir properties based on the signal generated by the DAS optical fiber.
According to the configuration of the seismic source and receivers, the scanned reservoir volume in between can be investigated. Heterogeneity and hydraulic barriers may be detected, and mapping such features can guide new drilling locations, and will help improve SAGD operations, for example by improving conformance and reducing operating expenses of overall SAGD operations.
The seismic wave source may be within a nearby SAGD or observation well, as described above, or may originate from holes shot near the surface, for example. Various seismic sources may be used, such as vibrators, weight drops, explosives, pulsers, sparkers, and so on. For surface seismic sources, the procedures are normally limited to winter time (e.g., for land accessibility) and the whole section from surface to reservoir is included in the signal and thus resolution may be lost. Downhole seismic wave sources may therefore provide various advantages.
DAS has other benefits of monitoring well production and other micro-seismic events (e.g., casing leaks, liner failures, etc.). Permanent installation of DAS optical fibers within SAGD
wells can contribute to overall cost savings in various ways over time.
It should also be noted that various implementations of the processes described herein can be used with traditional SAGD operations or SAGD variants such as solvent-assisted SAGD.

Claims

1. A startup process for a Steam-Assisted Gravity Drainage (SAGD) operation for increasing fluid mobility between a SAGD injection well and a SAGD production well having horizontal sections separated by an interwell region, the process comprising:
pressure pulsing from a pulsing source located within a horizontal section of at least one pulsing well selected from the SAGD injection well and/or the SAGD
production well, the pulsing source being within a startup fluid such that pressure pulses propagate from the pulsing source via the startup fluid and into a treatment zone of the interwell region, thereby providing micro-fracturing and/or dilation in the treatment zone; and providing a penetration pressure on the startup fluid such that a portion of the startup fluid penetrates into the treatment zone to increase fluid mobility in the treatment zone.

2. The startup process of claim 1, wherein the startup fluid comprises a hydrocarbon solvent for dissolving bitumen within the interwell region.

3. The startup process of claim 2, wherein the hydrocarbon solvent comprises at least one of toluene, xylene, diesel, butane, pentane, hexane, heptane and naphtha.

4. The startup process of claim 1, wherein the startup fluid comprises an aqueous solution including a bitumen emulsifier for emulsifying bitumen within the interwell region.

5. The startup process of any one of claims 1 to 4, wherein the startup fluid is a substantially incompressible liquid having a low viscosity within the horizontal section.

6. The startup process of any one of claims 1 to 5, wherein the penetration pressure is provided such that the startup fluid is in liquid phase within the horizontal section.

7. The startup process of any one of claims 1 to 6, wherein the penetration pressure is below the fracturing pressure of the reservoir.

8. The startup process of any one of claims 1 to 6, wherein the penetration pressure is above the fracturing pressure of the reservoir.

9. The startup process of any one of claims 1 to 8, further comprising:
introducing the startup fluid in order to substantially fill at least the horizontal section of the pulsing well.

10. The startup process of any one of claims 1 to 9, further comprising:
pre-heating the startup fluid prior to introducing the startup fluid into the pulsing well.

11. The startup process of any one of claims 1 to 10, further comprising:
providing a soak period for the startup fluid within the interwell region.

12. The startup process of any one of claims 1 to 11, further comprising:
displacing the pulsing source along the horizontal section of the pulsing well.

13. The startup process of claim 12, wherein the pulsing source is displaced along substantially an entire length of a slotted liner within the horizontal section.

14. The startup process of any one of claims 1 to 13, wherein the pressure pulses comprise shockwaves.

15. The startup process of any one of claims 1 to 14, wherein the pressure pulses are generated by ultrasonic pulses, electric sparks, gas expansion, mechanical release of pressurized fluid or exploded solid.

16. The startup process of any one of claims 1 to 15, further comprising:
inserting a pressure pulse generating device into the pulsing well to act as the pulsing source; and controlling the pressure pulse generating device to generate the pressure pulses.

17. The startup process of any one of claims 1 to 16, wherein the pulsing well is the SAGD
injection well.

18. The startup process of claim 17, wherein the pulsing well is a first pulsing well that is the SAGD injection well, and the process comprises providing a second pulsing well that is the SAGD production well.

19. The startup process of any one of claims 1 to 18, further comprising:
operating the SAGD production well to provide a pressure sink.

20. The startup process of any one of claims 1 to 19, further comprising:
providing steam circulation or bullheading via the SAGD injection well;
determining that fluid communication has not been established between the SAGD

injection well and a SAGD production well;
ceasing the steam circulation or bullheading;
introducing the startup fluid into the SAGD injection well; and commencing the pressure pulsing and providing a penetration pressure on the startup fluid.

21. The startup process of any one of claims 1 to 20, wherein the interwell region is part of a generally plastic formation, such that the pressure pulsing provides dilation and fracturing in the treatment zone.

22. The startup process of any one of claims 1 to 20, wherein the interwell region is part of a generally elastic formation, such that the pressure pulsing provides micro-fracturing in the treatment zone.

23. The startup process of any one of claims 1 to 22, wherein the SAGD
operation is in a shallow reservoir.

24. The startup process of any one of claims 1 to 23, wherein the SAGD
operation is in a reservoir having a low maximum operating pressure (MOP) limitation.

25. A method for enhancing Steam-Assisted Gravity Drainage (SAGD) startup of a SAGD
well pair, comprising simultaneously generating pressure pulses from within a horizontal section of a SAGD well of the SAGD well pair to provide micro-fracturing and/or dilation in an interwell region between the SAGD well pair and pressurizing a startup fluid within the SAGD well to penetrate the interwell region.

26. A process for producing hydrocarbons from a reservoir in a Steam-Assisted Gravity Drainage (SAGD) operation, comprising:
drilling a production wellbore and an injection wellbore into the reservoir, the wellbores having respective horizontal sections separated by an interwell region;
providing a slotted liner within the injection wellbore, thereby providing a lined injection well;
introducing a startup fluid into the lined injection well so as to provide a startup fluid-filled horizontal section;
pressure pulsing from a pulsing source located within the startup fluid-filled horizontal section, such that pressure pulses propagate from the pulsing source via the startup fluid and into the interwell region, thereby providing micro-fracturing and/or dilation therein;
providing a penetration pressure on the startup fluid such that a portion of the startup fluid penetrates into the interwell region to increase the fluid mobility therein;
completing the wells to provide a SAGD injection well and a SAGD production well;

providing steam circulation or bullheading via the SAGD injection well to heat the interwell region and achieve fluid communication between the SAGD injection well and the SAGD production well;
producing hydrocarbons from the SAGD production well while injecting steam through the SAGD injection well.

27. The process of claim 26, further comprising, prior to the step of completing the wells to provide the SAGD production well:
providing a second slotted liner within the production wellbore, thereby providing a lined production well;
introducing a second startup fluid into the lined production well so as to provide a second startup fluid-filled horizontal section;
pressure pulsing from a second pulsing source located within the second startup fluid-filled horizontal section, such that pressure pulses propagate from the second pulsing source via the second startup fluid and into the interwell region, thereby providing micro-fracturing and/or dilation therein;
providing a second penetration pressure on the second startup fluid such that a portion of the second startup fluid penetrates into the interwell region to increase the fluid mobility therein.

28. The process of claim 27, wherein the first and second startup fluids are the same.

29. The process of claim 27 or 28, wherein the first and second pulsing sources utilize a same mechanism to generate the pressure pulses.

30. The process of any one of claims 26 to 29, wherein the interwell region is part of a generally plastic formation, such that the pressure pulsing provides dilation and fracturing in the treatment zone.

31. The process of any one of claim 26 to 29, wherein the interwell region is part of a generally elastic formation, such that the pressure pulsing provides micro-fracturing in the treatment zone.