Patent Application
20230074077
The present application claims priority from Australian Provisional Patent Application No. 2020900274 titled “A METHOD FOR EXTRACTION OF HYDROCARBON” and filed on 31 JANUARY 2020, the content of which is hereby incorporated by reference in its entirety.
The present disclosure relates to a method to facilitate the extraction of hydrocarbon from a geological formation. In a particular form, the present disclosure relates to a method to facilitate the extraction of hydrocarbon from a coal seam gas formation.
Unconventional hydrocarbon reservoirs are commonly referred to as those that require greater than industry standard levels of technology or investment to commercialise. Declining production from conventional hydrocarbon reservoirs, coupled with increasing demand for energy worldwide, has led to a major shift towards the commercialisation and viability of unconventional hydrocarbon resources. This paradigm shift has been facilitated by a combination of higher prices and key technological breakthroughs over the past few decades.
When considering unconventional hydrocarbon reservoirs, unconventional gas and associated gas-condensate liquids are at the forefront relative to unconventional heavy oil (for example “tar sands”), due to the geographical abundance of gas, and the fact that its use as a fuel has less environmental impact than the combustion of heavy oil. Some of the common unconventional gas reservoir play types are low-permeability (tight) sandstones, thermogenic shale source rock formations, biogenic and thermogenic coal seams, and methane hydrate accumulations within shallow marine sediments. Some of the most challenging unconventional reservoirs from which to extract commercial hydrocarbon volumes are coal seam gas reservoirs, also referred to as coal seam gas formations.
Presently available drilling, wellbore completion and reservoir stimulation methodologies typically face four key challenges when it comes to extracting and commercialising hydrocarbon from coal seam gas formations, and in particular deep and ultra-deep coal seam gas formations (for which the pre-existing permeability available for gas extraction is typically very low). These challenges mainly apply in the context of the well-established practice, in most unconventional reservoirs, of drilling high-angle or horizontal wellbores. High-angle or horizontal wellbores are proven to be the best-practice approach for drilling and completing unconventional gas reservoirs, since they achieve the high surface area reservoir contact that is essential for the commercial extraction of hydrocarbon. The four main challenges associated with the extraction and commercialisation of hydrocarbon from coal seam gas formations and, in particular, deep and ultra-deep coal seam gas formations, are:
In addition to the above challenges, the most significant obstacle inhibiting the commercialisation of coal seam gas formations and, in particular, deep and ultra-deep coal seam gas formations, is the high initial reservoir confining stress and the extreme sensitivity of the very limited coal fabric apertures to increasing effective stress during extraction of the contained hydrocarbon.
Based on the challenges associated with the extraction of hydrocarbon from specific types of coal seam gas formations, and the commercialisation thereof, there is a need to provide a new, fit-for-purpose method for the extraction of hydrocarbon from such coal seam gas formations that may ideally utilise presently available conventional (standard) oilfield drilling and coiled tubing equipment, whilst being simple, low-cost and repeatable.
It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed.
Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein by way of illustration and example, an embodiment of the present invention is disclosed herein.
Throughout this description of the present invention, the term “abandon”, “abandoned”, “abandoning”, or “abandonment” when referring to a drill string, a lower portion of a drill string, a drilling assembly, a drill bit system, a mud motor, or a drill bit, refers to the act or operation of disconnecting any one of the above from being in connection to a drilling rig, a coiled tubing unit, or any other equipment at the surface that may be used to rotate, run, retrieve or manipulate any one of the drill string, the lower portion of the drill string, the drilling assembly, the drill bit system, the mud motor, or the drill bit. It will also be appreciated, by those skilled in the art, that any one of the terms “abandon”, “abandoned”, “abandoning”, or “abandonment” may refer to one or more of oilfield equipment positioned at a depth below the surface that is currently not connected to any one of the drilling rig, or any other equipment at surface that may be used to rotate, run, retrieve, or manipulate any one or more of the oilfield equipment.
Throughout this description of the present invention, the term “perforation” may refer to any one or more equivalent term(s), which may include, but not be restricted to terms such as “hole”, “aperture”, “port”, “opening”, “slot”, or any other term that may describe a fluid pathway that may be created in a drill string, a casing string, or any other form of production conduit, that facilitates the extraction of hydrocarbon from a geological formation.
Embodiments of the present disclosure relate to a method to facilitate the extraction of hydrocarbon from a coal seam gas formation, the method comprising the steps of: (a) drilling a wellbore using a drill string, to a depth to access at least a portion of the coal seam gas formation; (b) perforating a section of the drill string; (c) severing and abandoning a section of the drill string in the wellbore, comprising the perforated section; (d) setting a temporary plug to isolate the severed and abandoned section of the drill string; (e) installing a production tubing string above the temporary plug and the severed and abandoned section of the drill string, so as to create a fluid passageway to facilitate the extraction of hydrocarbon from the coal seam gas formation; (f) displacing a fluid above the temporary plug, so as to create a high pressure differential; (g) removing the temporary plug, thereby creating an initial stimulated reservoir volume to extract hydrocarbon from the coal seam gas formation and, resultantly, at least partially filling an annulus, formed between the severed and abandoned section of the drill string and the wellbore wall, with coal fragments of the coal seam gas formation; and (h) continuing to extract hydrocarbon from the coal seam gas formation, via the fluid passageway, at a high pressure drawdown, so as to create an expanding stimulated reservoir volume.
According to a first aspect, there is provided a method to facilitate the extraction of hydrocarbon from a geological formation, the method comprising the steps of: (a) drilling a wellbore below one or more casing string(s) using a drill string, to a depth to access at least a portion of the geological formation, wherein a lower portion of the drill string comprises a drilling assembly and one or more stabilising means; (b) perforating a section of the drill string, with access to the portion of the geological formation using coiled tubing, wherein the perforated section of the drill string comprises the lower portion of the drill string; (c) severing and abandoning a section of the drill string in the wellbore, with access to the geological formation, so as to create an abandoned section of the drill string having an open-ended stub disposed within the one or more casing string(s); (d) setting a temporary plug above the open-ended stub, so as to isolate the abandoned section of the drill string, the wellbore, and the geological formation below the temporary plug; (e) installing a production tubing string within the one or more casing string(s), to a depth above the temporary plug and the open-ended stub, thereby creating a fluid passageway to facilitate the extraction of hydrocarbon from the geological formation through the abandoned section of the drill string; (f) displacing a fluid above the temporary plug, so as to create a high pressure differential between the one or more casing string(s) above the temporary plug and the wellbore and the geological formation below the temporary plug; (g) removing the temporary plug, so as to allow the wellbore to produce through the fluid passageway, thereby creating an initial stimulated reservoir volume to facilitate the extraction of hydrocarbon from the geological formation and, resultantly, at least partially filling an annulus, formed between the abandoned section of the drill string and the wellbore wall, with fragments of the geological formation; and (h) continuing to extract hydrocarbon from the geological formation, at a high pressure drawdown, so as to create an expanding stimulated reservoir volume.
In one form, the geological formation from which hydrocarbon is extracted is a coal seam gas formation.
In one form, the wellbore produces through the fluid passageway, in response to a pressure differential between a flowline at a surface location of a drilling rig and the geological formation.
In one form, the expanding stimulated reservoir volume grows larger and more permeable over production time.
In one form, the abandoned section of the drill string functions as a production conduit to facilitate the extraction of hydrocarbon from the geological formation.
In one form, the production conduit provided by the abandoned section of the drill string is accessible from the fluid passageway created by the production tubing string, thereby facilitating the extraction of hydrocarbon from the geological formation.
In one form, the fragments of the geological formation are coal fragments that bulk the annulus formed between the abandoned section of the drill string and the wellbore wall.
In one form, the drilling assembly of the drill string comprises a drill bit system, comprising a mud motor and a drill bit.
In one form, a diameter of the drill bit is selected to maximise the size of the annulus formed between the abandoned section of the drill string and the wellbore wall in the geological formation.
In one form, the one or more stabilising means comprises one or more reamer(s), and/or stabiliser(s), and/or centraliser(s), so as to support the lower portion of the drill string in the wellbore.
In one form, the one or more stabilising means facilitate(s) the removal of any large fragments of the geological formation that may be present in the annulus formed between the abandoned section of the drill string and the wellbore wall, thereby minimising the risk of the drill string becoming stuck during the construction of the wellbore.
In one form, a drill pipe severing tool may be used to abandon a section of the drill string in the wellbore, with access to the geological formation.
In one form, one or more types of coiled tubing conveyed drill pipe severing tool(s) may be used to abandon a section of the drill string in the wellbore, with access to the geological formation.
In one form, the abandoned section of the drill string is left in situ with respect to the geological formation.
In one form, the abandoned section of the drill string is left unsecured with respect to the geological formation.
According to a second aspect, there is provided a method to facilitate the extraction of hydrocarbon from a geological formation, the method comprising the steps of: (a) drilling a wellbore below one or more casing string(s) using a drill string, to a depth to access at least a portion of the geological formation, wherein a lower portion of the drill string comprises a drilling assembly, one or more stabilising means, and one or more temporarily sealed, pre-perforated drill pipe segment(s); (b) removing, opening or breaking one or more temporary seal(s) of the one or more temporarily sealed, pre-perforated drill pipe segment(s), thereby creating one or more open perforation(s) along the lower portion of the drill string, so as to facilitate the extraction of hydrocarbon from the geological formation; (c) parting and abandoning a section of the drill string in the wellbore, with access to the geological formation, by “backing off” (unscrewing) a joint between adjoining drill pipe segments, at a “tensile free point” (or “free point”) in the drill string, so as to create an abandoned section of the drill string having an open-ended stub disposed within the one or more casing string(s); (d) setting a temporary plug above the open-ended stub, so as to isolate the abandoned section of the drill string, the wellbore, and the geological formation below the temporary plug; (e) installing a production tubing string within the one or more casing string(s), to a depth above the temporary plug and the open-ended stub, thereby creating a fluid passageway to facilitate the extraction of hydrocarbon from the geological formation through the abandoned section of the drill string; (f) displacing a fluid above the temporary plug, so as to create a high pressure differential between the one or more casing string(s) above the temporary plug and the wellbore and the geological formation below the temporary plug; (g) removing the temporary plug, allowing the wellbore to produce through the fluid passageway, thereby creating an initial stimulated reservoir volume to facilitate the extraction of hydrocarbon from the geological formation and, resultantly, at least partially filling an annulus formed between the abandoned section of the drill string and the wellbore wall with fragments of the geological formation; and (h) continuing to extract hydrocarbon from the geological formation, at a high pressure drawdown, so as to create an expanding stimulated reservoir volume.
In one form, the geological formation from which hydrocarbon is extracted is a coal seam gas formation.
In one form, the wellbore produces through the fluid passageway, in response to a pressure differential between a flowline at a surface location of a drilling rig and the geological formation.
In one form, the expanding stimulated reservoir volume grows larger and more permeable over production time.
In one form, the abandoned section of the drill string advantageously functions as a production conduit to facilitate the extraction of hydrocarbon from the geological formation.
In one form, the production conduit provided by the abandoned section of the drill string is accessible from the fluid passageway created by the production tubing string, thereby facilitating the extraction of hydrocarbon from the geological formation.
In one form, the fragments of the geological formation are coal fragments that bulk the annulus formed between the abandoned section of the drill string and the wellbore wall.
In one form, the one or more temporarily sealed, pre-perforated drill pipe segment(s) is/are temporarily sealed using one or more blanked-off shear-pin stub(s), one-way valve(s), one-way ball seal(s), or differential pressure-activated burst disk(s).
In one form, activation of one or more of the blanked-off shear-pin stub(s), the one-way valve(s), the one-way ball seal(s), or the differential pressure-activated burst disk(s) removes, opens or breaks one or more temporary seal(s) of the one or more temporarily sealed, pre-perforated drill pipe segment(s), thereby creating one or more open perforation(s) along the lower portion of the drill string, so as to facilitate the extraction of hydrocarbon from the geological formation.
In one form, the drilling assembly of the drill string comprises a drill bit system, comprising a mud motor and a drill bit.
In one form, a diameter of the drill bit is selected to maximise the size of the annulus formed between the abandoned section of the drill string and the wellbore wall in the geological formation.
In one form, the one or more stabilising means comprises one or more reamer(s), and/or stabiliser(s), and/or centraliser(s), so as to support the lower portion of the drill string in the wellbore.
In one form, the one or more stabilising means facilitate(s) the removal of any large fragments of the geological formation that may be present in the annulus formed between the abandoned section of the drill string and the wellbore wall, thereby minimising the risk of the drill string becoming stuck during the construction of the wellbore.
In one form, the abandoned section of the drill string is left in situ with respect to the geological formation.
In one form, the abandoned section of the drill string is left unsecured with respect to the geological formation.
Embodiments of the present disclosure will be discussed with reference to the accompanying drawings, wherein:
In the following description, like reference characters designate like or corresponding parts throughout the Figures.
In the embodiments of the present disclosure that follow, although the described method may particularly be applicable to coal seam gas formations, as well as other formation types, the present disclosure is specifically designed to be a fit-for-purpose solution to the severe, but not insurmountable, technical and commercial challenges imposed by coal seam gas formations that are deeper than the well-established “permeability depth limit” of conventional shallow coal seam gas (CSG) formations (approximately 6,000 feet / 1,830 metres). Such “deep” and “ultra-deep” coal seam gas formations represent a very different play type, having reservoir characteristics that more closely resemble those of a shale gas play. A new set of geological and environmental properties exists, for which a very different drilling, wellbore completion and reservoir stimulation approach is required. The current technical and commercial practices applied to shallow coal seam gas reservoirs are not applicable in “deep” and “ultra-deep” geological settings. As an example, “deep” and “ultra-deep” coal seam gas formations typically have no commercially significant pre-existing coal fabric (i.e. cleat) permeability, and contain an insignificant amount of mobile formation water. For this reason, the present invention disclosed herein deliberately excludes the use of any form of conventional (standard) artificial lift system, such as a downhole “electrical submersible pump” (ESP), for dewatering the coal seam gas formation, so as to reduce pressure within the coal seam gas formation and initiate desorptive gas production. In essence, the present invention disclosed herein describes a contrarian (or “disruptive”) holistic drilling, wellbore completion and reservoir stimulation process, which may be achieved by only a single, “one-way trip” of the drill string into the coal seam gas formation, whilst maintaining continuous contact of the drill bit with the cutting face. Current gas extraction techniques applied to shallow coal seam gas formations require multiple trips into the coal seam gas formation, which typically include; 1) drilling of the initial pilot hole, which invariably requires the drill bit to be removed from the cutting face on multiple occasions during “drill pipe connections”, “wiper trips”, and finally when the drill string is retrieved to surface, 2) installation of a production casing string and/or some form of wellbore completion string, and 3) installation of an artificial lift system, so as to de-water the shallow coal seam gas formation, which typically involves the use of a downhole electrical submersible pump.
Referring to any one of the Figures, there is illustrated a method to facilitate the extraction of hydrocarbon from a geological formation (100). The method generally relates to the extraction of hydrocarbon, such as gas from coal seams, and in particular “deep” and “ultra-deep”, very low permeability coal seams, that do not respond to presently available hydrocarbon extraction techniques (such as, for example, hydraulic fracture stimulation, hydraulic jetting, open-hole cavitation, or under-reaming techniques).
Particularly, the present invention relates to a method that may entirely utilise, but not necessarily be restricted to, presently available conventional (standard) oilfield drilling and coiled tubing equipment, methods, and techniques to:
More particularly, and referred to herein, the present invention relates to a method to facilitate the extraction of gas from a coal seam gas formation (100'). Thus, the reference to "gas" may be interchangeably used with "hydrocarbon", the reference to "geological formation" may be interchangeably used with "coal seam gas formation", or "coal seam formation", or "coal seam reservoir", and the terms "extract/extraction" may be interchangeably used with "produce/production". However, it will be appreciated, while the following method relates primarily to gas and coal seam formations, the method may also be applicable to the extraction of other hydrocarbon types (such as oil and gas-condensate liquids) from other geological formation types.
With reference to coal seam gas formations (100') in this description of the present invention, and the extraction of gas therefrom, the discussion below relates to background and theory with respect to i) the impact of stress on the permeability of coal seam gas formations and how this may be modulated by the prevailing geomechanical reservoir boundary condition, and ii) Pressure Arch Theory.
Stress is generally accepted to be a dominant variable that ultimately controls the permeability and hence flow rate capacity of all coal seam formations. For shallow coal seam gas (CSG) reservoirs (also commonly referred to as coalbed methane (CBM) reservoirs), gas extraction efficiency is primarily controlled by the initial stress state of the reservoir. Reservoir confining stress is generally relatively low, so shallow coal seams are typically permeable and flow freely. Thus, in many shallow coal seam gas formations, reservoir stimulation treatments may not be required. Over the life of a wellbore, production performance is typically modulated by the stress path, as desorption-induced coal matrix shrinkage interacts with the prevailing geomechanical reservoir boundary condition during the depletion/extraction of gas from the coal seam gas reservoir. That is to say, the permeability of coal seam gas reservoirs becomes dynamic.
The lower the native coal seam gas reservoir permeability, the more critical is the stress path to maintaining gas extraction For the specific type of coal seam gas reservoir being targeted by the present invention, the native stress state is too high for pre-existing commercial coal fabric permeability to exist. The stress path itself, when combined with a compatible up-front reservoir stimulation strategy, becomes the primary control on gas extraction efficiency from the coal seam gas reservoir. In this way, in order to achieve a commercial gas flow rate and ultimate gas recovery (extraction), a large, complex domain of enhanced permeability must be artificially created by engineering a stress path that leads to stress-reduction.
The fabric permeability of all coal seams during gas extraction is dynamic and very sensitive to reservoir confining stress. It is strongly controlled by the large-scale physical response of the coal seam and the surrounding host rock framework to the increasing effective stress generated by production pressure drawdown. Whether permeability increases, decreases, or does both over time, as gas is extracted (produced) from the coal seam gas reservoir, depends upon the complex, competitive interaction that occurs between ongoing desorption-induced coal matrix shrinkage and the prevailing geomechanical reservoir boundary condition. Hence, to understand the reservoir stimulation requirements of low-permeability coal seam gas formations, it is essential that the correct geomechanical reservoir boundary condition be identified. Owing to the generally extreme depths of the coal seam gas formations (100') specifically being targeted by the present invention, typical geomechanical reservoir boundary conditions applicable to shallow coal seam gas reservoirs cannot be assumed by default. The method of the present invention harnesses and optimises the phenomenon of desorption-induced coal matrix shrinkage, which counteracts the tendency for reservoir compaction by promoting the dilation of coal fabric apertures, to thereby increase permeability of the coal seam gas formation.
One of the most significant obstacles inhibiting the commercialisation of coal seams below the “permeability depth limit” of conventional shallow coal seam gas (CSG) formations is the high initial reservoir confining stress and the extreme sensitivity of the very limited coal fabric apertures to increasing effective stress during gas extraction. One solution to this obstacle may be the application of Pressure Arch Theory (or simply “pressure arching”), which is a well-established, widely recognised, macro-scale geomechanical concept, originally conceived in the context of the underground coal mining industry.
Pressure Arch Theory demonstrates that a proven mechanism may exist for dynamically enhancing the permeability of coal seam gas formations at extreme depth and stress. In principle, once desorptive gas production has been initiated around a wellbore by some form of up-front reservoir stimulation treatment, and the isolated fracture network stimulated reservoir volume (SRV) domain is exposed to continuous, high production pressure drawdown, pressure arching causes an “expanding reservoir boundary and decreasing confining stress” condition to be generated that locally neutralises the pre-existing reservoir confining stress and shields the production pressure transient region from the compaction effect caused by increasing production pressure drawdown-induced effective stress.
Pressure Arch Theory may not yet have been evaluated, modelled, and/or field-tested by the oil and gas industry as a potential tool for assisting in the commercialisation of coal seam gas reservoirs. As such, an opportunity exists for Pressure Arch Theory to be harnessed by the method of this present invention, so as to neutralise the detrimental effects of high initial reservoir confining stress and increasing effective stress during production. If these effects can be significantly reduced within the time frame of gas extraction, ongoing desorption-induced coal matrix shrinkage may generate an isolated “self-fracturing reservoir” domain, within which the coal fabric planes of weakness open, dilate and extend outwards, away from the wellbore, as gas is produced from the coal seam gas reservoir.
In essence, pressure arching with respect to geological formations is caused by a non-uniform areal distribution of reduced pore pressure and/or geomechanical competence. This, in turn, leads to a non-uniform areal distribution of increased effective stress and reduced reservoir confining stress. In this way, the amount of reservoir confining stress reduction is a function of pore pressure reduction and the effectiveness of pressure arch formation. Pressure arching is most effective when the region of reduced pore pressure and/or geomechanical competence is small and geomechanically compliant compared to the scale and rigidity of the surrounding host rock framework of the geological formation.
There are four main factors controlling the generation of pressure arch effects and their effectiveness as stress shields for underlying isolated voids, and they are (assuming, for simplicity and conceptual understanding, that the maximum stress direction is vertical):
Based on the discussion above regarding Pressure Arch Theory, the novel reservoir stimulation technique disclosed herein employs the creation of an initial, up-front subsurface excavation, or cavity, as this represents the most “incompetent” member of the geomechanical spectrum, and has maximum stress transmission contrast with respect to the host rock (geological formation) framework. In this way, the method disclosed herein may achieve optimal pressure arch development, and invoke the resultant de-stressing effect as a mechanism for allowing desorption-induced coal matrix shrinkage to increase the aperture width (i.e. permeability) of coal seam fabric planes of weakness, in defiance of the rapidly increasing effective stress during the extraction of hydrocarbon from the geological formation (100).
The method disclosed herein requires two presently available, conventional (standard) oilfield drilling and wellbore completion systems, and/or equipment, consisting of; a standard drilling rig (200), and a standard coiled tubing unit (300). In this way, it will be appreciated, by those skilled in the art, that the method advantageously may not require any specialised drilling, wellbore completion or reservoir stimulation equipment. Thus, standard, generic oilfield equipment may be used, or re-purposed, so as to achieve any one of the embodiments of the method disclosed below.
Referring now to any one of
The drilling rig (200), illustrated by any one of
The wellbore (110) may be drilled by the drilling rig (200) under pressure-overbalanced conditions, whereby the drilling fluid utilised may be selected to have an adequate mudweight, such that the resultant combination of drilling fluid hydrostatic pressure and drilling fluid circulation pressure is significantly greater than the pore pressure within the geological formation (100) being drilled. Pressure-overbalanced drilling conditions may advantageously serve to provide structural integrity to the wellbore (110), particularly in the coal seam gas formation (100’). This structural integrity may be achieved by counteracting the lithostatic and tectonic stresses that would otherwise promote the deformation or eventual collapse of the wellbore (110) in the coal seam gas formation (100'). In this way, maintaining high drilling fluid hydrostatic pressure, combined with high drilling fluid circulation pressure within the wellbore (110), may inhibit the release of large coal fragments (140) of the coal seam gas formation (100’) into the annulus (211) where, if not efficiently expelled from the wellbore (110) to surface, the large coal fragments (140) may impede drilling of the wellbore (110), and may potentially cause the drill string (220) to become stuck in the wellbore (110), thereby potentially preventing its ability to drill further into the coal seam gas formation (100'). Pressure-overbalanced drilling may be further advantageous in high-angle or horizontal wellbores (110) (as illustrated in any one of
The drill string (220) may comprise a lower portion (221). The lower portion (221) of the drill string (220) may comprise a drilling assembly (222), which may often be referred to as a bottomhole assembly (BHA), and one or more stabilising means (223).
The drilling assembly (222) of the drill string (220) may comprise a drill bit system (224) at the point at or near the advancing face (120) of the wellbore (110) being constructed. The drill bit system (224) may optionally comprise a motor (225), and a drill bit (226).
In one embodiment, the optional motor (225) may be a mud motor, comprising a rotor and a stator (both not shown), whereby the drill bit (226) may be driven by the circulation pressure of the drilling fluid. The use of the mud motor (225) in the drill bit system (224) and thus the drill string (220) to drill the wellbore (110), advantageously does not require the drill string (220) to be rotated in order for the drill bit (226) to drill the wellbore (110), and thereby the coal seam gas formation (100'). Hence, the use of the mud motor (225) may reduce or eliminate possible eccentric rotation (otherwise referred to as “whipping”) of the drill string (220) that may cause it to collide against and destabilise the wellbore wall (110), thereby potentially releasing large coal fragments (140) of the coal seam gas formation (100’) into the annulus (211).
In an alternative embodiment, the drill bit system (224) may comprise a rotary drilling system (not shown) and the drill bit (226). In this embodiment, the drill bit (226), the rotary drilling system (not shown), and thus the drill bit system (224), may be driven by rotational torque transmitted from the drilling rig (200) via the drill string (220) to thereby drill the wellbore (110).
In one embodiment, a diameter of the drill bit (226) may be selected, so as to maximise the size of the annulus (211) formed between the drill string (220) and the wellbore wall (110) in the geological formation (100). Maximising the size of the annulus (211) via the larger diameter drill bit (226) advantageously contributes to the overall success of the method, by correspondingly maximising the size of the initial stimulated reservoir volume (i-SRV) (800 in
In one embodiment, the one or more stabilising means (223) may comprise one or more reamer(s), and/or stabiliser(s), and/or centraliser(s) to support the lower portion (221) of the drill string (220) in the wellbore (110), as well as facilitating the removal (via a grinding action) of any large fragments (140) of the geological formation that may be present in the annulus, and which may obstruct the drilling process, thereby minimising the risk of the drill string becoming stuck during the construction of the wellbore. In an alternative embodiment, it will be appreciated that the one or more stabilising means (223) may also be positioned anywhere along the drill string (220), so as to support the drill string (220) in the wellbore (110), as well as providing the aforementioned wellbore cleaning function. In either of these embodiments, the one or more stabilising means (223) may be positioned in the drill string (220), and the lower portion (221) of the drill string (220), so as to be located in the high-angle and horizontal sections of the wellbore (110). In this way, the one or more stabilising means (223) may advantageously function to centralise the drill string (220), and the lower portion (221) of the drill string (220), thereby reducing drag whilst drilling the wellbore (110), and assist in the drilling of the coal seam gas formation (100') by grinding through any large coal fragments (140) that may have collapsed from the wellbore wall (110) and may now reside in the annulus (211) along the high-angle and horizontal sections of the wellbore (110), thereby reducing the risk of the drill string (220) becoming stuck prematurely during drilling.
In one embodiment, referring now to any one of
In the above embodiment, referring particularly to
In any one of the above embodiments, referring to any one of
Still referring to any one of the above embodiments, and
Referring now to any one of
In this embodiment, a pressure seal device (not shown) may be installed with the coiled tubing unit (300), which is well known, to those skilled in the art, as a “lubricator” or “stripper”, so as to allow the coiled tubing string (310) to be pushed down the inside of the drill string (220), without the drill string (220), the lower portion (221) of the drill string (220), or the drilling assembly (222) being exposed to atmospheric pressure, thereby maintaining well control.
In one embodiment, still referring to
In an alternative embodiment, whereby the drill string (220) includes one or more temporarily sealed (228a), pre-perforated drill pipe segment(s) (227), referring now to any one of
In this embodiment, whereby the lower portion (221) of the drill string (220) comprises one or more temporarily sealed (228a), pre-perforated drill pipe segment(s) (227), and the coiled tubing unit (300) is installed on the drilling rig (200), the coiled tubing (310) conveyed drill pipe perforating device may be positioned at a point at or near the end (320) of the coiled tubing string (310), and may perform the perforating mechanism, so as to create one or more additional direct perforation(s) (not shown). In this way, additional fluid pathways between the geological formation (100), the wellbore (110) and the lower portion (221) of the drill string (220) may be created in the drill string (220) that already comprises one or more temporarily sealed (228a), pre-perforated drill pipe segment(s) (227).
In any one of the above embodiments, referring now to any one of
Referring now to any one of
In an alternative embodiment, referring now particularly to
In either one of the above embodiments, as illustrated by
Additionally, in either one of the above embodiments, the section of the drill string (220) comprising the lower portion (221) of the drill string (220), and the drilling assembly (222), advantageously functioning as the production conduit to facilitate the extraction of hydrocarbon from the geological formation (100), may function in a similar manner to a typical “conventional” wellbore completion string, such as those used in presently available wellbore completion methods. It will be appreciated, by those skilled in the art, that advantageously, the method disclosed herein does not require any of the typical “conventional” wellbore completion strings used in presently available wellbore completion methods, rather, the drill string (220) utilised to drill the wellbore (110), with access to the geological formation (100), advantageously functions as the production conduit to facilitate the extraction of hydrocarbon from the geological formation (100). This reduces the time, cost and operational challenges that would otherwise be associated with the installation of typical “conventional” wellbore completion strings by presently available wellbore completion methods.
Prior to the next Step (d) of the method, optionally, the drilling rig (200) may be utilised to repeat Steps (a) to (c), so as to drill additional wellbores (not shown), by sidetracking procedures, that are well known to those in the art, originating from the same one or more casing string(s) (210). These additional wellbores (not shown) may be drilled, so as to be within or immediately adjacent to the coal seam gas formation (100’), or so as to target additional coal seam gas formations (not shown). This results in a multilateral well design (not shown). In this way, the multilateral well design (not shown) may include one or more additional open-ended stub(s) (not shown), associated with one or more additional abandoned drill string section(s) (not shown), abandoned within the additional wellbores (not shown) that may have access to the coal seam gas formation (100’), or target additional coal seam gas formations (not shown). It will also be appreciated that each of the subsequent one or more additional open-ended stub(s) (not shown), resultant from the one or more additional abandoned drill string section(s) (not shown), resultant from sidetracking procedures from the original one or more casing string(s) (210), may be positioned shallower in relation to the previous open-ended stub (229) (not shown). Thereby, each of the one or more additional open-ended stub(s) (not shown), associated with the one or more additional abandoned drill string section(s) (not shown), may provide one or more corresponding additional production conduit(s) (not shown), so as to further facilitate the extraction of hydrocarbon from the geological formation (100), or the coal seam gas formation (100'). Additionally, in this way, the repetition of Steps (a) to (c), so as to drill the additional wellbores (not shown), resulting in the multilateral well design (not shown), advantageously enables the consistent, non-problematic, and cost-effective drilling of long-reach high-angle wellbores (110) and long-reach horizontal wellbores (110) within inherently unstable geological formations (100).
Referring now to any one of
In the embodiment wherein the multilateral well design (not shown) is drilled by the drilling rig (200), so as to be within or immediately adjacent to the coal seam gas formation (100’), or additional “target” coal seam gas formations (not shown), the temporary plug (400) may be positioned within the one or more casing string(s) (210) at an optimal depth that is immediately above the shallowest positioned one or more additional open-ended stub(s) (not shown) associated with the one or more additional abandoned drill string section(s) (not shown). In this way, the temporary plug (400) may isolate the one or more additional abandoned drill string section(s) (not shown), the lower, openhole section of the one or more associated additional wellbore(s) (not shown), and the geological formation (100), or the coal seam gas formation (100'), which all lie below the temporary plug (400).
Still referring to any one of
In this embodiment, the production tubing string (600) may be installed via procedures that are well known to those skilled in the art, by way of either the drilling rig (220), or the coiled tubing unit (300), so as to position the production tubing string (600) to an optimal depth that is immediately above the temporary plug (400), and thence the open-ended stub (229) of the abandoned section of the drill string (220).
Also in this embodiment, whereby the production tubing string (600) may be installed within the one or more casing string(s) (210), a production tubing packer (620) may be positioned in an annulus (630) formed between the production tubing string (600) and the innermost casing string (210). The production tubing packer (620) may also be referred to as a production packer (620), to those skilled in the art, the function of which is to isolate zones within the wellbore (110), and direct extracted hydrocarbon from the geological formation (100), without loss of pressure or fluid to the annulus (221).
In any one of the above embodiments, in the instance that the multilateral well design (not shown) exists, the production tubing string (600) may be installed via procedures that are well known to those skilled in the art, so as to position the production tubing string (600) to an optimal depth that is immediately above the temporary plug (400), and thence the one or more additional open-ended stub(s) (not shown) of the one or more additional abandoned drill string section(s) (not shown) that may exist in the multilateral well design (not shown).
Still referring to any one of
In this embodiment, the blowout preventer (230) may be removed, so as to permit the installation of a wellhead (not shown), the functions of which are known, to those skilled in the art, to permit completion of the wellbore and allow the safe, controlled extraction of hydrocarbon from the geological formation (100). The wellhead is typically installed so as to be compatible with the one or more casing string(s) (210). Optionally, the drilling rig (200) may be demobilised, so as to drill one or more additional wellbore(s) (not shown) elsewhere, as a part of a drilling program, whereby, prior to the creation of one or more initial stimulated reservoir volume(s) (i-SRV) (800 in
Referring now to any one of
In this embodiment, the initial stimulated reservoir volume (i-SRV) (800 in
Additionally, in this embodiment, although the abandoned section of the drill string (220) is left in situ and unsecured with respect to the geological formation (100), it will be appreciated, by those skilled in the art, that a by-product of the bulking of the annulus (211) between the abandoned section of the drill string (220) and the wellbore wall (110) may advantageously function to secure, and provide structural support, to the section of the drill string (220) abandoned within the wellbore (110), with access to the coal seam gas formation (100'). To those skilled in the art, the by-product advantage provided by the bulking of the annulus (211) may function similar to (without the inherent restrictions, but comprising similar structural benefits of) cementing the abandoned section of the drill string (220) in place, by the typical “conventional” cementing process. Furthermore, it will be appreciated, by those skilled in the art, that it is not the intention, and it would be counterproductive of the method disclosed herein, to introduce any one or more of a cement, a slurry, a gravel pack, and indeed casing and screens, which form the basis for more “conventional” wellbore completions.
Furthermore, in this embodiment, optionally, one or more follow-up reservoir stimulation event(s) may be performed, as described in this Step (g), at any time during the production life of the wellbore (110), so as to potentially enhance the size and permeability of the initial stimulated reservoir volume (i-SRV) (800 in
Still referring to any one of
In this embodiment, it will be appreciated, by those skilled in the art, being apparent due to the method disclosed herein, that the creation of the expanding stimulated reservoir volume (e-SRV) (900 in
In any one of the above embodiments, referring now to
Referring to any one of the above embodiments, and any one of
It will additionally be appreciated, that the method disclosed herein, comprising Steps (a) to (h), advantageously utilises presently available conventional (standard), generic oilfield equipment, primarily comprising the use of the drilling rig (200) and the coiled tubing unit (300). Thereby, the method disclosed herein provides for the use of presently available oilfield drilling and coiled tubing equipment, methods, and techniques, to facilitate the extraction of hydrocarbon from one or more coal seam(s) of the coal seam gas formation (100'), particularly those coal seams containing gas in deep and ultra-deep, very low permeability settings that do not respond to presently available hydrocarbon extraction and commercialisation methods and techniques. Advantageously, the method disclosed herein, comprising Steps (a) to (h), overcomes the four key challenges associated with the extraction and commercialisation of hydrocarbon from coal seal gas formations (100'), thereby providing a simple, low-cost, repeatable solution, which enables the commercialisation of coal seam gas formations (100') on a full-cycle standalone basis.
It will further be appreciated that the method disclosed herein advantageously achieves a commercial hydrocarbon flow rate and ultimate hydrocarbon recovery by “engineering” an artificial path of stress reduction within the coal seam gas formation (100') that leads to the creation of a large, complex domain of enhanced coal fabric permeability, comprising the initial stimulated reservoir volume (i-SRV) and the expanding reservoir volume (e-SRV) (800 and 900 respectively in
It will be apparent, to those skilled in the art, that the method to facilitate the extraction of hydrocarbon from the geological formation (100) disclosed herein, advantageously provides a new, contrarian (or “disruptive”) method for drilling and completing wellbores (110), that involves only a single, “one-way trip” of the drill string (220) into the geological formation (100), which is then deliberately abandoned in situ and left unsecured with respect to the geological formation (100). That is, those skilled in the art will identify that the method disclosed herein is contrary to currently accepted drilling, wellbore completion, and reservoir stimulation practices, whereby drill strings/casing strings/liner strings are ultimately cemented or secured in the wellbore (110) prior to performing operations that specifically facilitate the extraction of hydrocarbon. Advantageously, the method disclosed herein does not require the step of cementing, or securing in any other way, the abandoned section of the drill string (220) in the wellbore (110), with access to the geological formation (100), in order to facilitate the extraction of hydrocarbon. Indeed, such a “conventional” approach to wellbore completion would be deleterious to the method disclosed herein.
It will be appreciated, by those skilled in the art, that the geological formation (100) and the coal seam gas formation (100') that are the targets of the method disclosed herein, may be independent of conventional geological hydrocarbon-trapping structures sensu stricto (e.g. anticlines). Those skilled in the art will appreciate that thermogenic source rock reservoir types, such as deep, high-temperature shale formations, and deep, high-temperature coal seams, do not require a structural trapping mechanism for hydrocarbon (particularly gas) to accumulate. Hence, the geological target of the method disclosed herein may justifiably be referred to as a geological formation (100) and/or a coal seam gas formation (100').
Throughout the specification and the claims that follow, unless the context requires otherwise, the words “comprise” and “include”, and variations such as “comprising” and “including”, will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.
It will be appreciated, by those skilled in the art, that the disclosure is not restricted in its use to the particular application described. Neither is the disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions, without departing from the scope of the disclosure, as set forth and defined by the following claims:
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020900274 | Jan 2020 | AU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2021/000008 | 1/29/2021 | WO |
