WO2011000089A1 - Methods of fracturing hydrocarbon reservoirs - Google Patents

Methods of fracturing hydrocarbon reservoirs Download PDF

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Publication number
WO2011000089A1
WO2011000089A1 PCT/CA2010/000996 CA2010000996W WO2011000089A1 WO 2011000089 A1 WO2011000089 A1 WO 2011000089A1 CA 2010000996 W CA2010000996 W CA 2010000996W WO 2011000089 A1 WO2011000089 A1 WO 2011000089A1
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WO
WIPO (PCT)
Prior art keywords
fracture
hydrocarbon
reservoir
pressure
bridging agent
Prior art date
Application number
PCT/CA2010/000996
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French (fr)
Inventor
Grant Nevison
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Gasfrac Energy Services Inc .
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Publication date
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Publication of WO2011000089A1 publication Critical patent/WO2011000089A1/en

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Classifications

    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/2605—Methods for stimulating production by forming crevices or fractures using gas or liquefied gas
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/62—Compositions for forming crevices or fractures
    • C09K8/70—Compositions for forming crevices or fractures characterised by their form or by the form of their components, e.g. foams
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
    • C09K8/60—Compositions for stimulating production by acting on the underground formation
    • C09K8/80—Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K2208/00—Aspects relating to compositions of drilling or well treatment fluids
    • C09K2208/18—Bridging agents, i.e. particles for temporarily filling the pores of a formation; Graded salts

Abstract

A method of fracturing a hydrocarbon reservoir penetrated by a well, the method comprising introducing hydrocarbon fracturing fluid comprising liquefied petroleum gas into the hydrocarbon reservoir through the well at a pressure high enough to form a fracture in the hydrocarbon reservoir, narrowing the fracture and driving bridging agent into the fracture to form a bridged fracture that is restricted from further fracturing, the bridged fracture being permeable to fluids from the hydrocarbon reservoir, and increasing the pressure of the hydrocarbon fracturing fluid in the well to a pressure that is high enough to form a subsequent fracture in the hydrocarbon reservoir.

Description

METHODS OF FRACTURING HYDROCARBON RESERVOIRS
TECHNICAL FIELD
[0001] This document relates to methods of fracturing hydrocarbon reservoirs
BACKGROUND
[0002] Coal may be a low permeability reservoir Almost all the permeability of a coal bed is usually considered to be due to fractures, which in coal are in the form of cleats The permeability of the coal matrix may be negligible by comparison Production of gas from a coal bed is difficult
SUMMARY
[0003] A method is disclosed of fracturing a hydrocarbon reservoir penetrated by a well, the method comprising introducing hydrocarbon fracturing fluid comprising liquefied petroleum gas into the hydrocarbon reservoir through the well at a pressure high enough to form a fracture in the hydrocarbon reservoir, narrowing the fracture and driving bridging agent into the fracture to form a bridged fracture that is restricted from further fracturing, the bridged fracture being permeable to fluids from the hydrocarbon reservoir, and increasing the pressure of the hydrocarbon fracturing fluid in the well to a pressure that is high enough to form a subsequent fracture in the hydrocarbon reservoir
[0004] A method is also disclosed of fracturing a coal bed methane reservoir penetrated by a well, the method comprising introducing hydrocarbon fracturing fluid into the coal bed methane reservoir through the well at an injection rate high enough to form a fracture in the coal bed methane reservoir, reducing the injection rate of the hydrocarbon fracturing fluid to narrow the fracture and driving bridging agent into the narrowed fracture to bridge, and restrict further fracturing of, the narrowed fracture, the bridged fracture being permeable to fluids from the coal bed methane reservoir, and increasing the pressure of the hydrocarbon fracturing fluid in the well to a pressure that is high enough to form a subsequent fracture in the coal bed methane reservoir [0005] A method is also disclosed of fracturing a coal bed methane reservoir penetrated by a well, the method comprising introducing hydrocarbon fracturing fluid comprising liquefied petroleum gas into the coal bed methane reservoir through the well at an injection rate that is high enough to form a fracture in the coal bed methane reservoir, reducing the injection rate of the hydrocarbon fracturing fluid to narrow the fracture and driving bridging agent into the narrowed fracture to bridge, and restrict further fracturing of, the narrowed fracture, the bridged fracture being permeable to fluids from the coal bed methane reservoir, and increasing the pressure of the hydrocarbon fracturing fluid in the well to a pressure that is high enough to form a subsequent fracture in the coal bed methane reservoir
[0006] A method is also disclosed of fracturing a coal bed methane reservoir penetrated by a well and having a first zone and a second zone, the first zone having a first fracturing threshold and the second zone having a second fracturing threshold that is higher than the first fracturing threshold, the method comprising introducing hydrocarbon fracturing fluid into the well, subjecting the hydrocarbon fracturing fluid in the well to pressures above the first fracturing threshold to form a fracture in the coal bed methane reservoir, reducing the pressure on the hydrocarbon fracturing fluid in the well to narrow the fracture and driving bridging agent into the narrowed fracture to bridge and restrict further fracturing of the bridged fracture, the bridged fracture being permeable to fluids from the coal bed methane reservoir, and subjecting the hydrocarbon fracturing fluid in the well to pressures above the second fracturing threshold to form a second fracture in the coal bed methane reservoir
[0007] In various embodiments, there may be included any one or more of the following features At least a portion of the bridging agent may dissolve upon completion of the method The bridging agent may comprise proppant The bridging agent may be driven into the fracture with gelled hydrocarbon fracturing fluid The bridging agent may comprise gelled hydrocarbon fracturing fluid The bridging agent may be driven into the fracture from a slug of hydrocarbon fracturing fluid carrying bridging agent The well may comprise a horizontal well The horizontal well may be one or more of open hole, slotted liner, and perforated liner The hydrocarbon reservoir may comprise a coal reservoir The coal reservoir may be a coal bed methane reservoir The hydrocarbon reservoir may comprise a shale or sandstone reservoir Narrowing may comprise reducing an injection rate of the hydrocarbon fracturing fluid Increasing the pressure may be carried out by maintaining the reduced injection rate after the formation of the bridged fracture The bridging agent may be driven into the fracture after the fracture is narrowed The bridging agent may be driven into the fracture to bridge an entrance of the fracture The subsequent fracture may be narrowed and bridging agent driven into the subsequent fracture to form a bridged subsequent fracture that is restricted from further fracturing, the bridged subsequent fracture being permeable to fluids from the hydrocarbon reservoir Increasing the pressure may comprise increasing an injection rate of the hydrocarbon fracturing fluid to expand the subsequent fracture after detection of the formation of the subsequent fracture Increasing the pressure may further comprise increasing an injection rate of the hydrocarbon fracturing fluid after the detection of the bridging of the fracture The hydrocarbon reservoir may comprise plural hydrocarbon reservoirs penetrated by the well, introducing may comprise introducing at a pressure high enough to form the fracture in a first reservoir of the plural hydrocarbon reservoirs, and increasing may comprise increasing to a pressure that is high enough to form the subsequent fracture in a second reservoir of the plural hydrocarbon reservoirs
[0008] In some embodiments, this document describes a methodology for creating plural fractures along a horizontal wellbore within a coal bed methane formation These methods are applicable to completions including open hole horizontals, slotted liner horizontals, perforated liner horizontals, and multiple perforations along a horizontal wellbore
[0009] These and other aspects of the device and method are set out in the claims, which are incorporated here by reference
BRIEF DESCRIPTION OF THE FIGURES
[0010] Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which
[0011] Figs 1 - 4 are side elevation views, in section, that illustrate a method of fracturing a deviated coal bed methane reservoir [0012] Figs 5-8 are side elevation views, in section, that illustrate a further method of fracturing plural coal bed methane reservoirs penetrated by a well
[0013] Figs 9-10 are flow diagrams of various methods of fracturing
[0014] Figs 11 and 12 are hypothetical graphs of pressure, injection rate, and time, for two embodiments of the methods disclosed herein
[0015] Fig 13 illustrates the formation of a branched set of fractures and subsequent fractures
DETAILED DESCRIPTION
[0016] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims
[0017] Coal bed methane is a form of natural gas extracted from coal beds The term coal bed methane sometimes refers to methane adsorbed into the solid matrix of the coal, for example in a near-liquid state lining the inside of pores within the coal Coal bed methane is sometimes called 'sweet gas' because of its lack of hydrogen sulfide The presence of this gas is well known from its occurrence in underground coal mining, where it may present a serious safety risk Coalbed methane may contain very little heavier hydrocarbons such as propane or butane, and natural gas condensate, unlike natural gas from conventional reservoirs Further, coal bed methane may contain up to a few percent carbon dioxide
[0018] The fracturing of coalbed methane reservoirs may be used to increase the number and depth of fractures, and hence the permeability, of a reservoir Fracturing methods used on coalbed methane reservoirs include injecting gases such as nitrogen under pressure Carbon dioxide fracturing has also been contemplated, but can't be readily used since carbon dioxide is absorbed onto the coal, therefore making clean-up difficult Gas fracturing methods in general are disadvantageous, because they can't be used to carry a sufficient amount of proppant However, hydraulic fracturing with regular liquid
hydrocarbons is also disadvantageous because the liquid hydrocarbons tend to coat the coal, making clean-up difficult
[0019] Referring to Fig 1, a hydrocarbon reservoir such as a coal bed methane reservoir 16 is illustrated as penetrated by a well 12 Referring to Fig 9, a method of fracturing a hydrocarbon reservoir penetrated by a well 12 is illustrated Referring to Fig 1, in a stage 60 (shown in Fig 9) hydrocarbon fracturing fluid 11 comprising liquefied petroleum gas is introduced into the coal bed methane reservoir 16 through the well 12 at a pressure high enough to form at least one fracture 18 in the hydrocarbon reservoir A suitable pressure may be a pressure that is inciementally higher than the piessure lequiied to initiate a fiacture For example, the pressure may be achieved using a sufficient injection rate For further example, the viscosity of the injected fluid may be increased to increase the pressure a sufficient amount The reservoir 16 may be isolated by one or more packers 35, such as an uphole packer as shown In some embodiments, packers may be used at one or more locations along the horizontal section 14 to isolate one or more sections of the reservoir 16 as desired Fluid 11 may be introduced into reservoir 16 through a horizontal section 14 of the well 12 as is described further throughout this document The basic idea of fracturing and the machinery required are not discussed in detail herein
[0020] Referring to Figs 1 - 2, in a stage 62 (shown in Fig 9) the fracture is narrowed and bridging agent driven into the fracture to form a bridged fracture that is restricted from further fracturing For example, the injection rate of the hydrocarbon fracturing fluid 11 may be reduced to below fracturing rates and pressures, to narrow, but not entirely close, the fracture 18 Referring to Fig 2, bridging agent 20 may be driven into the fracture 18 after narrowing to bridge the fracture 18, and to restrict further fracturing of the narrowed fracture 18 The bridged fracture 18 is permeable to fluids from the coal bed methane reservoir 16 Thus, the bridging fracture is conductive to well fluids so that the bridged fracture does not become entirely screened out or plugged to the point where well fluids cannot be produced from the fracture 18 during subsequent production The bridging agent driven into the fracture 18 holds open the fracture 18, but impairs the fracture 18 from further cracking The narrowing of the fracture 18 and the driving in of bridging agent 20 may be done simultaneously or stepwise for example if bridging agent 20 is driven in before, after, or before and after narrowing
[0021] The methods disclosed herein may reduce the amount of bridging agent required to fracture relative to proppant used in conventional methods In some
embodiments, bridging agent 20 is selected such that at least a portion of the bridging agent 20 dissolves upon completion of the method Such bridging agents 20 may be salts, for example benzoic acid or other suitable bridging agents These bridging agents 20 may be soluble in fluids from the coal bed methane reservoir 16, such as in water from the reservoir 16
[0022] The bridging agent may be driven into the fracture 18 with gelled
hydrocarbon fracturing fluid As shown in Figs 1 and 2, the bridging agent 20 may be driven into the fracture 18 from a slug 21 of hydrocarbon fluid carrying bridging agent The size of the slug 21 is variable, and more than one slug 21 may be required to bridge the fracture 18 After the fracturing process begins in stage 60, the injection of slug 21 may be timed so that the slug 21 reaches the coal bed methane reservoir 16, for example the horizontal section 14, when the fracture 18 is narrowed In some embodiments, the slug 21 may be timed to reach the fracture 18 when the fracture 18 is narrowed Upon reaching a created fracture 18, at least a portion of the diversion slug 21 will enter the fracture 18 Due to the reduced injection rate, the narrowed fracture 18 causes the bridging agent 20 within the slug 21 to bridge within the fracture 18 and effectively stop the fracture from accepting additional fluid 11 to fracture This effect may be evidenced by an increase in pressure A series of slugs (not shown) may be injected in the methods disclosed herein, each slug separated by a volume of fracturing fluid 11 sufficient to create and narrow at least one fracture in the coal bed methane reservoir 16
[0023] Referring to Fig 3, the pressure of the hydrocarbon fracturing fluid 11 in the well 12 is increased in a stage 64 (shown in Fig 9) to a pressure that is high enough to form at least one subsequent fracture 22, for example fractures 22A and 22B, in the reservoir 16 When two or more fractures are simultaneously formed in any of these methods, each of the simultaneously formed fractures may be narrowed and bridged Referring to Fig 4, in a further stage, the injection rate of the hydrocarbon fracturing fluid 11 may be reduced to narrow the subsequent fractures 22A and 22B and bridging agent 24 driven into the subsequent fractures 22A and 22B to bridge and restrict, for example entirely prevent, further fracturing of the narrowed subsequent fractures 22A and 22B Again, the bridged subsequent fractures 22A and 22B are permeable to fluids from the coal bed methane reservoir 16 Creating and bridging the subsequent fractures 22A and 22B may be done according to any of the techniques used to create and bridge the fracture 18 The methods disclosed herein may be repeated to form any desired number of fractures in the one or more reservoirs 16, for example as many fractures as possible or as makes sense Referring to Fig 8, an embodiment is illustrated where three fractures are created and bridged
[0024] Referring to Fig 1, the well 12 may comprise a horizontal well (horizontal section 14) Coal bed methane reservoirs tend to exist in horizontal strata, and thus horizontal wells may be the most effective way of penetrating and exploiting such a reservoir 16 In some embodiments, the horizontal well is one or more of an open hole, slotted liner, and perforated liner Open hole horizontal wells are common in coal bed methane reservoirs, as it is generally difficult and sometimes impossible to suitably cement horizontal wells in coal The hydrocarbon reservoir penetrated by the well 12 may be a coal reservoir such as a coal bed methane reservoir In some embodiments the hydrocarbon reservoir is a shale or sandstone reservoir, such as a naturally fractured sandstone reservoir The methods may be used on low permeability reservoirs
[0025] The hydrocarbon fracturing fluid 11 used comprises liquefied petroleum gas
(LPG), and may be termed liquefied petroleum gas hydrocarbon fracturing fluid in some cases In some embodiments, the fracturing fluid 11 comprises predominantly propane, butane, or a mixture of propane and butane LPG is advantageous, because unlike nitrogen it can be used to carry bridging agent downhole Further, unlike carbon dioxide or heavier hydrocarbons, LPG does not coat or block the pores of the coal to a significant extent, thus resulting in improved post-fracturing production LPG can be easily recovered from the coal bed methane reservoir 16
[0026] In some embodiments, the bridging agent comprises gelled hydrocarbon fluid
In some embodiments the bridging agent 20 may comprise proppant, such as sand and other suitable particulates The fracture 18 may be narrowed to a width that corresponds with, for example is substantially the same as, the size of the proppant Thus, only an amount of proppant sufficient to bridge the fracture 18 may be required to prevent further extension of the fracture 18 This may mean that only the entrance of the fracture 18 is bridged as shown in Fig 6 Indeed, in some embodiments the bridging agent is driven into the fracture 18 to bridge the entrance of the fracture 18 Referring to Fig 13, in other embodiments a fracture 23A may be bridged by proppant 29 between an entrance 25 and a tip 27, for example at the intermediate location shown Upon carrying out stage 64, one or more subsequent fractures, such as fractures 23B and 23C, may form as off-shoots of fracture 23 A Subsequent fractures 23B and 23C may then be bridged, and further branching may occur in any of fractures 23 A- C The extent of branching depends on the nature of the reservoir 16, the width the fractures are reduced to in the rate reduction stage, and on the location where the bridging occurs [0027] Referring to Figs 5-8, in some embodiments the hydrocarbon reservoir comprises plural hydrocarbon reservoirs, such as reservoirs 16A and 16B, penetrated by the well 12 Referring to Fig 5 an embodiment is illustrated where uphole and downhole packers 35 are used to isolate two adjacent reservoirs 16 Referring to Fig 5, introducing in stage 60 may further comprise introducing the fracturing fluid 11 at a pressure high enough to form a fracture 42, for example using a sufficient injection rate, in at least one of the more than one reservoirs 16A and 16B Referring to Fig 7, increasing in stage 64 may further comprise increasing to a pressure that is high enough to form a subsequent fracture 44 in at least one of the plural reservoirs 16A and 16B Increasing the pressure may comprise increasing the injection rate
[0028] Referring to Figs 11 and 12, graphs are provided that illustrate different embodiments of methods of fracturing one or more coal bed methane reservoirs 16
[0029] Referring to Fig 11, the hydraulic fracturing fluid 11 is injected at T=O to begin the fracturing process, and the injection rate is increased to fracturing rates at T=O 8 The pressure rises accordingly until the formation of a fracture 18 (shown in Fig 1) at T=I 1 The fracture may be detected by a change in the rate of pressure increase, such as a pressure drop as shown, that indicates a fracture formation In the example shown, the pressure decreases after the fracture 18 is formed The rate may be adjusted or maintained at this point to create the desired fracture dimensions, such as to widen the fracture Upon detection of the fracture, the injection rate is reduced at T=I 3 - T=I 5 to narrow the fracture As shown in Fig 2, a slug 21 of bridging agent travels down the well 12 and bridges the fracture at T=2 2, as evidenced by an increase in pressure Referring to Fig 11, the injection rate may be increased after detection of the bridging of the fracture, for example after the detection of the pressure increase of the hydrocarbon fracturing fluid 11 indicative of the bridging of the narrowed fracture Upon detection of the increase in pressure, the injection rate is increased at T=2 3, and the subsequent fracture 22 (shown in Fig 3) forms at T=2 8 The method may then be repeated to create and bridge the desired number of fractures Fig 4 illustrates the reservoir 16 at T=4 0 on the graph of Fig 11
[0030] Referring to Fig 12, the hydraulic fracturing fluid 11 is injected at T=O to begin the fracturing process, and the injection rate is increased to fracturing rates at T=O 8 The pressure rises accordingly to peak at T=I 1, indicating the formation of a fracture Again, upon detection of the fracture 18 (shown in Fig 1), the injection rate is reduced, at T=I 3 - T=I 5 The bridging agent is sent down the well 12, and bridges the formed fracture 18 at T=2 0 as evidenced by an increase in pressure Again the pressure rises after bridging, but this time the rate is held steady at the reduced rate Thus, increasing the pressure in stage 64 (shown in Fig 9) may be carried out by maintaining the reduced injection rate after the formation of the bridged fracture Thus, the leak-off rate is lower than the injection rate, and thus the pressure continues to rise and a subsequent fracture 22 is formed at T=2 2 In this case, the formation of the subsequent fracture is indicated by a reduction in the rate of pressure increase characteristic of a fracture The reduction in the rate of pressure increase may comprise a pressure drop as shown in Fig 11 An algorithm may be used to determine when a fracture has occurred Upon detection of the subsequent fracture, the injection rate may be increased, for example as it is done so at T=2 3 - T=2 6, and then lowered at T=3 2, to expand the fracture The method stages may be repeated in order to produce and bridge the desired number of fractures
[0031] Referring to Fig 10, a method of fracturing a coal bed methane reservoir 16 is illustrated Referring to Fig 5, an embodiment of this method is described with more than one reservoir 16, such as reservoirs 16A and 16B Collectively, reservoirs 16A and 16B are penetrated by well 12 and have a first zone 36 and a second zone 38, the first zone 36 having a first fracturing threshold and the second zone 38 having a second fracturing threshold that is higher than the first fracturing threshold As shown, zone 36 is in reservoir 16B and zone 38 is in reservoir 16A, but this need not be the case Both zones may in fact be in the same reservoir 16 such as is shown in Fig 1 The reference to the second fracturing threshold being higher than the first fracturing threshold refers to the fact that when fracturing fluid 11 is introduced into the one or more reservoirs 16 and pressured up from the surface, the first zone 36 will fracture with less energy applied from the surface than the second zone 38 [0032] Referring to Fig 5, in a stage 70 (shown in Fig 10), hydrocarbon fracturing fluid 11 is introduced into the well 12 In stage 72 (shown in Fig 10), the hydrocarbon fracturing fluid 11 in the well is subjected to pressures above the first fracturing threshold to form a fracture 42 in the coal bed methane reservoir 16B Referring to Fig 6, in a stage 74 (shown in Fig 10) the pressure on the hydrocarbon fracturing fluid 11 in the well 12 is reduced in order to narrow the fracture 42 Bridging agent 40 is driven into the narrowed fracture 42 to bridge and restrict further fracturing of the bridged fracture 42, the bridged fracture 42 being permeable to fluids from the coal bed methane reservoir 16B
[0033] Referring to Fig 7, in a stage 76 (shown in Fig 10) the hydrocarbon fracturing fluid 11 in the well 12 is then subjected to pressures above the second fracturing threshold to form a second fracture 44 in the coal bed methane reservoir 16A As shown in Fig 7, in a further stage the pressure on the hydrocarbon fracturing fluid 11 in the well 12 may be decreased to narrow the second fracture 44 Bridging agent 46 is driven into the narrowed second fracture 44 to bridge, and restrict further fracturing of, the bridged second fracture 44 Again, the bridged second fracture 44 is permeable to fluids from the coal bed methane reservoir 16A As shown in Figs 5-8, the location of the next fracture zone is determined by the one or more reservoir 16, and thus subsequent fractures may be formed downstream or upstream from a previous fracture
[0034] The fracturing fluid 11 used to create the fractures may be un-gelled with bridging agent, un-gelled without bridging agent, gelled with bridging agent, or gelled without bridging agent, for example Proppant may be present in the hydrocarbon fracturing fluid 11 introduced in stage 60 Viscosified (gelled) fluids may have the capability to reduce viscosity upon completion of the treatment Gelled fluids may include a gelling agent and at least one of an activator and breaker, as is known in the art
[0035] LPG may include a variety of petroleum and natural gases existing in a liquid state at ambient temperatures and moderate pressures In some cases, LPG refers to a mixture of such fluids These mixes are generally more affordable and easier to obtain than any one individual LPG, since they are hard to separate and purify individually Unlike conventional hydrocarbon based fracturing fluids, common LPGs may be tightly fractionated products resulting in a high degree of purity and very predictable performance Exemplary LPGs include, propane, butane, pentane, or various mixes thereof As well, exemplary LPGs also include isomers of propane and butane, such as iso-butane Further LPG examples include HD-5 propane, commercial butane, and n-butane The LPG mixture may be controlled to gain the desired hydraulic fracturing and clean-up performance LPG fluids used may also include minor amounts of pentane (such as i-pentane or n-pentane), and higher weight hydrocarbons
[0036] LPGs tend to produce excellent fracturing fluids LPG is readily available, cost effective and is easily and safely handled on surface as a liquid under moderate pressure LPG is completely compatible with formations, such as coal bed methane reservoirs, formation fluids, is highly soluble in formation hydrocarbons and eliminates phase trapping - resulting in increased well production LPG may be readily and predictably viscosified to generate a fluid capable of efficient fracture creation and excellent proppant transport After fracturing, LPG may be recovered very rapidly, allowing savings on clean up costs In some embodiments, LPG may be predominantly propane, butane, or a mixture of propane and butane In some embodiments, LPG may comprise more than 80%, 90%, or 95% propane, butane, or a mixture of propane and butane
[0037] The embodiments of the methods disclosed herein may be used in other embodiments of the methods disclosed herein
[0038] In the claims, the word "comprising" is used in its inclusive sense and does not exclude other elements being present The indefinite article "a" before a claim feature does not exclude more than one of the feature being present Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be constaied as essential to all embodiments as defined by the claims

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1 A method of fracturing a hydrocarbon reservoir penetrated by a well, the method comprising
introducing hydrocarbon fracturing fluid comprising liquefied petroleum gas into the hydrocarbon reservoir through the well at a pressure high enough to form a fracture in the hydrocarbon reservoir,
narrowing the fracture and driving bridging agent into the fracture to form a bridged fracture that is restricted from further fracturing, the bridged fracture being permeable to fluids from the hydrocarbon reservoir, and
increasing the pressure of the hydrocarbon fracturing fluid in the well to a pressure that is high enough to form a subsequent fracture in the hydrocarbon reservoir
2 The method of claim 1 in which at least a portion of the bridging agent dissolves upon completion of the method
3 The method of any one of claim 1 - 2 in which the bridging agent comprises proppant
4 The method of any one of claim 2 - 3 in which the bridging agent is driven into the fracture with gelled hydrocarbon fracturing fluid
5 The method of any one of claim 1 - 4 in which the bridging agent comprises gelled hydrocarbon fracturing fluid
6 The method of any one of claim 1 - 5 in which the bridging agent is driven into the fracture from a slug of hydrocarbon fracturing fluid carrying bridging agent
7 The method of any one of claim 1 - 6 in which the well comprises a horizontal well 8 The method of claim 7 in which the horizontal well is one or more of open hole, slotted liner, and perforated liner
9 The method of any one of claim 1 - 8 in which the hydrocarbon reservoir comprises a coal reservoir
10 The method of claim 9 in which the coal reservoir is a coal bed methane reservoir
11 The method of any one of claim 1 - 8 in which the hydrocarbon reservoir comprises a shale or sandstone reservoir
12 The method of any one of claim 1 - 11 in which narrowing further comprises reducing an injection rate of the hydrocarbon fracturing fluid
13 The method of claim 12 in which increasing the pressure is carried out by
maintaining the reduced injection rate after the formation of the bridged fracture
14 The method of any one of claim 1 - 13 in which the bridging agent is driven into the fracture after the fracture is narrowed
15 The method of any one of claim 1 - 14 in which the bridging agent is driven into the fracture to bridge an entrance of the fracture
16 The method of claim 1 - 15 further comprising narrowing the subsequent fracture and driving bridging agent into the subsequent fracture to form a bridged subsequent fracture that is restricted from further fracturing, the bridged subsequent fracture being permeable to fluids from the hydrocarbon reservoir 17 The method of any one of claim 1 - 16 in which increasing the pressure further comprises increasing an injection rate of the hydrocarbon fracturing fluid to expand the subsequent fracture after detection of the formation of the subsequent fracture
18 The method of any one of claim 1 - 17 in which increasing the pressure further comprises increasing an injection rate of the hydrocarbon fracturing fluid after the detection of the bridging of the fracture
19 The method of any one of claim 1 - 18 in which the hydrocarbon reservoir comprises plural hydrocarbon reservoirs penetrated by the well, and in which
introducing further comprises introducing at a pressure high enough to form the fracture in a first reservoir of the plural hydrocarbon reservoirs, and
increasing further comprises increasing to a pressure that is high enough to form the subsequent fracture in a second reservoir of the plural hydrocarbon reservoirs
PCT/CA2010/000996 2009-07-02 2010-07-02 Methods of fracturing hydrocarbon reservoirs WO2011000089A1 (en)

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WO2012097424A1 (en) * 2011-01-17 2012-07-26 Enfrac Inc. Method for fracturing a formation using a fracturing fluid mixture
WO2013120260A1 (en) * 2012-02-15 2013-08-22 四川宏华石油设备有限公司 Shale gas production method
CN103696800A (en) * 2013-12-18 2014-04-02 中国矿业大学 Drilling, cutting, pressing and pumping method
CN103820096A (en) * 2012-11-16 2014-05-28 中国石油天然气股份有限公司 Efficient cleanup additive for gas well and preparing method of efficient cleanup additive
CN104912520A (en) * 2014-03-14 2015-09-16 郑州大学 Horizontally butted well hydraulic scour migration pressure relief outburst elimination gas extraction method
US9187996B1 (en) 2012-08-23 2015-11-17 Millennium Stimulation Services, Ltd. Reduced emissions method for recovering product from a hydraulic fracturing operation
WO2015181028A1 (en) * 2014-05-27 2015-12-03 Statoil Gulf Services LLC Applications of ultra-low viscosity fluids to stimulate ultra-tight hydrocarbon-bearing formations
CN106321046A (en) * 2016-08-31 2017-01-11 山西宏厦第建设有限责任公司 Hydraulic sand fracturing gas extraction method for underground coal seam with low air permeability
US9719340B2 (en) 2013-08-30 2017-08-01 Praxair Technology, Inc. Method of controlling a proppant concentration in a fracturing fluid utilized in stimulation of an underground formation
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