CA2644225A1

CA2644225A1 - Initiation and propagation control of vertical hydraulic fractures in unconsolidated and weakly cemented sediments

Info

Publication number: CA2644225A1
Application number: CA002644225A
Authority: CA
Inventors: Grant Hocking
Original assignee: Geosierra, Llc; Grant Hocking
Current assignee: GeoSierra LLC
Priority date: 2006-02-27
Filing date: 2007-02-05
Publication date: 2007-09-07
Also published as: US20070199713A1; WO2007100956A3; US7748458B2; WO2007100956A2; US7870904B2; US20090145606A1; US20100276147A9

Abstract

A method and apparatus for initiating and propagating a vertical hydraulic fracture in unconsolidated and weakly cemented sediments from a single bore hole to control the fracture initiation plane and propagation of the hydraulic fracture, enabling greater yield and recovery of petroleum fluids from the formation. An injection casing with multiple fracture initiation sections is inserted and grouted into a bore hole. A fracture fluid carrying a proppant is injected into the injection casing and opens the fracture initiation sections to dilate the formation in a direction orthogonal to the required fracture azimuth plane. Propagation of the fracture is controlled by supplying fracture fluid independent to the two opposing wings of the hydraulic fracture. The injection casing initiation section remains open after fracturing providing direct hydraulic connection between the production well bore, the permeable proppant filled fracture and the formation.

Description

INITIATION AND PROPAGATION CONTROL OF VERTICAL HYDRAULIC
FRACTURES IN UNCONSOLIDATED AND WEAKLY
CEMENTED SEDIMENTS
TECHNICAL FIELD

[0001] The present invention generally relates to enhanced recovery of petroleum fluids from the subsurface by injecting a fracture fluid to fracture underground formations, and more particularly to a method and apparatus to control the fracture initiation plane and propagation of the hydraulic fracture in a single well bore in unconsolidated and weakly cemented sediments resulting in increased production of petroleum fluids from the subsurface formation.

BACKGROUND OF THE INVENTION

[0002] Hydraulic fracturing of petroleum recovery wells enhances the extraction of fluids from low permeable formations due to the high permeability of the induced fracture and the size and extent of the fracture. A single hydraulic fracture from a well bore results in increased yield of extracted fluids from the formation. Hydraulic fracturing of highly permeable unconsolidated formations has enabled higher yield of extracted fluids from the formation and also reduced the inflow of formation sediments into the well bore. Typically the well casing is cemented into the borehole, and the casing perforated with shots of generally 0.5 inches in diameter over the depth interval to be fractured. The formation is hydraulically fractured by injected the fracture fluid into the casing, through the perforations and into the formation. The hydraulic connectivity of the hydraulic fracture or fractures formed in the formation may be poorly connected to the well bore due to restrictions and damage due to the perforations. Creating a hydraulic fracture in the formation that is well connected hydraulically to the well bore will increase the yield from the well, result in less inflow of formation sediments into the well bore and result in greater recovery of the petroleum reserves from the formation.

[0003] Turning now to the prior art, hydraulic fracturing of subsurface earth formations to stimulate production of hydrocarbon fluids from subterranean formations has been carried out in many parts of the world for over fifty years. The earth is hydraulically fractured either through perforations in a cased well bore or in an isolated section of an open bore hole. The horizontal and vertical orientation of the hydraulic fracture is controlled by the compressive stress regime in the earth and the fabric of the formation. It is well known in the art of rock mechanics that a fracture will occur in a plane perpendicular to the direction of the minimum stress, see U.S. Patent No. 4,271,696 to Wood. At significant depth, one of the horizontal stresses is generally at a minimum, resulting in a vertical fracture formed by the hydraulic fracturing process. It is also well known in the art that the azimuth of the vertical fracture is controlled by the orientation of the minimum horizontal stress in consolidated sediments and brittle rocks.

[0004] At shallow depths, the horizontal stresses could be less or greater than the vertical overburden stress. If the horizontal stresses are less than the vertical overburden stress, then vertical fractures will be produced; whereas if the horizontal stresses are greater than the vertical overburden stress, then a horizontal fracture will be formed by the hydraulic fracturing process.

[0005] Techniques to induce a preferred horizontal orientation of the fracture from a well bore are well known. These techniques include slotting, by either a gaseous or liquid jet under pressure, to form a horizontal notch in an open bore hole. Such techniques are commonly used in the petroleum and environmental industry. The slotting technique performs satisfactorily in producing a horizontal fracture, provided that the horizontal stresses are greater than the vertical overburden stress, or the earth formation has sufficient horizontal layering or fabric to ensure that the fracture continues propagating in the horizontal plane.
Perforations in a horizontal plane to induce a horizontal fracture from a cased well bore have been disclosed, but such perforations do not preferentially induce horizontal fractures in formations of low horizontal stress. See U.S. Patent No. 5,002,431 to Heymans.

[0006] Various means for creating vertical slots in a cased well bore have been disclosed.
The prior art recognizes that a chain saw can be used for slotting the casing.
See U.S. Patent No. 1,789,993 to Switzer; U.S. Patent No. 2,178,554 to Bowie, et al., U.S.
Patent No.
3,225,828 to Wisenbaker; and U.S. Patent No. 4,119,151 to Smith. Installing pre-slotted or weakened casing has also been disclosed in the prior art as an alternative to perforating the casing, because such perforations can result in a reduced hydraulic connection of the formation to the well bore due to pore collapse of the formation surrounding the perforation.
See U.S. Patent No. 5,103,911 to Heijnen. These methods in the prior art were not concerned with the individual growth of each fracture wing from each of the two opposing slots for the initiation and propagation of the hydraulic fracture from the well bore. These methods were an alternative to perforating the casing to achieve better connection between the well bore and the surrounding formation.

[0007] In the art of hydraulic fracturing subsurface earth formations from subterranean wells at depth, it is well known that the earth's compressive stresses at the region of fluid injection into the formation will typically result in the creation of a vertical two "winged"
structure. This "winged" structure generally extends laterally from the well bore in opposite .
directions and in a plane generally normal to the minimum in situ horizontal compressive stress. This type of fracture is well known in the petroleum industry as that which occurs when a pressurized fracture fluid, usually a mixture of water and a gelling agent together with certain proppant material, is injected into the formation from a well bore which is either cased or uncased. Such fractures extend radially as well as vertically until the fracture encounters a zone or layer of earth material which is at a higher compressive stress or is significantly strong to inhibit further fracture propagation without increased injection pressure.

[0008] It is also well known in the prior art that the azimuth of the vertical hydraulic fracture is controlled by the stress regime with the azimuth of the vertical hydraulic fracture being perpendicular to the minimum horizontal stress direction. Attempts to initiate and propagate a vertical hydraulic fracture at a preferred azimuth orientation have not been successful, and it is widely believed that the azimuth of a vertical hydraulic fracture can only be varied by changes in the earth's stress regime. Such alteration of the earth's local stress regime has been observed in petroleum reservoirs subject to significant injection pressure and during the withdrawal of fluids resulting in local azimuth changes of vertical hydraulic fractures.

[0009] The method of controlling the azimuth of a vertical hydraulic fracture in formations of unconsolidated or weakly cemented soils and sediments by slotting the well bore or installing a pre-slotted or weakened casing at a predetermined azimuth has been disclosed. The method disclosed that a vertical hydraulic fracture can be propagated at a pre-determined azimuth in unconsolidated or weakly cemented sediments and that multiple orientated vertical hydraulic fractures at differing azimuths from a single well bore can be initiated and propagated for the enhancement of petroleum fluid production from the formation. See U.S. Patent No. 6,216,783 to Hocking et al., U.S. Patent No.
6,443,227 to Hocking et al and U.S. Patent No. 6,991,037 to Hocking. The method disclosed that a vertical hydraulic fracture can be propagated at a pre-determined azimuth in unconsolidated or weakly cemented sediments and that multiple orientated vertical hydraulic fractures at differing azimuths from a single well bore can be initiated and propagated for the enhancement of petroleum fluid production from the formation.

[00010] Accordingly, there is a need for a method and apparatus for controlling the growth of the individual wings of hydraulic fractures in a single well bore in formations of unconsolidated or weakly cemented sediments. Also, there is a need for a method and apparatus that hydraulically connects the installed hydraulic fractures to the well bore without the need to perforate the casing.

SUMMARY OF THE INVENTION

[00011] The present invention is a method and apparatus for dilating the earth by various means from a bore hole to initiate and propagate a vertical hydraulic fracture formed at various orientations from a single well bore in formations of unconsolidated or weakly cemented sediments. The fractures are initiated by means of preferentially dilating the earth orthogonal to the desired fracture azimuth direction. This dilation of the earth can be generated by a variety of means: a driven spade to dilate the ground orthogonal to the required azimuth direction, packers that inflate and preferentially dilate the ground orthogonal to the required azimuth direction, pressurization of a pre-weakened casing with lines of weaknesses aligned in the required azimuth orientation, pressurization of a casing with opposing slots cut along the required azimuth direction, or pressurization of a two "winged" artificial vertical fracture generated by cutting or slotting the casing, grout, and/or formation at the required azimuth orientation. The growth of each wing of the hydraulic fracture is controlled by the individual connection of each of the opposing wings of the hydraulic fracture to the pumping system supplying the fracturing fluid.

[00012] Once the first vertical hydraulic fracture is formed, second and subsequent multiple vertical hydraulic fractures can be initiated by a casing or packer system that seals off the first and earlier fractures and then by preferentially dilating the earth orthogonal to the next desired fracture azimuth direction, the second and subsequent fractures are initiated and controlled. The sequence of initiating the multiple azimuth orientated fractures is such that the induced earth horizontal stress from the earlier fractures is favorable for the initiation and control of the next and subsequent fractures. Alternatively multiple vertical hydraulic fractures at various orientations in the single well bore can be initiated and propagated simultaneously with the growth of each individual wing of each hydraulic fracture controlled by the individual connection and control of flow of fracturing fluid from the pumping system to each wing of the hydraulic fractures.

[00013] The present invention pertains to a method for forming a vertical hydraulic fracture or fractures from a single bore hole with the growth of each opposing fracture wing controlled to enhance extraction of petroleum fluids from the formation surrounding the bore hole. As such any casing system used for the initiation and propagation of the fractures will have a mechanism to ensure the casing remains open following the formation of each fracture in order to provide hydraulic connection of the well bore to the hydraulic fractures.

[00014] The fracture fluid used to form the hydraulic fractures has two purposes. First the fracture fluid must be formulated in order to initiate and propagate the fracture within the underground formation. In that regard, the fracture fluid has certain attributes. The fracture fluid should not leak off into the formation, the fracture fluid should be clean breaking with minimal residue, and the fracture fluid should have a low friction coefficient.

[00015] Second, once injected into the fracture, the fracture fluid forms a highly permeable hydraulic fracture. In that regard, the fracture fluid comprises a proppant which produces the highly permeable fracture. Such proppants are typically clean sand for large massive hydraulic fracture installations or specialized manufactured particles (generally resin coated sand or ceramic in composition) which are designed also to limit flow back of the proppant from the fracture into the well bore.

[00016] The present invention is applicable to formations of unconsolidated or weakly cemented sediments with low cohesive strength compared to the vertical overburden stress prevailing at the depth of the hydraulic fracture. Low cohesive strength is defined herein as the greater of 200 pounds per square inch (psi) or 25% of the total vertical overburden stress.
Examples of such unconsolidated or weakly cemented sediments are sand and sandstone formations, which have inherent high permeability but low strength that requires hydraulic fracturing to increase the yield of the petroleum fluids from such formations and simultaneously reducing the flow of formation sediments towards the well bore.
Upon conventional hydraulic fracturing such formations will not yield the full production potential of the formation due to the lack of good hydraulic connection of the hydraulic fracture in the formation and the well bore, resulting in significant drawdown in the well bore causing formation sediments to flow towards the hydraulic fracture and the well bore.
The flow of formation sediments towards the hydraulic fracture and the well bore, results in a decline over time of the yield of the extracted fluids from the formation for the same drawdown in the well.

[00017] Although the present invention contemplates the formation of fractures which generally extend laterally away from a vertical or near vertical well penetrating an earth formation and in a generally vertical plane in opposite directions from the well, i.e. a vertical two winged fracture, those skilled in the art will recognize that the invention may be carried out in earth formations wherein the fractures and the well bores can extend in directions other than vertical.

[00018] Therefore, the present invention provides a method and apparatus for initiating and controlling the growth of a vertical hydraulic fracture or fractures in a single well bore in formations of unconsolidated or weakly cemented sediments.

[00019] Other objects, features and advantages of the present invention will become apparent upon reviewing the following description of the preferred embodiments of the invention, when taken in conjunction with the drawings and the claims.

BRiEF DESCRIPTION OF THE DRAWINGS

[00020] FIG. 1 is a horizontal cross-section view of a well casing having a single fracture dual winged initiation sections prior to initiation of the controlled vertical fracture.

[00021] FIG. 2 is a cross-sectional side elevation view of a well casing single fracture dual winged initiation sections prior to initiation of the controlled vertical fracture.

[00022] FIG. 3 is an enlarged horizontal cross-section view of a well casing having a single fracture dual winged initiation sections prior to initiation of the controlled vertical fracture.

[00023] FIG. 4 is a cross-sectional side elevation view of a well casing having a single fracture dual winged initiation sections prior to initiation of the controlled vertical fracture.

[00024] FIG. 5 is a horizontal cross-section view of a well casing having a single fracture dual winged initiation sections after initiation of the controlled vertical fracture.

[00025] FIG. 6 is a cross-sectional side elevation view of two injection well casings each having a single fracture dual winged initiation sections located at two distinct depths prior to initiation of the controlled vertical fractures .

[00026] FIG. 7 is a horizontal cross-section view of a well casing having dual fracture dual winged initiation sections prior to the initiation of the controlled vertical fractures.

[00027] FIG. 8 is a cross-sectional side elevation view of a well casing having dual fracture dual winged initiation sections prior to initiation of the controlled vertical fractures.

[00028] FIG. 9 is a horizontal cross-section view of a well casing having dual fracture dual winged initiation sections after initiation of the second controlled vertical fracture.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT

[000291 Several embodiments of the present invention are described below and illustrated in the accompanying drawings. The present invention involves a method and apparatus for initiating and propagating controlled vertical hydraulic fractures in subsurface formations of unconsolidated and weakly cemented sediments from a single well bore such as a petroleum production well. In addition, the present invention involves a method and apparatus that provides a high degree of hydraulic connection between the formed hydraulic fractures and the well bore to enhance production of petroleum fluids from the formation, that enables each of the individual fracture wings to propagate individually from its opposing fracture wing, and that allows each fracture and fracture wing to re-fracture individually in order to achieve thicker and more permeable in place fractures within the formation.

[00030] Referring to the drawings, in which like numerals indicate like elements, FIGS. 1, 2, and 3 illustrate the initial setup of the method and apparatus for forming a single controlled vertical fracture with individual propagation control of each fracture wing. A
conventional bore hole 4 is completed by wash rotary or cable tool methods into the formation 7 of unconsolidated or weakly cemented sediments to a predetermined depth 6 below the ground surface 5. Injection casing 1 is installed to the predetermined depth 6, and the installation is completed by placement of grout 3 which completely fills the annular space between the outside the injection casing 1 and the bore hole 4. Injection casing 1 consists of two initiation sections 11 and 21 (FIG. 3) to produce two hydraulic partings 71 and 72 which in turn produce a fracture orientated along plane 2, 2' as shown on FIG. 5. Injection casing 1 must be constructed from a material that can withstand the pressures that the fracture fluid exerts upon the interior of the injection casing 1 during the pressurization of the fracture fluid. The grout 3 can be any conventional material that preserves the spacing between the exterior of the injection casing 1 and the bore hole 4 throughout the fracturing procedure, preferably a non-shrink or low shrink cement based grout.

[00031] The outer surface of the injection casing 1 should be roughened or manufactured such that the grout 3 bonds to the injection casing 1 with a minimum strength equal to the down hole pressure required to initiate the controlled vertical fracture. The bond strength of the grout 3 to the outside surface of the casing 1 prevents the pressurized fracture fluid from short circuiting along the casing-to-grout interface up to the ground surface 5.

[00032] Referring to FIGS. 1, 2 and 3, the injection casing 1 comprises a single fracture dual winged initiation sections 11 and 21 installed at a predetermined depth 6 within the bore hole 4. The winged initiation sections 11 and 21 can be constructed from the same material as the injection casing 1. The winged initiation sections 11 and 21 are aligned parallel with and through the fracture plane 2, 2'. The fracture plane 2, 2' coincides with the azimuth of the controlled vertical hydraulic fracture formed by partings 71 and 72 (FIG.
5). The position below ground surface of the winged initiation sections 11 and 21 will depend on the required in situ geometry of the induced hydraulic fracture and the reservoir formation properties and recoverable reserves.

[00033] The winged initiation sections 11 and 21 of the well casing 1 are preferably constructed from two symmetrical halves as shown on FIG. 3. The configuration of the winged initiation sections 11 and 21 is not limited to the shape shown, but the chosen configuration must permit the fracture to propagate laterally in at least one azimuth direction along the fracture plane 2, 2'. In FIG. 3, prior to initiating the fracture, the two symmetrical halves of the winged initiation sections 11 and 21 are connected together by shear fasteners 13 and 23 and the two symmetrical halves of the winged initiation sections 11 and 21 are sealed by gaskets 12 and 22. The gaskets 12 and 22 and the fasteners 13 and 23 are designed to keep the grout 3 from leaking into the interior of the winged initiation sections 11 and 21 during the grout 3 placement. The gaskets 12 and 22 align with the fracture plane 2, 2' and define weakening lines between the winged initiation sections 11 and 21.
Particularly, the winged'initiation sections 11 and 21 are designed to separate along the weakening line that coincides with the fracture plane 2, 2'. During fracture initiation, as shown in FIGS. 5 and 6, the winged initiation sections 11 and 21 separate along the weakening line without physical damage to the winged initiation sections 11 and 21. Any means of connecting the two symmetrical halves of the winged initiation sections 11 and 21 can be used, including but not limited to clips, glue, or weakened fasteners, as long as the pressure exerted by the fastening means keeping the two symmetrical halves of the winged initiation sections 11 and 21 together is greater than the pressure of the grout 3 on the exterior of the winged initiation sections 11 and 21. In other words, the fasteners 13 and 23 must be sufficient to prevent the grout 3 from leaking into the interior of the winged initiation sections 11 and 21. The fasteners 13 and 23 will open at a certain applied load during fracture initiation and progressively open further during fracture propagation and not close following the completion of the fracture. The fasteners 13 and 23 can consist of a variety of devices provided they have a distinct opening pressure, they progressively open during fracture installation, and they remain open even under ground closure stress following fracturing. The fasteners 13 and 23 also limit the maximum amount of opening of the two symmetrical halves of the winged initiation sections 11 and 21. Particularly, each of the fasteners 13 and 23 comprises a spring loaded wedge 18 that allows the fastener to be progressively opened during fracturing and remain open under compressive stresses during ground closure following fracturing with the amount of opening permitted determined by the length of the bolt 19.

[00034] Referring to FIG. 3, well screen sections 14, 15, 24 and 25 are contained in the two winged initiation sections 11 and 21. The screen sections 14, 15, 24 and 25 are slotted portions of the two winged initiation sections 11 and 12 and limit the passage of soil particles from the formation into the well bore. The screen sections 14, 15 and 24, 25 provide sliding surfaces 20 and 30 respectively enabling the initiation sections 11 and 21 to separate during fracture initiation and propagation as shown on FIG. 5. Referring to FIGS. 3 and 4, the passages 16 and 26 are connected via the injection casing 1 top section 8 to openings 51 and 52 in the inner casing well bore passage 9, which is an extension of the well bore passage 10 in the injection casing initiation section.

[00035] Referring to FIGS. 3, 4 and 5, prior to fracture initiation the inner casing well bore passage 9 and 10 is filled with sand or inflatable packer 17 to below the lowest connecting opening 51. A single isolation packer 60 is lowered into the inner casing well bore passage 9 of the injection casing top section 8 and expanded within this section at a location immediately below the lowermost opening 51 as shown on FIG. 4. The fracture fluid 40 is pumped from the pumping system into the pressure pipe 50, through the single isolation packer 60, into the openings 51 and 52 and down to the passages 16 and 26 for initiation and propagation of the fracture along the azimuth plane 2, 2'. The isolation packer 60 controls the proportion of flow -of fracturing fluid by a surface controlled value 55 within the packer that control the proportional flow of fracturing fluid that enters either of the openings 51 and 52 which subsequently feed the passages 16 and 26 respectively and thus the flow of fracturing fluid that enters each wing 75 and 76 of the fracture. Referring to FIG. 5, .as the pressure of the fracture fluid 40 is increased to a level which exceeds the lateral earth pressures, the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21 will begin to separate along the fracture plane 2, 2' of the winged initiation sections 11 and 21 during fracture initiation without physical damage to the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21. As the two symmetrical halves 61, 62 separate, the gaskets 12 and 32 fracture, the screen sections 14, 15 and 24, 25 slide allowing separation of the two symmetrical halves 61, 62 along the fracture plane 2, 2', as shown in FIG. 5, without physical damage to the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21. During separation of the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21, the grout 3, which is bonded to the injection casing 1(FIG. 5) and the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21, will begin to dilate the adjacent sediments 70 forming partings 71 and 72 of the soil 70 along the fracture plane 2, 2' of the planned azimuth of the controlled vertical fracture. The fracture fluid 40 rapidly fills the partings 71 and 72 of the soil 70 to create the first fracture. Within the two symmetrical halves 61, 62 of the winged initiation sections 11 and 21, the fracture fluid 40 exerts normal forces 73 on the soil 70 perpendicular to the fracture plane 2, 2' and opposite to the soil 70 horizontal stresses 74. Thus, the fracture fluid 40 progressively extends the partings 71 and 72 and continues to maintain the required azimuth of the initiated fracture along the plane 2, 2'. The azimuth controlled vertical fracture will be expanded by continuous pumping of the fracture fluid 40 until the desired geometry of the first azimuth controlled hydraulic fracture is achieved. The rate of flow of the fracturing fluid that enters each wing 75 and 76 respectively of the fracture is controlled to enable the fracture to be grown to the desired geometry. Without controlled of the flow of fracturing fluid into each individual wing 75 and 76 of the fracture, heterogeneities in the formation 70 could give rise to differing propagation rates and pressures and result in unequal fracture wing lengths or undesirable fracture geometry.

[00036] Following completion of the fracture and breaking of the fracture fluid 40, the inflatable packers in the injection casing well bore passages 9 and 10 are removed or the sand is washed out so that the injection casing can act as a production well bore for extraction of fluids from the formation at the depths and extents of the recently formed hydraulic fractures.
The well screen sections 14, 15 and 24, 25 span the opening of the well casing created by the first fracture and act as conventional well screen preventing proppant flow back into the production well bore passages 10 and 9. If necessary and prior to washing the sand from the production well bore passages 9 and 10 for fluid extraction from the formation, it is possible to re-fracture the already formed fractures by first washing out the sand in passages 16 and 26 through the openings 51 and 52 and thus re-fracture the first initiated fracture. Re-fracturing the fractures can enable thicker and more permeable fractures to be created in the formation.
[00037] Referring to FIGS. 4 and 5, once the fracture is initiated, injection of a fracture fluid 40 through the well bore passage 9 in the injection casing 1, into the inner passages 16 and 26 of the initiation sections 11 and 21, and into the initiated fracture can be made by any conventional means to pressurize the fracture fluid 40. The conventional means can include any pumping arrangement to place the fracture fluid 40 under the pressure necessary to transport the fracture fluid 40 and the proppant into the initiated fracture to assist in fracture propagation and to create a vertical permeable proppant filled fracture in the subsurface formation. For successful fracture initiation and propagation to the desired size and fracture permeability, the preferred embodiment of the fracture fluid 40 should have the following characteristics.

[00038] The fracture fluid 40 should not excessively leak off or lose its liquid fraction into the adjacent unconsolidated soils and sediments. The fracture fluid 40 should be able to carry the solids fraction (the proppant) of the fracture fluid 40 at low flow velocities that are encountered at the edges of a maturing azimuth controlled vertical fracture.
The fracture fluid 40 should have the functional properties for its end use such as longevity, strength, porosity, permeability, etc.

[00039] The fracture fluid 40 should be compatible with the proppant, the subsurface formation, and the formation fluids. Further, the fracture fluid 40 should be capable of controlling its viscosity to carry the proppant throughout the extent of the induced fracture in the formation. The fracture fluid 40 should be an efficient fluid, i.e. low leak off from the fracture into the formation, to be clean breaking with minimal residue, and to have a low friction coefficient. The fracture fluid 40 should not excessively leak off or lose its liquid fraction into the adjacent unconsolidated or weakly cemented formation. For permeable fractures, a gel composed of starch should be capable of being degraded leaving minimal residue and not impart the properties of the fracture proppant. A low friction coefficient fluid is required to reduce pumping head losses in piping and down the well bore.
When a hydraulic permeable fracture is desired, typically a gel is used with the proppant and the fracture fluid. Preferable gels can comprise, without limitation of the following: a water-based guar gum gel, hydroxypropylguar (HPG), a natural polymer or a cellulose-based gel, such as carboxymethylhydroxyethylcellulose (CMHEC).

[00040] The gel is generally cross-linked to achieve a sufficiently high viscosity to transport the proppant to the extremes of the fracture. Cross-linkers are typically metallic ions, such as borate, antimony, zirconium, etc., disbursed between the polymers and produce a strong attraction between the metallic ion and the hydroxyl or carboxy groups. The gel is water soluble in the uncrossed-linked state and water insoluble in the cross-linked state.
While cross-linked, the gel can be extremely viscous thereby ensuring that the proppant remains suspended at all times. An enzyme breaker may be added to controllably degrade the viscous cross-linked gel into water and sugars. The enzyme typically takes a number of hours to biodegrade the gel, and upon breaking the cross-link and degradation of the gel, a permeable fracture filled with the proppant remains in the formation with minimal gel residue. For certain proppants, pH buffers can be added to the gel to ensure the gel's in situ pH is within a suitable range for enzyme activity.

[00041] The fracture fluid-gel-proppant mixture is injected into the formation and carries the proppant to the extremes of the fracture. Upon propagation of the fracture to the required lateral and vertical extent, the predetermined fracture thickness may need to be increased by utilizing the process of tip screen out or by re-fracturing the already induced fractures. The tip screen out process involves modifying the proppant loading and/or fracture fluid 40 properties to achieve a proppant bridge at the fracture tip. The fracture fluid 40 is further injected after tip screen out, but rather then extending the fracture laterally or vertically, the injected fluid widens, i.e. thickens, the fracture. Re-fracturing of the already induced fractures enables thicker and more permeable fractures to be installed, and also provides the ability to preferentially inject steam, carbon dioxide, chemicals, etc to provide enhanced recovery of the petroleum fluids from the formation.

[00042] The density of the fracture fluid 40 can be altered by increasing or decreasing the proppant loading or modifying the density of the proppant material. In many cases, the fracture fluid 40 density will be controlled to ensure the fracture propagates downwards initially and achieves the required height of the planned fracture. Such downward fracture propagation depends on the in situ horizontal fonnation stress gradient with depth and requires the gel density to be typically greater than 1.25 gm/cc.

[00043] The viscosity of the fracture fluid 40 should be sufflciently high to ensure the proppant remains suspended during injection into the subsurface, otherwise dense proppant materials will sink or settle out and light proppant materials will flow or rise in the fracture fluid 40. The required viscosity of the fracture fluid 40 depends on the density contrast of the proppant and the gel and the proppant's maximum particulate diameter. For medium grain-size particles, that is of grain size similar to a medium sand, a fracture fluid 40 viscosity needs to be typically greater than 100 centipoise at a shear rate of 1/sec.

[00044] Referring to FIG. 6, two injection casings 91 and 92 are set at different distinct depths 93 and 94 in the bore hole 95 and grouted into the formation by grout filling the annular space between the injection casings 91 and 92 and the bore hole 95.
The lower injection casing 91 is fractured first, by filling the well bore passage 110 with sand or inflatable packer to just below the lower most openings 101 and 102. The isolation packer 100 is lowered into the well bore passage 110 to just below the lowest opening 101 and expanded in the well bore passage 110 to achieve individual flow rate control of the fracturing fluid that enters the openings 101 and 102 respectively. The fracture fluid 120 is pumped into the isolation packer pipe string 105 and passes through the isolation packer 100 and into the openings 101 and 102 to initiate the vertical hydraulic fracture as described earlier. Following completion of the fracture in the first injection casing 91, the process is repeated by raising the isolation packer 100 to just below the lower most openings 111 and initiate the first fracture in the second injection casing 92, and the whole process is repeated to create all of the fractures in the injection casings installed in the bore hole 95.

[00045] Another embodiment of the present invention is shown on FIGS. 7, 8 and 9, consisting of an injection casing 96 inserted in a bore hole 97 and grouted in place by a grout 98. The injection casing 96 consists of four symmetrical fracture initiation sections 121, 131,' 141 and 151 that install a total of two hydraulic fractures on the different azimuth planes 122, 122' and 123, 123'. The passage for the first initiated fracture inducing passages 126 and 166 are connected to the openings 127 and 167, and the first fracture is initiated and propagated along the azimuth plane 122, 122' with controlled propagation of each individual wing of the fracture as described earlier. The second fracture inducing passages 146 and 186 are connected to the openings 147 and 187, and the second fracture is initiated and propagated along the azimuth plane 123, 123' as described earlier. The process results in two hydraulic fractures installed from a single well bore at different azimuths as shown on FIG. 9.

[00046] Finally, it will be understood that the preferred embodiment has been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.

Claims

1. A method for creating a vertical hydraulic fracture in a formation of unconsolidated and weakly cemented sediments, comprising:

a. drilling a bore hole in the formation to a predetermined depth;

b. installing an injection casing in the bore hole at the predetermined depth;

c. injecting a fracture fluid into the injection casing with sufficient fracturing pressure to dilate the injection casing and the formation in a preferential direction and thereby initiate a vertical fracture at an azimuth orthogonal to the direction of dilation; and d. controlling the rate of fracture fluid injection into each individual opposing wing of the initiated and propagating hydraulic fracture thereby controlling the geometry of the hydraulic fracture.

2. The method of Claim 1, wherein the method further comprises:

a. installing the injection casing at a predetermined depth in the bore hole, wherein an annular space exists between the outer surface of the casing and the bore hole, b. filling the annular space with a grout that bonds to the outer surface of the casing, wherein the casing has multiple initiation sections separated by a weakening line so that the initiation sections separate along the weakening line under the fracturing pressure.

3. The method of Claim 2, wherein the fracture fluid dilates the grout and the formation to initiate the fracture in the formation at a weakening line.

4. The method of Claim 1, wherein the fracture fluid does not leak off into the formation from the fracture.

5. The method of Claim 1, wherein the fracture fluid comprises a proppant, and the fracture fluid is able to carry the proppant of the fracture fluid at low flow velocities.

6. The method of Claim 1, wherein the fracture fluid is clean breaking with minimal residue.

7. The method of Claim 1, wherein the fracture fluid has a low friction coefficient.

8. The method of Claim 1, wherein the fracture fluid comprises a water based guar gum gel slurry.

9. The method of Claim 3, wherein the casing comprises two initiation sections with two directions of dilation.

10. The method of Claim 3, wherein the casing comprises two initiation sections with two directions of dilation and the first and second weakening lines are orthogonal.

11. The method of Claim 3, wherein the casing comprises three initiation sections with three directions of dilation.

12. The method of Claim 3, wherein the casing comprises four initiation sections with four directions of dilation, with the first and second weakening lines being orthogonal to each other and the third and fourth weakening lines being orthogonal to each other.

13. The method of Claim 2, wherein the initiation sections remain separated after dilation of the casing by the fracture fluid to provide hydraulic connection of the fracture with the well bore following completion of hydraulic fracturing.

14. The method of Claim 2, wherein the fracture fluid comprises a proppant and the initiation sections each contain well screen sections separating the proppant in the hydraulic fracture from the production well bore and thus preventing proppant from flowing back from the fracture into the production well bore during fluid extraction.

15. The method of Claim 1, wherein the method further comprises re-fracturing of each previously injected fracture.

16 16. The method of Claim 1, wherein the dilation of the formation is achieved by first cutting a vertical slot in the formation at the required azimuth for the initiated fracture, injecting a fracture fluid into the slot with a sufficient fracturing pressure to dilate the formation in this preferential direction and thereby initiate a vertical fracture at an azimuth orthogonal to the direction of dilation; controlling the flow rate of the fracture fluid entering each individual opposing wing of the vertical hydraulic fracture and thereby controlling the geometry of the hydraulic fracture.

17. A well in a formation of unconsolidated and weakly cemented sediments, comprising a bore hole in the formation to a predetermined depth; an injection casing in the bore hole at the predetermined depth; a source for delivering a fracture fluid into the injection casing with sufficient fracturing pressure to dilate the injection casing and the formation and initiate a vertical fracture at an azimuth orthogonal to the direction of dilation, wherin the injection casing further comprises:

a. multiple initiation sections separated by a weakening line b. multiple passages within the initiation sections and communicating across the weakening line for the introduction of the fracture fluid to dilate the casing and separate the initiation sections along the weakening line, wherein the passages to each opposing wing of the fracture are connected to the source of fracture fluid to dilate the injection casing and the formation in a preferential direction and thereby initiate the vertical fracture at the azimuth orthogonal to the direction of dilation and to control the propagation rate of each individual opposing wing of the hydraulic fracture.

18. The well of Claim 16, wherein the fracture fluid does not leak off into the formation from the fracture.

19. The well of Claim 16, wherein the fracture fluid comprises a proppant, and the fracture fluid is able to carry the proppant of the fracture fluid at low flow velocities.

20. The well Claim 16, wherein the fracture fluid is clean breaking with minimal residue.

21. The well of Claim 16, wherein the fracture fluid has a low friction coefficient.

22. The well of Claim 16, wherein the fracture fluid comprises a water based guar gum gel slurry.

23. The well of Claim 16, wherein the initiation sections remain separated after dilation of the casing by the fracture fluid to provide hydraulic connection of the hydraulic fracture with the well bore following completion of hydraulic fracturing.

24. The well of Claim 16, wherein the fracture fluid comprises a proppant and the initiation sections each contain well screen sections separating the proppant in the hydraulic fracture from the production well bore and thus preventing proppant from flowing back from the fracture into the production well bore during petroleum fluid extraction.

25. A well in a formation of unconsolidated and weakly cemented sediments, comprising a bore hole in the formation to a predetermined depth; an injection casing in the bore hole at the predetermined depth, the injection casing comprising multiple initiation sections separated by a weakening line, passages within the initiation sections communicate a fracture fluid to each opposing wing of a selected weakening line, wherein each weakening line corresponds to one of a plurality of fracture planes;
and a source for delivering the fracture fluid with sufficient pressure to separate the initiation sections adjacent the selected weakening lines, dilate the formation, and initiate a fracture in the formation along the desired fracture plane.

26. A well in a formation of unconsolidated and weakly cemented sediments, comprising a bore hole in the formation to a predetermined depth; an injection casing in the bore hole at the predetermined depth, the injection casing comprising multiple initiation sections separated by a weakening line, passages within the initiation sections communicate a fracture fluid to each opposing wing of a selected opposed pair of weakening lines, wherein each opposed pair of weakening lines corresponds to one of a plurality of desired fracture planes; and a source for delivering the fracture fluid with sufficient pressure to separate the initiation sections adjacent the selected opposed pairs of weakening lines, dilate the formation, and initiate a fracture in the formation along the desired fracture plane.