BAKER HUGHES, A GE COMPANY,
`LLC AND BAKER HUGHES
`OILFIELD OPERATIONS LLC
`Exhibit 1036
`BAKER HUGHES, A GE COMPANY,
`LLC AND BAKER HUGHES
`OILFIELD OPERATIONS LLC v.
`PACKERS PLUS ENERGY
`SERVICES, INC.
`IPR2016-01380
`
`Page 1 of 25
`
`

`

`United States Patent
`
`[191
`
`[11] Patent Number:
`
`' 5,360,066
`
`Nov. 1, 1994
`Venditto et al.
`[45] Date of Patent:
`
`||||||Illlllll|l||||l|IlllllllllllllllllllIllllllllllllllIlllllllllllll||||
`USOOS360066A
`
`[54] METHOD FOR CONTROLLING SAND
`PRODUCTION OF FORMATIONS AND FOR
`OPI'MZING HYDRAULIC FRACI'URING
`THROUGH PERFORATION ORIENTATION
`
`[75]
`
`Inventors:
`
`James J. Venditto; Hazim H. Abass;
`David E. McMechan; Matthew E.
`Blanch, all of Duncan, Okla.
`
`[73] Assignee: Halliburton Company, Duncan, Okla.
`
`[21] Appl. No.: 992,847
`
`[22] Filed:
`
`Dec. 16, 1992
`
`[51]
`Int. Cl.5 .............................................. E21B 43/26
`
`[52] US. Cl. .............................. 166/250; 166/308
`[58] Field of Search ................ 166/250, 308, 271, 297
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`2,414,997 1/ 1947 Atkins ................................ 285/973
`
`.. 166/308 X
`4,220,205 9/1980 Coursen et a1.
`
`4,523,649 6/1985 Stout ....................... l75/4.51
`4,529,036 7/1985 Daneshy et a1.
`.
`166/254
`
`..... 73/153
`4,542,648 9/1985 Vinegar et al.
`
`4,637,478 1/1987 George .............
`.. 175/4.51
`..... 33/178
`4,673,890 6/1987 Copland et al.
`
`4,714,115 12/1987 Uhri ..
`166/308
`
`.. 175/4.51
`4,830,120 5/ 1989 Stout .........
`
`....... 166/300
`4,848,468
`7/1989 Hazlett et al.
`4,869,322 9/1989 Vogt, Jr. et a1.
`.
`.. 166/308 X
`
`4,889,186 12/1989 Hanson et a1.
`166/308 X
`.
`....... 166/250
`4,974,675 12/1990 Austin et a1.
`
`4,977,961 12/1990 Avasthi ................... 166/297
`
`5,025,859
`6/1991 Hanson et a1.
`....... 166/308
`................. 166/308 X
`5,111,881
`5/1992 Soliman et al.
`
`OTHER PUBLICATIONS
`
`Vinegar, H. J., “X—Ray CT and NMR Imaging of
`Rocks”, J. of Petroleum Technology, Mar. 1986, pp.
`257—259.
`
`Bergosh, J. L., Marks, T. R., and Mitkus, A. F., “New
`Core Analysis Techniques for Naturally Fractured Res-
`ervoirs”, SPE Paper 13653, presented at the 1985 SPE
`California Regional Meeting, Bakersfield, Mar. 27-29,
`1985.
`Honarpour, M. M., et 21., “Reservoir Rock Descrip-
`tions Using Computed Tomography (CT)”, SPE Paper
`14272 presented at the 60th Annual Technical Confer-
`
`ence and Exhibition of the Society of Petroleum Engi-
`neers held in Las Vegas, Sep. 22—25, 1985.
`Hunt, P. K., et :11, “Computer Tomography as a Core
`Analysis Tool: Applications and Artifact Reduction
`Techniques”, SPE Paper 16952, presented at the 62nd
`Annual Technical Conference and Exhibition of the
`Society of Petroleum Engineers held in Dallas, Sep.
`27-30, 1987.
`Gilliland, R. E., “Use of CT scanning in the Investiga-
`tion of Damage to Unconsolidated Cores”, SPE Paper
`19408, presented at the SPE Formation Damage Con-
`trol Symposium held in Lafayette, Feb. 2223, 1990.
`Suzuki, F., “X—Ray Computed Tomography for Car-
`bonate Acidizing Studies”, Paper No. CIM/SPE 90-45,
`presented at the CIM/SPE Meeting in Calgary, Jun.
`10—13, 1990.
`'
`Halliburton Logging Services,
`EL—1055, Aug. 1989(3 pages).
`Seiler, Edmiston, Torres and Goetz, “Field Perfor-
`mance of a New Borehole Televiewer Tool and Associ-
`ated Image Processing Techniques”, Jun. 1990 (19
`pages).
`>
`(List continued on next page.)
`
`Inc. Publication No.
`
`__
`Primary Examiner—William P. Neuder
`Attorney, Agent, or Firm—-—Arnold, White & Durkee
`
`[57]
`
`ABSTRACT
`
`An improved method for fracturing oil wells is dis—
`closed and claimed herein. In particular, the present
`invention involves the determination of the direction of
`fracture propagation,
`i.e., perpendicular to the mini-
`mum stress existing within a given formation and the
`alignment of perforations produced by a variety of
`perforating devices with the previously determined
`direction of fracture propagation. The methods dis-
`closed and claimed herein will eliminate many problems
`encountered in the prior art, including reducing the
`pressure required to initiate fractures and reducing the
`undesirable effects of near wellbore tortuosity.
`
`8 Claims, 9 Drawing Sheets
`
`
`
`Page 1 of 25
`Page 1 of 25
`
`

`

`5,360,066
`
`Page 2W
`
`OTHER PUBLICATIONS
`
`Goetz, Seiler and Edmiston, “Geological and Borehole
`Features Described by the Circumferential Acoustic
`Scanning Tool”, SPWLA 31st Annual Logging Sym—
`posium, Jun. 1990 (21 pages).
`Torres, Strickland and Gianzero, “A New Approach to
`Determining Dip and Strike Using Borehole Images”;
`SPWLA 3lst Annual Logging Symposium, Jun. 1990
`(16 pages).
`Halliburton Logging Services, Inc. “Telecast”flier; Jan.
`1990 (1 page).
`Halliburton Logging Services, Inc. publication, “An
`Introduction to the HLS Borehole Televiewer”; 1990
`(15 pages).
`Halliburton Logging Services, Inc. publication, “CaS'
`t—The Circumferential Acoustic Scanning T001”; 1990
`(3 pages).
`Aadnoy, Bemt 8., “Modeling of the Stability of Highly
`Inclined Boreholes in Anisotropic Rock Formations”,
`SPE Drilling Engineering, Sep. 1988, p. 263.
`
`Teufel, L. W., “Strain Relaxation Method for Predict-
`ing Hydraulic Fracture Azimuth from Oriented Core”,
`SPE/DOE 9836 (1981).
`»
`
`Teufel, L. W., “Prediction of Hydraulic Fracture Azi-
`muth from Anelastic Strain Recovery Measurements of
`Oriented Core”, Proceeding of 23rd Symposium on
`Rock Mechanics: Issues in Rock Mechanics, Ed. by R.
`E. Goodman and F. F. Hughes, p. 239, SME of AIME,
`New York, 1982.
`
`Blanton, T. L., “The Relation Between Recovery De-
`formation and In—Situ Stress Magnitudes”, SPE/DOE
`11624 (1983).
`
`El Rabaa, W., and Meadows D. L., “Laboratory and
`Field Application of the Strain Relaxation Method”,
`SPE 15072 (1986).
`El Rabaa, W., “Determination of Stress Field and Frac-
`ture Direction in Danian Chalk”, 1989.
`Halliburton Logging Services, Inc. publication, “Full
`Wave Sonic Log”, Mar. 1986 (11 pages).
`
`Page 2 of 25
`Page 2 of 25
`
`

`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 1 of 9
`
`5,360,066
`
`
`
`Page 3 of 25
`Page 3 of 25
`
`

`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 2 of 9
`
`5,360,066
`
`PERFORM CT ANALYSIS
`
`AND STORE IMAGES
`
`ROTATE IMAGES WITH
`
`OF IMAGE
`
`PRINCIPAL SCRIBE AT TOP
`
`Fig. 3
`
`CONSTRUCT AND STORE
`
`COMPUTER IMAGE TRACE
`
`CONSTRUCT AND STORE
`
`TEMPLATE OF SPECIFIC
`
`COMPUTER CORE
`
`
`
`
`
`
`
`
`
`
`CIRCUMFERENCE TRACE
`
`
`
`USING CORE DIAMETER
`
`SCRIBE LINE ANGLES
`
`BETWEEN PRINCIPAL
`
`AND SECONDARY SCRIBES
`
`
`
`SELECT DESIRED CT AXIAL
`
`CORE IMAGE AND IDENTIFY
`
`AT LEAST TWO SCRIBE LINES
`
`OVERLAY AND ALIGN SCRIBE
`
`LINE AND CIRCUMFERENCE
`
`IMAGE ONTO CT CORE IMAGE
`
`
`
`SUPERIMPOSE AND
`
`TRANSLATE FRACTURE TRACE
`
`IMAGE THROUGH CENTER OF CORE
`
`MEASURE DEVIATION ANGLE
`
`FROM PRINCIPAL SCRIBE LINE
`
`(CLOCKWISE on
`COUNTERCLOCKWISE )
`
`Page 4 of 25
`Page 4 of 25
`
`

`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 3 of 9
`
`5,360,066
`
` “THET“
`
`TOOL NsoE
`
`\
`
`T
`
`SOUTH
`
`Page 5 of 25
`Page 5 of 25
`
`

`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 4 of 9
`
`5,360,066
`
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`
`
`Page 7 of 25
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`

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`US. Patent
`
`Nov. 1, 1994
`
`Sheet 6 of 9
`
`5,360,066
`
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`

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`US. Patent
`
`Nov. 1, 1994
`
`Sheet 7 of 9
`
`5,360,066
`
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`Page 9 of 25
`Page 9 of 25
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`
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`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 8 of 9
`
`5,360,066
`
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`Page 10 of 25
`Page 10 of 25
`
`
`

`

`US. Patent
`
`Nov. 1, 1994
`
`Sheet 9 of 9
`
`5,360,066
`
`
`
`Fig. 15
`
`Page 11 of 25
`Page 11 of 25
`
`

`

`1
`
`5,360,066
`
`METHOD FOR CONTROLLING SAND
`PRODUCTION OF FORMATIONS AND FOR
`OPTIIMIZING HYDRAULIC FRACI'URING
`THROUGH PERFORATION ORIENTATION
`
`BACKGROUND OF THE INVENTION
`
`The present invention relates generally to improved
`methods for perforating wells, such as oil and gas wells,
`and particularly to methods for generally aligning per-
`forations along the direction relative to horizontal
`stresses in the formation surrounding the wellbore.
`In the completion of oil and gas wells, it is common to
`utilize multiple charge perforating guns to perforate the
`well casing and the formation surround the wellbore
`within a zone of interest. Such perforations may be
`directed toward one side of the wellbore or another.
`For example, see U.S. Pat. No. 4,194,577 issued Mar. 25,
`1980 to Roy R. Van, and entitled “Method and Appara-
`tus for Completing a Slanted Wellbore.” US. Pat. No.
`4,194,577 discloses orienting a perforating gun through
`gravity to perforate the low side of a non-vertical well-
`bore. Techniques have been proposed in co-pending
`parent application No. 897,358, filed Jun. 11, 1992, in
`the names of some of the inventors named herein, for
`determining the direction of stress fields within a forma-
`tion, and for orienting perforations relative to those
`stress fields to promote efficient, subsequent, hydraulic
`fracturing of the formation. The orientation apparatus is
`described also in application Ser. No. 897,257, filed Jun.
`11, 1992, by James J. Venditto, David McMechan, Cal-
`vin Kessler, and Harold E. Peelman.
`Some formations, however, such as those conven-
`tionally referred to as “loosely consolidated” or “un—
`consolidated” formations, often present problems in the
`production of sand or larger formation pieces. A rela-
`tively high production rate from a relatively loosely
`consolidated formation typically results in a relatively
`increased pressure drawdown across the formation
`proximate the wellbore (i.e.,
`in the “near wellbore
`area”). This pressure drawdown places increased stress
`on the formation. Where this stress (coupled with the
`pre-existing in situ stress) exceeds the shear strength of
`the formation, failure of the formation will typically
`occur, leading to sand production from the well.
`In such circumstances, conventional practice is to
`install some type of sand control apparatus within the
`well. This may include merely placing a prepacked
`gravel pack screen within the well to minimize solids
`production into the wellbore. Production through such
`a pre—packed screen, however, may often become re—
`duced over time due to collapsing and compacting of
`the formation around the screen.
`Another, more expensive, remedy is to gravel pack
`the perforated zone by placing a volume of gravel in the
`formation, and actually in the perforations surrounding
`the well, to maintain the perforations in an open condi-
`tion. Many techniques for gravel packing are well
`known to the industry. In general, however, gravel
`packing a well adds substantial additional time and ex-
`pense to the process of completing the well. As a result,
`in many cases the decision as to whether or not to
`gravel pack a well will be based upon factors including
`how the degree of unconsolidation of the formation, the
`resulting sand production and other disadvantages asso-
`ciated therewith, may be balanced against the cost of
`the gravel pack. At least in some cases, wells could be
`completed more efficiently if it were possible to mini-
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`2
`mize primary sand production from a well in a loosely
`consolidated or unconsolidated formation.
`Accordingly, the present invention provides a new
`method and apparatus for determining the stress fields
`within the formation in the zone of interest surrounding
`a wellbore and for orienting the perforating gun to
`orient the perforations relative to the determined stress
`fields to thereby minimize sand production from the
`well. This method and apparatus have the further ad-
`vantages that should the well be subsequently fractured,
`where the perforations are oriented generally in line
`with the maximum horizontal stress within the forma-
`tion, the perforation tunnel will retain maximum stabil-
`ity; and any subsequent hydraulic fracturing operations
`should result
`in a maximum near-wellbore fracture
`width, and a desirable single fracture of maximum di-
`mension.
`
`SUMMARY OF THE INVENTION
`
`The present inventiOn is directed to a method for
`improving the perforation tunnel stability of formation
`perforations, and also for optimizing subsequent hy-
`draulic fracturing operations by generally aligning well-
`bore perforations with the direction of the maximum
`principal horizontal stress existing within the formation
`surrounding the wellbore. The direction of maximum
`horizontal stress in the formation may also be consid-
`ered as the direction of fracture propagation. In an
`unclosed portion of a wellbore, application of hydraulic
`pressure to a formation will typically cause a fracture
`along the axis of maximum horizontal stress. This perfo-
`ration orientation offers the advantage of establishing
`optimally stable perforation tunnels, and thereby limit-
`ing the undesirable production of sand or other forma-
`tion pieces from the well. The present method may be
`used on both vertical and deviated wells, e.g. horizontal
`wells or wells drilled at an angle relative to a vertical
`well. Where fracturing operations follow the perfora-
`tions, fractures may be initiated at lower pressures, and
`problems associated with near wellbore tortuosity may
`be avoided.
`The method of the present invention may be per
`formed through use of any of several different tech—
`niques to determine the orientation of stress fields
`within a formation. One representative method involves
`performing a small volume hydraulic fracturing (micro-
`frac) test in an open wellbore in a formation, and there-
`after taking an oriented core from the formation and
`observing the direction of the induced fracture where it
`intersects the core. Such observation may be made
`visually or through use of computed tomography (CT)
`techniques. Another representative technique is the use
`of a downhole tool to measure borehole deformation
`before and after fractures have been initiated in the
`wellbore, and, based upon that data, determining the
`direction of fracture propagation within a formation.
`Additionally, the direction of fracture orientation may
`also be determined through use of various strain relax—
`ation measurements which are known to those skilled in
`the art. Apparatus for performing such strain relief
`measurement is disclosed in US. Pat. Nos. 4,673,890;
`4,625,795; and 4,800,753. Yet another representative
`technique would be the use of an oriented downhole
`circumferential acoustic scanning tool (CAST) that
`allows observation of the fractures in the formation as
`they are initiated, or open and close, thereby allowing
`determination of the direction of fracture propagation.
`
`Page 12 of 25
`Page 12 of 25
`
`

`

`5,360,066
`
`3
`After the orientation of the stress field is determined,
`.an oriented perforating device is positioned such that
`the perforations produced when such device is fired
`will be generally aligned with the direction of the maxi-
`mum horizontal stress field.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. la is a cross-sectional view of a horizontal CT
`scan image through a cylinder core.
`FIG. 1b is a cross-sectional view of axial and longitu-
`dinal CT scan images through a cylindrical core.
`FIG. 2 is a schematic for obtaining fracture orienta-
`tion from CT slice data in reference to orientation
`scribes.
`FIG. 3 is a flowchart representing the steps of a com-
`puter software program for measuring the orientation of
`a fracture.
`FIG. 4 is an induced fracture strike orientation plot.
`FIG. 5 illustrates the generalized fracture orientation
`with respect to wellbore orientation and stress orienta-
`tion.
`
`FIG. 6 is a graphical solution to the fracture orienta-
`tion for deviated or horizontal wellbore/core.
`FIG. 7 represents a horizontal cross-section through
`a vertical wellbore showing the angularly offset direc-
`tions in which wellbore diametral displacements are
`preferably measured.
`FIG. 8 is a graph showing the diametral displace-
`ments of a wellbore versus pressure.
`FIG. 9 is a polar graph showing the diametral en-
`largements of a wellbore as a result of the pressure
`increase over the time period identified as phase B in
`FIG. 8.
`
`FIG. 10 is a photograph of a representation of an
`open fracture in a wellbore as shown on the amplitude
`raster scan image produced by use of a circumferential
`acoustic scanning tool.
`FIG. 11 is another photograph of a representation of
`an open fracture in a wellbore as shown on the travel
`time raster scan image produced by use of a circumfer-
`ential acoustic scanning tool.
`FIG. 12 is a cross-sectional view of a subterranean
`well within which is suspended an exemplary wireline
`tool.
`FIG. 13 is a cross-sectional view of a subterranean
`well within which is suspended an exemplary wireline
`tool.
`FIGS. 14—15 illustrate an exemplary directional radi-
`ation detector that may be used in accordance with the
`present invention.
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`The stress field around a wellbore is most likely to
`result in compressive shear failure of the formation in
`the direction of the minimum horizontal stress. The
`maximum stress concentration occurs in the direction of
`the minimum horizontal stress; while the minimum
`stress concentration is in the direction of the maximum
`horizontal stress. The shear failure of a formation is a
`function of the ratio of the minimum to maximum hori-
`zontal stresses, the cohesive strength of the formation
`and the coefficient of internal friction.
`Where the ratio of minimum to maximum horizontal
`stresses is high, and where the cohesive strength of the
`formation is low, perforation tunnels extending gener-
`ally in the direction of the minimum horizontal stress
`field are relatively prone to collapse or otherwise dete-
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`40
`
`45
`
`50
`
`55
`
`6S
`
`4
`riorate, potentially resulting in the production of sand
`or other formation particles from the well. In contrast,
`perforation tunnels extending in the direction of the
`maximum horizontal stress are less likely to deteriorate
`to cause such problems. Additionally, perforations ori-
`ented in such manner should provide optional points
`from which formation fractures may subsequently be
`initiated.
`Utilizing conventional techniques, whenever a well is
`fractured, there is no way to assure at which radially
`distributed perforation sites a fracture will
`initiate.
`Sometimes, the fractures initiate at a perforation site
`that is not aligned with the direction in which the frac-
`ture will propagate through the formation. Generally
`speaking, the initiation of a fracture at a perforation site
`is less dependant upon the direction of the perforation
`than it is upon the local stress conditions of the forma-
`tion immediately adjacent to the perforation tunnel. In
`fact, whether a fracture initiates at a given perforation
`site is greatly affected by the extent of damage caused to
`the formation during the perforation process. There-
`fore, fractures may be initiated at nonaligned perfora-
`tion sites, even though the initiation and propagation of
`a fracture at a nonaligned perforation site would, in
`theory, require higher pressures than would be required
`to initiate and propagate a fracture at a perforation site
`aligned with the direction of fracture propagation. In
`general, with use of conventional perforation tech-
`niques, orientation of a perforating device was a sub-
`stantial problem in that few, if any, perforations pro-
`duced by such device would align with the plane of an
`inferred fracture, such as that determined by a micro-
`frac test.
`By way of example only, assume that the direction of
`fracture propagation existing within a field is along a
`horizontal line that corresponds to the 0°—180" axis of a
`horizontal plane passing through the wellbore when
`viewed from above. During fracturing operations, a
`fracturing fluid is pumped into the wellbore under high
`pressure to induce and propagate the fracture. This
`operation may result in the initiation and propagation of
`a fracture in a nonaligned perforation tunnel (which is
`typically 6"—15" in length), e.g., a tunnel oriented at 30°.
`Thereafter, after the initial fracture has propagated a
`given distance away from the wellbore, approximately
`2—3 wellbore diameters, the fracture will turn towards,
`or align with, a direction perpendicular to the minimum
`principle stress existing within the formation (i.e., align
`with the maximum horizontal stress field), to reduce the
`energy required to propagate the fracture. This results
`in a curved flow path through which the fracturing
`fluid must be pumped to complete the fracturing opera-
`tions. This phenomenon, which is commonly referred
`to as near wellbore tortuosity, causes many problems
`during fracturing procedures.
`The phenomenon of near wellbore tortuosity may
`also occur under distinctly different circumstances. In
`particular, if a good seal is not achieved between the
`cement and the formation in a cased well, and if the
`fracturing fluid has access to the cement-formation
`interface, then fractures may be initiated on the surface
`of the wellbore face in a direction perpendicular to the
`minimum principle stress in the formation, and not at
`one of the perforation sites. Since the energy required to
`fracture the formation in the direction of the nonaligned
`perforations is larger than the energy required to propa—
`gate the fractures at the wellbore face, a curved or
`convoluted flow path for the fracturing fluid may be
`
`Page 13 of 25
`Page 13 of 25
`
`

`

`5
`established between the perforations and the fractures
`initiated at the wellbore face as the fracturing fluid
`flows between the cement and the formation.
`The near wellbore tortuosity phenomenon can result
`in excessively high pressure drops as the fracturing fluid
`is pumped through the fractures initiated in the non-
`aligned perforation tunnels. This curved flow path for
`the fracturing fluid may also result in fracture narrow-
`ing for two reasons. First, since the perforation tunnel is
`not aligned with the natural direction of fracture propa-
`gation, the force required to induce and propagate the
`fracture initiated at the nonaligned perforation tunnel
`necessarily exceeds the minimum principle stress in the
`field,
`thereby resulting in a narrower fracture then
`would be produced if the perforations, and resulting
`fractures, were aligned with the direction of fracture
`propagation. Additionally, since a given well has a
`maximum allowable well head pressure, the pressure
`drop incurred in pumping the fracturing fluid through
`the nonaligned perforation tunnels limits the energy
`available to propagate the main fracture fully into the
`formation, i.e., if excessive pressure drop is encountered
`in pumping the fracturing fluid through a fracture initi-
`ated at a nonaligned perforation tunnel, then a lesser
`amount of energy will be available to further open the
`fractures and force them further into the formation.
`Another problem that may be encountered is bridg-
`ing the fracture with proppants typically used in frac-
`turing procedures. In particular, if a fracture is aligned
`perpendicular to the direction of minimum principle
`stress, then the main body of the fracture may be as
`much as approximately l” wide. However, in the case
`of fractures induced in nonaligned perforation tunnels,
`the width of the fracture may be significantly narrower.
`Given that proppants typically used in fracturing fluids
`may be approximately 0.026” in diameter, there exist a
`real possibility that proppants may bridge in the nar-
`rower fractures initiated in nonaligned perforation tun-
`nels. If this occurs, then fracturing operations may be
`prematurely terminated which, results in, at best, an
`inefficient well.
`Although the tortuous path created as a result of
`fractures being initiated in nonaligned perforation tun-
`nels is not directly observable from the surface during
`fracturing operations, the effects of near wellbore tortu-
`osity may be observed. In particular, if the fracturing
`fluid must be pumped at pressures substantially in excess
`of the pressure required to hold the fractures open, then
`it is likely that any additional pressure drop is associated
`with this phenomenon of near wellbore tortuosity.
`Given the relatively short length of the initial fractures,
`if the pressure drop associated with the flow of fluid
`through the initial fractures is relatively large, then the
`high pressure drop must be due to the losses incurred in
`forcing the fracturing fluid through a very narrow frac-
`ture over such a short distance.
`
`The present inventive methods and procedures over-
`come these as well as other problems existing due to this
`phenomenon by determining the direction of existing
`horizontal stress fields, and the response of hydraulic
`fracture propagation within a formation, and providing
`a mechanism for aligning the perforations produced
`with any of several known prior art devices with the
`previously determined direction of maximum horizon—
`tal stress in the formation.
`In particular, the direction or azimuth of formation
`stress fields may be determined using any of a variety of
`methods. Representative methods include: (1) perform-
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`ing an open hole microfrac test and thereafter taking an
`oriented core from below the bottom of the wellbore,
`thereby allowing observation of the direction of the
`induced fracture, and thereby determining azimuthal
`orientation of maximum horizontal stress, from the
`core; (2) using computed tomography (CT) techniques
`to determine fracture direction and rock anisotropy
`orientation from an oriented core that is obtained after
`an open hole microfrac test; (3) employing a high preci-
`sion multi-armed caliper, such as the Total Halliburton
`Extensiometer, to measure the borehole deformation
`before and after fracturing to determine the fracture and
`stress direction; (4) performing strain relaxation mea-
`surements on an oriented core obtained from the rele-
`vant area of observation to determine the direction of
`least principle stress existing within the field; and (5)
`using an oriented downhole tool, such as Halliburton’s
`Circumferential Acoustic Scanning Tool (CAST), to
`provide a full borehole image which allows direct ob-
`servation of an induced fracture during fracturing oper-
`ations. However, these methods are merely representa-
`tive techniques that may be employed to determine the
`direction of fracture propagation, and should not be
`considered as specific limitations of this invention. Each
`of these methods will be discussed more fully herein.
`I. Visual Observation Of The Direction Of An Induced
`Fracture In An Oriented Core
`
`The techniques and methods employed during the
`open hole microfrac test to determine the direction of
`fracture propagation, and thus of the maximum horizon~
`tal stress field, are fully disclosed in US. Pat. No.
`4,529,036, which is hereby incorporated herein by refer-
`ence. Generally speaking, during an open hole micro-
`frac test, microfractures are induced in an open hole
`wellbore by pumping a relatively small amount of frac—
`turing fluid into the wellbore. Since this technique is
`employed in an open wellbore, these fractures will natu-
`rally align with the direction of fracture propagation,
`i.e., perpendicular to the minimum principle horizontal
`stress existing within the formation. Additionally, this
`procedure results in the initiation of fractures in the
`formation for a given depth under the bottom of the
`open hole wellbore.
`Thereafter, an oriented core sample is taken from the
`formation. The orientation of the core is determined by
`certain orientation grooves, both principal and second-
`ary scribe lines, that are marked on the core as the core
`is being cut. Knives inside the core barrel cut the scribe
`lines as the core enters the core barrel. The orientation
`of the principal scribe with respect to a compass direc-
`tion is recorded prior to running the core barrel into the
`borehole. Thus, one can determine the orientation of
`the principal scribe line from the compass readings at
`each recorded interval. The secondary scribe lines are
`used as a reference for identifying the principal scribe.
`A survey record will exist at the conclusion of the cored
`section which accurately reflects the orientation of the
`core’s principal scribe line throughout the interval.
`Orientation of the core is considered a critical part of
`obtaining accurate orientation measurements of planar
`core features such as fractures.
`Once the oriented core is removed from the well, it is
`visually inspected to determine the direction of fracture
`propagation and the types of fractures observed are
`classified (ic) induced as natural). This method has the
`additional benefit that the fracture direction is deter-
`mined from observation of a fracture existing below the
`
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`5,360,066
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`7
`well, i.e., as it exists in the formation in its natural state
`away from the effects of the drilling operations. Typi-
`cally, this procedure may be used to determine the
`direction of fracture propagation above, below, and
`within the area of the formation under consideration.
`
`II. Observation Of The Direction Of An Induced
`Fracture In An Oriented Core Through Use Of
`Computed Tomography Imagery
`Fracture orientation may also be determined through
`use of computed tomography (CT) techniques, com-
`monly known in the medical field as CAT scanning
`(“computerized axial tomography” or “computed as-
`sisted tomography”). This method is the subject of a
`separate pending patent application which is also as-
`signed to the assignee of the present application (appli-
`cation Ser. No. 897,256, filed Jun. 11, 1992, by Matthew
`E. Blanch and James I. Venditto).
`In this method, fractures are induced in the formation
`through use of the microfrac technique, thereafter an
`oriented core is taken from the bottom of the wellbore.
`However,
`in this method, the oriented core sample
`remains inside a sleeve surrounding the core throughout
`the analysis of the core. Although this technique may be
`employed on any type of formation, it is particularly
`useful when dealing with friable type formations that
`prohibit physical handling of the core sample. The CT
`techniques allows observation of the direction of frac—
`tures as well as orientation directions on the core, and
`thereby allow determination of the direction of fracture
`propagation.
`By way of background, CT technology is a nonde-
`structive technology that provides an image of the in-
`ternal structure and composition of an object. What
`makes the technology unique is the ability to obtain
`imaging which represents cross sectional “axial” or
`“longitudinal” slices through the object. This is accom-
`plished through the reconstruction of a matrix of x-ray
`attenuation coefficients by a dedicated computer system
`which controls a scanner. Essentially, the CT scanner is
`a device which detects density and compositional dif-
`ferences in a volume of material of varying thicknesses.
`The resulting images and quantitative data which are
`produced reflect volume by volume (voxel) variations
`displayed as gray levels of contrasting CT numbers.
`Although the principles of CT were discovered in the
`first half of this century, the technology has only re-
`cently been made available for practical applications in
`the non-medical areas. Computed tomography was first
`introduced as a diagnostic x—ray technology for medical
`applications in 1971, and has been applied in the last
`decade to materials analysis, known as non-destructive
`evaluation. The breakthroughs in tomographic imaging
`originated with the invention of the x-ray computed
`tomographic scanner in the early 1970’s. The technol-
`ogy has recently been adapted for use in the petroleum
`industry.
`A basic CT system consists of an x-ray tube; single or
`multiple detectors; dedicated system computer system
`which controls scanner functions and image reconstruc-
`tions and post processing hardware and software. Addi-
`tional ancillary equipment used in core analysis include
`a precision repositioning table; hard copy image output
`and recording devices; and x-ray “transparent” core
`holder or encasement material.
`A core may be laid horizontally on the precision
`repositioning table. The table allows the core to be
`incrementally advanced a desired distance thereby en-
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`suring consistent and thorough examination of each
`core interval. The x-ray beam is collimated through a
`narrow aperture (2 mm to 10 mm), passes through the
`material as the beam/o