U.S. patent application number 13/519572 was filed with the patent office on 2013-12-05 for method for controlling the trajectory of a hydraulic fracture in strata-containing natural fractures.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. The applicant listed for this patent is Dmitry Chuprakov, Eduard Siebrits. Invention is credited to Dmitry Chuprakov, Eduard Siebrits.
Application Number | 20130319657 13/519572 |
Document ID | / |
Family ID | 44226678 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130319657 |
Kind Code |
A1 |
Siebrits; Eduard ; et
al. |
December 5, 2013 |
METHOD FOR CONTROLLING THE TRAJECTORY OF A HYDRAULIC FRACTURE IN
STRATA-CONTAINING NATURAL FRACTURES
Abstract
The method of controlling the parameters of a hydraulic fracture
comprises creating a matrix of relationship between initial
formation, injection and fracture parameters of and a predicted
increment of a hydraulic fracture path. The matrix is used for
retrieving and deriving the predicted increment of the fracture
path, depending on the actual initial parameters of a fracture
being created. The actual increment of the hydraulic fracture path
is measured and compared with the predicted increment of the
fracture path. In case of a discrepancy between the actual and
predicted increments, the actual initial parameters of the fracture
are changed.
Inventors: |
Siebrits; Eduard; (Salt Lake
City, UT) ; Chuprakov; Dmitry; (Belmont, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siebrits; Eduard
Chuprakov; Dmitry |
Salt Lake City
Belmont |
UT
MA |
US
US |
|
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
SUGAR LAND
TX
|
Family ID: |
44226678 |
Appl. No.: |
13/519572 |
Filed: |
December 30, 2009 |
PCT Filed: |
December 30, 2009 |
PCT NO: |
PCT/RU2009/000746 |
371 Date: |
October 12, 2012 |
Current U.S.
Class: |
166/250.1 |
Current CPC
Class: |
E21B 43/26 20130101 |
Class at
Publication: |
166/250.1 |
International
Class: |
E21B 49/00 20060101
E21B049/00; E21B 43/26 20060101 E21B043/26 |
Claims
1. Method for controlling a hydraulic fracture path in formations
containing natural fractures comprising: a) creating a matrix of
relationship between initial formation, injection and fracture
parameters and a predicted increment of a hydraulic fracture path,
b) starting a hydraulic fracturing process, c) measuring actual
initial parameters of a hydraulic fracture being created, d) using
the matrix for retrieving and deriving the predicted increment of
the fracture path, depending on the actual initial parameters of
the fracture being created, e) measuring an actual increment of a
path of the hydraulic fracture being created , f) comparing the
actual increment of the path of the fracture being created with the
predicted increment of the fracture path, and g) in case of a
discrepancy between the actual and the predicted increments
changing the actual initial parameters of the fracture being
created.
2. Method of claim 1, wherein the matrix of relationship between
initial formation, injection and fracture parameters and the
predicted increment of the hydraulic fracture path is created
through numerical calculations or experiments or both.
3. Method of claim 1, wherein the initial formation, injection and
fracture parameters include formation and natural fracture
parameters, fracturing fluid injection parameters and initial
fracture path parameters.
4. Method of claim 3, wherein formation mechanical stresses are
used as the formation and natural fracture parameters.
5. Method of claim 3, wherein coefficients of interface adhesion
are used as the formation and natural fracture parameters.
6. Method of claim 3, wherein coefficients of interface friction
are used as the formation and natural fracture parameters.
7. Method of claim 3, wherein a relative angle between the
hydraulic fracture and a natural fracture in a point of their
contact is used as the formation and natural fracture
parameters.
8. Method of claim 3, wherein a parameter characterizing the
location of natural fractures is used as the formation and natural
fracture parameters.
9. Method of claim 3, wherein a natural fracture size parameter is
used as the formation and natural fracture parameters.
10. Method of claim 3, wherein a viscosity of a fracturing fluid to
be injected is used as the fracturing fluid injection
parameter.
11. Method of claim 3, wherein a fracturing fluid injection rate is
used as the fracturing fluid injection parameter.
12. Method of claim 3, wherein an average fracturing fluid pressure
in the hydraulic fracture is used as the fracturing fluid injection
parameter.
13. Method of claim 3, wherein a fracture length is used as the
initial fracture path parameter.
14. Method of claim 3, wherein a gap between a hydraulic fracture
tip and an interface is used as the initial fracture path
parameter.
15. Method of claim 1, wherein the initial formation, injection and
fracture parameters and the predicted increment of the hydraulic
fracture path are represented in the matrix as normalized
values.
16. Method of claim 1, wherein operations c), d), e), f), g) are
performed in the real-time mode of the hydraulic fracturing
process.
17. Method of claim 1, wherein operations c), d), e), f), g) are
performed by using a control device.
18. Method of claim 17, wherein the control device is capable of
converting the actually measured values into normalized values, and
vice versa.
19. Method of claim 1, wherein the actual initial parameters of the
hydraulic fracture being created are measured by using measuring
techniques.
20. Method of claim 1, wherein the actual increment of the
hydraulic fracture being created is measured by using measuring
techniques.
Description
FIELD OF THE DISCLOSURE
[0001] This invention relates to methods for controlling and
optimizing parameters of a hydraulic fracture created during the
hydraulic fracturing of oil-bearing and gas-bearing reservoirs
containing an existing network of natural (geological) fractures,
and can be used in appropriate oil and gas fields.
BACKGROUND OF THE DISCLOSURE
[0002] Hydraulic fracturing is a widely used method for stimulating
hydrocarbon inflow from a formation into oil wells or gas wells. To
ensure that the best economic result is achieved from the hydraulic
fracturing treatment, a design model of the treatment is developed.
This model is based on mechanical characteristics of the formation
(such as formation stresses, moduli of elasticity and plasticity of
the formation, cracking resistance, permeability, etc.), as well as
on the selection of optimum parameters for injection of a
fracturing fluid into the formation, including the selection of a
proper fracturing fluid, proppants, injection conditions, etc. The
design model of the fracture plays a rather important role which
consists in ensuring that the actual parameters of the fracture
geometry will be consistent with the predicted values, and that the
selected fracturing fluid and proppant, as well as their
quantities, injection rates and the proppant schedule are
acceptable for successful implementation of the hydraulic
fracturing process.
[0003] Most of the design models offered nowadays for commercial
use (STIMPLAN, NSI Technologies; FracProPT, MFRAC, etc.), as well
as the data contained, for example, in Thiercelin, M. J. 2009,
"Hydraulic fracture propagation in discontinuous media," Proc.:
International Conference on Rock Joints and Jointed Rock masses,
Tucson, 4-10 Jan 2009. pp. 12; Daneshy, A., 2003, "Off-balance
growth: A new concept in hydraulic fracturing," Journal of
Petroleum Technology, 55, 4, April 2003: 78-85, etc. are based on
the assumption that a single hydraulic fracture plane is created in
the formation under treatment. The fracture initiates from the
wellbore and increases in length and in height over time as the
fracturing fluid and proppant are injected. The in-situ stress
condition in the reservoir is such that that there is generally a
minimum stress in one of the three stress components, and the
created hydraulic fracture tends to propagate in the plane normal
to the minimum stress. This assumption about a single planar
fracture is usually acceptable for the hydraulic fracturing
treatment in a formation consisting of horizontally homogeneous
layers.
[0004] However, the number of hydraulic fracturing treatments in
unconventional oil-bearing formations has recently begun to
increase. For complex reservoirs (e.g., for shale-gas reservoirs
containing a network of natural (geological) fractures), the
assumption about the planar geometry of the hydraulic fracture
becomes unjustified. In such formations, the fracturing fluid
penetrates so-called "connection branches," thus creating a complex
network of crisscross fractures.
[0005] It has become obvious that conventional tools intended for
development of optimum hydraulic fracturing treatment strategies
and based on planar distribution do not produce the required effect
when used in the producing layers having a complex
three-dimensional configuration. In such cases, new development
tools are required for determination of optimum hydraulic
fracturing treatment strategies.
[0006] For example, based on the purpose which consists in
conducting a hydraulic fracturing process in formations containing
natural (geological) fractures, the closest analogue of the claimed
invention is the method of fracturing a naturally fractured rock
(WO 2008093264, E 21 B 43/26, published on Jul. 8, 2008). The
method is used for conducting a hydraulic fracturing process in
formations containing geological fractures. The method comprises:
a) acquiring subterranean formation layer geomechanical properties,
well completion and reservoir data for the subterranean formation,
and a natural fracture network description for the subterranean
formation; b) simulating a fracture treatment for the formation,
the simulation comprising inputting data acquired into a model
which simulates propagation of a network of fracture branches by
dividing fracture segments into a plurality of elements to form a
fracture grid; c) determining and preparing an optimum fracture
fluid composition to achieve the fracturing objective; and, d)
injecting the fracturing fluid into a wellbore at a pressure
sufficient to fracture the subterranean formation.
[0007] However, the known method has disadvantages consisting in
the fact that the proposed method is characterized by a great
calculation resource intensity, which increases the capital
investments required for implementation of this method. In
addition, the method does not include any design model correction
to be made by comparing the calculated measurements and the
actually obtained measurements, which increases the experimental
error and results in a low accuracy of the method on the whole.
SUMMARY OF THE DISCLOSURE
[0008] The claimed invention provides higher efficiency and
accuracy of the hydraulic fracturing process control (namely, of
the hydraulic fracture propagation path control in formations
containing natural (geological) fractures), as well as reduced
capital investments required for implementation of this
invention.
[0009] The method comprises the following operations: [0010] a)
creating a matrix of relationship between initial formation,
injection and fracture parameters and a predicted increment of a
hydraulic fracture path; [0011] b) starting a hydraulic fracturing
process; [0012] c) measuring actual initial parameters of a
hydraulic fracture being created; [0013] d) using the matrix for
retrieving and deriving the predicted increment of the fracture
path, depending on the actual initial parameters of the fracture
being created; [0014] e) measuring an actual increment of a path of
the hydraulic fracture being created; [0015] f) comparing the
actual increment of path of the fracture being created with the
predicted increment of the fracture path; and [0016] g) in case of
a discrepancy between the actual and predicted increments, changing
the actual initial parameters of the fracture being created.
BRIEF DESCRIPTION OF THE FIGURES
[0017] FIG. 1 illustrates a schematic representation of main
parameters in case where a hydraulic fracture approaches an
interface.
[0018] FIG. 2 is a schematic representation of possible cases of
the hydraulic fracture propagation in case where a hydraulic
fracture interacts with an interface.
[0019] FIG. 3 is a schematic representation of three possible base
cases of the hydraulic fracture propagation in case where a
hydraulic fracture interacts with a natural fracture.
[0020] FIG. 4 shows a fragment of a matrix of relationship between
normalized parameters, and characteristics of the offset of the
hydraulic fracture at the interface.
DETAILED DESCRIPTION
[0021] There are many factors that control the complexity of a
hydraulic fracture geometry. In cases where the hydraulic fracture
interacts with a bedding layer, a natural fracture, or a fractional
fault (all of them being hereinafter referred to as the
"interface"), the hydraulic fracture may expand right through the
interface, may end at the interface, or may continue to propagate
at a certain offset along the interface (FIG. 3).
[0022] The key parameters which control the selection of one of the
possible fracture propagation paths listed above include, but are
not limited to, the following: a fracturing fluid injection rate
(Q); a fracturing fluid viscosity (.mu.); a remote stress
difference (.sigma.1-.sigma.3); interface properties, such as a
friction (.sigma.), an adhesion (C), an angle of approach (.beta.)
of the hydraulic fracture to the interface, and a gap (d) between
the nearest hydraulic fracture tip and the interface (FIG. 1).
[0023] FIG. 2 shows possible hydraulic fracture propagation paths
in case where a hydraulic fracture intersects an interface. FIG. 1
and FIG. 2 show the interface as a thin horizontal line which cuts
each drawing in half; "Mat 1" and "Mat 2" shows potentially
different materials on each side of the interface, and the fracture
approaches it from the bottom of the drawing. For schematic
representation of a possible hydraulic fracture propagation path,
these drawings are based on the assumption that the fracture has a
planar geometry although the process can be expanded to a
three-dimensional model.
[0024] By varying independently each of these control parameters
through a series of physical experiments or through a numerical
simulation, it is possible to determine the conditions under which
different scenarios (cases) of the hydraulic fracture intersecting
the interface (i.e., the behavior and the direction of the
hydraulic fracture), shown in FIG. 2, are most likely to happen.
This may require a great number of scenarios (series of
experiments), depending on the required resolution. But with a
numerical simulation made by using state-of-the-art computers, this
is quite feasible and industrially applicable.
[0025] The obtained results can be summarized as a matrix (a
database, a reference table, or other data files) containing key
data which determine whether the hydraulic fracture will tend to be
more planar during the fracturing fluid injection in one extreme
case, or whether it will tend to branch out into many fractures
covering a great reservoir volume in the other extreme case, or
whether the propagating hydraulic fracture will stop growing at the
interface without further propagation. This matrix can be developed
through numerical calculations and/or physical experiments.
[0026] In addition, it is also necessary to obtain information on
geometrical complexity of the hydraulic fracture propagation
through a network of existing natural fractures. This information
can be based on the result of the interaction between the hydraulic
fracture and existing natural fractures at the interface. The known
result of this interaction with a natural fracture can be
superimposed to give the resulting path of the hydraulic fracture
propagation through a sequence of natural fractures in a fractured
formation. From now on, the hydraulic fracture path change which
considers the hydraulic fracture characteristics (such as the
behavior, the geometry and the direction of the fracture) will be
regarded as the fracture "increment."
[0027] So, the first step of the proposed method is to find a
solution to the problem of the interaction between a hydraulic
fracture and an existing natural fracture and to keep this solution
for further use.
[0028] Since the result of the fracture propagation through the
interface depends on such parameters as: 1) formation and natural
fracture parameters, 2) fracturing fluid injection parameters, 3)
initial fracture path parameters, we consider that, for the
purposes of the claimed invention, the above-mentioned parameters
form the "initial" parameters of formation, injection and
fracture.
[0029] So, the "initial" parameters include, but are not limited
to, the following: [0030] formation and natural fracture parameters
(properties): formation mechanical stresses in this point,
coefficients of interface adhesion and coefficients of interface
friction, a relative angle of the formation and natural fracture
slope relative to the hydraulic fracture, location and size of
natural fractures, [0031] fracturing fluid injection parameters
(properties): a viscosity of a fracturing fluid to be injected and
the fracturing fluid injection rate, or an average fracturing fluid
pressure in the hydraulic fracture, [0032] initial fracture path
(geometry) parameters (properties): a fracture length, a gap (if
any) between a hydraulic fracture tip and an interface, etc.
[0033] The results obtained for each parameter under investigation
can be kept in a relevant data file (a reference table, a database
or a spreadsheet), i.e., in a matrix of relationship, where a
relevant predicted path (that is to say, a hydraulic fracture
propagation increment) has been derived and kept for each specific
set of initial parameters obtained in the course of numerical
calculations or in the course of a physical experiment.
[0034] So, the matrix of relationship shall be developed for an
independent set of parameters in order to reduce excessive data
volume, database creation time and final retrieval time. After the
set of parameters has been determined, it is necessary to specify
the optimum resolution of parameter values for each independent
parameter.
[0035] A hydraulic fracturing process is then implemented and
actual measurements of initial parameters of a fracture being
created (including formation and natural fracture parameters,
fracturing fluid injection parameters, initial fracture path
parameters) are taken.
[0036] For example, a number of hydraulic fracture and formation
parameters are measured by using measuring instruments (e.g.,
sensors distributed over relevant zones of the formation, seismic
and acoustic measuring instruments, tiltmeters, etc.). For example,
the above-mentioned parameters are determined in the real-time
mode, which allows to monitor continuously the hydraulic fracturing
treatment and to increase the hydraulic fracturing process control
efficiency.
[0037] To be able to use the said matrix of relationship during the
implementation of the claimed method, it is necessary to use a
programming tool capable of performing parameter change operations
and logical data processing operations.
[0038] The design tool known from WO 2008093264, E 21 B 43/26
published on Jul. 8, 2008, can be used as such tool. Such a
combined tool can be used for developing, monitoring and
controlling the hydraulic fracturing treatment in the real-time
mode, as well as for evaluating the results of the hydraulic
fracturing treatment in a relevant formation containing natural
fractures or faults.
[0039] The design tool shall be capable of accessing the matrix of
relationship to determine the location of fracture re-initiation or
different fracture propagation path (increment).
[0040] So, first of all, when conducting the hydraulic fracturing,
it is necessary to provide a design tool with actual initial
parameters which characterize a formation and natural fractures, a
fracturing fluid injection and an initial hydraulic fracture path,
and which are measured by using sensors or by taking dedicated
measurements, as described above. The above-mentioned parameters
measured during the hydraulic fracturing process shall also be
provided in the real-time mode to the design tool.
[0041] These actually measured parameters shall be then converted
into independent parameters (normalized values) because the
parameters in the matrix of relationship are represented as
normalized (non-dimensional) values. The said design tool is
therefore capable of converting the parameters actually measured
during the hydraulic fracturing process into normalized values (and
vice versa).
[0042] In addition, the design tool is capable of accessing the
matrix of relationship to retrieve a direct scenario (path) or a
scenario (path) obtained by interpolation between two, or more than
two, scenarios which represent the predicted increment of the
hydraulic fracture propagation path, depending on the actually
measured initial parameters of the hydraulic fracture being
created.
[0043] The design tool then determines from the matrix of
relationship the resulting fracture propagation path (the predicted
fracture increment) along with relevant fracture characteristics
(parameters), such as the offset of the fracture re-initiation
along the interface on the opposite side of the fracture. And the
normalized parameters are then converted into units of measurable
physical quantities (for example, the actual distance of the
offset).
[0044] While the fracture grows during the hydraulic fracturing
process, the actual increment of the resulting fracture path is
measured by using sensors or other measurement methods which allow
to determine the required characteristics of the fracture. The said
data are provided to the design tool.
[0045] The actual increment of the resulting fracture path is
compared with the predicted increment of the fracture path. This
comparison operation is performed by a control device.
[0046] In fact, the actually measured data on the hydraulic
fracture propagation may differ from the results of the
calculations made by the control device. To minimize prediction
errors and to improve the final result of the hydraulic fracturing
treatment, it is possible to use any discrepancies between the
predicted data and the measured data to change the actual initial
parameters of the resulting fracture in the near-real-time mode
(which certainly allows you to optimize the entire method as a
whole).
[0047] In such an operation, certain initial parameters are
corrected (changed) during the hydraulic fracturing process. For
example, it is possible to change the geometry or the pressure, the
injection rate and the viscosity of the fracturing fluid in the
near-real-time mode, considering the error resulting from the
comparison operation.
[0048] Thus, we improve the consistency between the predicted
parameters and the measured parameters during the implementation of
the method, which, in turn (in combination with the essential
features listed above), results in a higher efficiency of the
hydraulic fracture path control.
[0049] So, first, it is necessary to create a matrix of
relationship between initial parameters characterizing a formation
and natural fractures, a fracturing fluid injection and an initial
fracture path before the interaction with a natural fracture, on
the one hand, and a predicted increment of a hydraulic fracture
path after the interaction with the natural fracture, on the other
hand. This matrix can be developed, for instance, by finding a
numerical solution to the problem of the mechanical interaction
between the hydraulic fracture at a constant internal pressure and
the natural fracture at the moment of their contact, and can be
represented in the form of a table as shown in FIG. 4.
[0050] To reduce the number of independent parameters of the
problem, it is necessary to normalize all values in the numerical
problem, so the solution represents the function of the coefficient
of friction on the natural fracture .lamda., the angle of slope of
the natural fracture .beta., the non-dimensional formation
differential stress
.DELTA.=(.sigma..sub.1-.sigma..sub.3)/(.sigma..sub.1+.sigma..sub.3)
and the non-dimensional hydraulic fracture excess pressure
.PI.=2(p-.sigma..sub.3)/(.sigma.+.sigma..sub.3). Considering that,
having come across the natural fracture, the hydraulic fracture
will continue to propagate if a new tensile crack initiates on the
other side of the natural fracture, the offset of the tensile
stress peak along the natural fracture and the stress peak itself
are then selected as the characteristics of the hydraulic fracture
path increment at the natural fracture. As a result of the
normalization, the offset will be normalized to the hydraulic
fracture length L.sub.HF and the stress will be normalized to the
average formation stress
.sigma..sub.m=(.sigma..sub.1+.sigma..sub.3)/2.
[0051] Then, hydraulic fracturing process is started and actual
initial formation, injection and hydraulic fracture parameters are
measured. At a certain stage, it is necessary to learn how a
hydraulic fracture path will change after a hydraulic fracture has
interacted with a natural fracture crossing its path. The measured
formation stresses are equal to .sigma..sub.1=6 MPa,
.sigma..sub.3=4 MPa, a hydraulic fracture pressure is estimated as
p=5.5 MPa, and a current hydraulic fracture length is equal to
L.sub.HF=100 m. The natural fracture has a friction coefficient of
0.5. Let us then assume two possible orientations of the natural
fracture with respect to the hydraulic fracture: a) 10.degree. and
b) 40.degree..
[0052] By using the normalization rules from the table, we obtain:
.lamda.=0.5, .DELTA.=0.2, .PI.=0.3, and the angles for the first
case (a): .beta.=10.degree., for the second case (b):
.beta.=40.degree..
[0053] The matrix of relationship is then used for retrieving and
deriving a predicted increment of the fracture path, in particular,
an offset value and a stress peak value, depending on the given
parameters. Based on the above-mentioned parameters, we retrieve
the values of the hydraulic fracture path increment characteristics
to find that the offset of the fracture is equal to 0.049 and the
stress is equal to -0.0163 in the first case. In the second case,
the offset of the fracture is equal to 0.025 and the stress is
equal to -0.7929 (the relevant lines of the table shown in FIG. 4
are highlighted).
[0054] The normalized values are then converted into dimensional
units of relevant characteristics. We obtain for case a):
offset=4.9 m and stress=0.08 MPa, for case b): offset=2.5 m and
stress=3.96 MPa.
[0055] Then, based on the comparison of the tensile stress peak
with the tensile strength of the rock, a conclusion is made as to
whether a secondary fracture will or will not be formed at the
natural fracture. Assuming that the tensile strength is equal to 4
MPa, the hydraulic fracture will intersect the natural fracture at
a distance of 2.5 m in case a). In case b), no intersection will
take place and the hydraulic fracture will stop at this natural
fracture.
[0056] Let us then assume that the hydraulic fracture path
increment characteristics (namely, the intersection and the offset
of the fracture in case a)) have been measured, and these
measurements show that the offset is actually equal to 1.3 m.
[0057] The actual increment of the resulting fracture path is then
compared with the predicted increment of the fracture path. As
these values turned out to be different, the actual initial
parameters of the resulting fracture shall be changed. In this
case, the fluid pressure value shall be corrected. Having retrieved
the required data from the matrix, we find that this value
corresponds to a non-dimensional pressure of 0.2 for the given
hydraulic fracture length. Conversion into dimensional units gives
a new well pressure value of 5 MPa which will be used as a more
accurate value in subsequent applications of the method.
[0058] The above embodiments of the invention are made for
illustrative purposes only because the invention can be modified
and can be practically used in a variety of similar ways which are
obvious to persons who are skilled in this art and who can make use
of the advantages offered by the concepts described in this
application. Moreover, the applicant had no intention to impose any
limitations on the details of the designs or developments shown
herein, except for those described in the Claims below. It is
therefore obvious that the specific embodiments of the invention,
disclosed above, can be changed or modified, and all such
modifications shall be considered to be protected in accordance
with the scope and the nature of the invention.
* * * * *