U.S. patent application number 15/634061 was filed with the patent office on 2017-12-28 for method for predicting post-fracking pressure build-up in shale.
The applicant listed for this patent is University of Louisiana at Lafayette. Invention is credited to ASADOLLAH HAYATDAVOUDI, KAUSTUBH SAWANT.
Application Number | 20170370209 15/634061 |
Document ID | / |
Family ID | 60675327 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170370209 |
Kind Code |
A1 |
HAYATDAVOUDI; ASADOLLAH ; et
al. |
December 28, 2017 |
METHOD FOR PREDICTING POST-FRACKING PRESSURE BUILD-UP IN SHALE
Abstract
During fracking processes, fluid is injected into the injection
wells to cause micro-fractures in the shale. Contact between shale
and water causes the development of micro-fractures. Given the deep
location of the injection wells, the water is under high pressure
that can build up over time and could potentially cause tremors.
Based upon experiments on Pierre shale, it has been determined that
the appearance of micro-fractures in shale begin with the
saturation of capillaries, followed by ionic and diffusive
transport of water into the shale clays. Using this discovery, a
method for predicting the post-fracking pressure build-up in shale
is disclosed.
Inventors: |
HAYATDAVOUDI; ASADOLLAH;
(Lafayette, LA) ; SAWANT; KAUSTUBH; (Lafayette,
LA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Louisiana at Lafayette |
Lafayette |
LA |
US |
|
|
Family ID: |
60675327 |
Appl. No.: |
15/634061 |
Filed: |
June 27, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62355363 |
Jun 28, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/58 20130101; E21B
49/00 20130101; E21B 43/24 20130101; E21B 47/06 20130101; E21B
43/26 20130101; C09K 8/592 20130101; C09K 8/84 20130101; E21B
43/267 20130101; E21B 43/20 20130101 |
International
Class: |
E21B 47/06 20120101
E21B047/06; E21B 43/24 20060101 E21B043/24; E21B 43/267 20060101
E21B043/267; E21B 43/20 20060101 E21B043/20 |
Claims
1. A method for increasing gas and liquid production in
post-fractured shale, comprising: (a) saturating the capillaries in
the post-fractured shale with fluid; (b) determining the hydraulic
potential of the fluid; (c) determining the chemical potential of
the fluid; (d) determining the bond dissociation energy of the
post-fractured shale; (e) using the bond dissociation energy to
determine the Gibbs free energy; (f) monitoring the initiation of
additional pore pressure in the post-fractured shale capillaries;
(g) monitoring the initiation of random micro-fractures in the
post-fractured shale; and (h) collecting increased gas or liquid
production.
2. The method of claim 1, wherein the fluid applied is freshwater
or low quality steam.
3. The method of claim 1, wherein the fluid applied is water with
included additives.
4. The method of claim 3, wherein the additives added to the fluid
comprises sand particles.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Patent Application Ser. No. 62/355,363, filed Jun. 28,
2016, titled the "Method of Predicting Post-Fracking Pressure
Build-UP in Shale Using Chemo-Physical Modeling."
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A "SEQUENCE LISTING", A TABLE, OR COMPUTER PROGRAM
[0003] Not applicable.
DESCRIPTION OF THE DRAWINGS
[0004] The drawings constitute a part of the specification and
include exemplary examples of the METHOD FOR PREDICTING
POST-FRACKING PRESSURE BUILD-UP IN SHALE, which may take the form
of multiple embodiments. It is to be understood that in some
instances, various aspects of the invention may be shown
exaggerated or enlarged to facilitate an understanding of the
invention. Therefore, the drawings may not be to scale.
[0005] FIG. 1 depicts the first and second hydration shells for a
sodium ion. The image demonstrates that there is an existence of an
ionic bond (shown by the dashed lines in FIG. 1) between the sodium
and oxygen due to the presence of hydration shells.
[0006] FIG. 2 is a plot of the change in Gibbs free energy versus
the Hayatdavoudi Hydration Index ("HHI") for different clay
families. The Y-axis (which represents the estimated change in
Gibbs free energy in Kcal/mole) has been increased by a scale of
1000.
[0007] FIG. 3 is the plot f the Gibbs free energy versus the HHI,
plotted as a function of new HHI values.
[0008] FIG. 4(a) is a plot of bottomhole pressure versus time for a
standard hydraulic fracture.
[0009] FIG. 4(b) is a plot of bottomhole pressure versus time that
demonstrates the post-fracture pressure build-up in Pierre Shale as
an effect of Gibbs free energy due to the ionic action indicated on
the dotted line. This figure shows the effect of Gibbs free energy
as a source of pressure built up in the shale mass that could only
come about with the excess oxygen in the clay monolayer. This
figure is not to scale.
[0010] FIG. 5 is a diagram depicting the post-fracking build-up of
pressure process within the shale.
[0011] FIG. 6 is an example Montmorillonite cell structure.
[0012] FIG. 7 provides a table that shows the excess oxygen, new
HHI, and Gibbs free energy for each increasing number of water
molecules.
[0013] FIG. 8 provides a chart of the post-fracturing process
diagram with additional methods of shale characterization.
FIELD OF THE INVENTION
[0014] The subject matter of the present invention generally
relates to the field of hydraulic fracturing. More specifically,
this invention is related to the determination of internal forces
and pressures within the bottomhole of a well after fracking, which
can assist fracking professionals in maximizing production.
BACKGROUND OF THE INVENTION
[0015] Novel oilfield technologies such as horizontal drilling and
hydraulic fracturing have allowed producers to generate a
tremendous amount of hydrocarbon from tight, ultra-low permeability
source rock such as shale and similar formations. The process of
fracking involves the high-pressure injection of fracking
fluid--which is typically a mixture of water, sand, and other
additives--into a wellbore to create cracks in the deep rock
formations. The grains of sand or other hydraulic fracturing
proppants hold these micro-fractures open, allowing natural gas,
petroleum, and brine to flow more freely. More often than not, the
wells begin producing immediately after fracking.
[0016] At the beginning of the well's production, there is a period
of high production rate, also known as "flash production." After
that time, oil and gas production levels rapidly decline.
Consequently, tracking the process of the formation of
micro-fractures in the shale is important to maximize
production.
SUMMARY OF THE INVENTION
[0017] Based upon experiments performed on Pierre shale, it has
been determined that the appearance of micro-fractures in shale
begin with the saturation of the capillaries, followed by ionic and
diffusive transport of water into the shale clays. Based on this
discovery, a method for predicting the post-fracking pressure
build-up in shale, which consequently increases gas and liquid
production in post-fractured shale, is disclosed. In this method,
the post-fractured shale is saturated with fluid, and then the
hydraulic and chemical potential of the fluid and bond dissociation
energy of the shale is determined. The bond dissociation energy is
then used to find the Gibbs free energy. By then monitoring the
additional pore pressure and increase in micro-fractures, and
increase in gas or liquid production is obtained from the
fracking.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The subject matter of the present invention is described
with specificity herein to meet statutory requirements. However,
the description itself is not intended to necessarily limit the
scope of the claims. Rather, the claimed subject matter might be
embodied in other ways to include different steps or combinations
of steps similar to the ones described in this document, in
conjunction with other present or future technologies.
[0019] Furthermore, the described features, structures, or
characteristics may be combined in any suitable manner into one or
more embodiments.
[0020] When performing fracking, contact between a fluid, such as
water, and the shale causes fractures in the shale, often because
the shale is hit with fluid at a high pressure. Contact between the
shale and fluid results in the development of micro-fractures of a
size that is typically possible using standard hydraulic
fracturing. Based upon experiments performed on Pierre shale, it
has been determined that the appearance of micro-fractures begin in
two stages. The first stage is the saturation of capillaries under
hydraulic potential. The second stage is by ionic and diffusive
transport of fluid into the shale clays.
[0021] During these two stages, the fluid's properties (pH, Eh, and
temperature) are monitored using a pH/ATC (Automatic Temperature
Compensation) meter. The activity coefficients of the ions and the
saturation indices of various potential minerals in the shale are
also calculated using a software package that is known to those
having ordinary skill in the art. An X-ray diffraction, SEM/EDS
(EDAX), was carried out for the examination of minerals in shale.
Methods of performing this X-ray diffraction are also known to
those having ordinary skill in the art. Additionally, using an
Inductively Coupled Plasma-Mass Spectroscopy ("ICP-MS"), the
concentration of ions present in the fracking fluid, the fluid's
conductivity, and the fluid's resistivity are recorded.
[0022] Once the capillaries in the shale are saturated,
micro-fractures are made in the shale as a result of the conversion
of ionic activity or exchange to excess pore pressure that did not
exist prior to fracking. Contrary to standard fracking mechanisms,
the micro-fractures initiated in this manner are not induced
through hydraulically induced fracturing. This results in lowering
the effective stress in the capillaries of shale mass, thus
initiating the onset of micro-fractures at saturated sites. This
indicates that the propagation and areal extent of micro-fractures
may be influenced by time, which has not previously been considered
in existing macro/micro-fracture models.
[0023] Fluid adsorption/absorption in the shale capillaries can now
be explained as hydration energy of the clays that are part of
shale. This hydration energy can be defined as Gibbs free energy,
which is directly proportional to the Hayatdavoudi Hydration Index
("HHI"). Additionally, it has been determined during this testing
that the number of oxygen molecules inside of the cell structures
of clays as well as those contained in the clay monolayer which
contributed to the Gibbs free energy and creation of
micro-fractures. The creation of the micro-fractures results in
sustained gas and liquid production.
[0024] The water to be used to create the micro-fractures in shale
is dependent upon the type of clay distribution, the clay cell
structure, the type of ions inside the cells, their concentration,
activity coefficients of those ions and saturation indices of their
potential minerals. FIG. 2 provides a plot representation of the
change in Gibbs free energy versus the HHI for different clay
families where fracking is often applied. These values are also
plotted in FIG. 3, which shows the plots of Gibbs free energy
versus the HHI instead plotted as a function of the new HHI
values.
[0025] FIGS. 4(a) and 4(b) shows the effect of Gibbs free energy as
the source of pressure build up in the shale mass which could only
have come about with the excess oxygen in the clay monolayer. FIG.
4(a) provides the plot of the bottomhole pressure in the shale mass
for a standard hydraulic fracture. FIG. 4(b) provides the plot of
the bottomhole pressure versus time that demonstrates the
post-fracture pressure build-up in Pierre Shale as an effect of
Gibbs free energy due to the ionic action indicated on the dotted
line. This figure shows the effect of Gibbs free energy as a source
of pressure built up in the shale mass that could only come about
with the excess oxygen in the clay monolayer.
[0026] Energy is the most fundamental characteristic of any system.
In order to account for the excess oxygen in the clay monolayer, it
is important to consider the bond dissociation energies ("BDE") of
the clay structure. An example cell structure of montmorillonite is
shown in FIG. 6, which is known in the art. The C-axis spacing is
defined as the distance between the Aluminum atoms of two unit
cells. To estimate the excess oxygen contributed to the monolayer
by water contained in the clays, it is important to consider both
cell units:
Excess O=((BDE).sub.Na--O)cell structure/BDE).sub.Si--O
[0027] As shown in FIG. 1, the number of water molecules in the
first and second hydration shells for a sodium ion range from 4 to
8. Due to the hydration shells for both unit cells, sodium forms an
ionic bond with the oxygen from the water, thus giving rise to
excess oxygen into the main cell structure. Consequently, as
represented in the below equation, the previous formula for excess
oxygen can be rewritten in the following new form:
Excess O=2(BDE.sub.Na--O).sub.cell
structure)+(BDE.sub.Na--O).sub.monolayer
water))/(BDE.sub.Si--O)
Accordingly, for one molecule of water in the monolayer:
Excess O=2(64.5+64.5)/191.1
Excess O=1.351
In the above calculation, 64.5 kcal/mol is the bond dissociation
energy of Na--O bond and 191.1 kcal/mol is the bond dissociation
energy of the Si--O bond.
[0028] For Smectite--the original HHI was O/OH=20/4=5. However, the
new HHI is equal to (original oxygen+excess
oxygen)/OH=(20+1.351)/4=5.337. The Gibbs free energy with the new
formula, considering excess oxygen:
.DELTA.G=R Tln(HHI)=R Tln(O/OH)
.DELTA.G=[1.987.times.10.sup.-3(kcal/mol.K)].times.[298.13
K].times.ln(5.337)
.DELTA.G=0.992 kcal/mol
[0029] FIG. 7 provides a table that shows the excess oxygen, new
HHI, and Gibbs free energy for each increasing number of water
molecules in Smectite. The Gibbs free energy can be adjusted using
pure freshwater without additives all the way to adjusted
formulation of additives, given that there must always be a
differential ionic distribution, no matter how small, between the
fracturing water and shale water to induce ion exchange and the
propagation of micro fractures.
[0030] The post-fracturing process then leads to the pressure build
up due to chemical potential according to the process chart seen in
FIG. 5.
[0031] Consequently, a method for increasing the gas or liquid
production is disclosed. The user would first saturate the
capillaries in the post-fractured shale with fluid. In the
preferred embodiment, that fluid is water. In additional
embodiments, that fluid comprises water and additional additives,
such as sand. After determining the hydraulic and chemical
potentials of the fluid and the bond dissociation energy of the
post-fractured shale to determine the Gibbs free energy, the
initiation of additional pore pressure in the saturated
post-fractured shale capillaries can be monitored.
[0032] As pore pressure increases in the capillaries, additional
micro-fractures are created in the post-fractured shale, which
allows increased gas or liquid to escape the shale and be collected
by the user.
* * * * *