CA1161358A - Maximizing fracture extension in massive hydraulic fracturing - Google Patents
Maximizing fracture extension in massive hydraulic fracturingInfo
- Publication number
- CA1161358A CA1161358A CA000378568A CA378568A CA1161358A CA 1161358 A CA1161358 A CA 1161358A CA 000378568 A CA000378568 A CA 000378568A CA 378568 A CA378568 A CA 378568A CA 1161358 A CA1161358 A CA 1161358A
- Authority
- CA
- Canada
- Prior art keywords
- treating pressure
- fracture
- formation
- bottomhole
- pressure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
During fracture treatment of a subterranean for-mation, multiple hydraulic fracturing cycles are performed wherein the bottomhole treating pressure of a wellbore is controlled to not exceed a maximum bottomhole treating pressure for the formation, thereby attaining maximum principle fracture extension and limiting initiation of secondary fractures transverse to the principle fracture extension.
During fracture treatment of a subterranean for-mation, multiple hydraulic fracturing cycles are performed wherein the bottomhole treating pressure of a wellbore is controlled to not exceed a maximum bottomhole treating pressure for the formation, thereby attaining maximum principle fracture extension and limiting initiation of secondary fractures transverse to the principle fracture extension.
Description
11~i13S8 1~ MAXIMIZlNG FRACTURE EXTENSION IN MASSIVE HYDRAULIC
FRACTURING
BACKGROUND OF THE INVENTION
1. Field of the Invention The method of this invention relates to lS hydraulic fracturing of subterranean formations by a frac-turing fluid. Particularly, this invention relates to control of hydraulic fracturing treatments of tight gas sands,
FRACTURING
BACKGROUND OF THE INVENTION
1. Field of the Invention The method of this invention relates to lS hydraulic fracturing of subterranean formations by a frac-turing fluid. Particularly, this invention relates to control of hydraulic fracturing treatments of tight gas sands,
2, Setting of the Invention 2~ Oil and gas accumulation~ usually occur in porous and permeable underground rock formations. In order to produce the oil and gas contained in a formation, a well is drilled into the formation. The oil and gas may be contained in the porosity or pore spaces of the forma-25 tion, hydraulically connected by means of permeability or interconnecting channels between the pore spaces. After the well is drilled into the formation, oil and gas are displaced to the wellbore by means of fluid expansion, natural or artificial fluid displacement, gravity 30 drainage, capillary expulsion, etc. These various pro-cesses may work together or independently to remove the hydrocarbons in the wellbore to existing flow channels.
In many instances, however, production of the well may be impaired by drilling fluids that enter into and plug the 35 flow channels, by insufficient natural channels leading to the particular borehole, of by insufficient permeability surrounding the borehole which may result in a noncommer-cial well. The problem then becomes one of treating the ,, formation in a manner which will increase the ability of the formation rock to conduct fluid to the wellbore.
Various methods of hydraulically fracturing a formation to increase the conductivity of the formation 5 have been developed. Hydraulic fracturing may be defined as the process in which fluid pressure is applied to exposed formation rock until total failure or fracturing occurs. After failure of the formation rock, a sustained application of fluid pressure extends the crevice or frac-10 ture outward from the point of failure. The fracture,propped by a proppant, creates high capacity flow channel and exposes new surface area along the fracture. However, the height of such a fracture should be confined to the zone of interest. No methods are presently available to 15 limit this height.
In many instances, however, production of the well may be impaired by drilling fluids that enter into and plug the 35 flow channels, by insufficient natural channels leading to the particular borehole, of by insufficient permeability surrounding the borehole which may result in a noncommer-cial well. The problem then becomes one of treating the ,, formation in a manner which will increase the ability of the formation rock to conduct fluid to the wellbore.
Various methods of hydraulically fracturing a formation to increase the conductivity of the formation 5 have been developed. Hydraulic fracturing may be defined as the process in which fluid pressure is applied to exposed formation rock until total failure or fracturing occurs. After failure of the formation rock, a sustained application of fluid pressure extends the crevice or frac-10 ture outward from the point of failure. The fracture,propped by a proppant, creates high capacity flow channel and exposes new surface area along the fracture. However, the height of such a fracture should be confined to the zone of interest. No methods are presently available to 15 limit this height.
3 Relevant Publications A ~.S. Patent 3,933,205, Othar Meade Kiel, i~sued January 20, 1976 and entitled "Hydraulic Fracturing Pr~c~s~ Using R~verse Flow" di~closes a method of mul-20 tiple h~draulic fracturing c~cles. The disadvantage tothe method of Kiel is that a predetermined amount of the fracture fluid is bro~en up into multiple treatments to obtain and initiate secondary fractures transverse to the principle fracture. In the method of this invention, it 25 is desirable to create deeply penetrating fractures which are confined to the producing horizon. In order that this may be accomplished, the initiation of secondary fractures or fractures extending into horizons above or below the producing horizon must be minimized.
SUMMARY OF THE INVENTION
By this invention, a method is described for hydraulic fracturing a formation 5 the fracturing treatment including (a~ injecting a fluid into the formation until the bottomhole treating pressure equals maximum bottomhole 35 treating pressure, (b) discontinuing the injection for a predetermined period of time, (c) measuring the bottomhole treating pressure, repeating steps (a), ~b), and (c) sequentially until the measured bottomhole treating ~1~13~8 pressure amount to at least 90% of the maximum bottomhole treating pressure.
Additionally, a method is described for hydraulic fracturing a formation, the fracturing treatment 5 including (a) alternately injecting a fluid into the for-mation until the bottomhole treating pressure equals the ma~imum bottomhole treating pressure, (b) followed by dis-continuing the injection until the bottomhole pressure is reduced to a level below the maximum bottomhole treating 10 pressure until bottomhole treating pressure at the end of the period of time when the pumping is discontinued amounts to at least 90% of the maximum bottomhole treating pressure. By this method a fracture can be extended to greater lengths into a producing horizon without initi-15 ating secondary fractures or extending the fracture into horizons a~ove or below the producing horizons.
BRIEF DESCRIPTION OF THE ~RAWINGS
Figure 1 is a graph showing bottomhole treating pressure versus distance from the wellbore.
Figure 2 is a graph showing bottomhole treating pres~ure versws time, DETAILED DESCRlPTION OF THE INVENTION
In fracturing stimulation of tight gas sands, the primary goal is to create deep penetrating fractures 25 which are confined to the producing horizon, The successof a stimulation will depend upon how well the adjacent zones confine a fracture, This in turn will depend upon the mechanical proper~ies and the thickness of the adja-cent zones relative to the zone of interest being frac-30 tured. However, if the injection pressure of the frac-turing fluid becomes toG high, the fracture may cross the boundaries out of the zone of interest and begin to extend vertically into the adjacent zones. In othèr formations high fracturing pressure can open fractures perpendicular 35 to the primary fracture, thereby terminating the e~tension of the primary fracture into the production horizon.
In accordance with this invention, it has been found that multiple fracturing cycles where the fracturing ~161358 pressure is controlled to not exceed a pressure at which undesirable fracturing occurs will bring about maximum primary fracture growth to the exclusion of secondary fractures or the extension of fractures into undesirable 5 horizons either above or below the formation of interest.
In operation of the present invention, the bottomhole pressure is maintained at a level below the maximum bottomhole treating pressure and the treatment is conducted by alternately injecting fluid into the fracture 10 followed by shutting the well in.
In preparation for the present invention, a for-mation is initiallg fractured by applying pressure via a wellbore on its exposed surfaces with a fracturing fluid until fracture results. Any fracturing fluid may be used 15 for accomplishing initial fracturing of the formation.
After the fracture is formed in the formation, a quantity of fluid is pumped into the fracture at a pres-sure equal to or greater than the pressure required to extend a fracture through the formation.
The pumping pressure is increased to a bottom-hole pressure Pl at tl, Pl being not greater than the max-imum bottomhole treating pressure, at which reduced frac-ture extension rate occurs.
Various methodsiof determining the maximum bottom-25 hole treating pressure include mechanical tests on core samples or field experience in the area.
As shown in Figure 1, the fracture has extended dl feet into the formation from the wellbore. Pumping is then discontinued and the bottomhole pressure decreases 30 with time. It is thought that this is due to the increased fluid density in the fracture which is due to fluid leakoff and additional fracture volume created ~y f~35B
fracture extension due to pressure equalization at the fracture tip.
At the time the pumping is discontinued, the pressure at the tip is greater than that needed to 5 propagate the fracture while the pressure at the bottom of the wellbore remains at or below the maximum bottomhole treating pressure.
The pumping is discontinued for a predetermined period of time which allows the bottomhole pressure and 10 the pressure along the fracture to equalize to P2 and the fracture to extend to d2 feet from the wellbore at ti.
An additional quantity of fracturing fluid is then pumped into the fracture. The pumping pressure increases with time to bottomhole pressure, P3 at t2 when 15 the pumping is discontinued. Pressure P3 does not exceed the maximum bottomhole treating pressure. The fracture extends to d3 feet from the wellbore into the formation.
The pumping is again discontinued for a predet-ermined period o~ time which allows the bottomhole and 20 racture pressures to equali~e to P4 and the fracture to extend to d4 feet from the borehole at t2.
Additional quantities of fracturing fluid are then pumped into the fracture. The pumping pressures increase with time to bottomhole pressures P5, at P7 at t3 25 and t4 respectively when the pumping is discontinued. The pumping is discontinued for a predetermined period of time which allows the pressure to equalize to P6 and P8 and the fracture to extend to d6 and d8 feet from the wellbore, at times t3 and t4 respectively.
The cycles of injection and discontinued pumping continues until the bottomhole treating pressure at the end of the period of discontinued pumping, P2, very nearly equals the maximum bottomhole treating pressure. Theoret-ically, the cycles could be repeated an infinite number of 35 times until the equilibrium fracture pressure equals the reduced fracture extension rate pressure. Preferably, however, the cycles are discontinued when the bottomhole pressure at the end of period during which pumping is dis-continued 90% of the maximum bottomhole treating pressure.
... ....
~13S8 The last cycle should be followed by an injection of a displacing fluid without proppant in order to extend the proppant into the newly created fracture volume. This final injection should serve also to flush 5 the casing.
Preferably, the fracturing fluid is designed so that the proppant is not allowed to settle during the periods when pumping is discontinued. A fracturing fluid having a viscosity in excess of 10 centipoise is pre-10 ferred.
More preferably, the fluid has a viscosity inexcess of 10 centipoise but still in the pumpable range.
Preferably the fluid is not thioxtropic. Also, prefer-ably, a propping agent is included in the fluid. Suitable 15 propping agents include sand, walnut hulls, glass beads, etc.
The shut-in periods, that is, the periods in which equilibrium pressure is allowed to be attained ~hould be between half a minute and half an hour, Prefer-20 ab~y, however, the shwt-in periods should be be~ween one and five minutes.
The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as those inherent therein.
25 While presently preferred embodiments of the invention are given for the purpose of disclosure, numerous changes can be made which will readily suggest themselves to those skilled in the art, and which are encompassed within the spirit of the invention disclosed herein.
SUMMARY OF THE INVENTION
By this invention, a method is described for hydraulic fracturing a formation 5 the fracturing treatment including (a~ injecting a fluid into the formation until the bottomhole treating pressure equals maximum bottomhole 35 treating pressure, (b) discontinuing the injection for a predetermined period of time, (c) measuring the bottomhole treating pressure, repeating steps (a), ~b), and (c) sequentially until the measured bottomhole treating ~1~13~8 pressure amount to at least 90% of the maximum bottomhole treating pressure.
Additionally, a method is described for hydraulic fracturing a formation, the fracturing treatment 5 including (a) alternately injecting a fluid into the for-mation until the bottomhole treating pressure equals the ma~imum bottomhole treating pressure, (b) followed by dis-continuing the injection until the bottomhole pressure is reduced to a level below the maximum bottomhole treating 10 pressure until bottomhole treating pressure at the end of the period of time when the pumping is discontinued amounts to at least 90% of the maximum bottomhole treating pressure. By this method a fracture can be extended to greater lengths into a producing horizon without initi-15 ating secondary fractures or extending the fracture into horizons a~ove or below the producing horizons.
BRIEF DESCRIPTION OF THE ~RAWINGS
Figure 1 is a graph showing bottomhole treating pressure versus distance from the wellbore.
Figure 2 is a graph showing bottomhole treating pres~ure versws time, DETAILED DESCRlPTION OF THE INVENTION
In fracturing stimulation of tight gas sands, the primary goal is to create deep penetrating fractures 25 which are confined to the producing horizon, The successof a stimulation will depend upon how well the adjacent zones confine a fracture, This in turn will depend upon the mechanical proper~ies and the thickness of the adja-cent zones relative to the zone of interest being frac-30 tured. However, if the injection pressure of the frac-turing fluid becomes toG high, the fracture may cross the boundaries out of the zone of interest and begin to extend vertically into the adjacent zones. In othèr formations high fracturing pressure can open fractures perpendicular 35 to the primary fracture, thereby terminating the e~tension of the primary fracture into the production horizon.
In accordance with this invention, it has been found that multiple fracturing cycles where the fracturing ~161358 pressure is controlled to not exceed a pressure at which undesirable fracturing occurs will bring about maximum primary fracture growth to the exclusion of secondary fractures or the extension of fractures into undesirable 5 horizons either above or below the formation of interest.
In operation of the present invention, the bottomhole pressure is maintained at a level below the maximum bottomhole treating pressure and the treatment is conducted by alternately injecting fluid into the fracture 10 followed by shutting the well in.
In preparation for the present invention, a for-mation is initiallg fractured by applying pressure via a wellbore on its exposed surfaces with a fracturing fluid until fracture results. Any fracturing fluid may be used 15 for accomplishing initial fracturing of the formation.
After the fracture is formed in the formation, a quantity of fluid is pumped into the fracture at a pres-sure equal to or greater than the pressure required to extend a fracture through the formation.
The pumping pressure is increased to a bottom-hole pressure Pl at tl, Pl being not greater than the max-imum bottomhole treating pressure, at which reduced frac-ture extension rate occurs.
Various methodsiof determining the maximum bottom-25 hole treating pressure include mechanical tests on core samples or field experience in the area.
As shown in Figure 1, the fracture has extended dl feet into the formation from the wellbore. Pumping is then discontinued and the bottomhole pressure decreases 30 with time. It is thought that this is due to the increased fluid density in the fracture which is due to fluid leakoff and additional fracture volume created ~y f~35B
fracture extension due to pressure equalization at the fracture tip.
At the time the pumping is discontinued, the pressure at the tip is greater than that needed to 5 propagate the fracture while the pressure at the bottom of the wellbore remains at or below the maximum bottomhole treating pressure.
The pumping is discontinued for a predetermined period of time which allows the bottomhole pressure and 10 the pressure along the fracture to equalize to P2 and the fracture to extend to d2 feet from the wellbore at ti.
An additional quantity of fracturing fluid is then pumped into the fracture. The pumping pressure increases with time to bottomhole pressure, P3 at t2 when 15 the pumping is discontinued. Pressure P3 does not exceed the maximum bottomhole treating pressure. The fracture extends to d3 feet from the wellbore into the formation.
The pumping is again discontinued for a predet-ermined period o~ time which allows the bottomhole and 20 racture pressures to equali~e to P4 and the fracture to extend to d4 feet from the borehole at t2.
Additional quantities of fracturing fluid are then pumped into the fracture. The pumping pressures increase with time to bottomhole pressures P5, at P7 at t3 25 and t4 respectively when the pumping is discontinued. The pumping is discontinued for a predetermined period of time which allows the pressure to equalize to P6 and P8 and the fracture to extend to d6 and d8 feet from the wellbore, at times t3 and t4 respectively.
The cycles of injection and discontinued pumping continues until the bottomhole treating pressure at the end of the period of discontinued pumping, P2, very nearly equals the maximum bottomhole treating pressure. Theoret-ically, the cycles could be repeated an infinite number of 35 times until the equilibrium fracture pressure equals the reduced fracture extension rate pressure. Preferably, however, the cycles are discontinued when the bottomhole pressure at the end of period during which pumping is dis-continued 90% of the maximum bottomhole treating pressure.
... ....
~13S8 The last cycle should be followed by an injection of a displacing fluid without proppant in order to extend the proppant into the newly created fracture volume. This final injection should serve also to flush 5 the casing.
Preferably, the fracturing fluid is designed so that the proppant is not allowed to settle during the periods when pumping is discontinued. A fracturing fluid having a viscosity in excess of 10 centipoise is pre-10 ferred.
More preferably, the fluid has a viscosity inexcess of 10 centipoise but still in the pumpable range.
Preferably the fluid is not thioxtropic. Also, prefer-ably, a propping agent is included in the fluid. Suitable 15 propping agents include sand, walnut hulls, glass beads, etc.
The shut-in periods, that is, the periods in which equilibrium pressure is allowed to be attained ~hould be between half a minute and half an hour, Prefer-20 ab~y, however, the shwt-in periods should be be~ween one and five minutes.
The present invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as those inherent therein.
25 While presently preferred embodiments of the invention are given for the purpose of disclosure, numerous changes can be made which will readily suggest themselves to those skilled in the art, and which are encompassed within the spirit of the invention disclosed herein.
Claims (4)
1. A method for hydraulic fracturing a subter-ranean formation, comprising:
(a) injecting a fracturing fluid into said formation under fracture extending conditions until maximum bottomhole treating pressure approaches a maximum bottomhole treating pressure for said forma-tion, and (b) discontinuing said injection of the fracturing fluid, and (c) measuring bottomhole treating pressure, and sequentially repeating Steps (a), (b), and (c) until said measured bottomhole treating pressure amounts to at least 90% of said maximum bottomhole treating pressure.
(a) injecting a fracturing fluid into said formation under fracture extending conditions until maximum bottomhole treating pressure approaches a maximum bottomhole treating pressure for said forma-tion, and (b) discontinuing said injection of the fracturing fluid, and (c) measuring bottomhole treating pressure, and sequentially repeating Steps (a), (b), and (c) until said measured bottomhole treating pressure amounts to at least 90% of said maximum bottomhole treating pressure.
2. A method of fracturing a formation sur-rounding a wellbore, said formation having a maximum bot-tomhole treating pressure, comprising:
(a) injecting a fracture fluid into said wellbore under fracture extending conditions until the bottomhole treating pressure of said fracture fluid equals said maximum bottomhole treating pres-sure, and (b) discontinuing injection of said frac-turing fluid, and (c) measuring said treating pressure, and (d) repeating in sequence Steps (a), (b), and (c) until said measured treating pressure amounts to at least 90% of said maximum bottomhole treating pressure.
(a) injecting a fracture fluid into said wellbore under fracture extending conditions until the bottomhole treating pressure of said fracture fluid equals said maximum bottomhole treating pres-sure, and (b) discontinuing injection of said frac-turing fluid, and (c) measuring said treating pressure, and (d) repeating in sequence Steps (a), (b), and (c) until said measured treating pressure amounts to at least 90% of said maximum bottomhole treating pressure.
3. The method of Claim 2 wherein the wellbore is shut in after the injection of said fracturing fluid is discontinued.
4. A method of hydraulically fracturing a sub-terranean formation from a wellbore extending into the formation, which comprises alternately injecting during a first period a fracturing fluid into a fracture extending into the subterranean formation under fracture extending conditions until the bottomhole treating pressure approaches a maximum bottomhole treating pressure of said formation followed by discontinuing said injection of fracturing fluid during a second period such that no sub-stantial volumes of fracturing fluid are injected into the fracture or permitted to flow from said fracture into the wellbore, continuing said alternating steps until the bot-tomhole treating pressure of said formation measured after said second period amounts to at least 90% of said maximum bottomhole treating pressure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16882980A | 1980-07-10 | 1980-07-10 | |
| US168,829 | 1980-07-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1161358A true CA1161358A (en) | 1984-01-31 |
Family
ID=22613106
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378568A Expired CA1161358A (en) | 1980-07-10 | 1981-05-28 | Maximizing fracture extension in massive hydraulic fracturing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1161358A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4665982A (en) * | 1986-06-26 | 1987-05-19 | Brown Billy R | Formation fracturing technique using liquid proppant carrier followed by foam |
-
1981
- 1981-05-28 CA CA000378568A patent/CA1161358A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4665982A (en) * | 1986-06-26 | 1987-05-19 | Brown Billy R | Formation fracturing technique using liquid proppant carrier followed by foam |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |