Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIEL~ OF THE INyENTION
This invention relates to a method for increasing
the productivity or injectivity from hydrocarbon-bearing
formations, employing a deviated well-drilling scheme and a
fracture technique.
DESCRIPTION OF THE PRIOR ART
Production of hydrocarbons from a hydrocarbon-
bearing formation is usually effected by drilling through
the hydrocarbon-bearing formation or stratum and opening up
the formation around the well bore so as to cause the
hydrocarbons therein to flow into the well bore from which
they are recovered by conventional methods. The particular
method employed to cause the hydrocarbons to be displaced
in the formation depends among other things upon the
permeability of the hydrocarbon-bearing formation. In
formations having a matrix with high permeability of the
order of about 100 md. to above 200 md., displacement may
be easily obtained with minimum resistance to passage through
the matrix. However, many hydrocarbon-bearing formations
exist that have low permeability and thus are not amenable
to practical commercial production or recovery by conventional
methods. These formations may be limestones or tight sand
~ormations in which the permeability may be of the order
of 1-2 md.
Various methods have been proposed for increasing
the productivity and increasing the drainage area within
a desired producing zone or interval. Among these methods
for stimulating production, the use of fracturing involving
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hydraulic fracturing techniques, has generally been employed.
Fracturing normally requires the in~ection into a well bore
of a fracturing fluid that may contain a suspended propping
agent under sufficient pressure to open a fracture in the
exposed formation. Continued pumping of fluid into the
well at a high rate extends the fracture and leads to the
buildup of a bed of propping agent particles between the
fracture walls. These particles prevent complete closure
of the fracture as the fluid subsequently leaks off into
the ad~acent formation and results in permeable channels
extending from the well bore into the formation. The fluid
conductivities of these channels depend upon the fracture
dimensions, the size of the propping agent particles, the
particle spacing, and the confining pressures. Equations
that can be used to compute the fracture dimensions and
fluid conductivities that will be obtained under particular
operating conditions have been published in the technical
literature and will be familiar to those skilled in the art.
Hydraulic fracturing may be defined as the process
ln which fluid pressure is applied to the exposed formation
rock or matrix until failure or fracturing occur~. After
failure of the formation rock, a sustained application of
fluid pressure extends the crevice or fracture outward from
the polnt of failure. This fracture creates new and larger
flow channels. Generally, once the fracture has been created,
selected grades of propping agents are then added to the
fracturing fluid in various quantities and deposited in
the fractures to support and hold the fracture open. The
propping agent is usually placed in the fracture at a0 pressure equal to or greater than the pressure required to
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initially fracture the formation. Once the propping agent
has been placed and the pressure removed from the formation,
the fractures in the formation will tend to close due to
overburden pressures in the formation, but are held open
by the propping agent. However, application has been
limited by the inability to extend fracture channels
appreciable distances without the necessity of multiple
well drilling.
Accordingly, it is the object of the present
invention to provide a method for increasing the effective
size of the well bore or the drainage area without the
necessity of multiple well drilling by providing a
relatively high permeability for channels that interconnect
in the producing area thereby increasing the drainage area.
STATEMENT OF INVENTION
The present invention is a method to increase the
effective permeability of a suterranean hydrocarbon-bearing
formation having at least one productive interval comprising
the steps of:
a) drilling a first well bore traversing said
productive interval of said hydrocarbon-bearing formation,
b) fracturing said first well bore adjacent said
productive interval,
c) setting a bridge plug above said
productive interval in said first well bore and thereafter
undertaking a cementing operation in said first well bore
to a desired depth,
d) drilling a second well bore having the
upper portion thereof in common with said first well bore
and deviated from said first well bore from the top of said
cementing operation and thereafter fracturing said
productive interval adjacent said deviated second well bore,
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e) setting a bridge plug above the productive
interval in said second well bore and thereafter undertaking
a cementing operation in said second well bore to a desired
depth,
f) repeating steps td) and (e) to provide
additional similarly deviated well bores,
g) drilling a final similarly deviated
well bore and completing said final well bore by setting
tubing and packer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In accordance with the present invention the
method to improve the productivity or injectivity of a
hydrocarbon-bearing formation comprises drilling a well bore
traversing the hydrocarbon-bearing formation or the
production stratum and thereafter fracturing the production
stratum or productive interval adjacent the well bore.
After the fracturing has been accomplished and propped, if
necessary, the well bore is isolated by setting a bridge plug
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at the top of the formation and cementing to a desired
depth intermediate between the top of the formation and the
surface. A second well bore having its upper portion in
common with the first well bore but deviated or diverted
from the point of the cementing is then drilled. Thereafter,
the productive stratum adjacent the deviated or diverted well
bore is fractured through the productive interval so as to
~oin with the first fractures and provide communication between
the well bores. The second well bore is plugged back by a
cementing operation. Additional similarly directionally-
drilled holes are then drilled from the common portion
of the first well bore and similarly fracturing operations
are carried out. By the method of the invention, the
final directional well bore is completed by setting casing
and perforating it across the desired productive interval
so that the well bore becomes a producing well. The method
may also be employe~d wherein the final well bore is completed
as an in~ection well, thereby providing for improved
lnjectivity, as for example, for a steam flood operation.
Thus, by the method of the invention, the productivity
(or in~ectivity) of a large area of the formation is
effectively increased by a method utilizing a single surface
well bore.
In more detail, the practice of the invention
involves first drilling a well bore in conventional fashion
traversing the hydrocarbon-bearing or productive interval.
Thereafter a fracturing fluid is introduced via the drill
pipe and is placed in the well bore adjacent with and in
contact with the face of the formation to be fractured.
Retrievable packers and bridge plugs may be employed to
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isolate and con~ine the fracturing fluids to the portion
of the productive interval or stratum ad~acent the well
face desired to be fractured. After the packer is set in
the well on the tubing to isolate and confine the selected
portion of the formation which is to be fractured, the
fracturing operation is carried out utilizing a fracturing
fluid such as water or oil, and which may contain
a propping agent such as sand, glass beads, or the like.
In hydrostatic fracturing, a low-penetrating fluid is
pumped into the well. When it reaches the formation which
is to be fractured, it tends to stay in the well and build up
a high pressure due to its retarded tendency to penetrate
the interstices of the formation. Pressure is then applied
by the fracture fluid to cause the formation to be fractured
and form fissures therein. The pressure required to fracture
the formation will depend on the depth and/or the formation
being fractured. Suitable fracturing pressures may be in
the range of 1,000 to 15,000 psi.
In the situation where the formation thickness is
such that more than one fracturing operation is required,
or there are multiple hydrocarbon-bearing strata~ after
the desired fracturing has been accomplished in the selected
area, the retrievable packer and bridge plug may be
collapsed and relocated across the next selected interval.
Thereafter, the fracturing operation is repeated. By
continuing this procedure, the desired extent of the productive
interval is fractured and propped from the given well bore.
~ ollowing the fracture stimulation procedure for
each well bore the well bore is cleaned out, since it is
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desirable to insure that any residue resulting from the
stimulation procedure is removed so that the well will
flow properl~. Cleaning of fracture channels and
determination of the effectiveness of the fracture treatment
is especially important for the well bores that are to be
sealed thereafter and which, therefore, would be inaccessible
later. Along with the clean out procedure a production test
or testing may also be employed to determine the flow
characteristics of the well bore.
After testing the fracture treatment, an open
hole brldge plug, that forms the upper limit of the desired
producing interval, is set. The well bore or hole is then
cemented above the bridge plug up to a point where the well
can be side tracked and a second hole directionally is
drilled from the point of cementing, and using the same
surface well bore. At a level of the well bore, a second
well is directionally drilled by the aid of a whipstock
or a similar device at an angle from the surface well bore.
In locating and allowing for the directionally
drilled second hole, this second well bore should be
drilled such that the distance from the bottom of the
second hole is in the direction of the first hole so that
upon fracturing there will be provided communication
between this deviated well bore and the previously drilled
well bore.
Once the well bore has been directionally drilled
at the desired angle and to the desired depth and desired
bottom hole location, the well bore is fractured, cleaned
out and tested in the manner as described above. Thereafter,
the well bore is closed by means of a bridge plug and
cemented at this depth.
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After the completion of the second well bore, a
third hole is directionally drilled having the desired angle
of deviation, desired depth an~ desired bottom hole location.
The third deviated hole is then completed as a producing
well and thereafter communication with the other two holes
is established by induced fractures. Completion of the
third hole follows conventional techniques. The hole may
be open hole completed through the production interval or
it may be cased, depending upon the type of productive
formation. If a cased hole technique is employed, after
setting the casing through the producing interval the
well is cleaned and tested with the completion fluid and
then perforated over the desired producing interval, then
fractured employing a procedure similar to those used in the
previously drilled deviated holes. The well is then
completed as a producing well incorporating the conventional
setting of a packer and the necessary tubing means for
production.
Additional wells may then be drilled to provide
additional directional bore holes in accordance with
the procedures for drilling and completing as described
above. For purposes of illustration, the method is
described in which only three well bores are employed in
the producing formation. Nonetheless, the method may be
employed for two or more well bcres. In addition, although
the illustration describes completing the well as a
producing well, the well may be completed as an injection
well.
Thus by the invention, productivity and recovery
0 of reservoir fluids is enhanced by increasing the effective
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permeability or drainage area in the formation and increasing
flow into all three ~or more~ well bores and along the lines
of the induced fractures, to the completed well bore from
which the fluids are produced by conventional means.
Further, it is within the scope of the invention
to apply the method for improving the in;ectivity of
in~ection wells. The method may also be utilized in a
steam huff-puff operation whereby the completed well serves
not only as a steam in~ection well, but also as the producing
well during the production portlon of the operation.
