U.S. patent application number 12/145803 was filed with the patent office on 2009-12-31 for well drilling method for prevention of lost circulation of drilling muds.
Invention is credited to Brian Dempsey, Wade Duty.
Application Number | 20090321142 12/145803 |
Document ID | / |
Family ID | 41445261 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090321142 |
Kind Code |
A1 |
Dempsey; Brian ; et
al. |
December 31, 2009 |
Well Drilling Method for Prevention of Lost Circulation of Drilling
Muds
Abstract
An improved well drilling method for directional drilling in
subterranean formations which comprises incorporating into the
drilling fluid an effective amount of fibrillated hydrophobic
polypropylene fibers to form a suspension and injecting the
suspension into the drill string whereby debris is swept from the
borehole and seepage of drilling fluid into the subterranean
formation is reduced.
Inventors: |
Dempsey; Brian; (Orlando,
FL) ; Duty; Wade; (Ada, OK) |
Correspondence
Address: |
DUNLAP CODDING, P.C.
PO BOX 16370
OKLAHOMA CITY
OK
73113
US
|
Family ID: |
41445261 |
Appl. No.: |
12/145803 |
Filed: |
June 25, 2008 |
Current U.S.
Class: |
175/72 |
Current CPC
Class: |
C09K 8/035 20130101;
C09K 8/5083 20130101; E21B 21/003 20130101; C09K 8/516 20130101;
C09K 2208/08 20130101 |
Class at
Publication: |
175/72 |
International
Class: |
E21B 7/00 20060101
E21B007/00 |
Claims
1. An improved well drilling method for drilling in subterranean
formations wherein a drilling fluid is injected into a drill string
having a bottom hole assembly inserted into a borehole and the
borehole can deviate from a vertical orientation by as much as 90
degrees, the improvement which comprises incorporating into the
drilling fluid an effective amount of fibrillated hydrophobic
polypropylene fibers to form a suspension and circulating the
suspension through the drill string whereby debris is swept from
the borehole and loss of drilling fluid into the subterranean
formation is reduced.
2. The improvement of claim 1 wherein an effective amount of
fibrillated hydrophobic polypropylene fibers is from 1.5 lbs up to
50 lbs of fibrillated hydrophobic polypropylene fibers per joint of
pipe in the drill string.
3. The improvement of claim 2 wherein the circulating suspension of
fibrillated hydrophobic polypropylene fibers is immediately
followed by circulating one or more suspensions of other additives
selected from the group consisting of cedar fibers, mica, cotton
seed hulls and mixtures of such additives.
4. In a directional well drilling process wherein the orientation
of the borehole can deviate from vertical by as much as 90 degrees,
an improved method for simultaneously sweeping debris from the
borehole with a circulating drilling fluid while reducing lost
circulation which comprises incorporating into the drilling fluid
an effective amount of fibrillated hydrophobic polypropylene
fibers.
5. The method of claim 4 wherein an effective amount of fibrillated
hydrophobic polypropylene fibers is from 1.5 lbs up to 50 lbs of
fibrillated hydrophobic polypropylene fibers per joint of pipe in
the drill string.
6. The method of claim 5 which includes the additional step of
circulating one or more suspensions of other additives selected
from the group consisting of cedar fibers, mica, cotton seed hulls
and mixtures of such additives in series with said fibrillated
hydrophobic polypropylene fibers.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a method for stopping the
loss of drilling fluid circulating in well bores, and, more
particularly, to the prevention of lost circulation due to all
causes during directional, i.e., non-vertical, drilling in
subterranean formations.
[0002] Most oil and gas reservoirs are much more extensive in their
horizontal dimensions than in their vertical, i.e., thickness,
dimension. By drilling a well which intersects such a reservoir
parallel to its plane of more extensive dimension, horizontal
drilling may expose more reservoir rock to the well bore than would
be the case with a conventional well that penetrates the reservoir
perpendicular to its plane of more extensive dimension.
[0003] The initial vertical portion of a directional, or
horizontal, well is typically drilled using the same rotary
drilling technique that has been used to drill most vertical wells,
wherein the drill string is rotated at the surface. The drill
string consists of many joints of steel alloy pipe, drill collars,
and the drill bit itself. From the entry point of the vertical
section into the curved section of the directional well, the curved
section is drilled using a hydraulic motor mounted directly above
the bit and powered by the drilling fluid. The current generation
of horizontal drilling capability that can attain longer, deeper
and more accurate placement of multiple horizontal well bores has
also produced new problems in adapting conventional drilling fluids
to overcome situations of lost circulation and/or debris removal in
non-vertical bore holes. Lost circulation can occur as seepage
losses, i.e., a slow, steady loss of drilling fluid into the zone
during the process of drilling a well; or it can occur as a partial
loss of fluid wherein drilling mud introduced into the borehole is,
for whatever reason, simply not capable of being recovered; or the
loss of drilling fluid can be an immediate, catastrophic loss that
can result from a fracture in a given subterranean zone. The nature
of horizontal drilling also produces new problems in that debris
may gradually form into sediment along the bottom section of the
elongated borehole which, in turn, tends to reduce drilling fluid
circulation and requires more pressure to be exerted for the
drilling fluid to continue flowing properly. Increased pressure,
however, can also cause ruptures in the mud cake surrounding the
borehole, which may also lead to significant drilling fluid losses
due to subterranean zone fracture.
SUMMARY OF THE INVENTION
[0004] The present invention according to one embodiment is an
improved well drilling method for drilling in subterranean
formations wherein a drilling fluid is injected into a drill string
having a bottom hole assembly inserted into a borehole and the
borehole can deviate from a vertical orientation by as much as 90
degrees. The improvement comprises incorporating into the drilling
fluid an effective amount of fibrillated hydrophobic polypropylene
fibers and injecting the fluid and fiber combination, i.e., the
suspension, into the borehole whereby debris is more efficiently
swept from the borehole and seepage, i.e., lost circulation, of
drilling fluid into the subterranean formation is simultaneously
reduced and/or eliminated.
[0005] According to another embodiment, the present invention is an
improved method for simultaneously sweeping debris from a borehole
and reducing seepage and/or lost circulation into subterranean
formations using a circulating drilling fluid or drilling mud. The
invention is particularly applicable in a directional drilling
process wherein the orientation of the borehole in the subterranean
formation can deviate from vertical by as much as 90 degrees, i.e.,
the borehole curves from vertical and can become horizontal. The
improved method comprises incorporating into the drilling fluid an
effective amount of fibrillated hydrophobic polypropylene fibers to
form a suspension, optionally with one or more other additives, and
then circulating the suspension through the borehole. The optional
one or more other additives may be incorporated directly into the
suspension of fibrillated hydrophobic polypropylene fibers, or they
may be circulated through the borehole in succession, depending on
the particular drilling situation encountered.
[0006] An effective amount of fibrillated hydrophobic polypropylene
fibers can vary over a wide range depending on many factors known
to those skilled in the art of conventional and directional
drilling, e.g., drilling fluid engineers, but typically the amount
may range from 1.5 lbs (0.68 kg) up to 50 lbs (22.7 kg) of
fibrillated hydrophobic polypropylene fibers per joint of pipe in
the drill string. The invention is effective is controlling all
situations of lost circulation, such as more gradual seepage
losses, i.e., a slow, steady loss of drilling fluid into the zone
during the process of drilling a well; or the loss of drilling
fluid that may result from any other cause, such as an immediate,
catastrophic loss event, e.g., an unexpected fracture in a given
subterranean zone.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0007] FIG. 1 is an sectional elevation view of a directional well
in comparison to a vertical well.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The present invention is an improved well drilling method
particularly suited for directional drilling in subterranean
formations wherein an effective amount of fibrillated hydrophobic
polypropylene fibers is incorporated into the drilling fluid to
form a suspension, and the fluid and fiber suspension is injected
into the drill string having a bottom hole assembly inserted into
the borehole. Debris is swept from the borehole and seepage of
drilling fluid into the subterranean formation is reduced.
[0009] Drilling fluid, or "mud" is a vital part of drilling
operations. Its composition, which can vary over a wide range
during any drilling operation depending on peculiarities in the
subterranean formation being drilled, is continually evaluated
based on many factors. The composition needs to be selected to
almost simultaneously provide (i) appropriate hydrostatic pressure
on the borehole wall to prevent uncontrolled production of
reservoir fluids, (ii) lubrication and cooling of the drill bit,
(iii) carrying or "sweeping" of the drill cuttings from the bottom
of the borehole up to the surface, and (iv) consistency for forming
a "mud-cake" on the interior surface of the borehole. Sealing the
interior surface of the borehole can be critical to prevent
drilling fluid invasion of, or seepage into, the surrounding
subterranean formation.
[0010] As drilling proceeds, the mud tends to accumulate small
particles of the rocks which are being drilled through, and its
properties can change. One of the most important mud properties is
the mud weight, i.e., density. If the mud exceeds the fracture
pressure of the formation being drilled, the formation may
fracture, or fracture prematurely, and large quantities of mud can
be lost into the formation. This is a situation that is more
typically referred to as "lost circulation", and lost circulation,
which can occur unexpectedly without prior warning, has been
observed to be particularly troublesome to correct in horizontal
drilling operations.
[0011] As used in describing the present invention, however, the
term "lost circulation" is intended to broadly cover all fluid loss
situations that can occur, including seepage losses, i.e., a slow,
steady loss of drilling fluid into the zone during the process of
drilling a well; or a partial loss of fluid wherein drilling mud
introduced into the borehole is, for whatever reason, simply not
capable of being recovered; and the catastrophic loss of drilling
fluid that can result from a fracture in a given zone.
[0012] Referring now to FIG. 1, the initial vertical portion 10 of
a horizontal well A is typically drilled using the same rotary
drilling technique that is used to drill most vertical wells B. The
entire drill string is rotated at the surface. From a "kickoff"
point 12 to an entry point 14 of the target oil reserve, the curved
section 16 of a horizontal well is drilled using a hydraulic motor
mounted directly above the bit and powered by the drilling fluid.
The drill bit can be rotated by the hydraulic motor without
rotating the drill pipe from the motor to the surface. Current
horizontal drilling technique uses a steerable downhole motor (not
shown). By orienting the bend in the motor, the hole can be steered
around a curve, or bend, from vertical to horizontal, with the
curved section typically having a radius of from 300-500 feet
(91.4-152.4 meters). Somewhat unique to horizontal drilling is that
debris may gradually form into sediment along the bottom section of
the bend and along the bottom section of the elongated horizontal,
or near horizontal, borehole which, in turn, tends to reduce the
available annular volume for drilling fluid circulation. This
reduction in volume translates to requiring more pressure to be
exerted for the drilling fluid to continue flowing properly and
sweeping debris from the borehole.
[0013] According to the present invention, conditions encountered
in horizontal drilling can be quickly and satisfactorily resolved
by incorporating into the circulating drilling mud from 1.5 lbs
(0.68 kg) up to 50 lbs (22.7 kg) of fibrillated hydrophobic
polypropylene fibers per joint of pipe in the drill string. The
combination of a conventional drilling fluid with a precise amount
of fibrillated hydrophobic polypropylene fibers is directed, i.e.,
forced, through sections of the well bore where a condition of lost
circulation or sweeping difficulty has been detected. The
fibrillated hydrophobic polypropylene fibers form a suspension in
the drilling mud that is freely pumpable. The fibers have been
observed to exhibit a structural stiffness that is capable of
forming a fibrous mat in the region of lost circulation to thereby
seal the void. The tendency for debris to form into sediment along
the bend and elongated sections of a directional borehole has also
been overcome using the fiber suspension of the invention, with or
without optional additives, in place of a conventional drilling
mud.
[0014] In a preferred embodiment of the invention, the suspension
of fibrillated hydrophobic polypropylene fibers is first circulated
through the well bore. The results are closely monitored, and if
they are not completely satisfactory, the suspension of fibrillated
hydrophobic polypropylene fibers is followed by one or more
suspensions of other additives selected from the group consisting
of cedar fibers, mica, cotton seed hulls and mixtures of such
additives. The order in which the suspensions of other additives
are circulated through the well bore is not critical, and will be
selected depending on the analysis of subterranean formation being
drilled.
[0015] As used herein, the term "fibrillated" is intended to mean
that the fiber has been abraded and fibrils have been created along
the fiber's length. The fibers contemplated for use according to
the invention may also be referred to as fibrillated fibrous
structures. A fiber tow is chopped to a specific length, usually in
the range of about 1 millimeter to about 8 millimeters, although
the length can vary over a wide range. The chopped fibers are
fibrillated in a device having characteristics similar to a
blender, or on a large scale, in machines commonly referred to as a
"hi-low", a "beater" or a "refiner". The fiber is subjected to
repetitive stresses, while further chopping and the reduction of
fiber length is minimized. As the fibers undergo these stresses,
the synthetic fibers tend to split as a result of weaknesses
between amorphous and crystalline regions, thus becoming
fibrillated. A preferred fibrillated fiber for use according to the
invention is a 100 percent virgin homopolymer polypropylene
fibrillated fiber available commercially as FIBERMESH.RTM. 300
Synthetic Fiber from Propex Concrete Systems. The polypropylene
fibrillated fiber is hydrophobic and contains no reprocessed olefin
materials.
[0016] The description of the invention is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the invention.
* * * * *