Wells – Means for forming filter beds
Reexamination Certificate
2000-03-07
2002-11-19
Bagnell, David (Department: 3673)
Wells
Means for forming filter beds
C166S205000, C166S235000
Reexamination Certificate
active
06481494
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
FIELD OF THE INVENTION
The present invention relates to improved methods and apparatus for completing wells in unconsolidated subterranean zones. More particularly, the present invention relates to improved methods and apparatus for achieving effective frac treatments and uniform gravel packs in completing such wells. Still more particularly, the present invention relates to improved methods for achieving effective frac treatments and uniform gravel packs over long and/or deviated production intervals and maximizing the internal production area of the screen assembly by removing an inner flow-control service assembly after treatment.
BACKGROUND OF THE INVENTION
Oil and gas wells are often completed in unconsolidated formations containing loose and incompetent fines and sand that migrate with fluids produced by the wells. The presence of formation fines and sand in the produced fluids is disadvantageous and undesirable in that the particles abrade and damage pumping and other producing equipment and reduce the fluid production capabilities of the producing zones in the wells.
Completing unconsolidated subterranean zones typically comprises a frac treatment and a gravel pack. A frac/gravel pack apparatus, which includes a sand screen assembly and the like, is commonly installed in the wellbore penetrating the unconsolidated zone. During frac treatment, the zone is stimulated by creating fractures in the rock and depositing particulate material, typically graded sand or man-made proppant material, in the fractures to maintain them in open positions. Then the gravel pack operation commences to fill the annular area between the screen assembly and the wellbore with specially sized particulate material, typically graded sand or man-made proppant. The particulate material creates a barrier around the screen and serves as a filter to help assure formation fines and sand do not migrate with produced fluids into the wellbore. Preferably, to simplify operations, the frac treatment particulate material is the same as the gravel packing particulate material. However, as described herein, the term “proppant” refers to the frac treatment particulate material and the term “gravel” refers to the gravel packing particulate material.
In a typical frac/gravel pack completion, a screen assembly is placed in the wellbore and positioned within the unconsolidated subterranean zone to be completed. As shown in
FIG. 1
, a screen assembly
130
and a wash pipe
140
are typically connected to a tool
100
that includes a production packer
120
and a cross-over
110
. The tool
100
is in turn connected to a work or production string
190
extending from the surface, which lowers tool
100
into the wellbore until screen assembly
130
is properly positioned adjacent the unconsolidated subterranean zone to be completed.
To begin the completion, the interval adjacent the zone is first isolated. The bottom of the well
195
typically isolates the lower end of the interval or alternatively a packer can seal the lower end of the interval if the zone is higher up in the well. The production packer
120
typically seals the upper end of the interval or alternatively the wellhead may isolate the upper end of the interval if the zone is located adjacent the top of the well. The cross-over
110
is located at the top of the screen assembly
130
, and during frac treatment a frac fluid, such as viscous gel, for example, is first pumped down the production string
190
, into tool
100
and through the cross-over
110
along path
160
. The frac fluid passes through cross-over ports
115
below the production packer
120
, flowing from the flowbore of production string
190
and into the annular area or annulus
135
between the screen assembly
130
and the casing
180
.
Initially the assembly is in the “squeeze” position where no fluids return to the surface. In the squeeze position, valve
113
at the top of the wash pipe is closed so fluids cannot flow through wash pipe
140
. During squeeze, the frac fluid, typically viscous gel mixed with proppant, is forced through perforations
150
extending through the casing
180
and into the formation. The frac fluid tends to fracture or part the rock to form open void spaces in the formation. As more rock is fractured, the void space surface area increases in the formation. The larger the void space surface area, the more the carrier liquid in the frac fluid leaks off into the formation until an equilibrium is reached where the amount of fluid introduced into the formation approximates the amount of fluid leaking off into the rock, whereby the fracture stops propagating. If equilibrium is not reached, fracture propagation can also be stopped as proppant reaches the tip of the fracture. This is commonly referred to as a tip screen out design. Next a slurry of proppant material is pumped into the annulus
135
and injected into the formation through perforations
150
to maintain the voids in an open position for production.
In a frac treatment, the goal is to fracture the entire interval uniformly from top to bottom. However, because cross-over
110
introduces frac fluid at the top of the formation interval through ports
115
at a very high flow rate, friction causes a large pressure drop as the frac fluid flows down annulus
135
to reach the bottom
195
of the interval. Therefore, more pressure is exerted on the upper extent of the formation interval than on the lower extent of the interval so that potentially full fracturing occurs adjacent the top of the production zone while reduced or no fracturing occurs adjacent the bottom. Additionally, formation strength tends to increase at greater depths such that the longer the zone or interval, the greater the strength gradient between the rock at the top and bottom. Because higher fluid pressures are exerted on the weaker rock at the top, and lower fluid pressures are exerted on the stronger rock at the bottom, the strength gradient adds to the concern that only the upper extent of the interval is being fully fractured. To resolve these problems and achieve more uniform fracturing, it would be advantageous to have a frac apparatus capable of injecting frac fluid into the formation at fairly uniform pressures along the entire interval length from top to bottom. It would also be advantageous to have a frac apparatus capable of continuing to apply frac pressure to the lower extent of the formation even when fractures in the upper interval reach a “tip screen out” condition and therefore stop accepting frac fluids or do so at a reduced rate.
Once the frac treatment is complete, the gravel pack commences, or the gravel pack may take place simultaneously with the frac treatment. During gravel pack, the objective is to uniformly fill outer annulus
135
with gravel along the entire interval. Prior to introducing the gravel pack slurry, the assembly is placed in the “circulation” position by opening valve
113
to allow flow through wash pipe
140
back to the surface. The slurry is then introduced into the formation to gravel pack the wellbore. As slurry moves along path
160
, out cross-over paths
115
and into annulus
135
, the fluid in the slurry leaks off along path
170
through perforations
150
into the subterranean zone and/or through the screen
130
that is sized to prevent the gravel in the slurry from flowing therethrough. The fluids flowing back through the screen
130
, enter the inner annular area or annulus
145
formed between the screen
130
and the inner wash pipe
140
, and flow through the lower end of wash pipe
140
up path
185
. The return fluids flow out through cross-over port
112
into annulus
105
above the production packer
120
formed between the work string
190
and the casing
180
, then back to the surface.
The gravel in the slurry is very uniform in size and has a very high permeability. As the fluid leaks off through the screen
130
, the gravel drops out of the slurry and builds up from the formation
Dusterhoft Ronald Glen
Hailey, Jr. Travis Thomas
Bagnell David
Halliburton Energy Service,s Inc.
Herman Paul I.
Kreck John
Piper Michael W.
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