Wells – Processes – Graveling or filter forming
Reexamination Certificate
2001-08-14
2004-12-14
Bagnell, David (Department: 3672)
Wells
Processes
Graveling or filter forming
C166S227000, C166S231000, C166S235000, C166S236000
Reexamination Certificate
active
06830104
ABSTRACT:
TECHNICAL FIELD
This invention relates to improved methods and apparatus for completing wells, and more particularly to improved methods and apparatus for gravel packing, fracturing or frac-packing wells to provide alternative flow paths and a means of bypass to bypass isolated or problem zones and to allow complete gravel placement in the remainder of the wellbore as well as in the bypass area.
BACKGROUND OF THE INVENTION
Long horizontal well completions have become more viable for producing hydrocarbons, especially in deepwater reservoirs. Gravel packing with screens has been used to provide sand control in horizontal completions. A successful, complete gravel pack in the wellbore annulus surrounding the screen, as well as in the perforation tunnels if applicable, can control production of formation sand and fines and prolong the productive life of the well.
Cased-hole gravel packing requires that the perforations or fractures extending past any near-wellbore damage as well as the annular area between the outside diameter (OD) of the screen and the inside diameter (ID) of the casing be tightly packed with gravel. See Brochure: “Sand Control Applications,” by Halliburton Energy Services Inc., which is incorporated herein by reference for all purposes. The open-hole gravel-pack completion process requires only that the gravel be tightly packed in the annulus between the OD of the screen and the openhole.
Several techniques to improve external gravel-pack placement, either with or without fracture stimulation, have been devised. These improved techniques can be performed either with the gravel-pack screen and other downhole equipment in place or before the screen is placed across the perforations. The preferred packing methods are either 1) prepacking or 2) placing the external pack with screens in place, combined with some sort of stimulation (acid-prepack), or with fracturing or acidizing. The “acid-prepack” method is a combination stimulation and sand control procedure for external gravel-pack placement (packing the perforations with gravel). Alternating stages of acid and gravel slurry are pumped during the treatment. The perforations are cleaned and then “prepacked” with pack sand.
Combination methods combine technologies of both chemical consolidation and mechanical sand-control. Sand control by chemical consolidation involves the process of injecting chemicals into the naturally unconsolidated formation to provide grain-to-grain cementation. Sand control by resin-coated gravel involves placing a resin-coated gravel in the perforation tunnels. Resin-coated gravel is typically pumped as a gel/gravel slurry. Once the resin-coated gravel is in place, the resin sets up to form a consolidated gravel filter, thereby removing the need for a screen to hold the gravel in place. The proppant pumped in a frac treatment may be consolidated into a solid (but permeable) mass to prevent proppant-flow back without a mechanical screen and to prevent formation sand production. U.S. Pat. No. 5,775,425, which is incorporated herein by reference for all purposes, discloses an improved method for controlling fine particulates produced during a stimulation treatment, including the steps of providing a fluid suspension including a mixture of a particulate coated with a tackifying compound and pumping the suspension into a formation and depositing the mixture within the formation.
A combined fracturing and gravel-packing operation involves pumping gravel or proppant into the perforations at rates and pressures that exceed the parting pressure of the formation. The fracture provides stimulation and enhances the effectiveness of the gravel-pack operation in eliminating sand production. The fracturing operation produces some “restressing” of the formation, which tends to reduce sanding tendencies. See Brochure: “STIMPAC Service Brochure,” by Schlumberger Limited, which is incorporated herein by reference for all purposes. The high pressures used during fracturing ensure leakoff into all perforations, including those not connected to the fracture, packing them thoroughly. Fracturing and gravel packing can be combined as a single operation while a screen is in the well.
“Fracpacking” (also referred to as “HPF,” for high-permeability fracturing) uses the tip-screenout (TSO) design, which creates a wide, very high sand concentration propped fracture at the wellbore. See M. Economides, L. Watters & S. Dunn-Norman,
Petroleum Well Construction
, at 537-42 (1998), which is incorporated herein by reference for all purposes. The TSO occurs when sufficient proppant has concentrated at the leading edge of the fracture to prevent further fracture extension. Once fracture growth has been arrested (assuming the pump rate is larger than the rate of leakoff to the formation), continued pumping will inflate the fracture (increase fracture width). The result is short but exceptionally wide fractures. The fracpack can be performed either with a screen and gravel-pack packer in place or in open casing using a squeeze packer. Synthetic proppants are frequently used for fracpacks since they are more resistant to crushing and have higher permeability under high confining stress.
In a typical gravel pack completion, a screen is placed in the wellbore and positioned within the zone which is to be completed. The screen is typically connected to a tool which includes a production packer and a cross-over port, and the tool is in turn connected to a work string or production string. A particulate material which is usually graded sand, often referred to in the art as gravel, is pumped in a slurry down the work or production string and through the cross-over port whereby it flows into the annulus between the screen and the wellbore and into the perforations, if applicable. The liquid forming the slurry leaks off into the subterranean zone and/or through the screen which is sized to prevent the sand in the slurry from flowing therethrough. As a result, the sand is deposited in the annulus around the screen whereby it forms a gravel pack. The size of the sand in the gravel pack is selected such that it prevents formation fines and sand from flowing into the wellbore with produced fluids.
The “Alpha-Beta” gravel-pack technique has been used to place a gravel pack in a horizontal hole. See Dickinson, W. et al.: “A Second-Generation Horizontal Drilling System,” paper 14804 presented at the 1986 IADC/SPE Drilling Conference held in Dallas, Tex., February 10-12; Dickinson, W. et al.: “Gravel Packing of Horizontal Wells,” paper 16931 presented at the 1987 SPE Annual Technical Conference and Exhibition held in Dallas, Tex., September 27-39; and M. Economides, L. Watters & S. Dunn-Norman,
Petroleum Well Construction
Section 18-9.3, at 533-34 (1998), which are all incorporated herein by reference for all purposes.
The Alpha-Beta method primarily uses a brine carrier fluid that contains low concentrations of gravel. A relatively high flow rate is used to transport gravel through the workstring and cross-over tool. After exiting the cross-over tool, the brine-gravel slurry enters the relatively large wellbore/screen annulus, and the gravel settles on the bottom of the horizontal wellbore, forming a dune. As the height of the settled bed increases, the cross-sectional flow area is reduced, increasing the velocity across the top of the dune. The velocity continues to increase as the bed height grows until the minimum velocity needed to transport gravel across the top of the dune is attained. At this point, no additional gravel is deposited and the bed height is said to be at equilibrium. This equilibrium bed height will be maintained as long as slurry injection rate and slurry properties remain unchanged. Changes in surface injection rate, slurry concentration, brine density, or brine viscosity will establish a new equilibrium height. Incoming gravel is transported across the top of the equilbrium bed, eventually reaching the region of reduced velocity at the leading edge of the advancing dune. In this manner, the deposition process continue
Gibson Ron
Lord David
McMechan David
Nguyen Philip D.
Sanders Michael W.
Bagnell David
Collins Giovanna
Halliburton Energy Service,s Inc.
Schroeder Peter V.
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