Wells – Processes – Providing porous mass of adhered filter material in well
Reexamination Certificate
2000-10-27
2002-05-21
Suchfield, George (Department: 3672)
Wells
Processes
Providing porous mass of adhered filter material in well
C166S287000, C166S293000, C166S296000, C166S376000
Reexamination Certificate
active
06390195
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention provides methods and compositions for forming permeable cement sand screens in well bores to prevent sand from flowing into the well bores with produced hydrocarbons and other fluids.
2. Description of the Prior Art
Oil, gas and water producing wells are often completed in unconsolidated subterranean formations containing loose or incompetent sand which flow into the well bores with produced fluids. The presence of the sand in the produced fluids rapidly erodes metal tubular goods and other production equipment which often substantially increases the costs of operating the wells.
Heretofore, gravel packs have been utilized in wells to prevent the production of formation sand. In gravel packing operations, a pack of gravel, e.g., graded sand, is placed in the annulus between a perforated or slotted liner or screen and the walls of the well bore in the producing interval. The resulting structure provides a barrier to migrating sand from the producing formation while allowing the flow of produced fluids.
While gravel packs successfully prevent the production of sand with formation fluids, they often fail and require replacement due, for example, to the deterioration of the perforated or slotted liner or screen as a result of corrosion or the like. The initial installation of a gravel pack adds considerable expense to the cost of completing a well and the removal and replacement of a failed gravel pack is even more costly.
Thus, there are continuing needs for improved methods of preventing the production of formation sand, fines and the like with produced subterranean formation fluids.
SUMMARY OF THE INVENTION
The present invention provides improved methods and compositions for forming permeable cement sand screens in well bores which meet the needs described above and overcome the deficiencies of the prior art. The methods of the invention are basically comprised of the following steps. A foamed cement composition is prepared comprised of a hydraulic cement, a particulate solid cross-linked gel containing a delayed internal breaker which after time causes the gel to break into a liquid and water present in an amount sufficient to form a slurry. A pipe containing perforations which are sealed by an acid soluble sealant is placed in a well bore whereby it traverses a fluid producing zone therein. Thereafter, the prepared cement composition is placed in the annulus between the perforated pipe and the walls of the well bore and the cement composition is allowed to set. The particulate cross-linked gel containing a delayed internal breaker in the set cement composition is next allowed to break whereby vugs and channels are formed in the set cement. An acid is then introduced into the perforated pipe so that the acid dissolves the acid soluble sealant on the pipe, flows through the perforations in the pipe into contact with the set cement composition and dissolves portions of the set cement composition connecting the vugs and channels therein whereby the set cement composition is permeated.
The resulting permeable set cement in the well bore functions as a sand screen, i.e., the permeable cement allows produced fluids to flow into the well bore, but prevents formation sand and the like from flowing therein. Because the permeable cement sand screen fills the portion of the well bore adjacent to a producing interval and bonds to the walls of the well bore, the permeable cement can not be bypassed and does not readily deteriorate.
The compositions of this invention for forming a permeable cement sand screen in a well bore are basically comprised of a hydraulic cement, a particulate cross-linked gel containing a delayed internal breaker which after time causes the gel to break into a liquid and water present in an amount sufficient to form a slurry.
It is, therefore, a general object of the present invention to provide improved methods and compositions for forming permeable cement sand screens in well bores.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
DESCRIPTION OF PREFERRED EMBODIMENTS
In accordance with the methods of this invention, a permeable cement sand screen is formed in a well bore adjacent to a producing interval or zone so that loose and incompetent sand and fines are prevented from entering the well bore with fluids produced from the interval or zone. The methods are basically comprised of the following steps. A foamed cement composition is prepared comprised of a hydraulic cement, a particulate cross-linked gel containing a delayed internal breaker which after time causes the gel to break into a liquid and water present in an amount sufficient to form a slurry. A pipe, e.g., casing or a liner, containing perforations which are sealed by an acid soluble sealant is placed in the well bore whereby it traverses a producing zone therein. Thereafter, the prepared cement composition is placed in the annulus between the perforated pipe and the walls of the well bore and the cement composition is allowed to set therein whereby the cement composition fills and forms a column in the well bore adjacent to the producing interval or zone and bonds to the walls of the well bore. The particulate cross-linked gel containing a delayed internal breaker in the set cement composition is next allowed to break whereby vugs and channels are formed in the set cement column. An acid is then introduced into the perforated pipe whereby the acid dissolves the acid soluble sealant on the pipe, flows through the perforations in the pipe into contact with the set cement composition and dissolves portions of the set cement composition connecting the vugs and channels therein whereby the set cement composition is permeated throughout its length and width.
After the permeable set cement column has been formed in the well bore, the well is produced and the permeable set cement column functions as a sand screen. That is, produced liquids and gases flow through the permeable set cement column into the well bore, but formation sand and fines in the formation are prevented from passing through the permeable set cement.
While a variety of hydraulic cements can be utilized in the foamed cement composition of this invention, Portland cements or their equivalents are generally preferred. Portland cements of the types defined and described in
API Specification For Materials And Testing For Well Cements
, API Specification 10, Fifth Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred such API Portland cements include classes A, B, C, G and H, with API classes G and H being more preferred and class H being the most preferred.
While various cross-linked gels and internal breakers can be utilized, a preferred particulate cross-linked gel containing a delayed internal breaker for use in accordance with this invention is comprised of water; a hydratable polymer of hydroxyalkylcellulose grafted with vinyl phosphonic acid; a delayed breaker selected from the group of hemicellulase, encapsulated ammonium persulfate, ammonium persulfate activated with ethanol amines or sodium chlorite; and a cross-linking agent comprised of a Bronsted-Lowry or Lewis base.
The particular delayed internal breaker utilized in the cross-linked gel depends on the temperature in the well bore at the location where the cement composition is placed. If the temperature is in the range of from about 80° F. to about 125° F., hemicellulase is utilized. If the temperature is in the range of from about 80° F. to about 250° F., encapsulated ammonium persulfate is utilized. If the temperature is in the range of from about 70° F. to about 100° F., ammonium persulfate activated with ethanol amines is used, and if the temperature is in the range of from about 140° F. to about 200° F., sodium chlorite is utilized. The amount of the delayed internal breaker utilized in the cross-linked
Barton Johnny A.
Brown David L.
Crook Ronald J.
Nguyen Philip D.
Dougherty, Jr. C. Clark
Halliburton Energy Service,s Inc.
Roddy Craig W.
Suchfield George
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