CA1287565C - Gravel pack method and device for horizontal wellbores - Google Patents

Abstract

GRAVEL PACK METHOD AND DEVICE FOR HORIZONTAL WELLBORES

ABSTRACT

A process for the removal of particulate matter from produced fluids where a fused porous refractory section is placed within a horizontal wellbore for utilization in a loosely consolidated or an unconsolidated formation. The process comprises placement of centralizers around at least one section of fused porous refractory tubing which section has placed therearound at least one centralizer. A flexible tubing of a composition and strength sufficient to withstand the formation environment is connected to each section and one end of the tubing is connected to the production string. When in place, the fused refractory section excludes particulate matter from liquefied resources, particularly formation fines during the production of hydrocarbonaceous fluids.

Description

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GRAVEL PACK METHO~ AND DEVICE FOR HORIZONTAL WELLBORES
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This invention relates to -the control of particulate matter, such as sand or fines via a fused porous refractory device when producing subterranean resources, particularly hydrocarbonaceous fluids in a loosely consolidated or unconsolidated formation. The device comprises fluidly communicating sections of alternating flexible tubing and fused porous refractory sections connected to a productive tubing string assembly.
Recovery of formation resources such as petroleum from a subterranean formation is frequently difficult when the subterranean formation is comprised of one or more incompetent or unconsolidated sand layers or zones. Sand particles in the incompetent or unconsolidated sand zone move or migrate into a wellbore during the recovery of formation fluids from that zone, or sand particles move away from the wellbore during the injection of secondary or tertiary recovery fluids into the formation. In the instance of recovering the fluid from the formation, the movement of sand into the wellbore can cause the wellbore to cease production of fluids. Also, small sand particLes can plug small openings and porous masses formed around the well~ore for the purpose of restraining the flow of sand, such as screens or slotted liners which are frequently placed in wells for this purpose. Not only can fluid production be reduced or even stopped altogether, if sand particles flow through the well to the surface, but also considerable mechanical problems can result from passage of abrasive sand particles through pumps and other mechanical devices.
Many techniques have been described in the prior art for preventing or decreasing the flow of sand into a well during petroleum production, including the use of sand screens, filters, and perforated or slotted liners. These prior art attempts have ~`

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been successful in some limited instances, but have nok always been entirely satisfactory for a number of reasons. Mechanical devices usually restrain only the larger particle sand and are not completely effective for the purpose of restraining or preventing the flow of fine particles from the formation into the well and ultimately to the surface. Furthermore, the devices interfere with various types of completions and workover operations. Additionally7 many of the devices were not able to withstand the combination of high temperatures and high pH often encountered.
In addition to the problem areas mentioned above, use of conventional gravel pack methods in a deviated or horizontal wellbore are virtually impossible. This often occurs because the angle of incidence is so severe that a conventianal gravel pack cannot be made to turn through the angle formed by the vertical tubing and the deviated tubing. Deviated or horizontal wellbores extend the drainage capacity of a well.
Serious problems have been encountered in attempting to use conventional production strings in conjunction with enhanced recovery techniques involving steam injection, acidizing, or workover fluids. Where the high temperature steam, acid, or hot water under high flow rates contact the conventional string, it has been found that such strings are quickly eroded away or dissolved and must therefore be replaced at frequent intervals.
ûften formation fines and sand particles are difficult to exclude by conventional production strings. Removal and replacement of conventional production strings greatly increase the costs of producing a well. These problems are exacerbated where the production is utilized in a deviated or horizontal wellbore.
Therefore, what is needed is a production string which has a section composed of a material which: (1) can withstand high temperatures and pH environments, (2) can be cleared frequently in-situ without erosion, (3) which can be placed in a deviated or horizontal wellbore with minimum tooling and expense, and (4) which can be "tailor-made" to the dictates of the formation characteristics.

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This invention is directed to a process for controlling formation fines during the production of resources, particularly hydrocarbonaceous fluids from a formation where alternate flexible and porous refrac-tory sections are affixed to a production tubing string within a deviated or horizontal wellbore. To accomplish this, at least one fused refractory section having a closed end is formed. Other open ended sections can be interspersed therebetween combined with sections of flexible tubing thereby increasing the length and effectiveness of the refractory tubing. Each refractory section is of a strength, composition, and porosity sufficient to allow entry of li~uefied resources, particularly hydrocarbonaceous ~luids therethrough while excluding particulate matter, e.g.
formation fines or sand. The refractory tubing is formed to allow entry into a wellbore and affixation to alternate sections of flexible tubing where one end of a flexible tubing section is affixed to and fluidly communicated with a production tubing string.
The refractory material from which said refractory section is made is able to withstand high temperatures and pH conditions encountered in the formation's environment. Each of the refractory sections has affixed therearound a centralizer for proper placement within the wellbore.
One refractory section is affixed to one end of a flexible tubing section and the other end of the flexible tubing is affixed to the vertical production string at a point sufficient to allow placement of the refractory section adjacent to the formation's productive interval. At least one flexible section should be located substantially within the wellbore at the angle of incidence formed by the deviated wellbore. A production string with alternating flexible sections and fused refractory sections in place is positioned within the wellbore so that the flexible section is adjacent to the formation's production interval. The conbined flexible and fused refractory sections culminate with a closed end refractory section. Having obtained flexibility because of the flexible sections the combined sections are able to turn through the angle of incidence formed by the deviated or horizontal wellbore.

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, Afterwards, resource liquids, hydrocarbonaceous fluids are produced from the formation to the surface while particulate matter such as formation fines and sand are excluded from khe flulds by the combined sections.
The fused refractory section allows particulate matter, e.g.
accumulated fines or sand to be removed therefrom in-situ ~y acids known to those skilled in the art. Hydrofluoric acid can be used to remove formation fines from the flexible and fused refractory sections. Solvents generally used for production, well completion, and clean up can be used with minimum damage to the section. Also, the flexible section can be used when steam is injected into the wellbore, or into the formation when a steam flood is employed.
This section is able to withstand high formation temperatures and pressures as well as steam temperatures.
The drawing depicts a cross-sectional view of alternate combined flexible and fused refractory sections affixed to each other with one flexible end affixed to a production tubing string within a deviated or horizontal wellbore located in a formation's productive interval.
In the practice of this invention, referring to Figure l, formation lO contains a production interval which is penetrated by a deviated or horizontal wellbore 12. Wellbore 12 contains perforations 24 which are fluidly connected with the production interval of formation 10. Production tubing string 14 is directed into wellbore 12. Affixed to production tubing string assembly 14 is a flexible tubing 16 which is of a size, strength, and composition sufficient to withstand the pressures and heat encountered in a subterranean formation. Affixation can be by any manner known to those skilled in the art such as screwing, strapping, or the use of adhesives.
In one embodiment where only a small productive interval exists, a fused refractory closed end section 22 can be affixed to a flexible tubing section 16 and flexible tubing 16 can be located subst.antially near the angle of incidence formed by wellbo~e 12.
Said end section 22 can be formed to allow fixation by methods - , ,.
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~L~ 7 similar to those above mentioned. Section 22 can be rnolded so that a metal strap can be ~ittingly adapted ko fit over flexible section 16 to hold said flexible section 16 within a circumferential depression near the open end of fused porous refractory section 22.
In order to keep fused porous refractory section 22 off the bottom of wellbore 12 thereby decreasing its particulate matter removing efficiency, refractory section 16 can also be formed to receive a centralizer 20.
To keep fused refractory tubular sections 18 and 22 from lying on the bottom of wellbore 12 thereby decreasing the particulate matter removal efficiency of sections 18 and 22, a centralizing or spacing means is required. A centralizer 20 which can be utilized for centering or for circumferential space equalization within wellbore 12 is shown in Figure 1. Spacing means 20 centers said refractory sections 18 and 22 within wellbore 12. This centering causes sections 18 and 22 to be lifted up and away from perforations 24 on the low side o~ inclined wellbore 12.
Centralizing or spacing means 20 can comprise a multiple metallic lea~ spring means. Such sp~ing means can be made of a metal suitable for use within the productive interval of wellbore 12. Of course, the spring means can be composed of any other suitable material, e.g. thermoplastic materials, as is known to those skilled in the art. As is preferred, at least two spring means should be used to properly centralize fused refractory sections 18 and 22. However, in order to provide greater stability and rigidity, additional spring means can be employed.
In a pre~erred embodiment one or more refractory sections 18 having both ends open and having a flexible tubing 16 affixed thereto can be affixed between flexible tubing 16 which is attached to production string assembly 1~ and fused refractory section 22.
In this manner, combinations of flexible tubing 16 and refractory section 18 can be made to any length desired for the removal of a solubilized resource, particularly hydrocarbonaceous liquids, depending upon the length of the productive interval in formation . , . : , . .
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a size, strength, composition, and porosity su~ficient to allow entry therethrough of solubilized resources while excludiny particulate matter.
Particulate matter as defined herein includes ~ormation fines, sand fines, dirt, and other undesired materials commonly encountered in solubilized resources as is known to those skilled in the art.
Exemplary resources comprise geothermal energy, iron, copper, and uranium ores, shale oil, coal, tar sands, and hydrocarbonaceous fluids such as oil.
Flexible tubing 16 can be made from any material suitable to withstand the high temperatures, pressures and harsh environment commonly encountered during the removal of resources from a subterranean formation. Plastic flexible tubing is preferred for fabricating section 16. A plastic tubing suitable for this purpose is called Coflexip tubing ~hich is sold by Coflexip Corp. in Houston, Texas. Flexible tubing 16 should comprise a material sufficient to be flexed ~ithin the angle of incidence formed by the deviated wellbore and the vertical production tubing string.
When the well 12 is produced, solubilized or liquefied resources such as hydrocarbonaceous fluids leave formation lû via perforations 24 and enter fused refractory section 18 and 22 ~here particulate matter, e.g. formation fines entrained in hydrocarbonaceous fluids are removed. The fines are removed because pores in sections 18 and 22 are smaller than the particulate matter in the fluid.
Fused refractory sections 18 and 22 can be made by using silicon carbide. A method can be used as disclosed in U.S. Patent No.
4,571,414 for molding silicon carbide sections 18 and 22.
Another method for molding tubing section 16 is discussed in u.S. Patent No. 4,341,725 issued to Weaver et al. on July 27, 1982.

Fused refractory sections 18 and 22 are constructed of silicon carbide of a density sufficlent to exclude fines of a size anticipated to be encountered in a formation. By utilizing this * Trademark ~ , . . .

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invention7 fused refractory sections 18 and 22 can be made of a porosity sufficient for the formation where deployed. Generally, the denslty will be abou-t 3.0 to about 3.6 gms. per cubic centimeter. It can also be constructed of the desired porosity while retaining the required thermal and chemlcal resistance characteristics. Although the porosity will vary because of differing envlronments within a formation, the pores in the refractory tubing should be about 44 to about 500 microns in size.
Fused refractory sections 18 and 22 are preferably made of ceramic which provides resistance to high temperatures encountered which can be from about ambient up to about 6û0F while at the sarne time providing for good heat transfer. Most ceramics have low thermal conductivity with the exception of silicon carbide and silicon nitride which are preferred for use in the present invention. ûther ceramics can be used which have a thermal conductivity of at least 3 BTU/hr/ft 2 /F./ft. Similar ceramics are discussed in U.S. Patent No. 4,332,295 issued to LaHaye et al.
on June 1, 1982. For example, fused refractory sections 16 and 22 can be cast from a commercially available castable silicon carbide such as"Carbofrax li, a product of the Carborundum Company of Niagara Falls, New York. This product is typically mixed with water and cast to a desired shape and then fired to temperatures over 180ûF to develop strength and good thermal conductivity. The castable silicon carbide may also use a material such as calcium-aluminate as a binder. This silicon carbide material may be cast at room temperature and allowed to cure at room temperature.
It may then be preheated for a period of time and then first at above 2100F for a period of about four hours.
Fused refractory sections 18 and 22 should be composed of a ceramic material having a density preferably of about 65 to about 75% of the full density. The silicon carbide that is selected is preferably of a density of in the order of about 3.0 grams per cubic centimeter. Where silicon nitride is used, it similarly has a density on the order of about 3.0 grams per cubic centimeter. It is preferred that sections 18 and 20 have a density greater than about 65% of theoretical full density.
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~ X~ g F-~115 -8-Fused refractory sections 1~ and Z should be comprised ofmaterials to make it resistant to thermal shock and also resistant to chemical attack at high temperatures. Alloys of silicon carbide, silicon nitride, or other similar cerarnics can be used to construct sections 18 and 22. U.5. Patent No. 4,332,295 issued to LaHaye et al. discloses other ceramic compositions which can be used in constructing sections 18 and 22.

Fused refractory sections 18 and 22 can be made sufficiently porous to admit liquefied resources such as hydrocarbonaceous fluid while excluding formation flnes. The desired porosity can be obtained by varying the density of the ceramic material utilized.
Also the size, shape, diameter, chemical resistance, and thermal resistance can be modified to conform to the dictates of the particular formation where utilized. As is preferred, said refractory sections 18 and 2û should have a wall thickness of about 5 to about 40 millimeters and sufficient to withstand pressures of from about 1,000 to about 15,000 psig.
This invention, as disclosed below, can be utilized in many applications. One such application is for facilitating the removal of ores from a formation containing same. Sareen et al. in U.S.
Patent No. 3,896,879, disclose a method for increasing the permeability of a subterranean formation penetrated by at least one well which extends from the surface of the earth into the formation. This method comprises the injection of an aqueous hydrogen peroxide solution containing therein a stabilizing agent through said well into the subterranean formation. After injection, the solution diffuses into the fractures of the formation surrounding the well. The stabilizing agent reacts with metal values in the formation which allows the hydrogen peroxide to decompose. Decomposition of hydrogen peroxide generates a gaseous medium causing additional fracturing of the formation. Sareen et al. were utilizing a method for increasing the fracture size to obtain increased removal of copper ores from a formation.

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' ' ' 5~5 In addition to removing ores, particularly copper ores and iron ores from a formation, the present invention can be used to recover geothermal energy more efficiently. A method for recovering geothermal energy is disclosed in U.S. Patent No. 3,86~,709 which issued to Fitch on February ~, 1975. Disclosed in this patent is a method and system for recovering geothermal energy from a subterranean geothermal formation having a preferred vertical fracture orientation. At least two deviated wells are provided which extend into the geothermal formation in a direction transversely of the preferred vertical fracture orientation. A plurality of vertical fractures are hydraulically formed to intersect -the deviated wells.
A fluid is thereafter injected via one well into the fractures to absorb heat from the geothermal formation and the heated fluid is recovered from the formation via another well.
The present invention can also be used to remove thermal energy produced during in-situ combustion of coal. A method wherein therrnal energy so produced by in-situ combustion of coal is disclosed in U.S. Patent No. 4,û19,577 which issued to Fitch et al. on April 26, 1977. Disclosed therein is a method for recoverin~ thermal energy from a coal formation which has a preferred vertical fracture orientation. An injection well and a production well are provided to extend into the coal formation and a vertical fracture is formed by hydraulic fracturing techniques. These fractures are propagated into the coal formation to communicate with both the wells. The vertical fracture is propped in the lower portion only. Thereafter, a combustion-supporting gas is injected into the propped portion of the fracture and the coal is ignited. Injection of the combustion-supporting qas is continued to propagate a combustion zone along the propped portion of the fracture and hot production gases generated at the combustion zone are produced to recover the heat or thermal energy of the coal. Wate.r may also be injected into the fracture to transport the heat resulting from the rombustion of the coal to the production well for recovery therefrom. Both the - . . . : ~ - ,, : . . .
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injection and production wells can be deviated wells which penetrate the coal ~ormation in a dlrection transversely of the preferred fracture orientation.
Recovery of thermal energy from subterranean formations can also be used to generate s-team. A method for such recovery is disclosed in U.S. Patent No. 4,015,663 which issued to Strubhar on April 5, 1977.
Obviously, many other variations and modifications of this invention, as previously set forth, may be made without departing from the spirit and scope of this invention as those skilled in the art readily understand. Such variations and modifications are considered part of this invention and within the purview and scope of the appended claims.

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Claims (17)

1. A process for controlling particulate matter during the production of solubilized or liquefied resources from a formation where a production tubing string is used in a deviated wellbore comprising:
(a) affixing to said production string substantially near its angle of wellbore incidence, one end of a flexible tubing of a size, strength, and composition sufficient to withstand the formation environment while flowing solubilized or liquefied resources therethrough;
(b) affixing to the opposite end of said flexible tubing an open ended section of a fused porous refractory tubing, the other end of said porous tubing being closed, where said porous tubing is of a size, strength, composition, and porosity sufficient to allow entry of solubilized or liquified resources therethrough while excluding particulate matter; and (c) directing said production string into a deviated wellbore in a manner sufficient to place said flexible tubing, with said refractory tubing attached thereto substantially near the angle of incidence.

2. The process as recited in claim 1 where in step (a) said flexible tubing comprises a flexible plastic material sufficient to be flexed within said angle of incidence.

3. The process as recited in claim 1 where in step (b) said refractory tubing has a centralizer therearound for circumferential space equalization within said wellbore.

4. The process as recited in claim 1 where in step (b) at least one opened ended refractory tubing, with flexible tubing attached, is affixed between the flexible tubing attached to said production string and said closed refractory tubing.

5. The process as recited in claim 1 where after step (c) a hydrocarbonaceous fluid flows through the porous refractory section while excluding particulate matter.

6. The process as recited in claim 1 where in step (b) said refractory tubing comprlses a ceramic material selected from a member of the group consisting of silicon carhide or silicon nitride and which has a density of from about 65 to about 75% of said member's full density.

7. The process as recited in claim 1 where in step (b) said refractory tubing is capable of withstanding pressures of from about 1,000 to about 15,000 psig.

8. The process as recited in claim 1 where in step (b) said refractory tubing is capable of withstanding temperatures of from about ambient to about 600°F.

9. The process as recited in claim 1 where in step (b) said refractory tubing is used during steam injection or a steam flood when producing said resources from said formation.

10. The process as recited in claim 1 where in step (b) said refractory tubing has a pore size from about 44 to about 500 microns.

11. The process as recited in claim 1 where in step (b) said refractory tubing has a wall thickness of about 5 to about 40 millimeters.

12. The process as recited in claim 1 where in step (b) said refractory tubing comprises silicon carbide of a density of from about 3.0 to about 3.5 g/cc.

13. The process as recited in claim 1 wherein the solubilized or liquefied resources comprise hydrocarbonaceous fluids produced from a loosely consolidated formation.

14. An apparatus for controlling particulate matter during the production of hydrocarbonaceous fluids from a loosely consolidated or unconsolidated formation where a production tubing string is placed into a deviated wellbore comprising:
(a) a means for affixing to said production string substantially near its angle of wellbore incidence, one end of a flexible tubing of a size, strength, and composition to withstand the formation environment while flowing hydrocarbonaceous fluids therethrough;

(b) a means for affixing to the opposite end of said flexible tubing an open ended section of an unsupported fused porous refractory tubing, the other end of said porous tubing being closed, where said porous tubing is of a size, strength, composition, and porosity sufficient to allow entry of hydrocarbonaceous fluids therethrough while excluding particulate matter; and (c) a means for directing said production string into a deviated wellbore in a manner sufficient to place said flexible tubing, with said porous refractory tubing attached, substantially near the angle of incidence.

15. The apparatus as recited in claim 14 wherein said flexible tubing comprises a flexible plastic material sufficient to be flexed within said angle of incidence.

16. The apparatus as recited in claim 14 wherein said refractory tubing has a metal centralizer therearound for circumferential space equalization within said wellbore, said refractory tubing comprising a ceramic material selected from a member of the group consisting of silicon carbide or silicon nitride and which has a density of from about 65 to about 75% of said member's full density.

17. The apparatus as recited in claim 14 wherein at least one opened ended refractory tubing, with flexible tubing attached, is affixed between the flexible tubing attached to said production string and said closed refractory tubing with centralizers thereon which allows hydrocarbonaceous fluids to flow therethrough excluding particulate matter.