Through Tubing Well Cleanout Method Using Foam

Abstract

A method of cleaning out a well having a production tubing located therein without removing the production tube from the well by providing a flushing tube inside the production tube, generating pre-formed foam having a liquid volume to gas volume ratio in the range of from 0.05 to 0.1, injecting said foam into the flushing tube and down the well at a pressure within the range of from 350 to 1,000 or more psi and circulating the foam up the annulus between the production tube and the flushing tube while maintaining the annular velocity of the foam within the range of from 600 to 1,000 feet per minute.

Description

FIELD OF THE INVENTION

The present invention is directed to a method of removing sand and other undesirable material from a cased well having a production tubing located therein without removing the production tubing from the well. More specifically, the present invention provides for positioning a flushing tube within a production tube located in a well and injecting a gas/liquid foam down the flushing tube and a circulating the foam up the annulus between the flushing tube and the production tube to provide a through tubing method of cleaning a well.

BACKGROUND OF THE INVENTION

A serious problem is often caused during production of oil from wells from sand or other undesirable material entering the wells with the production fluids and accumulating to a point where production is hindered or even halted because of the sand or other debris in the well. In many wells, sand entering the well with the production fluids is also undesirable because of the damage that the sand can cause to the tubing and surface equipment by abrasion. In many wells a production tubing is positioned in the well and forms with the outer well casing an annular chamber. In wells which penetrate two or more formations and in which dual or higher multiple completions are accomplished, oil is produced through individual production tubes for each completed zone or up the casing production tubing annulus from an upper zone and up the production tubes from the lower zones. It is often desirable to clean the lower zone without removing the production tubing from the hole since this removal requires a great deal of expense even in single zone completions. In dual zone completions removing the production tubing from the hole in the well requires shutting in both zones from production.

Heretofore, methods have been suggested for cleaning a well utilizing a flushing tube positioned inside of a production tube. In U.S. Pat. No. 3,489,222, for example, it is taught that a flushing tube may be positioned inside a production tube and a circulation fluid used to remove undesirable sand from the well. Circulating fluids such as water, oil or foam are suggested for use. It has now been found that foam is an excellent circulating fluid for such use. However, certain specific techniques are necessarily utilized in circulating the foam through the well to achieve success.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a method of through tubing well cleanout which permits removal of sand or other undesirable material from a well without removing the production tubing therefrom. A flushing tube having an outside diameter slightly smaller than the inside diameter of the production tube is inserted into the production tube to a position adjacent the sand. A specially prepared foam having a liquid volume/gas volume ratio in the range of from 0.05 to 0.1 is injected down the flushing tube at a pressure of from 350 to 1,000 or more psi. The foam entrains the sand in the well and is circulated up the annulus between the flushing tube and the production tube at a velocity within the range of from 600 to 1,000 feet per minute. The foam containing the sand is flowed to the surface and is disposed of.

OBJECTS OF THE INVENTION

A particular object of the present invention is to provide a method of removing sand or other undesirable material from a well having a production tubing located therein utilizing a flushing tube and foam circulating fluid in a through tubing well cleanout. Further objects and advantages of the present invention will become apparent from the following detailed description read in view of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a sectional view of a cased well having a production tube located therein, said well penetrating a producing formation which has sanded up the well;

FIG. 2 is a sectional view and shows a flushing tube positioned in the well for use in circulating undesirable sand from the well;

FIG. 3 is a sectional view and illustrates foam being circulated through the flushing tube and up the annulus between the flushing tube and the production tube for removing sand from the well;

FIG. 4 is a sectional view of the cased well having the production tube located therein and shows the well in condition for returning to production.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a well 20 is shown penetrating various non-productive earth strata 22 and 24 and an upper producing zone 21 and a lower producing zone 26. The well is cased over the non-producing intervals 22 and 24 by means of suitable casing 28 and 29. Production liners 30 and 31 having slots 32 and 33 are used to line the well adjacent the oil-producing zones. Alternatively, the well may be cased over its entire depth and the producing intervals perforated. Production fluids from the production zones enter the well through the slots or perforations. The slots or perforations also somewhat assist in restraining sand and other undesirable materials from entering the well.

Production tubing 34 extends down the well to the vicinity of producing zone 26 for production of fluids therefrom. Fluids from producing zone 21 may be produced up the annulus 36 between the casing and the production tubing 34. The annulus 36 between the well casing 28 and the production tubing 34 is packed off by suitable means such as a production packer 38. Thus, well fluids may be simultaneously produced in both producing zones. As is known in the art, production may be by natural flow or may be assisted by artificial means such as by pumping or gas lift. As illustrated schematically in FIG. 1, sand particles 27 from formation 26 have entered the well through slots 32 in liner 30 and have plugged the well to a point where production of the lower zone of the well is hindered or in some cases halted.

In accordance with the invention and as illustrated in FIG. 2, a flushing tube 42 of smaller diameter than the diameter of the production tube 34 is run down the inside of the production tube forming an annulus between the inside of the production tube 34 and the outside of the flushing tube 42. The flushing tube may be made up of a number of individual pipe sections coupled together by suitable couplings 40.

In typical well completions, the inside diameter of a production tube is 1.995 inches. A sectional tube having an outside diameter of 1.315 and an inside diameter of 0.97 is utilized as a flushing tube. Couplings for the flushing tube have an outside diameter of 1.66. Thus as is evident the clearances in the annulus between the flushing tube and the production tube are very close and, therefore, in accordance with the invention foam velocity in this annulus must be maintained at a velocity which will prevent fallout of particles which might bridge and stick the flushing tube in the well. If such sticking occurs the well might be lost.

It is desirable to extend the flushing tube 42 down the production tube to a position adjacent the upper portion of the sand located in the lower portion of the well. Foam is then circulated to remove sand from the well. The foam is circulated down the flushing tube 42 and up the annulus between the flushing tube 42 and the production tube 34. This arrangement causes the sand to be carried to the surface. Foam may be refluxed, i.e., down the annulus and up the flushing tube. The latter circulation arrangement is sometimes desirable because it assists in preventing possible bridging of sand in the annulus around the flushing tube which could cause sticking of the flushing tube in the production tube.

Foam is provided to flushing tube 42 from a suitable foam generator 43. A source of foamable solution is flowed to the foam generator 43 through line 47. Control of the foamable solution is done by valve 47. Gas under pressure is flowed to the foam generator 43 through conduit 49. Flow through this conduit is controlled by valve 51. The foamable liquid and the gas are brought together in the foam generator so that the liquid volume/gas volume ratio is maintained between 0.05 and 0.1. Maintaining the liquid volume/gas volume ratio within these limits provides a foam which can be circulated through the restricted opening between the flushing tube and the production tube. The foam is circulated at a pressure between 350 to 1,000 psi or higher and the annular velocity in the annulus between the flushing tube and the production tube is maintained between 600 and 1,000 feet per minute. Higher foam pressures may be necessary in deep high pressure wells, however, the foam velocity in the annulus must be maintained. If the velocity falls too low the foam may plug in the annulus and cause the flushing tube to stick. Thus foam velocity within the range of 800 to 1,000 feet per minute is preferred.

For the generation of aqueous gas and liquid foam, water containing a detergent concentrate and gas are delivered to the foam generator. Numerous gases such as air, nitrogen, natural gas and carbon dioxide are useful with an aqueous surfactant solution to form a foam. Water and a detergent and, if desired, suitable stabilizing agents are mixed to produce a foamable solution. Suitable foams and specific surfactants which go into the foamable solution which make them are described in detail in U.S. Pat. No. 3,463,231 issued Aug. 26, 1969. The disclosure of such patent is incorporated here by reference. A preferred surfactant for use in the present invention is a C.sub.11 -C.sub.14 alkyl benzene sulfonate (ABS) preferably of the ammonia salt. The surfactant should be added to water to form a foamable solution in an amount between 0.5 to 1.0 parts per weight per 100 parts of water. The foamable solution is mixed with gas in a liquid volume/gas volume relationship as set out herein.

FIG. 3 illustrates the sand being removed from the well by the foam circulating in the flushing tube 42 and the flushing tube-production tube annulus 46. The foam is moved through annulus 46 at an annular velocity of from 600 to 1,000 feet per minute and is injected into the flushing tube at a pressure of at least 350. The circulating foam tends to pick up sand from within the well and also to assist in removing sand from the slots or perforations of the well liner. When the well is a dual completion well, production from the upper zone may be continued during the time that the through tubing well cleanout with foam is being accomplished. FIG. 4 shows the well ready to resume production from the lower zone. The flushing tube has been removed from the well and the clean well is now ready for production from the lower zone.

Although only specific embodiments of this invention have been described in detail, the invention is not to be limited to only such described embodiments but is meant to include all embodiments coming within the scope of the appended claims.

Claims

I claim:

1. A method of removing sand or other undesirable material from a well, said well having a casing and a production tubing located therein, without removing the production tube from the well comprising the steps of positioning a flushing tube inside a production tube to form an annular passage between said flushing tube and said production tube, forming a pre-formed foam having a liquid volume/gas volume ratio between 0.05 and 0.1, injecting said foam down said well through said flushing tube at a pressure of at least 350 psi and circulating said foam up the annulus between said flushing tube and said production tube while maintaining the annular velocity in said annulus between 600 and 1,000 feet per minute.

2. The method of claim 1 further characterized in that the annular velocity of the foam is maintained between 800 to 1,000 feet per minute.

3. The method of claim 1 further characterized in that the injection pressure of the foam is between 350 and 1,000 psi.