US3059469A

US3059469A - Determination of cavity size in earth formations penetrated by a borehole

Info

Publication number: US3059469A
Application number: US116532A
Authority: US
Inventors: Joseph A Caldwell
Original assignee: Jersey Production Research Co
Current assignee: Jersey Production Research Co
Priority date: 1961-06-12
Filing date: 1961-06-12
Publication date: 1962-10-23
Anticipated expiration: 1979-10-23

Description

INVENTOR.

JOSEPH A. CALDWELL ATTORNEY- Q d v., www

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ATTORN EY.

United States Patent Olice 3,659,469 Patented Oct. 23, 1962 DETERMINATION F CAVITY SIZE DI EARTH FORMA'IIUNS PENE'IR'IED BY A BQREHGLE Joseph A. Caldwell, Houston, Tex., assignor, by mesne assignments, to Jersey Production Research Company,

Tulsa, Okla., a corporation of Delaware Filed June 12, 1961, Ser. No. 116,532 4 Claims. (Cl. 73--149) This invention relates generally to well operations, such as sand consolidation operations, and more particularly to determination of the presence of and size of cavities that may exist around boreholes through which earth formation fluids are produced.

There are a number of circumstances under which it is desirable to detect and determine the size of cavities in earth formations. Such operations are particularly desirable in connection with consolidation of loose sands from which hydrocarbons are produced. When hydrocarbons are produced from loose sands, it is usual that a substantial amount of sand will iind its way through perforations in the casing pipe string usually lining the wall of a borehole. This sand either will accumulate at the bottom of the borehole or will be produced with the hydrocarbons or other earth formation fluids. In the latter case, substantial damage may be done tollow tubing pumps and other well apparatus.

It is known to consolidate loose sands by injecting plastic or resinous sand consolidating compositions into the sands to bind together the sand grains while leaving pore spaces through which earth formation fluids can flow. Not all attempts at consolidating sands with resinous or plastic compositions have been successful. A reason for such failures is believed to be as described below. If an unsuspected cavity should surround the borehole in the earth formation, an insutlicient amount of the sand consolidating composition will be pumped into the earthformation. Should the amount of the sand consolidating composition be insufcient to even fill the cavity, manifestly a considerable portion of the formation around the upper part of the cavity will not be contacted by the consolidating composition. Furthermore, if the existence of the cavity `should be suspected and too much of the consolidating composition should be pumped into the well, the hardening catalyst that usually follows the consolidating composition will not contact the earth formation to harden the consolidating composition before formation fluids are produced again from the sand. The result will be the same as if no attempt at all were made to consolidate the sand, and the consolidation attempt will be a failure.

In accordance with the teachings of the present invention, use is made of a testing liquid that is incapable of penetrating the earth formation containing the cavity and that is immiscible with other fluids that may be present in the Well. The liquid is injected through a pipe string of known dimensions into the borehole at known ilow rate to a level at which it is believed a cavity exists. Fluid in the borehole before the liquid is injected thereinto is forced ahead of the liquid into an earth formation containing the cavity. In the event that it is not known for sure whether the fluid forced ahead of the liquid is capable of penetrating the formation, the fluid is displaced with a fluid that is positively known to be able to penetrate the formation and to be immiscible with the testing liquid. The testing liquid is injected until a sharp pressure rise is obtained which indicates that no more iluid can be forced into the formation and that the testing liquid entirely lllls the cavity. Since the dimensions lof the pipe string are known, the difference between the volume of the testing liquid pumped into the well as described above and the volume of the pipe string will give the volume of the cavity.

Objects and features of the invention not apparent from the above description will become evident upon consideration of the following descriptive matter taken in connection with the accompanying drawings, wherein:

FIGS. l and 2. are schematic representations of well installations illustrating steps in the performance of the invention;

FIG. 3 is a schematic representation similar to FIG. 2 illustrating a modification of the invention; and

FIG. 4 is a graph of testing liquid pumping pressure as a function of time, which graph is useful in understanding the invention.

With reference now to FIGS. 1 and 2, there is shown a well installation including a borehole 24 in the earth that penetrates a hydrocarbon earth formation 35 containing a cavity 41. A `casing pipe string 23 in borehole 24 is cemented to the side of the borehole in the usual manner by a cement sheath 25. The casing and cement sheath are assumed to have been perforated so as to produce perforations 43 which provide iluid communication between productive earth formation 35 and the interior of the casing. The -flow tubing 15 is suspended in the casing string 23 in the usual manner by wellhead apparatus 21.

It will be assumed that the Well has been produced for a time interval sutlicient to cause a substantial amount of sand to flow into the casing, as the result of which cavity 41 is formed in earth formation 35. A substantial amount of sand 45 is shown as having accumulated in the bottom of the casing 23.

The usual tlow lines `17 and 14 are respectively connected to the wellhead so as to respectively provide communication with the tubingcasing annulus andthe bore of the tubing. The

lines

17 and 14 are respectively controlled by valves 19 and v13. A liquid pump 5 having a suction line 3 and an exhaust or pressure line 11 is shown as being provided with a pressure gauge 9. The exhaust line 11 is connected to line 14, and the suction line 3 is connected to a source of liquid which will be described below.

Reference numeral 29 designates well bore iluids that were found to be originally present in the well. The fluids may be drilling fluids, earth formation iluids, testing liquids previously injected into the well, or combinations thereof. If it is desirable to remove such fluids from the tubing and the lower part of the well bore, crude oil 33 is pumped into the tubing string by pump 5, and the originally present lluids are circulated up the tubing-casing annulus and out line 17. Only a portion of the iluid 29 need be so circulated as shown in FIGS. l and 2. The lower portion of the tubing should be immersed in crude oil. Wellhead valve 19 is closed after the desired amount of iluid is removed.

A low filtration rate testing liquid 31 is now pumped into tubing string 15. Preferred compositions for this testing liquid 31 will be described below. The oil 33 is forced ahead of the testing liquid into the earth formation 35 as indicated by arrows 42. The liquid 29 in the upper portion of tubing-casing annulus will be virtually unaffected by the iluid llow and will remain in the annulus except at the lower end of tubing 15, as shown in FIG. 2. The low filtration rate liquid 31 will flow down the tubing 15, into the casing bore below the lower end of the tubing 15 through perforations 43, and into the cavity 41. As the testing liquid 31 is pumped into the well and before it enters the cavity, the pressure noted by gauge 9 will remain at a relatively low value over the time interval from time zero to time T1 as indicated on the graph of FIG. 4. During the interval that the cavity is filling with testing liquid (i.e., during the time interval from time T1 to time T2), the pressure will gradually rise as more and more of the testing liquid nds its way to the cavity-formation interface. At time T2 the cavity will be substantially filled with testing liquid and a sharp pressure rise will be noted as the flow rate of testing liquid sharply drops off. During this entire operation the flow rate of testing liquid preferably is kept constant, but under all circumstances the total volume of testing liquid is measured by a suitable ilow meter 2 in the line 3. Inasmuch as the dimensions of the tubing and casing Z3 are known, the volume of testing liquid within tubing 15 and the portion of casing 23 below the lower end of tubing 15 also will be known. By subtracting this known volume from the 'volume of testing liquid injected into tubing 15 during the time interval from time zero to time T2, the volume of cavity 41 can be very accurately determined.

The embodiment of the invention shown in FIG. 3 differs from that shown above in that the liquid originally used to remove fluids originally in the borehole consists of water, preferably salt water. The water is injected into the tubing-casing annulus by connecting exhaust line 11 to line 17. The water displaces the original lluids 29 either entirely or to a suitable distance up the tubing 15. The water is then followed with an oil-based testing liquid 32 which, like the liquid 31, is characterized by a low filtration rate. The reason that the liquids must be injected into the tubing-casing annulus is that the testing liquid 32 would bubble up through the salt water 34 if the procedure shown in FIG. 1 were followed, thus resulting in an inaccurate determination of cavity size. Otherwise, the steps followed in the embodiment of FIG. 3 are substantially the sa-me as the steps followed in the embodiment described with respect to FIGS. l and 2.

The testing liquid 31 used in the embodiment described with respect to FIGS. l and 2 is immiscible with the liquid pumped thereahead. Preferably, the liquid 31 consists of any of the following: 1 to 10 lbs. of carboxy methyl cellulose to l bbl. of water; 1 to 10 lbs. of an organic gum such as guar gum or gum tragacanth, to 1 bbl. of water; or 1 to l0 lbs. of gelatinized starch to 1 bbl. of water. The testing liquid 32 used in the embodiment of FIG. 3 may consist of 0.5 to 5 parts of a metal soap such as napalm (a mixture of aluminium palmonate and aluminum oleate) to `100 parts of oil, or 0.5 to 5.0 parts of partially polymerized butadiene to l0() parts of oil. Other suitable mixtures may be used.

Testing fluids that can be used both in the technique described with reference to FIGS. 1 and 2 and in the technique described with reference to FIG. 3 are the oil-inlwater emulsions described in U.S. Patent 2,805,722-Priest et al. These oil-in-water emulsions are emulsied by nonionic and anionic agents such as polyoxyethylene sorbitan monolaurate and a film strengthening agent such as sulfonate phenol formaldehyde polymer, sodium carboxy methyl cellulose, and sodium lignosulfonate. The density of the emulsion can be controlled by using soluble salts such as sodium or calcium chloride or high density liquids such as tetrachlorethane.

In the practice of the invention, it will be determined that on occasion the fluids originally in the well are suficiently immiscible with the

testing fluids

31 and 32 and are suiciently capable of penetrating formation 35 to be used with the invention. In such a case, there will be no necessity of pumping

fluids

33 and 34 into the wellhead of the testing liquid. However, it is usually found that earth formation fluids consist not of oil or of water but mixtures of oil and water, and should be displaced from the flow path of the testing liquids before the testing liquids are injected into the well.

While the invention has been described with respect to sand consolidating operation, it is manifest that it can be used in other oil well operations such as cementing, fracturing, and acidizing. Furthermore, apparatus and interconnections of apparatus may be used other than that described above.

What is claimed is:

l. A method of measuring the total volume of an earth formation cavity and Well pipe means of known volume disposed in a borehole penetrating the cavity for the purpose of obtaining the volume of the cavity, comprising: forcing fluids in the well pipe means and the cavity into the earth formation by pumping through the Well pipe means at known flow rate a fluid incapable of penetrating the formation while continuously measuring the lluid pressure; and discontinuing pumping when a sharp increase in pressure is obtained.

2. A method of measuring the total volume of an earth formation cavity and well pipe means of known volume disposed in a borehole penetrating the cavity for the purpose of obtaining the volume of the cavity, comprising:

displacing fluid initially in the well pipe means with lluid known to be capable of readily penetrating the earth formation containing the cavity; forcing the fluid capable of penetrating the earth formation into the earth formation by pumping through the well pipe means at known flow rate a fluid incapable of penetrating the formation while continuously measuring the fluid pressure; and discontinuing pumping when a sharp increase in pressure is obtained.

3. In a method of measuring the volume of a cavity in an earth formation penetrated by a well bore having therein a rst fluid adapted to be forced into the formation, the improvement comprising: pumping at known ilow rate into the cavity through well pipe means of known volume extending to the depth of the cavity, a second fluid substantially incapable of penetrating the formation to force the first iluid into the formation; and discontinuing pumping when a sharp rise in pressure occurs.

4. A method of measuring the volume of a cavity in an earth formation penetrated by a well bore cased and tubed with tubing and perforated casing of known dimensions, comprising: circulating down tubing and at least part way up the tubing-casing annulus to a level above vthe cavity, a liquid adapted to penetrate into the earth formation containing the cavity to be measured; forming a. second iluid immiscible with the first lluid and incapable of appreciably penetrating into `said earth formation with the casing bore closed, pumping said second fluid into the tubing at known flow rate to force said first iluid into the formation until a sharp pressure rise indicates that the cavity is substantially filled With said second fluid, whereby the volume occupied by said second fluid in the tubing and in `the casing adjacent the formation may be subtracted from the measured volume of said second fluid pumped into the well bore to determine the volume of the cavity.

McConnell Mar. 18, 1941 Huntington Mar. 23, 1943