US2251712A - Means for shooting oil wells - Google Patents

Description

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MEANS FOR SHOOTING OIL WELLS Filed March 4, 1938 FIG. FIG, 2

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FIGS.

Patented :Aug. 5, 1941 UNITED STATES PATENT OFFICE fiiiitftlfiatif Application March 4, 1938, Serial No. 193,818 I 1 1 Claim.

This invention pertains to a method of shooting" deep wells to increase recovery of fluid therefrom.

' The shooting of wells has been practiced for a number of years by the oil industry, sometimes with-success and sometimes with disappointingresults. By practical experiments over a period of some 20 odd years I have become definitely convinced (as have others) that the type of shot which effects one well favorably will not necessarily, or even probably, effect another well in the same manner. The underground formations differ. Difierent sands vary in physical characteristics, in compressive strength, elasticity, in degree of homogeneity. A harder formation does not react to a shot the same as a softer formation. The formations overlying and underlying a particular sand also aifect the results produced in that sand by a "shot."

Since the primary purpose of treating a well in any manner is to make it produce the greatest totalnumber of barrels of oil at the lowest pose sible cost per barrel, then the effect of a shot on the well must be seriously considered if the shooting" method of treatment is to be used. If the "shot" breaks down the wall of the well and necessitates a fiv or six day clean ou job, and a more or less continuous cleaning ou treatment thereafter because of cave-ins,- the cost of production may be-very materially increased, instead of decreased.

Up to the present time, due to the diificulty of actually inspecting a hole after it has been shot, and also due to the fact the explosive manufacturers have not been sufficiently interested in the problems of the oil industry as to make explosives of varying strengths and speeds, the effect of certain type shots" on certain. type formations has not even been generally determined. It might be said that there are as many positive expert" opinions on this subject today as there are experts. Most of these experts do agree, however, that it is not the actual enlargementv of the diameter of the hole proper which produces the best results, but the enlargement or increase of the;

effective surface area of the sand in communicadifferent type "shots on different type underground formations.

The speed at which an explosive expands has, so far as I know, been entirely ignored asa factor governing, or partially governing, the effect produced by the shot on a particular formation. As previously mentioned, this is so main.- ly because liquid nitroglycerine has been almost universally employed as the explosive and the mere varying. of the quantity of the liquid nitroglycerine used per foot of sand does not in any way ailect the rate of speed at which the liquid expands when detonated. If,- as I have proven.

by experiment, the fissuring effect produced in the. hole varies materially with the speed of expension of the explosive used, then the only proper way of shooting a well to produce the desired results would be to employ shots having varying rates of expansion. Since it is also true that many sho extend avertical distance within the hole up to 450 feet, and several different type formations may occur within this distance, then it would appear that shots made up of several different grades of explosives, each having a different rate of expansion, would be valuable. These are the reasons back of the conception of my invention.

The chief object of the invention, therefore.

is to provide a method of "shooting oil wells which will simultaneously produce substantially uniform results in several different types of underground formations, regardless of their varying physical characteristics.

tion with the hole. In other words fissures, or

crevices extending radially outward from the hole in the production sand are sometimes created by a particular shot. Sometimes these fissures extend for a considerable distance vertically along I the hole, and sometimes not. At times the fis-' Another object is to provide a method of shootin'g" wells which will produce the desired eilect on various different type underground formations with the least possible tearing down ef- 1 feet on the wall of the well. 7

Another object is to provide a method of shooting" wells which makes possible the utilization of the maximum total expansion of the particular explosive used, yet at the same time permits the use of a slower speed of expansion,

when needed, to produce a desired eflect on different types of formations being "shot."

Another object is to provide a method of shooting wells which will produce a large underground surface areaconnecting with a well ho le proper, extending over a certain vertical dis tance in the hole, even though formations havin considerably diflerent physical characteristics occur within that vertical distance.

, Other objects of the invention will be better understood from the following description when 66 read in connection with the accompanying drawing, which are chosen. for illustrative purposes only, and in which:

Figure l is a diagrammatic view illustrating the results produced in a well when present shooting methods are used;

Figure 2 is a similar view illustrating the results produced'in the same well when my new method is used; and,

Figure 3 is an enlarged sectional view of the upper end of an explosive container, and the lower end of another container, with a detonator between.

The invention consists simply in employing different grades of explosives, each having a predetermined rate of expansion, so that when the entire column of explosive is placed in the well, the explosive having the proper rate of expansion to affect a particular type formation in a desired manner will be positioned adjacent that particular formation, and so that when the entire shot is detonated the results produced on the different formations being shot" will be substantially uniform. Such a result andmethod is illustrated in Figure 2 of the drawing. Formation A is one that can best be fractured or fissured by an explosive having a comparatively slow rate of expansion, say 14,000 ft. per second, so that grade explosive is placed in the containers adjacent formation A. Likewise, formations B and C are formations which can best be fissured by explosives having rates of expansion of approximately 20,000 ft. per second and 26,000 ft. per second, respectively, so those particular grades of explosive are placed in the containers adjacent those respective formations. The results produced when the shot is detonated are marked by the dotted line in the figure. This line does not mean that the well is enlarged as a whole to that particular diameter, but it does indicate that the efl'ective underground surface area bared by the shot is substantially uniform in the three different formations. This is in contrast to the results produced by an explosive having one particular rate of expansion, as illustrated in Figure 1, which is according to the presently used method of shooting." It will be seen, as indicated by the dotted line illustrating the results produced by the explosion, that the explosive having an expansion rate of 26,000 feet per second was really suitable only for formation C. Formation B really should have been shot by an explosive having a slower rate of expansion in order to produce as good results as were produced in formation C, and an explosive having a still lower rate of expansion should have been placed'adjacent formation A.

Conversely, had a column of explosive of smaller diameter but having the same rate of expansion, been used, the results still could not have been uniform, or even nearly so. At present, this varying of the diameter of the explosive containers is the only known method of even attempting to produce different results in the hole, and it is not in the least effective because-the rate of expansion is not changed simply by reducing the quantity of explosive used per foot of sand; Containers of a 3 /2 inch diameter are the type most widely used, and when the diameter of the containers used is cut from 3 inchesto 2 /2 inches, there is a loss in total expansion of 50% since the quantity of liquid explosive per vertical foot is cut from 2 quarts to l'quarth Withmy method the total expansion of the explosive used is utilized because the diameter of the container is not re- 5 duced. It is only the rate of expansion and not the maximum quantity of expansion which is changed. And I have definitely proven that there are a number of different types of underground formations which are'not fractured or fissured satisfactorily by an explosive-having a high rate of expansion, but are flssured in a very satisfactory manner by an explosive having substantially the same volume of expansion but a slower rate of expansion. A high speed explosive often tears out .a large hole and increases the diameter of the hole in one particular formation, but the mere enlarging of the diameter does not produce the desired results; it is the fracturing or cracking of the formation which produces the desired. increase in the surface area exposed to the well hole, Often, too, the enlarging of the hole diameter at one point, 01' over a certain vertical distance, causes the wall of the well to cave in from time to time, necessitating clean out jobs which not only cost money, but also lose valuable production time. A mere cavity would only increase the effective producing surface by the actual area of its immediate surface, while each crack produced which extends radially outward from the hole provides a very great increase in effective oil producing surface. Each crack is a channel through which oil may drain into the central hole.

Without some method of shooting which makes it possible to create these cracks in each different underground formation, according to its own individual physical characteristics, the desired increase in oil production cannot be obtained by shooting. My method makes it possible to shoot each formation with the grade of explosive with which it should be shot to produce the desired cracks or fissures. The method comprises the use of containers of one diameter throughout the vertical column of the shot, and the use of different grades or. types of explosive having the desired predetermined rate of expansion to properly affect each different underground formation lying adjacent the column of explosive. With my method the diameter of the containers used would not have to be reduced in order to protect a particular formation against breaking down, tearing out, or caving in. Thus, surface area-does not have to be sacrificed to prevent injury to the well hole, as must be done with the methods of shooting presently in use.

In practice, my method contemplates the testing of the various underground formations to be shot to ascertain their individual physical characteristics. A choice of explosives having the proper rate of expansion for each respective formation is then made, the correct number of containers (depending on their length) are then filled with the respective grades explosive to be used, each container, or spaced containers may be fitted with the usual detonator (all of which are designated in the drawing by the numeral 5), and the containers are lowered into the well (individually or in groups) and are anchored in the well so that the explosive having a rate of expansion to properly fracture a certain type formation lies adjacent that particular type formation in the hole. Last, a time bomb (designated in the drawing by the numeral 6) is preferably lowered into the hole to rest immediately adjacent the upper end of the uppermost explosive container,

and when it explodes, the entire column of explosive is simultaneously exploded. Any other desired or suitable method or means of exploding the column may be used, however, and I do not wish to be limited to the use of a time bomb in connection with my method.

One important thing to bear in mind, however, is the fact that each different grade of explosive, whether it has an expansion rate of 14,000, 20,000,

. 26,000 or more feet per second, should preferably be detonated at its maximum speed. To accomplish this I prefer to use a detonator preferably at. the top of each individual container, but certainly at the top of each individual grade of explosive, which will detonate each separate grade of explosive at its maximum speed. The speed of expansion of the explosive is determined when it is manufactured and that speed cannot be increased regardless of the speed at which it is detonated. The predetermined speed of expansion of any explosive can, however, be lowered below its maximum because of weak or improper detonation. The'detonators which I use are prefer-.

ably pieces of dynamite having a sufliciently high nitroglycerine content to be more sensitive than the explosive charge to be detonated. Dynamite detonators in which the nitroglycerine content is as high as 85% are ordinarily satisfactory, and will set off the 14,000 grade of explosive at its maximum rate of 14,000 feet persecond and will also set off the 26,000 grade of explosive at 26,000 feet per second. These detonators may be in stick form or in any other form. In Figure 3 I have shown one form of dynamite detonatorwhich I have found satisfactory for use with the particular type containers illustrated.

Having described and illustrated my method of shooting wells, I make the following claim:

A bomb for shooting oil wells'formed through I occurs, and a detonator in cooperating relation to each container and being of suiiicient strength to detonate the respective charges at their maximum rates of expansion.

ORLAND C. MAYS.

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