US2316596A - Shooting wells - Google Patents

Description

April 13, 1943. KENNEDY 2,316,596

SHOOTING WELL Filed Nov. 4, 1938 :5 LIQUID EXPLOSJNE .BENTON ITE i g i slvfi'z DETONflTOR-ll CHARGE OF EXPLOSIVE grwem/o'n HaJW qy Tfterpnew Patented Apr. 13, 3

SHOGTING WELLS Harvey '1. Kennedy, Oant, Pa., assignor to Gulf Research & Development Comy, Pittsburgh, Pa., a corporation of Delaware- Application November 4, 1938, Serial No. 238391 '3 Claims. (Cl. 102-23) This invention or discovery relates to shooting wells; and it comprises a method of opening up fluid-permeable rock formations adjacent wells to permit more ready flow of liquids therethrough,

including the steps of injecting under pressure into the permeable formations adjacent the well a charge of high explosive in liquid form; and exploding the explosive in the interstices of the rock formation to shatter it; the process often being repeated after removal of debris from the first explosion; all as more fully hereinafter set forth and as claimed.

One achieved object of the invention is the more effective application of high explosives to the opening up of oil-producing formations adjacent oil wells. Another object is the provision of a process whereby a well cavity in pervious rock may be successively enlarged to facilitate production through the rock. Another object is the provision of an improved method of treating oil wells to increase oil production. Another object is the provision of a well shooting method involving injection into permeable rock formaor like high explosive, in forms insensitive to shock and adapted to penetrate into the pores ability of the rock is low, flow of oil may be small or practically zero, even though huge quantities of oil are present in the rock. Furthermore, a formation may be reasonably pervious at the beginning of production, but become clogged by asphaltic or waxy substances deposited therein during production.

Various methods have been proposed for opening up, the oil-producing rock-adjacent the well A bore, to increase production. The most common procedures are acid treatment, and shooting. In acid treatment, an acid such as hydrochloric acid is injected into the well under highpressure, to diffuse into the oil rock and dissolve it in part, thereby opening up oil channels. Acid treatment depends to a considerable extent for its efiectiveness on the presence of limestone or dolomite in the producing rock; most acids will not attack pure sandstone. Acid treatment and shooting are not interchangeable; commonly shooting is used at the beginning of production, to open up new wells, while acid treatment is ordinarily carried out as an incident to the later stages of production.

In shooting a well in the ordinary way to increase production, a charge of nitroglycerine or similar explosive is introduced into the well in one or more containers (shells) and is set off by means of a clock-timed detonator, or a detonator actuated by a falling weight or line squib or other suitable means. 'A shooting job, properly carried out, shatters the faces of the oil rock and opens it up to some extent. The conditions under which well shooting is performed are, however, inherently ill adapted for effective utilization of the disruptive effect of the explosive. The explosive force is directed against un'yieldingly massive rock. and to get any results, the most powerful explosives known must be used, in concentrated form and in large amount. It is not uncommon to use 500 quarts of nitroglycerine in shooting a. well, to secure a disintegration only a small fraction as extensive as in surface blasting or in some mining operations. And by the' same token, the effect of the explosion is sometimes just opposite the heavy explosion, concentrated in the well bore, sometimes does damage to the lower end of the casing, or caves in the well. Attempts to explode ga in the rock have not been fruitful because even with high pressures there is far too little explosive force-available to shatter hard rock satisfactorily under the conditions obtaining in wells. 7

The present invention is based on the discovery that with proper precautions nitrogl cerine, or emulsions or solutions of nitroglycerine, can be injected under pressure into permeable rock formations, so as to penetrate therein a considerable distance, and can then be exploded in place. The explosion tends to blow the rock outwardly, so to speak, into the well, rather than inwardly as heretofore. As a result, the same quantity of explosive results in amuch more effective shattering and opening up of the oil rock. At the same time, accidental damage is largely eliminated because most of the force of the explosion is expended in the interior of the rock.

The liquid explosive is advantageously intro-.

duced into the well bottom by means of a dump bailer or the like, and then a charge of gelatinous bentonite suspension is introduced into the well.

Finally water or oil is introduced and pressure 2 is applied to drive the nitroglycerine into the permeable formations. The step of introducing the bentonite suspension, while notv always necessary is advantageous in that it prevents the explosive from being driven too far into the rock. Upon applying pressure as described, the nitroglycerine flows into the rock until the well cavity is exhausted of nitroglycerine and becomes filled with bentonite. The bentonite is a non-penetrating liquid. Because of its gelatinous nature it cannot enter fine pores, so it acts as an automatic stop to 'further inward penetration of nitroglycerine,

The explosive liquid having been distributed in the rock as described, it is now fired. This is conveniently done by lowering a shell of nitroglycerine equipped with a detonator to the well bottom (through the water and bentonite) in a manner common in conventional shooting of wells, and exploding it in a known way, 'as by dropping an iron weight (godevil) down the well, or by means of one of the several forms of squibs well known in the art. The shock wave fires the Fig. 1 is a schematic View in vertical section of a well with liquid explosive being injected into the rock, and

Fig. 2 is a similar view of the well after completion of the injection step and ready for firing.

Referring to the drawing, the process of the invention is carried out in a well bore cased part way down as shown at 5, which penetrates a permeable rock formation 6 to be opened up. A

charge of liquid explosive 1, deposited in the well by a dump bailer of known type (not shown) is injected into the rock under a loading of bentonite suspension 8 and a water column 9; these liquids are introduced by a pump l2. Sufficient pressure is applied to force the explosive into the rock. The explosive diffuses into the rock as indicated diagrammatically by dots (Fig. 2). When injection is complete a charge of nitroglycerine in a shell I is deposited at the well bottom in a way known per se and a time detonator ll of conventional type is lowered upon it. After a predetermined lapse of time the detonator fires the charge in the well which in turn sets off the explosive in the rock. The bentonite and water columns confine the shot.

Pure nitroglycerine, while desirable to use because of its high explosive effect, is quite sensitive to shock, and in many cases it is better to employ a less sensitive fluid. Emulsions or solutions of nitroglycerine in water or inert organic solvents have high explosive power yet are relatively insensitive to mechanical shock. For example, 10 volumes of water can be emulsified with 1 gallon of nitroglycerine, with the aid of a little sulfonated castor oil as emulsifying agent, to form a stable fluid well applicable for the present purposes. Solutions of nitroglycerine in alcohol, benzol and other inert organic solvents are suitable. Other things being equal it is better to employ as the diluent a liquid freely compatible with oil, so that the fluid will readily enter the oily sands. Instead of nitroglycerine, picric acid, trinitrotoluene and other high ex- In theplosives can be injected in liquid condition as described, withgood results. The more concentrated, and the more powerful, the explosive used. the greater will be the shattering eflect per unit weight of explosive. Operating according to the invention it is simple to secure a high concentration of explosives in the rock; a high disruptive force.

The quantity of actual explosive to be injected (not counting diluent liquid if present) varies from a few quarts to 100 quarts or more, depending on the character of the explosive and the character of the rock. The concentration of the fluid employed in practice varies from-100 per cent (pure explosive) down to the lowest concentration at. which the liquid can still be detonated as described.

Instead of lowering the explosives in a bailer,

they may be flowed into the well thr ugh tubing,

.is treated with 50 quarts of or since liquid high explosives and mixtures are generally considerably heavier than 011 or water standing in the hole, they may be lowered by pouring them into the well and allowing them to settle to the bottom or tothe desired level. A convenient method of injecting these materials is to inject them through tubing under a packermade of wood,-or othernon-metallic material, from which the tubing may be unscrewed when the explosive material is in place. The explosive may be detonated by means of a clock mechanism conveniently located in the packer or by means of a weight striking a detonating device near the explosive after the tubing is removed.

In an example illustrative of the operation of my process, a well having a tight oil-bearing sandstone formation at the bottom, two feet thick, pure nitroglycerine, let down in a dump bailer. Five barrels of a fluid bentonite suspension are dumped ontop of the nitroglycerine, and water is then introduced, in the well to a. height of a few hundred feet, so as to provide a hydrostatic head greater than the formation pressure so as to force the nitroglycerine into the rock against formation pressure. When all the nitroglycerine has gone into the rock, the pressure rises sharply, due to the plugging effect of the bentonite. Then a small shell of nitroglycerine equipped with a detonator is lowered into the well bottom, and an iron godevil dropped in to explode the charge. The debris is bailed out and the well is ready to produce.

My invention is of particular value in increasing the productivity of sandy strata where it is desired to open permeable streaks for an appreciable distance away from the well such as is now accomplished by means of acid treatment in lime wells. The explosive applied in this Way is found to be a great deal more effective than the same quantity of explosive set oif within a. well, since in the latter case most of the energy of the explosive is used up in shattering rock, Whether permeable or impermeable, immediately surrounding the well. When, however, the explosive is injected into the formation, as described, be-' of very tight formations where oil is present but great difficulty is experienced in obtaining it in commercial quantities. My process can often be advantageously employed as a preliminary to acid treatment, or following acid treatment.

The term rock is used herein inits geological sense, as including unconsolidated sands, shales, etc. as well as hard rock. .And while the invention has been described principally in connection with oil wells, the process can of course of applied to bores producing other valuable fluids, where the opening up of pervious rock formations is desirable or necessary.

Usually the formation to be treated is at the bottom of the well, but if not, the well can be filled up to the level of treatment with bentonite gel or packed ofi in known ways, so that the injection of the explosive is confined to the desired level. a

What I claim is:

1. A process of increasing the productivity of a well having a producing rock formation of at least some permeability to fluids, comprising the steps of introducing into the well a charge of a mobile liquid explosive capable of shattering rock with production oftchannels leading to the well and introducing into the well a column of a liquid material of such character as to be incapable of penetrating into fine pored rock and of density less than that of the liquid explosive, applying apressure to the non-penetrating liquid column and the explosive of magnitude greater than formation pressure, for a time sumcient to force the explosive out of the well and into the permeable rock formation, maintaining pressure on the explosive while in the rock formation and detonating said explosive in the rock formation, whereby explosion takes place well within the pores and channels of therock itself.

2. A process of increasing the productivity of a well having a rock formation of at least some permeabiltiy in the producing, zone, comprising the steps of depositing a charge of a dilute detonating-type shattering explosive in mobile liquid state directly in the portion of the well adjacent the rock formation, introducing into the well a loading column of a nonpenetrating fluid material of such physical character as to resist penetration into said rock formation under pressures substantially exceeding the formation pressure at said formation, said fluid material having a lower density than the explosive, so as to float on the explosive, and maintaining the column under such pressure as to exceed formation pressure at a P said formation, so as to force the explosive out into the pores of the rock leaving the lower part of the well filled with said liquid loading column, and exploding the explosive in the pores whereby to shatter the rock.

3. A process of increasing the productivtiy of a well having a producing rock formationof at least some permeability to fluids, comprising the steps of introducing into the well a charge of a mobile liquid explosive capable of shattering rock with production of channels leading to the well and introducing into the well a column of a liquid suspension of bentonite of such concentration as to render the liquid incapable of penetrating into line pored rock and of density less than that of the liquid explosive, applying a pressure to said non-penetrating liquid column and the explosive, of magnitude greater than formation pressure, for a time sufllcient to force-the explosive out of the well and into the permeable rock formation, maintaining pressure on the explosive while in the rock formation and detonating said explosive in the rock formation, whereby explosion takes place well within the pores and channels of the rock itself.

HARVEY '1'. KENNEDY.

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