US2748867A - Process for reactivation of flowing wells - Google Patents

Description

United PROCESS FORREACTIVATION OF BLOWING WELLS No Drawing. Application August 5, 1953, Serial No. 372,591 v Claims. (Cl. 166-45) This invention is concerned with a new, novel and'economical method for re-initiating flow of fluid in oil wells.

The invention maybe characterized by the language of the claims, which may be illustrated'b y the. followingz' In the process of reactivation of a temporarily non-active well; said Well being of the normally self-flowing type; non-activity of said well being due tothe fact-that the normal flow was interrupted by the hydrostatic pressure in the well piping being momentarily greater than bottom hole pressure; the step of introducing in the bottom of said well a disintegrable capsule containing a metalhy; dride selected from the class consisting of alkali metal and alkaline earth metal hydrides;.permitting said capsule to disintegrate followed by reaction between water-and said metallic hydride; the amount of metallic hydride in said capsule being suflicient to release-enough hydrogen gas in the well piping to reduce the apparent density of the wellfluid responsible for the hydrostatic head to a point less than the bottom hole pressure and permitting normal flow to resume.

Oil wells may be classified-into two types based on method of production. In many oil wells the oil well fluids will flow spontaneously from the top of the'producing pipe string due to the pressure in the oil reservoir, i. e., the bottom hole pressure. These wells are known as flowing wells.

In wells where the bottom hole pressure is not enough to overcome the hydrostatic head in the piping, the wells must be produced by artificial means. This is done usually by one of several types of pumps or other lifting devices.

'These wells are known as pumping wells, or other equivalent characterization. V I This invention, as previously noted, is concerned par ticula'rly with the flowing Well type. Certain wells have only a limited pressure on the reservoir zone and this pressure is not quite enough-to overcome the hydrostatic head of the fluids in the perpendicular' piping leading to the surface. The activating pressure in the reservoir involves-solely, or atleastin part, the pressure of chemical compounds-which normally are gassesbut are liquefied and dissolved in the petroleum fluidunderconditions existing in the strata. Normally when the liquid travelling through the oil bearing strata reaches the bottom of the well, which is emptyor practically-empty of anycontents at the moment, there is at least a slight decrease in pressure. Thisiscaused by' th'e inherent nature of the combined structure involving both the strata system under natural pressure andthewell mechanism which includes piping leading'tothe surface. Momentarily at least and usually for rather extended periods decrease in pressure at the strata exit (i. e., the bottom well entrance) lowers the solubility of the gaseous constituents of the hydrocarbon oiland bubbles-are formedin the oil, passing into the piping. This means that instead of having the fluid consisting essentially of a liquid or'two liquids there is a fluid permeated with an insoluble gas'which, in effect, renders theliqui'd-portion be said to render a glass of Water porous, porosity being a characterization comparable to nonhomogeneity. The total effect is to lower the density of the oil column and decrease the hydrostatic head to a point Where the Well will flow. Such well will continue to flow so long as the reservoir pressure is greater than the hydrostatic head of the frothed (foam permeated) fluid. Wells may stop flowingtemporarily for either one of two reasons; (a) a decrease in the reservoir pressure or because (b) foaming due to gasification stops momentarily. If a Well is produced too rapidly the bottom hole pressure may diminish to a point Where flow stops. Once the flow stops the bottom hole pressure may gradually return to approximately the previous point but perhaps not sufliciently enough to overcome the hydrostatic head of the nonfoaming or nonporous (homogeneous) liquids in the well. Needless to say, when the flowing well either is shut in intentionally or when the flow stops and the commingled gases escape, or when the gases evolve too slowly, the result is that the density of the fluids in the well represents the maximum nonporous or homogeneous density,

and'the' fluids are then too dense to be lifted by the then existing reservoir pressure.

Such wellscan be kicked-01f or caused to resume flow by decreasing the density of the oil column in the pipe to a point where the bottom hole pressure will lift it again; this is usually accomplished by swabbing. A plunger is run down the well and the heavy column of oil lifted-out drawing with it a fresh oil which will froth and the well will begin flowing again. Several other methods also areused but each, in principle, consists of mechanically displacing the heavy, dead oil with fresh oil from the formation. All of these methods require expensive equipment and considerable labor. They also take considerable time. If the right equipment is not available expensive delays result. My new, novel and useful method has the advantage that it does not require bulky or expensive equipment, neither does it require a crew of several men. It can be used rapidly and the necessary materials can be kept in stock since they require a minimum of storage space.

In the practice of the present invention, hydride of an alkali or alkaline earth metal is introduced into the oil well fluids in such a way that hydrogen gas is generated atthe bottom of the well and a stream of bubbles released into the oil column. This reduces the density of the oil column as previously discussed and the well resumes flow.

. The hydrides which may be used most suitably are calcium hydride, magnesium hydride, sodium hydride, potassium hydride and lithium hydride. I prefer to use calcium hydride primarily because it is most economical and easy to handle.

It has been suggested previously to introduce various compounds or mixtures into oil wells for a variety of purposes. In some instances it is even possible that various gas generating devices have been proposed in an effort to overcome the difficulty above noted in connection with flowing wells.

In order for a particular gas to be effective as a lifting agent in wells of this type it must have certain special properties. It must be stable over the range of temperatures and pressures encountered. This is required stability up to 1000 pounds per square inch pressure and 150 F; temperature. It must be a gas over this range, that is, it must not be liquefied under these conditions.

It must berelatively non-toxic, non-reactive with either p'orou's'in the same way that an effervescent tablet may I l the oil well fluids or the metal pipe, and relatively insoluble in the oil well fluids. These specifications limit the choice of-gases considerably. It is, for instance, well known to generate carbon dioxide in oil wells by the action of an'acidic substance on a carbonate. However, carbon-dioxide is liquefied at pressures of less than pounds per square inch and is also very soluble in water. Thus, it will not yield a gas at the conditions found at the well bottom. The generation of acetylene from calcium carbide is also a well known procedure but acetylene is not satisfactory for the purposes of this invention due both to its solubility in oil well fluids and to its tendency to decompose with explosive violence when subjected to elevated pressures and temperatures.

I am also aware that the production of hydrogen in oil wells has been proposed by the use of the action of sodium hydroxide on aluminum. This reaction has been the subject of several patents. The reaction generates considerable heat and as such has been used to melt paraffin deposits from oil well tubing. The use of this reaction has several disadvantages. The caustic is corrosive to. any container and diflicult to store. Introduction of the reactants into the oil well is diflicult, the reaction is hard to control, and the reactants must be mixed just prior to use, or complicated means taken to prevent premature reaction.

In the practice of my process, hydrogen is generated at the bottom of the well tubing by the action of water on a metal hydride, preferably calcium hydride. The metal hydrides are, in general, dry solids that are easily packaged. Calcium hydride is available in a variety of forms including tablets and powder. It is easily handled and with the exception of its reactivity with water it is relatively stable. The products of the reaction are hydrogen and calcium hydroxide. These materials are relatively noncorrosive and can be easily flushed from the well.

Specifically, my invention is practiced as follows: An alkali metal hydride or alkaline earth metal hydride in a suitable state of subdivision is encased in an essentially cylindrical container. Said container may be constructed from virtually any material that is soluble in either the oil well fluids or water, provided that the material has satisfactory physical properties for the use intended. As specific examples may be mentioned waxes, such as paraflin wax, microcrystalline waxes, or blends of waxes. Water-soluble materials that have been found satisfactory include gelatin, high molecular weight polyalkylene glycols and polyvinyl alcohol. My preference, for reasons explained subsequently, is to use a water-soluble encasing material. The essential requirements are that the container must be stable at the usual conditions encountered in storage, soluble or dispersible in either oil well fluids or water so that it breaks up and flushes from the well without clogging the well tubing or fittings, is physically strong enough to stand filling, shipping, and handling, and tough enough to withstand the abrasion and shock encountered when the container is dropped down the well.

The previously specified hydride, encased as described above, in a cylinder small enough to pass through the oil well tubing is introduced into the well head and allowed to fall to the bottom of the well. Upon reaching the bottom of the well the casing disintegrates due to the action of the oil well fluids or water and the hydride is released. The hydride then reacts with water present to generate hydrogen which re-activates the well through its density-reducing action in rising through the tubing. Most wells of this type contain water at the bottom of the hole as well as oil. However, if water is not known. to be present it may be introduced in sufficient quantity to activate the hydride prior to introduction of the container of hydride.

In most flowing wells the cognate fluid emerging from the well includes water. Thus, the past history of a well which has ceased to flow obviously will indicate whether or not there is water present in the bottom of the well. If in doubt, of course water could be added at the well opening. In any event the usual probing devices could be employed to determine at what depth water stands in the well and at what depth oil stands in the well. Such data are also of significant value in determining the approximate amount of calcium hydride or the equivalent used to start flow action. Needless to say, the amount of water at the bottom of the well is not critical and should be more than sufficient to cover generously the capsules or equivalent material injected into the well. Reference in the claims to a temporarily non-active well having a measurable quantity of aqueous fluid at the well bottom refers to either water or brine and merely to an amount suflicient for the purpose intended, i. e., disintegration of the capsule and reaction with the hydride. As previously noted, there is no critical relationship whatsoever in this phase of the operation.

If the hydride, such as calcium hydride, is encased in an oil-soluble water-insoluble material and is dropped into a well in which water is standing at the bottom it is obvious that if the encasing material has not disintegrated or dissolved during the downward passage through the oil depth it probably will not do so on reaching the water level. Since water is almost invariably present, or can be added as noted, my preference is to use a casing which is water-dispersible or preferably water-soluble. My preferred material is polyvinyl alcohol.

In the treatment of a well in which there is no water at the bottom, and no water has been added, it is obvious the hydride may be added in an oil-soluble capsule such as one in which paraflin wax forms the outer coating. Such capsule can be allowed to deteriorate by simply resting in the bottom of the well and then the evolution of hydrogen can be started by the mere addition of water. This involves no difliculty in any way and can be handled with the usual devices available at the well head.

Since the amount of reagent required varies with a number of factors as, for example, the height of the fluid in the well and the negative pressure at the bottom of the well, i. e., the diflerential pressure between the hydrostatic head and the reservoir pressure, it becomes apparent that considerable calculation is required to determine even an approximate charge. Actually, since the material used, for example, calcium hydride, is comparatively inexpensive it is usually more expedient simply to make an initial charge using a comparatively minimum amount of the material, and note whether the desired results are obtained or if not, use the usual probing device to determine how high the effluent fluids rose in the well. The usual way to do this is to prepare a convenient charge containing approximately 2% to 3% pounds of calcium hydride. This can be placed in commercially available polyvinyl alcohol casing having a diameter of approximately 1 to 1%. This will make a sausage-like charge having a length of 2 to 3 feet, or thereabouts. One or two of these charges can be dropped in a well at a comparatively small cost. In the majority of cases it is quite probable that even a single charge may be enough but, in any event, the use of two such capsules is sufficient to trigger-off and start most wells. In event the well does not start, the next step is to use a suitable probing device and determine how high the eflluent fluid goes in the well. Based on these data a second charge can be made which presumably will be sufficient to raise the efliuent fluid to the top of the well. If such charge does not raise the efliuent fluid to the top of the well and the well does not kick-off and flow, then some other factor is involved other than what has been embodied herein.

The following examples are included purely by way of illustration and are not to be construed as limiting the scope of the invention.

Example 1 quarts of water and 2 quarts of crude oil. There were 5 about 6 quarts of free vapor space above the liquid' col umn. A gelatin capsule containing 8 g'rams'ofcalc'ium hydride-was dropped into the topofthe apparatus and the gate valve closed. Within 20 minutes the"bo'mb had "fired and a pressure of 920 pounds per'square inch was developed.

Example 2"" A cylindrical shell was slush molded from a mixture of Carbowax 6000 and 15% xylene. This capsule was filled with calcium hydride andfffired in the mock oil well of Example 1. It tired in 18 minutes and generated a pressure of 350'pounds per square inch.

Example 3- A casing. of polyvinyl alcohol 1.25 inchesin diameter and 34 inches inlength was filled with powderedcalcium hydride-. The ends were closed by tyinga knot in the casing. This bomb. was droppeddown an actual oil well which had stopped flowing. After '30 minutes the master gate valve was closed and left shut'for minutes. Upon reopening the valve foam appeared at the tubing head and within 5 minutes the well was flowing steadily.

Example 4 A kick-off bomb of the type described in Example 3 was dropped down another actual oil well. This well had been reactivated by swabbing about two weeks previously, had produced about barrels of oil per day for a few days and then died again. The well was about 7,000 feet deep. This well had a gas pressure of about 250 pounds per square inch shut in. It was vented and no flow resulted. The bomb was dropped down the well and the valve closed. Five minutes later the well was vented again. It vented to almost zero pressure. After about one-half hour a slight increase in pressure was noted. After one hour there was a strong increase in pressure and the well began to produce oil. Flow increased steadily until the gauge on the tubing head showed 100 pounds with the one-inch bleeder wide open. After about one-half hour fragments of the bomb casing were flushed from the well head. They cleared the choke and bleeder without clogging.

Example 5 As an example of the qualitative calculations involved in the practice of the present invention, consider a typical well drilled to a depth of 4400 feet. The fluid level in this well when dead is around 1500 feet. The bottom hole pressure will be about 900 pounds per square inch and the bottom hole temperature about 90 F. The well has a 6-foot subsection below feet of perforated tubing at the bottom of the well. The production string, i. e., the pipe through which the well is produced, is 2 inches inside diameter. The total volume of tubing in this well is 335 cubic feet. There are 131 cubic feet of fluid in the well.

Calcium hydride releases 17.1 cubic feet of hydrogen per pound of CaHz. The critical constants for hydrogen are -239.9 C. and 12.8 atmospheres, which means that hydrogen cannot be liquefied at the conditions obtaining at the bottom of the well.

The bottom receptacle fitting, sometimes referred to as a sub in the well will hold about 0.5 cubic feet of water if filled. This water at 77 F. and 75 atmospheres pressure will dissolve about 0.01 cubic feet of hydrogen. This figure can be taken as a maximum since higher temperatures and lower pressures will obtain at the well bottom.

At 77 F. and 60 atmospheres pressure the oil Well fluids will dissolve about 4 cubic feet of hydrogen per cubic foot of fluid. If we require as an arbitrary figure that 100 feet of fluid column be saturated with hydrogen this would take about 36 cubic feet of hydrogen gas. Reducing these volumes to the pressure and temperatures of the well bottom gives a value of about 0.61 cubic feet 6 ofhydrogen gas at-900 pounds per' square inch pressure, and" 'Fi temperature. To produce a 10-foot' piston ofigas atthe'well bottom would require 0.875 cubic feet of gas at the same temperature and pressure. This gives a total volume of gas requiredof0.875 plus 0.61 plus 0.01 or 1.495 cubic feet. We can then assume that cubic feet of gas would be enough for the purpose. This volume reduced back to ordinary temperaturesandpressures amounts to 88 cubic feet of gas at 77 F. and at atmospheric pressure. This would require 4.7 pounds of calcium hydride to react with about one gallon of water. The sub in the well contains about 4 gallons of water-in thiscase and so there is more than enough water for both disintegration and reaction. This reaction gene'- rates a large amount of heat and so the solubility will be less and pressure greater than those taken above. The

general validity of these calculations'are attested to by the fact that when a bomb of the'type described in Example 3; preceding, containing 3.5 pounds of calcium'hydride was dropped down the described well, gas "generation and increase of well head pressure were observed and the well resumed flow in about one hour after introduction of the bomb.

Example 6 A cylindrical capsule, constructed of blended waxes, and filled with calcium hydride was dropped down a well which was known to be producing no Water from the formation. After 4 to 5 hours no reaction or pressure increase were noted. About 3 gallons of water were then poured into the well. After about one hour the well began to show a pressure increase and in about 5 minutes began to foam over into the slush pit. The main gate valve was closed and the well resumed normal flow through a choke into the flow line.

Since hydrides are comparatively heavy, for instance, calcium hydride has a specific gravity of about 2, there is no requirement in regard to the addition of a weighting agent. Needless to say, an inert weighting agent such as barium sulfate could be mixed with the hydride but as far as I have been able to determine this is unnecessary and ha no advantage. I

In light of what has been said previously, particularly in view of the examples which appear in the prior text, it is obvious the effectiveness of the present process depends on the fact that when hydrogen gas is generated or expands or moves upward in the perpendicular tubing, such action is energetic enough to be at least partially responsible in off-setting the hydrostatic head. This can be illustrated in the following way: If a line were one-third full of fluid and if this hydrostatic head were too great for the natural bottom hole pressure the well presumably would not flow. However, if porosity or foaming or ga evolution were to take place slowly so as to expand the volume of the fluid two hundred per cent, i. e., so as to fill the entire perpendicular tubing to the top of the well, the hydrostatic head would still remain approximately the same. In other words, the volume would be three times as great with the specific gravity one-third its original value. For this reason it is obvious that what has been said previously in regard to the upward rush of the generated hydrogen gas is in essence the eifective factor in the present process.

Having thus described my invention, what I claim as new and desire to secure by Letter Patent is 1. In the process of reactivation of a temporarily non-active well; said well being of the normally selfflowing type; non-activity of said well being due to the fact that the normal flow was interrupted by the hydrostatic pressure in the well piping being momentarily greater than bottom hole pressure; the step of introducing in the bottom of said well a disintegrable capsule containing a metal hydride selected from the class consisting of alkali metal and alkaline earth metal hydrides; permitting said capsule to disintegrate followed by reaction between water and said metallic hydride; the amount of metallic hydride in said capsule being sufficient to release enough hydrogen gas in the well piping to reduce the apparent density of the well fluid responsible for the hydrostatic head to a point less than the bottom hole pressure and permitting normal flow to resume.

, 2. In the process of reactivation of a temporarily nonactive well having a measureable quantity of aqueous fluid; said well being of the normally self-flowing type; non-activity of said well being due to the fact that the normal flow was interrupted by the hydrostatic pressure in the well piping being momentarily greater than bottom hole pressure; the step of introducing in the bottom of said well a water-disintegrable capsule containing a metal hydride selected from the class consisting of alkali metal and alkaline earth metal hydrides; permitting said capsule to disintegrate followed by reaction between water and said metallic hydride; the amount of metallic hydride in said capsule being sufiicient to release enough hydrogen gas in the well piping to reduce the apparent density of the well fluid responsible for the hydrostatic head to a pointless than the bottom hole pressure and permitting normal flow to resume.

3. The process of claim 2 wherein the hydride is an alkaline earth hydride;

4; The process of claim 2 wherein the hydride is'calcium hydride.

5. The process of claim 2 wherein the hydride is calciumhydride and the capsule encasing material is polyvinyl alcohol.

References-Cited in the file of this patent UNITED STATES PATENTS Lorenz Mar. 16, 1954 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, 1923, vol. 3, pp. 650 and 651.

Uren: Petroleum Production Engineering Exploitation (2nd Edit.), published 1939 by McGraw-Hill, New York, N. Y., page 94.

Claims (1)

1. IN THE PROCESS OF REACTIVATION OF A TEMPORARILY NON-ACTIVE WELL; SAID WELL BEING OF THE NORMALLY SELFFLOWING TYPE; NON-ACTIVITY OF SAID WELL BEING DUE TO THE FACT THAT THE NORMAL FLOW WAS INTERRUPTED BY THE HYDROSTATIC PRESSURE IN THE WELL PIPING BEING MOMENTARILY GREATER THAN BOTTOM HOLE PRESSURE; THE STEP OF INTRODUCING THE BOTTOM OF SAID WELL A DISINTEGRABLE CAPSULE CONTAINING A METAL HYDRIDE SELECTED FROM THE CLASS CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL HYDRIDES; PERMITTING SAID CAPSULE TO DISINTEGRATE FOLLOWED BY REACTION BETWEEN WATER AND SAID METALLIC HYDRIDE; THE AMOUNT OF METALLIC HYDRIDE IN SAID CAPSULE BEING SUFFICIENT TO RELEASE ENOUGH HYDROGEN GAS IN THE WELL PIPING TO REDUCE THE APPARENT DENSITY OF THE WELL FLUID RESPONSIBLE FOR THE HYDROSTATIC HEAD TO A POINT LESS THAN THE BOTTOM HOLE PRESSURE AND PERMITTING NORMAL FLOW TO RESUME.