US 2119563 A
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G. M. WELLS METHOD OF AND MEANS FOR FIJOWING OIL WELLS Filed March 2, 1957 gjgd June 7, 1938.
CONCRETE lNvENToR ofggef l/lls BY 4?/ M; @1547K ATTORNEYS Patented June 7, 1938 PATENT OFFICE METHOD 0F AND MEANS FOR FLOWING OIL WELLS George M. Wells, Upper Montclair, N. J.
Application March 2, 1937, Serial No. 128,561
My invention relates to a method of and means for flowing oil wells.
An object of my invention is to flow petroleum from wells which could not be flowed by methods available heretofore, and to increase the rate of flow as well as the length of time over which a. well will ow after it has been brought in, thereby increasing the total amount of petroleum recoverable from a well.
More particularly, my invention has as an object to obtain petroleum free from sand, by employing filtering means that prevents the petroleum bearing formations from being removed along with the petroleum, and which means also does not clog with sand so as to stop the flow.
An additional object of my invention is to provide a method utilizable in connection with wells that are drilled with a heavy circulating drilling uid that is retained in the well in a circulating condition when the well is not being flowed. n
'In drilling an oil well and preparing the same for flowing petroleum therefrom, the common practice is to drill down through the various formations until one or more strata are reached that contain petroleum that it is desired to remove. These strata containing the petroleum are generally composed of sand, shales or other porous material containing small voids. The petroleum generally occurs as a fluid saturating or at least partially filling the voids in the porous material. The petroleum in such strata is generally under a great pressure. As the petroleum is removed through the Well it flows under pressure through the porous formation towards the well. f
At all times during a drilling operation and subsequently except when the well is being flowed, it is necessary to have the well filled with a heavy viscous mud, termed drilling fluid, whichv is circulated by pumps. It is this circulating drilling uid that removes the strata cuttingsA that are cut away by the drilling tool or any other strata material that may be in the well due to slumng or cavings. .At all times, while the drilling fluid`is in the well, it is essential that the fluid should be kept in circulation in order to prevent any vstrata particles in the fluid from settling out. If a given critical velocity were not maintained, any strata particles in the fluid would be deposited at the bottom of the well and would have to be drilled out again.
When a petroleum bearing stratum is reached in the drilling, the weight of the column of the drilling uid in the well exerts a force which (Cl. 16S-21) acts in opposition to the pressure on the petroleum in the porous stratum, and as long as the drilling fluid is present, the petroleum is prevented from flowing through the stratum into the well.
In accordance with thecommon practice of flowing a well, the drilling apparatus is withdrawn after a petroleum bearing stratum is reached; the casing is then cemented, the well under-teamed and a pipe is inserted at the end of which is a screen having very small openings 10 which are intended to filter sand from the petroleum. The circulating drilling fluid is then gradually replaced by water and the pressure ex erted against the petroleum in the porous stratum will be progressively lessened because 15 of the lower specific gravity of the Water. This reduced pressure is generally such as to permit the petroleum to flow into the well through the porous formation.
The sand of the porous stratum disintegrates 20 or moves under the flow of the petroleum. Before the flow is started, the pressure exerted by the drilling fluid holds the porous sand formation in its original position However', when this pressure is lowered by replacing the drilling fluid with water, and during the time the petroleum is flowing through the stratum, there is nothing to hold these formations in position. There is often an initial caving of the sand against the screen, or a bodily movement of a large mass of sand mixed with the mud that has penetrated into the formation, which moves against the screen. Particularly is this the case when the petroleum is under great pressure and when the initial velocity of the petroleum is relatively high.
When petroleum flows through the stratum to the well, it also carries sand with it, and if the screen has not become clogged by an initial caving, it is often clogged by the sand flowing with the petroleum. As a result, the flow of petroleum 40 through the screen and into the-pipe is considerably reduced or stopped entirely. Numerous instances are of record in which-a Well does not Y flow at all, or flows freely at first followed by a quick decrease until the'flow is small or nil.
If the openings in the screen are made suiflciently small so as to filter out most of the sand, the small openings are easily clogged with sand particles and mud. During the drilling operation a certain amount of the drilling fluid penetrates the porous formation, and the mud particles ofthe drilling fluid, which are in the formation, are not removed by the washing operation. As the petroleum moves into the well through the stratum, it brings with it these fine LL n Before a ltering action can he estao 'shed by the l r ger particles the screen openings generally will have been cut to such a large size ever t larger sand particles are restrained a ld there is no filtering action whatsoever.
lin screens having larger openings peirron leurs Aflows at a greater velocity and carries a larger amount of sand particles through the "lgs, both of which augment the cutting network ci sand. particles could be built up around the screen by employing a screen having large openings which permits the mud and small particles to pass through the screen initially and exclude only the larger sand` particles. ln such instances, however, by the time such a condition has been established, the quantity of sand which has passed through .the screen is usually so great that the screen is cut so that the openings are not able to even hold bacia the larger sand particles. Y
-he employment oi a screen as a filtering medium, therefore, gives rise to a dilemma in which the use oi openings of any size have such disadvantages as to render a screen a very undesirable filtering means as compared withthat available in accordance with my invention.
ln the usual prior practice, after a screen has become clogged, an attempt is iirst made to remove the screen by pulling it out and inserting a new screen. The sand in the formation, however, usually has become packed against the screen so tightly that the screen stlclis and cannot be removed. llf the well is to be nov/ed further or drilled deeper, it is necessary-to out out .the screen and remove it in pieces. This usually proves to be a tedious and expensive operation.
I have heretofore proposed a method of flowing an oil Well by placing iron or steel balls, or equivalent material, in the wel] to hold the porous l formation in position and prevent lt from caving. The balls also act as an effective filtering medium for excluding the sand from the petroleum. By that method, the well can be iiowedA at high rates over a long period of time, and petroleum obtained free from sand.
That method is particularly suitable when the petroleum bearing stratum is of relatively small depth. When the stratum is relatively deep the iron or steel balls tend to move down through the sand stratum until they are supported hy a firm material. In employing that method for owing petroleum from a. relatively deep sand stratum, a larger quantity of balls is necessary.
I have now discovered that all 'of the unobvi ous advantages of my previously proposed method may be availed of, and that the disadvantages thereof may be eliminated if the balls are confined by a perforated restraining means. By such a means the balls are held immovable in a ilxed position Within `the well and cannot move in the sand formation. The method is suitable in y process.
accordance the illust embodiment of my inyen .on sh wn in :e the Well is drilled to a petroleum bearing which it is desired to .low and the casing is cemented in accordance voti?. the procedure well understood the art. A pipe, closed the bottom having the lower end perforated, is partially ,lied w ii a sufficient quantity of iron or steel balls to 'lul the portion the pipe adjaw cent perforations the lower end and usually extend somewhat above the perioratlons. The pipe is then lowered into the well so that the perforated portion extends into the potro leum bearing stratum. The drilling is then gradually replaced by Water and because of the deoreased'pressure on the petroleum in the stratum, due to the lower spe c gravity of water, the petroleum begins to YElow in from the stratum, through the perforations, through the voids the balls, 'and up 'through the pipe.
lt is also possible to insert the perforated pipe into the well without the balls, and to pour the halls into the pipe alter it has been placed in the well.
The petroleum initially flowing 'from the formation when the v/ell is brought in usually car ries sand and mud with The particles of sand vary in size, and the larger particles become entrappecl in the voids in the balls. As the voids "become filled with the larger sand particles, these particles in turn hold back smaller sand particles. This continues until a perfect itering network oi sand particles is formed in the voids of the balls, which holds back sand particles of all sizes. After the well has been flowing for a short time, this filtering network is established and is effective in holding back even the finest sand particles, and as a result the well flows clear of sand.
'During the initial flow after the well is brought in, While a filter of sand particles is being established in the voids of the balls, the ne sand and the mud is not held back and reaches the surface of the well. The mixture of mud and other fine particles, which would normally clog and seal the small openings in a screen, will have initially passed through the voids in the balls. All of the mud in the formation will have flowed out of the well by the time the flnal illtering network that excludes smaller sand particles is established. The initial ow of petroleum contains sand, but this is inconsequential as compared with the Aflow that is subsequently obtained free from sand.
In view of my explanation, it will be understood that materials of a relatively low specific gravity, such as gravel or crushed rocks, could not be successfully employed as a ltering medium; such materials are not heavy enough to be held in position in a perforated restraining means. Filtering materials having a specific gravity of the same order as the specic gravity of th'e sand particles would be moved, or even raised to the surface, by the flowing petroleum, because velocities of the petroleum which are suflicient to flow the sand particles through a strata are sufficient to flow material of similar specific gravity beingemployed as a filtering medium; By employing iron or steel balls as a filtering medium, I am enabled to flow the well free from sand, at an increased rate, and over a long period of time.
Because of the large number of balls and the many voids therein through which the flow of the petroleum is distributed, the petroleum flows through the voids at a relatively low velocity, andany cutting action of the sand that originally flows through the balls is minimized. Further, due to the hardness of the balls, they are not cut as readily as a screen. The flow of the sand is also arrested sufficiently before any cutting'` takes place that would interfere withthe action Ivhave described.
Other advantages are also obtained by using iron or steel balls. During the time the filter network of sand particles is being established in the voids of the balls, and subsequently during the continued filtering action, it is essential that the lter structure be preserved. Any movement of the balls would disturb the filter and release the sand in the voids of the balls. This, of course, is undesirable because the petroleum would not only contain this released sand, but also because the filter Vnetwork would be destroyedand would have to be re-establlished. Because of the high specific gravity of the balls their weight holds them firmly and securely in the perforated restraining means and they resist movement that would be imparted to material of less specific gravity by an unevenness in the pressure of the flow.
In accordance with the illustrative example shown in Figure 2 the oil well is provided with a lcasing that extends through a petroleum bearing stratum. At a suitable point in the casing, generally near the bottom but at any point in the petroleum bearing stratum, the casing is sealed by cementing a plug therein according to procedures well known in the art. The casing is then perforated above the plug and adjacent the petroleum bearing stratum. During the perforating and at all times prior thereto, the drilling fluid .is circulating and the weight of the fluid prevents the petroleum from entering n so through the perforations inthe casing. Iron or steel balls are then poured into the casing; they descend through the circulating uid and rest upon the cement plug, extending upwardly in the casing adiacentthe perforations and into the imperforate portion of the casing if desired. Water is then substituted for the drilling fluid and the pressure decreased in the usual manner; the petroleum will then begin to flow in from the stratum. It enters the perforations in the casing and then flows between the voids in the balls passing upwardly .out through the casing or through a center pipe that is often employed for that purpose. The sand which initially flows through the stratum with the petroleum` and enters the perforations in the casing will become lodged in the voids between the balls and a filtering network will be built up in the balls which will effectively eliminate the flow of further sand as has been described in detail heretofore.
drilling fluid as soon as the balls are inserted into the casing, and they will settle in position in the perforated restraining means. Filtering material having a lower specific gravity, for example, gravel and crushed rock, could not be inserted in the well in this manner against the ilow of the drilling fluid because the velocities of the drilling fluid which would keep strata material in circulation would also circulate such filtering material. A particular reason for keeping the fluid circulating at a velocity that will keep strata material in suspension, is to prevent it from settling in the voids of the balls before the well is washed and brought in. If the strata material settles in the voids, it is very difiicult to remove by washing.
Although the balls are heavy enough to be inserted against the velocity normally maintained in the circulating drilling fluid, nevertheless the balls are not so heavy as to prevent their .subsequent removal by a temporary higher velocity of the fluid specially introduced for that purpose.
In many instances a easing extends through a number of petroleum bearing strata. In accordance with my invention, a plug is cemented at each stratum it is desired to flow. The casing is then perforated adjacent the stratum and iron or steel balls are introduced as described above.
In accordance with my invention, it is possible to re-establish the flow in oil wells having clogged screens by perforating the screen and then introducing iron or steel balls to iill the screen and the tube inside thereof.
It is particularly desirable that as the well is brought in, the flow should be established in such a manner that it will continue uniformly over a long period of time, and not necessitate repeated adjustments or changes in the equipment used in flowing the wells. I found that the iron and steel balls employed in accordance with my invention accomplish this purpose admirably with much more uniformity and dependability of results than has been obtained heretofore.
By means of my invention it is possible to flow petroleum from a strata containing such fine sand that it has heretofore not been regarded as feasible to remove the petroleum therefrom by methods heretofore available. The filtering network provided by the balls and the sand entrapped therein, operates so effectively that an extremely fine sand stratum may be flowed, and
petroleum obtained from a stratum which has` heretofore been regarded as unowable.
The size of the balls may vary over wide limits depending upon the size of the well, the rate at which itzis to be flowed, the character of the formation, and the size of the sand. When the i sand particles are extremely fine I have obtained adjusted so as to be smaller than the size of the balls.
Heavy material other than iron or steel balls, having the capability oi' forming suitable voids may be used in my invention as an equivalent of balls, provided such material has the necessary high specific gravity in order that it may function in the manner pointed out heretofore. Such heavy material has a specific gravity of twice. or even two and one-half times, the specific gravity of the formation. Such material will preferably have a specific gravity of sin, or even seven to eight. Other metals, such as lead, or alloys having the prerequisite speciiic gravity may be used. Other heavy materials suc-h as ores of the requisite specific gravity and hardness may be employed.
The shape of the material may also vary. Material having a uniformity coemcient of substantial unity yis preferred. Cl@he volume of the voids in such material will be a maximum and the voids will be uniformly distributed. This permits the largest quantity oi petroleum 'to 'flow through the voids and due to the uniformity and even distribution of the voids the filter network of sand particles will be formed more readily. The surface need not necessarily be spherical and by the expression void-forming subdivided material used hereinafter, i refer to any material, which when brought together,` will leave suitable voids between the individual pieces of the material. A subdivided material having a uniiormity coemcient of unity represents the ideal.
it will be appreciated that many other modifications may be made in the exact procedure of flowing a Weil in accordance with my invention, depending upon the type of formation and the condition of the well at the time the flow isstarted. All such procedures in which void-forming material of a high specific gravity is introduced in a well and retained in position therein are intended to be Within the scope oi my invention, as set forth in the following claims.
1. In an oil well, an apparatus for flowing petroleum from the well and for maintaining the ilow against stoppage comprising a. rigid perforated restraining means in said oil well adjacent the petroleum bearing stratum thereof, and a void forming sub-divided material held in said restraining means and adjacent said perforations, said void forming material having a speciiic gravity of at least twice the specic gravity of the petroleum bearing stratum, whereby said void forming material is held by the action of gravity in said perforated restraining means and is undisturbed in its ltering action by petroleum iiowing through said void-forming material at a velocity that normally causes sand to flow with petroleum.
2. In an oil` well, an apparatus for flowing petroleum from the Well and for maintaining the iiow against stoppage comprising a rigid perforated restraining means in saidoil Well adjacent the petroleum bearing stratum thereof, and ironA balls held in said restraining means adjacent said perforations whereby said iron balls are held by the action of gravity in said perforated restraining means and are undisturbed in their illtering action by petroleum owlng through the vvoids aiiaeee in said iron balls at a 'velocity that normally causes sand to ow with petroleum.
3. In a method of flowing an oil well drilled to a petroleum bearing stratum and containing a circulating drilling iluid, the steps comprising inserting into said well within a rigid perforated restraining means, a void-forming sub-divided material having a specific gravity of at least twice the specific gravity of the petroleum bearing stratum, and then washing said well to remove the drilling iiuid, whereby said material is restrained against movement in the well and tilters the petroleum flowing therethrough.
e. In a method of flowing an oil well drilled to a petroleum bearing stratum and containing a circulating drilling fluid, the steps comprising inserting iron balls into .said well within a rigid perforated restraining means, and then washing said well to remove the drilling fluid, whereby said iron balls are restrained against movement in the well and lter the petroleum flowing therethrough. y
5. lin a method o flowing an oil well drilled to a petroleum bearing stratum and containing a circulating drilling i'luid, the steps comprising inserting into said well a perforated restraining means and a void-forming sub-divided material having a specic gravity of at least twice the specific gravity of the petroleum bearing stratum, which material is held in said restraining means, and then washing said well to remove the drilling uld, whereby said material is restrained against movement in the well and filters the petroleum flowing therethrough.
6. Themethod of flowing an oil Well which contains a rigid circumferential restraining means and in which a drilling uid is circulating,
the steps ycomprising sealing said restraining means adjacent a petroleum bearing stratum, perforating said restraining means, introducing thereinto a void-forming sub-divided material having a specific gravity of at least twice the specific gravity of the petroleum bearing stratum, and then washing said well to remove the'drilling uid, whereby said material is restrained against movement in the well and fil-