GRAVEL PACK FOR PETROLEUM OR WATER WELLS

Abstract: Prefabricated gravel pack for petroleum and water wells are prepared by combining gravel (in the appropriate sizes or particle size mixtures), and binder in a slurry and then casting the slurry on a cylindrical form or mold. In order to provide enhanced integrity to the granular mass, a wire cage (354) is used as reinforcement for the molded product. The wire cage is placed around the mold and the slurry (352) cast so as to incorporate the reinforcement within the body of the resultant cured product. The mold can, thereafter, be removed leaving a free-standing, prefabricated gravel pack. In one of the preferred embodiments of this invention, a perforated or slotted pipe (350) is used as a form upon which the slurry is cast. This perforated or slotted pipe can be retained in the finished product and, thus, provide additional physical integrity thereto. The perforated pipe also provides a relatively smooth surface for the channel defined by the gravel pack.

Description: GRAVEL PACK FOR PETROLEUM OR WATER WELLS BACKGROUND OF THE INVENTION 1. Field of the Invention - This invention relates to a prefabricated gravel pack for petroleum or water wells. More specifically, the subject matter of this invention is directed to both a method for the prefabrication of a structural, reinforced, cohesive gravel pack and to the use of such gravel pack in either a petroleum or a water well. 2. Description of the Prior Art - It is appreciated by those skilled in the art that where wells are drilled in a sandy formation, the fluid extracted from the resultant well will often contain sand and other paniculate matter. In order to avoid the extraction of such sand from the formation, a variety of techniques and equipment have been developed to meet this potentially serious problem. The traditional method for filtering sand from a sandy formation surrounding the well, is to provide a gravel pack around the well casing and well screen. This gravel pack is, as its name suggests, formed by the filling space between the casing and well screen and the bore hole in the formation, with paniculate matter of varying particle size. This process of forming the gravel pack is critical to the integrity of this filter bed and to its effectiveness in the trapping of sand and other paniculate matter which are contained in the fluids withdrawn from the formation. Where, as a consequence of operation of the well, suction gradients are created along the length of the well screen, the withdrawal of fluid from the formation will be non-uniform and thereby potentially disruptive to the formation. The extent of disruption can cause localized depletion of the sand in the formation surrounding the gravel pack and when this occurs, the gravel pack, will collapse. Where the gravel pack has collapsed, the weE screen is exposed directly to the formation and, thus, any particulate matter which is suspended in the fluid, drawn directly through the weE screen into the weE. In order to prevent damage to the pump and other support equipment, the rate of fluid extraction must be reduced to minimize sand extraction from the formation and, thus, weE efficiency compromised. In order to overcome this type of problem, it has been suggested that a flow control pipe be provided which incorporates its own filter medium as an integral component of the suction control pipe (hereinafter "composite suction control pipes"). In order to achieve such integrity, the filter medium can be contained within two concentric pipes (U.S. Patent 4,014,387 to Fink), or simply bonded to the outer surface of a single slotted pipe (U.S. Patent 4,624,319 to Van der Borght). In either case, the integration of the filter medium on the slotted pipe results in the fabrication of a flow control pipe whose purpose is a reduction in the suction gradient over the length of the suction pipe. The suction control pipes prepared in the above fashion are typically used in existing weEs where the gravel pack has coEapsed or can be used in new weEs in combination with the traditional weE casing, weE screen and gravel pack. As is evident from the above, the coEapse of the gravel pack greatly reduces the surface area of the filter bed surrounding the weE screen. The composite suction flow control pipes described above, whrile effective in the filtration of particulate matter have, by design and of necessity, are much smaEer diameter than the gravel pack for which they are designed to supplement and/or replace. Accordingly, the efficiency of the weE is substantiaEy compromised where the gravel pack integrity is impaired. Since the gravel pack is dependant upon the stabiEty of the formation and the casing/weE screen for its physical integrity, impairment of either generaEy results in a partial coEapse of the pack. To the extent that aE sandy formations are unstable to a greater or lesser degree, the integrity of the gravel pack necessarily deteriorates with changes in the formation and when it does, there is Ettle of any warning of its faEure. Where such faEure does occur, damage can result to the pump and other equipment involved in the fluid extraction process. This problem of gravel pack integrity has persistence and been accepted as a natural consequence of sandy formation weEs. No solution to this problem has as yet appeared. OBJECTS OF THE INVENTION It is the object of this invention to remedy the above as weE as related deficiencies in the prior art. More specificaEy, it is the principal object of this invention to provide a prefabricated, reinforced gravel pack which is suitable for use in petroleum or water weEs. It is another object of this invention to provide a gravel pack of unitary construction which incorporates the physical and structural integrity of the casing and weE screen. It is yet another object of this invention to provide a gravel pack of unitary construction which retains its physical integrity even in unstable well formations. It is stiE yet another object of this invention to provide a method for the formation of a prefabricated, reinforced gravel pack. SUMMARY OF THE INVENTION The above and related objects are achieved by providing a method for the formation of a prefabricated, reinforced gravel pack. The unique gravel pack of this invention can comprise a perforated pipe at its core and an adherent, cohesive aggregate layer having a reinforcing mesh integrated into the body of a porous, cohesive aggregate layer. In an alternative embodiment of this invention, the gravel pack is formed on a mold core, which is subsequently removed, thereby leaving the self-supporting reinforced gravel pack which can be used with or without a liner. In the prefened embodiments of this invention, the aggregate size is chosen to provide a prefabricated body having a f ter gradient of decreasing resistance from the top to the bottom of the weE. This variation in resistance is based upon proximity to the weE pump, with the greater resistance to flow being more closely associated with the segment of the gravel pack closest to the pump, and the least resistance being associated with the segment of the gravel pack most distant from the pump. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a typical weE in a sandy formation. Fig. 2 is a typical weE in which the formation has eroded, thereby resulting in localized coEapse of the gravel pack. Fig. 3 is a perspective view in partial section of the prefabricated, reinforced gravel pack of this invention. DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS The foEowing description of some of the embodiments of this invention is made with reference to the accompanying drawings. Where an individual element of these figures is depicted in more than one figure, it is assigned a common reference numeral for simplification and understanding. Preliminary to detaEed discussion of the preferred embodiments of this invention, the foEowing definitions are provided as an aid to understanding. The term "weE" as used herein is intended as descriptive of the combination of the gravel pack (if any), weE casing and weE screen. The term "formation" as used herein is intended as descriptive of the strata which sirrrounds the weE and from which the fluid is to be withdrawn. The phrase "static water level" as used herein is intended as descriptive of the level of water in the formation immediately sunounding the weE prior to the onset of water withdrawal from the well. The phrase "dynamic water level" as used herein is intended as descriptive of the level of water in the formation immediately sunounding the weE, foEowing the onset of water withdrawal from the weE. The phrase "cone of depression" as used herein is intended as descriptive of the profile of the water level in the formation between the original static water level and the dynamic water level. The phrase "flow control system" as used herein is intended as inclusive of a suction control pipe, and the means associated with the pipe for withdrawal of fluid from the weE. Fig. 1 is Elustrative of a typical weE configuration cunently in use throughout the world. For the purposes of simplification of this discussion, it is assumed that the fluid to be extracted from the sandy strata is water, and that the water is under Ettle, if any, pressure. InitiaEy, a bore hole (101) is driEed in the water bearing sandy strata (103), the diameter of the bore hole being somewhat larger than the diameter of a casing (105) and weE screen (107) which are to be inserted into the bore hole (101). FoEowing completion of drilling, a casing (105) and weE screen (107) are concentricaEy positioned within the center of the bore hole (101) and the space (109) between the exterior waE of these tubular elements fiEed with gravel (111). A pump (113) and suction pipe (115) are then lowered into the channel (117) defined by the casing and weE screen unt properly positioned relative to the static water level (119) in the weE. The pump (113) is lowered to a sufficient depth to position the suction pipe (115) to accommodate a drop in fluid level (draw down) foEowing start up and initial operation of the pump. Under ideal conditions, the gravel pack (111) is effective to filter out sand as water is withdrawn from the sandy formation sunounding the weE. In practice, however, the operation of the pump creates suction gradients along the length of the suction pipe, with the suction forces being significantly greater toward the end of the suction pipe closest to the pump. As water is progressively withdrawn from the sandy formation, fine sand is also withdrawn untE the formation is "developed". The proper development of the formation sunounding the bore hole is, however, dependant upon certain assumptions; one of the more critical being that the rate of withdrawal of water is relatively uniform over the length of the suction pipe. Where a relative uniform distribution of suction forces is not achieved over the length of the suction pipe, the formation wiE not develop properly. Quite the contrary, where the suction pump is operated without regard to proper development of the formation, excessive amounts of sand can be withdrawn along with the water, thereby creating cavities in the formation. As is evident from Fig. 2, the creation of cavities (201) within the formation (203) causes the gravel pack (111) to coEapse, thereby creating discontinuity in the filtration of the fluid along the length of the suction pipe. Once the weE has been damaged in this fashion, it can be salvaged, however, the conventional suction pipe (115) must be replaced with one which has an integral filter, such as Elustrated in U.S. Patents 4,014,387 (to Fink) and 4,624,319 (to Van der Borght), both of which are hereby incorporated by reference in their entirety. Fig. 3 is an Elustration of the prefened configuration of the prefabricated gravel pack of this invention. It is understood that the prefabricated gravel pack illustrated in this figure would be similar in overaE length and diameter to the traditional gravel pack of the prior art. Under the appropriate circumstances, this prefabricated gravel pack could be used independent of the weE casing and/or weE screen. The prefened embodiment of this gravel pack contemplates a slotted tubular member (350) serving as a support for the "green" molding formulation (slurry) of aggregate and. binder. Preliminary to forming the slurry (352) on the outer surface of the slotted tubular member (350), a reinforcing mesh (354) is placed around the tubular member. The mesh is positioned above the surface of the tubular member, during the casting of the slurry. Sufficient slurry is used to completely cover the mesh. The prefened configuration of gravel pack contemplates approximately the same amount of slurry above and below the level of the mesh. The nature of the binder provided is selected for its exceEent adhesion to the aggregate and to the tubular member. Upon curing of the binder, the gravel pack is ready for use. The gravel pack is then ready for insertion with a bore hole in a sandy formation. A pump and suction pipe can then be positioned within the channel defined by the gravel pack. After the pump and associated suction control pipe have been properly positioned within the weE, the pump is activated. In order to properly develop the formation sunounding the weE, the pump is operated at a fraction of its desired capacity. In a typical instaEation, the initial start up, or operational capacity of the pump, wiE generaEy be in the range of 200 to 500 gaEons per minute (GPM) (depending upon the diameter and length of the suction control pipe).

Claims: CLAIMS 1. A gravel pack for a weE comprising a cohesive, reinforced porous pipe having an essentiaEy uniform diameter, an outer surface, a top end, a bottom end, a channel running from said top end to said bottom end and which is lateraEy defined by a porous, cohesive particulate mass, said porous mass comprising gravel of a predetermined particle size, or mixture of particle sizes, binder and reinforcing mesh, said mesh being embedded within and extending through said porous mass, the binder and gravel being present in said porous mass at a concentration relative to one another to form, upon curing, a cohesive particulate pipe with sufficient porosity to aEow for the controEed flow of fluid from the outer surface of said porous pipe into the channel and yet provide for filtration of particulate matter which may be suspended in said fluid. 2. The gravel pack of claim 1, wherein the binder is a synthetic polymeric resin. 3. The gravel pack of claim 2, wherein the binder is an epoxy resin. 4. The gravel pack of claim 2, wherein the particulate mass of the gravel pack binder is elastomer or a synthetic polymer compound with elastomeric additives. 5. The gravel pack of claim 1, wherein the reinforcing mesh is conosion resistant or plated with a conosion resistant material. 6. The gravel pack of claim 5, wherein the reinforcing mesh is stainless steel. 7. The gravel pack of claim 5, wherein the reinforcing mesh is fiber glass. 8. The gravel pack of claim 5, wherein the channel is of sufficient diameter to accommodate means for conveyance of fluid from the bottom end to the top end of said gravel pack.

Inventors: JACKSON RICHARD C, JACKSON, RICHARD, C.
Applicants: PATENT COMPANY, THE PATENT COMPANY
Application year: 1988
Main classification: E21B43
IPC codes: B01D29, B01D39, E21B43