GB2169018A - Apparatus for producing viscous hydrocarbons utilizing a hot stimulating medium - Google Patents

Abstract

In a well completion apparatus for producing viscous hydrocarbons from a formation 12 comprised at least in part of unconsolidated sand particles the formation is thermally treated to enhance the flowability of the viscous hydrocarbons. The resulting hydrocarbon mixture together with sand particles, is passed through a filter 28 in which sand and other solid particles are retained. The latter can be periodically removed from the well and cleaned of solid matter. The filter 28 has an inner filter stage comprising a compressed mass of metal fibres, and an outer metal sheath having openings of a greater size than the passages through the inner mass of metal fibres. A plurality of lateral braces 23 extend from an inner perforated conduit 21 and divide the filter 28 into discrete segments. <IMAGE>

Description

SPECIFICATION Method and apparatus for producing viscous hydrocarbons utilizing a hot stimulating medium Production of bitumen from tar sand, or heavy crude oil from sandy substrates, embodies a number of problems which arise as a result of the viscous nature of the hydrocarbon itself.

This is particularly true at low temperatures which tend to reduce the level of viscosity.

In the instance of tar sands for example, to release the bitumen from the confines of the formation by way of a producing well, it is usually necessary to thermally stimulate the formation. Thereafter, with the flowable bitumen released, an aqueous emulsion or mixture is formed. The latter is then urged under pressure to the well head where the bitumen can be demulsified and subsequently upgraded.

The present method and the apparatus herein described, are applicable to producing a hydrocarbon fluid such as a bitumen mixture from tar sands. They also apply to production of viscous crude oils and even gas from a formation which is characterized by an amount of unconsolidated sand and other solid particles such as clay, in its composition. In either instance, whether the product be liquid or gaseous, as it leaves the confines of the unconsolidated formation it will convey with it sand particles of different sizes. These particles, if carried into the well completion or producing equipment, have a tendency to accumulate and pack. Further, if not accounted for, they will ultimately plug passages and ports in downstream processing equipment.

To simplify the following discussion, bitumen will be referred to as the produced hydrocarbon. The product formed by heating a bitumen containing substrate or formation with a stimulating medium such as steam, comprises primarily a hot aqueous mixture. Although said product could be considered as being an emulsion, depending on a number of factors it will be hereinafter referred to as an aqueous bitumen mixture.

One proven means for providing thermal stimulation of a formation is by the injection of a heating medium in either liquid or gaseous state. This medium, at an elevated temperature and under pressure, with or without modifying chemicals, is forced by way of an injection well into the formation. The contacted bitumen is thereby rendered into a less viscous condition and released from sand particles thereby to form into the above noted aqueous mixture with steam condensate and the chemical additives.

Depending on the consistency of the formation, the thermal stimulation process can be carried out in a single well. However it can also be achieved through a plurality of wells disposed in a desired pattern of injectors and producers.

When a single well is utilized, pressurized injection of a heating medium such as steam is maintained for a sufficient time period to preheat the well and its adjacent environment.

Further heating will then induce separation of the bitumen from the sand and clay particles and cause it form into the aqueous mixture.

Thereafter, as pressurized steam injection is discontinued, bitumen is produced as a result of the elevated formation pressure which drives the flowable mixture toward the lower pressure well and its well head. The thermal stimulating medium used in the following description can comprise a hot liquid or vapor such as water or steam. To simplify the discussion only steam will be referred to.

In the instance of a multi-well pattern, the released bitumen mixture gravitates toward one or more producer wells from which it can be extracted as a result of formation back pressure.

In a productive formation where the bitumen containing layer is relatively narrow in depth, the use of one of more horizontal wells offers an economic expedient. In this type of well, similar to thermal stimulation of a vertical well, the flowing bitumen will carry with it sand particles from the unconsolidated substrate.

Over a period of time, after a horizontal well or a number of said wells have been actively producing, they will generate substantial quantities of sand particles as well as clay, along with the hydrocarbon product. Both materials are normally carried to the well head as herein noted, in the hot, produced mixture. Thereafter, any process for separating bitumen from water and other materials becomes increasingly expensive as a function of the quantity of solid materials present.

One standard procedure practiced by the prior art toward overcoming or minimizing the presence of undesirable amounts of solids in a bitumen liquid mixture, is by the use of judicially placed gravel packs. While the later can be useful as a filtering element in achieving their purpose, they nonetheless are subject to both chemical and/or mechanical degradation and deterioration. Such packs are further sus ceptibie to plugging when subjected to prolonged contact with a hot stimulating medium as would be the instance of a steam stimu lated operation.

The problem of excessive sand in produced bitumen mixture is further accentuated in the instance of horizontal production wells. The very nature of a gravel pack is such that the gravel cannot be readily introduced in a manner to completely surround the installed well liner. The use of gravel which has been pretreated to form a relatively compact yet solidified mass, has also been tried without success.

U.S.P. 4,434,054 discloses a filter capable of removing particulate matter from a hot bitu men mixture. The mixture is caused to transverse a bed formed of metallic fibers whereby a selected range of solid particles are separated from the fluid flow. In this form of filter, however, the filter bed is confined within a heavy walled passage or chamber.

To limit the presence of sand particles in produced aqueous bitumen mixtures, the normal horizontal well liner which receives the mixture from the adjacent formation, is provided with a series of constricted access openings. The latter ideally are of such a magnitude that they will readily pass flowable bitumen mixture. They will, however, deter entry of a major segment of the solid component particularly in the form of sand particles.

For these liner openings to be practical, in one embodiment they comprise a series of thin, elongated slots having an open width on the order of magnitude of about 0.8 mm. It has, however, become an operational reality that such narrow openings over a period of time become progressively more constricted.

Eventually the openings will become completely closed due to bridging or the accumulation and hardening of the sand and clay particles across their open areas.

In contrast, if the liner access openings are made too large, they will pass copious amounts of solid particles. The consequence of the latter is that particulates can form undesirable, rigid build-ups within the various well passages. Over a period of time these build-ups or accumulations will harden and completely block enough passages and ports to render the well and its liner inefficient, or at worst inoperable.

Toward overcoming this operational hazard in both vertical and horizontal wells for producing bitumen, as well as for producing crude oil and gas from unconsolidated sandy formations, the following well completion and filtering systems are disclosed. There is presently shown and described an apparatus and method for obviating the tendency of solid materials to cause blockage of access ports and passages within a well liner and its ancillary flow passages. Further, the filtering apparatus can be readily and quickly removed to be cleaned or rejuvenated for reuse.

The invention thus provides a method and apparatus for treating the flow of a hydrocarbon mixture or emulsion from a producing well in a sandy substrate by progressively filtering particulate matter therefrom.

The invention further provides means for readily injecting a thermal stimulating agent such as steam or the iike, by way of an injection well, into a hydrocarbon holding reservoir comprised at least in part of unconsolidated sand whereby to produce a substantially solid free product.

The well liner is characterized by a plurality of wall openings that will readily pass an aqueous bitumen mixture as well as other solids from the productive formation. The solids, however, rather than entering the various well passages are retained within the present filter system.

A removable sand filter bed in the filter system is designed in multiple stages that the multitudinous passages therein will preferably pass only flowable fluids as well as smaller sized sand particles to the well head. Further, the bed will conduct a hot stimulating medium such as steam or hot water from the inner side of the filter system to the surrounding substrate or soil without sustaining thermal damage.

The invention still further provides a well completion, and particularly a well liner assembly adapted for injecting a thermal stimulating agent such as steam by way of a well liner into a tar sand substrate. The well liner includes an outer, pliable wall which is characterized by a limited open area defined by a series of discrete wall openings. The latter are such that they will readily pass hot aqueous bitumen mixture as well as some of the solid particles. The solids however, rather than entering the liner's liquid flow passage, are entrapped and retained within the filter bed.

The filter bed is fabricated of such a density and character that its multitudinous passages will allow the hot pressurized stimulating medium to pass outwardly into the substrate. It will further conduct the flow of a bitumen emulsion in the opposite direction during a producing phase.

The well completion includes an elongated perforated liner which registers in a borehole formed within a hydrocarbon producing substrate or layer. The liner can be at a vertical or a horizontal disposition to most effectively receive a flow of a bitumen mixture which has been formed by treating the productive layer with a hot stimulating medium.

A stimulant conductor which carries hot water or pressurized steam is positioned in the liner to define an intermediate passage.

Said conductor is removably received within the liner and at least partially supports a filter bed therein for receiving and treating a solids carrying flow of hydrocarbon mixture.

The filter bed extends outwardly, having its periphery contiguous with the liner wall. It is comprised of randomly disposed metallic fibers such as steel wool, which are compressed and held to a desired density thereby forming multitudinous passages through which stimulant flows and through which at least a portion of the particle carrying mixture will flow.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional elevation of a horizontal well of the type contemplated.

Figure 2 is an enlarged cross-sectional view taken along line 2-2 of Fig. 1.

Figure 3 is an alternative embodiment of the invention shown in Fig. 2 as applied to a vertical or conventional well.

Figure 4 is a cross-sectional view taken along line 4-4 in Fig. 3.

Referring to Fig. 1, in one embodiment a well completion 10 of the type contemplated is illustrated in position within a well bore 11.

Said well bore 11 is formed in a generally horizontal disposition while passing through a productive layer 12 holding a viscous hydrocarbon such as bitumen or the like.

The well upper end is communicated with the surface 13 and can be initially drilled in a vertical disposition, or at an angle to the surface 13.

Following normal practice, well bore 11 is provided for at least part of its length with a series of casings 14. The latter are connected and extend downwardly toward the productive or tar sand holding layer 12. The upper or producing end of the well completion is provided with a well head 16 which will be described in greater detail herein.

The well completion is comprised primarily of a liner assembly 17 which is inserted through the casings 14 and supported by a liner hanger 15. The liner assembly 17 is slidably registered in well bore 11 to establish its position in anticipation of a producing operation.

Liner assembly 17 as shown, is comprised in one embodiment of an elongated tubular outer casing or sleeve member 18 having a sufficient wall thickness to withstand the subterranean conditions normally encountered when tar sands are thermally stimulated.

Sleeve 18 is disposed contiguous with the walls of the well bore 11 or will be in contact with said bore after a producing operation commences.

The outer casing or sleeve 1 8 is generally formed of elongated steel tubing, a segment of the walls of which are provided with a series of access openings such as slots or holes 19. These perforations will be formed along that wall section which resides in productive layer 12 and when in the slot configuration can extend either longitudinally of the casing, or circumferentially thereabout.

Liner assembly 1 7 is provided with a sand filter comprised primarily of elongated perforated conduit 21 which is surrounded by a filter bed 18. Conduit 21 in one embodiment comprises a length of continuous tubing or pipe which extends longitudinally through the liner sleeve 18, having a series of openings 22 formed in the wall thereof. Rather than being in the form of a continuous conduit, conductor 21 can comprise a series of discrete pipe lengths which are coupled into a unit defining a perforate surface.

This internal conduit 21 functions in two capacities. First it serves to conduct pressurized thermal stimulant from well head 16 at surface 13, down into liner 17 Secondly the conduit, being in heated condition, serves to maintain the temperature of produced mixture fluid so that it can be extracted from the well.

In the shown embodiment, conduit 21 is supported along its length by a plurality of longitudinally spaced ribs or lateral brace members 23. The latter are disposed within the annular chamber formed by liner 18 and conduit 21. The braces function to position and support the spaced apart filter elements, not only while they function, but also when they are being transferred to or from the liner.

Lateral braces 23 as shown are shaped to permit central conduit 21 to be readily slid in and out of liner 18 as needed. The braces include a body or split collar 24 which fits about and is fastened to central conduit 21.

To permit an operable relationship between the respective support braces 23 and the inner wall of liner 19, collar 24 is provided with a radial element, or a plurality of radially spaced arms 26. Each arm is formed, or provided at its remote end with a skid-like appendage 27 having upturned edges to facilitate movement thereof through liner 19. The diameter of brace 23 as determined by the arm remote ends, is such that normally two of the skids 27 are in supported contact with the liner lower wall thereby maintaining conduit 21 substantially concentric relative to linear 19.

The longitudinal spacing between adjacent braces 23 is sufficient to minimize the curvature of conduit 21 when the latter is at rest, and still permit it to be readily moved through and register in the liner. Operationally, when conduit 21 is inserted or withdrawn from liner 19, the respective braces 23 will slidably engage the liner inner wall to minimize bending of the liner, yet facilitate movement of the filter unit.

Between each adjacent brace 23, a filter segment is delineated which in turn is provided with a filter bed 28. The latter as noted, is formed of a filter media or material comprised of randomly disposed and compressed metallic fibers which define multitudinous passages therethrough. Filter bed 28 can consist in one embodiment of a layer of the desired metallic filter media which is wound onto conduit 21 between the adjacent braces 23, thereby defining an inner filter stage.

In a preferred embodiment of the filter, a cylindrical bed or rigidized core comprises a preformed and compressed mass of the randomly disposed metallic fibers. With this arrangement, the filter core, because of its firm condition, can be slidably registered onto and along the peripheral surface of conduit 18, individual segments thereof being separated by a lateral brace 23.

The density of a filter bed 28 deemed to be appropriate for use in a particular environment, is determined in recognition of the consistency of the sandy substrate. It is appreciated that for each well site, the make-up of the formation will differ both as to the volume of the various elements, and as to the size of sand particles predominant in the formation. Thus, to provide the maximum degree of sand filtering action, the metallic filter core or bed 28 is fabricated to a desired density. Thus, the respective inner and outer filter stages will function most cooperatively and effectively.

Filter bed 28 outer stage 32 affords the dual function of establishing a thickness of sand filtering material, and also provides a durable surface along which the filter can be slid as it is forcibly inserted or removed from a well liner or casing 18. Said filter outer stage 32 is preferably formed of a screen-like structure having a sufficiently large mesh to provide the necessary filtering and partial confining action. Said stage, however, must be durable enough to withstand expected abrasive deterioration.

In any instance, outer stage 32 of the filter will normally be disposed contiguous with and preferably in rubbing contact with a well liner 18 in anticipation of a stimulating and a subsequent producing action on the well.

In an alternate embodiment of a well into which the disclosed sand filter can be incorporated, Fig. 3 illustrates a vertical well 40 which is formed into a productive substrate or formation 41. The latter as herein noted, can constitute a relatively short distance. Well 40 is thus provided as are most wells of this type, with a series of elongated casings 42 which traverse the overburden 43 to productive layer 41.

The lower part of casing 42 comprises an elongated tubular liner 44 which extends through at least part of overburden 43 and into the productive layer 41.

In the normal manner, weilbore 46 is initially drilled through both the overburden 43 and the productive layer 41, being of a sufficient diameter to receive lower casing or liner 44.

The latter can comprise the normal type of well casing which is supported by a hanger 47, and can be at least partially cemented in place.

Casing 44 can be initially provided with a series of wall ports through which hydrocarbon emulsion will subsequently flow after stimulation. Alternately, the casing can be perforated along its length which lies in productive layer 41 after the casing has been set into place.

The well completion, as shown, includes a well head 48 at the upper end which is provided with valve means 49 and 51 to regulate injection of the hot stimulating fluid, and the production of the flowable hydrocarbon emulsion.

The removable filter unit 50, as shown, is comprised of an elongated tubular conductor 52 similar in structure to the tubing utilized in the foregoing illustration of the invention.

However, in the present arrangement, since well 40 is disposed substantially vertically, conductor 52 need not be as flexible or subjected to bending as would be the instance in a horizontally aligned well.

The tubing or conductor 52 is provided with a series of perforations 57 for the length thereof which lies within productive layer 41.

These openings are adequate to permit the outward discharge of stimulating fluid whether the latter be steam or hot liquid, and the subsequent ingress of the flowable hydrocarbon mixture.

The outer surface of conductor 52 is provided with a series of adjacently positioned filter beds or cores 54 disposed one above the other. Each core 54 is separated one from the other by a metallic divider 56. To assure the downward flow of the bitumen mixture, rather than have the latter pass through the length of the aligned filter cores 54, the respective separators 56 are conical in shape.

They will thereby direct flowing hydrocarbon emulsion through the conductor openings 57 to permit a gravity flow of the emulsion into sump 58 at conductor 52 lower end.

While not presently shown, conductor 52 can be provided with an outflow conduit which in turn is communicated with the suction side of pump means whereby the hydrocarbon emulsion can be withdrawn from sump 58 as it is accumulated. Hot stimulating medium which passes through conductor 52 will maintain accumulated emulsion in sump 58 in heated, flowable form.

Each filter core or segment 54 is preferably premolded in cylindrical configuration having upper and lower contoured surfaces. The latter are adapted to mate with the corresponding surfaces on the next adjacent core, and to receive the above noted conical dividers 56 therebetween.

Each core segment 54, as herein noted, is comprised of randomly disposed preformed metallic fibers which are sufficiently compressed to define the inner filter stage tortuous passes through the filter segment. These passages are capable of filtering out sand particles within a particular size range.

The periphery of core 54 segment is provided with an outer filtering stage in the form of a screen-like member 61 having openings therethrough. At the latter, sand particles, generally of a larger size than those which are filtered out during the inner filter phase, are filtered out.

As shown in Figs. 3, and 4, when filter assembly 59 is removably registered within well casing 44, the casing and conductor 52 will be disposed substantially concentrically.

Thus, incoming hydrocarbon emulsion will be uniformly filtered from all directions as it is urged toward the lower pressure in conductor 52.

Functionally, and referring to Figs. 1 and 2, the generally horizontal well 10 can be operated primarily on a continuous basis when it is utilized in conjunction with other producing wells. However, when utilized by itself, it will function on a push-pull cycle whereby it is alternately subjected to stimulation and producing steps.

As herein noted, well liner 17 is initially registered in a preformed bore 11 within the productive formation 12. The well liner 17 is placed by setting the surface casing 14 into the wellbore. The bendable liner 17 is then urged through the surface casings and into wellbore 11 until it extends to the remote end of the latter.

Initial installation is usually facilitated by plugging the forward end of liner 17 with a suitable closure to avoid clogging the liner by formation segments picked up during the insertion step. Further toward facilitating the initial insertion, filter assembly 28 can be prepositioned into liner 17 as the latter is being inserted into the wellbore.

Alternatively, since filter assembly 28 is designed to be slidably removable from liner 17, it can be registered in the latter subsequent to the setting and the fixing of the liner 17 in place.

As with any push-pull operation in a thermally stimulated well, hot stimulating media is communicated with either the well head valves 36 and 37 such that both liner 18 and center conductor 21 of the completion, will receive a pressurized heated steam flow. During this preheat period, steam introduced under pressure, will progressively penetrate the formation surrounding the well, thereby to fluidize the otherwise viscous hydrocarbon and converting it into a flowable emulsion.

When a sufficient time has elapsed, the preheating step is discontinued and steam will be introduced only by way of valve 37 through conductor 21. Steam flow through valve 36 into the annulus will be discontinued. This secondary heating step will be followed by complete discontinuance of steam injection to depress the pressure within the liner 17. However, a minimal low pressure steam flow through conductor 21 will serve to maintain the decreased viscosity of the flowable hydrocarbon mixture or emulsion such that it can be withdrawn to the well head 16.

The heated flowable emulsion will gravitate from the immediate surroundings of the horizontal well to enter the liner openings 19 and contact the outer stage 32 of the filter bed 28.

In this outer or filtering stage 32, larger sized sand particles will be intercepted and caused to accumulate about the filter openings. However, the bitumen or hydrocarbon flow will continue through the filter to enter the inner filter stage 31. In the latter, the smaller sized sand particles will be intercepted and removed, thereby permitting a substantially particle free hydrocarbon mixture to enter the center conduit of the liner assembly.

Since the latter is still heated by a minor inflow of steam at reduced pressure, hydrocarbon emulsion will maintain its fluid state and thus be removed in condition to be pumped to well head 16.

At such time as the filter becomes sufficiently burdened with sand particles to reduce its efficiency, the entire filter assembly 28 is withdrawn from well liner 17 for rejuvenation.

This latter operation is achieved by removing the well head 16 such that the filter assembly can be withdrawn in a manner to avoid or minimize damage to sand packed filter segments.

As the filter unit is withdrawn, the respective supporting shoes or braces 23 will contact the liner wall to reduce the damage or the abrasive action to the surface of the filter and yet accomplish the removal from the well liner.

Rejuvenation of a sand clogged filter can be achieved with the filter beds or cores 31 maintained in assembled condition about conduit 19. Alternately, the individual filter segments, as well as the intermediate braces 23 can be removed from conduit 19 and individually treated to remove the accumulated particles.

After being cleared of sand, the now rejuvenated filter cores 20 are again registered about center conduit 19 together with the spaced apart braces 23. The filter is now in condition to be again inserted into well liner 1 7 and production operation continued.

Claims (10)

1. Well completion apparatus for a borehole formed into a subterranean formation comprised in part of unconsolidated sand particles which releasably retain a viscous hydrocarbon material, the latter being released from said formation in response to thermal stimulation through contact thereof with a hot medium, said well completion apparatus including: a liner positionable in the borehole, a filter removably positioned in said well and adapted to receive a fluidized flow of the viscous hydrocarbon material from the formation, which flow carries with it varying sized sand particles, said filter comprising:: an elongate perforated conduit extending coextensively of the well and communicated at one end with a pressurized source of the hot stimulating medium, a cylindrical filter bed depending from and surrounding said elongate conduit and defining inner and outer filter stages, said inner filter stage including a mass of randomly disposed metallic fibers which are compressed to form tortuous passages therethrough of a size capable of passing said fluid ized hydrocarbon flow while deterring passage of said sand particles which fall within a predetermined size range, a metallic sheath enclosing said inner filter stage and having openings therein capable of passing the flow of hydrocarbon therethrough while deterring the passage of sand particles of a greater size than those particles which are detained at said inner filter stage, and a plurality of lateral braces which extend from said elongate perforated conduit and are spaced longitudinally thereof to separate said cylindrical filter bed into discrete segments.

2. Well completion apparatus according to claim 1 wherein said metallic sheath comprises a metallic woven screen.

3. Apparatus according to claim 1 wherein the metallic sheath comprises a perforated metal cylinder.

4. Apparatus according to any one of claims 1 to 3 wherein said inner filter stage is formed of randomly disposed steel fibers.

5. Apparatus according to any one of claims 1 to 4 wherein said perforated conduit comprises a continuous flexible conductor, which is capable of assuming the contour of said wellbore as said filter is urged into the wellbore.

6. Apparatus according to any one of claims 1 to 5 wherein said lateral braces each include a body which depends from the elongate conduit and at least one radial element which extends outwardly from said body to a point adjacent the wall of said well completion apparatus.

7. Apparatus according to any one of claims 1 to 6 wherein said metallic sheath is disposed externally of said lateral braces.

8. Apparatus according to any one of claims 1 to 7 wherein said liner is positioned horizontally in said borehole, and said lateral braces support the elongate conduit relative to said well liner.

9. Apparatus according to claim 8 wherein said conduit is supported substantially concentrically of said well liner.

10. Well completion apparatus substantially as described herein with reference to the accompanying drawings.