REFERENCE TO PRIOR APPLICATION
- FIELD OF INVENTION
This application claims the benefit of U.S. Provisional Application No. 60/972,013, filed Sep. 13, 2007, which is incorporated herein by reference.
The present invention relates to a sand control system and a method for controlling sand production in a long horizontal or deviated well.
The art of completing wells to exclude solids particles produced by well fluids is commonly known in the literature as gravel packing. In many well completions, unwanted formation solids (e.g. sands, fine materials, and other debris) are produced into the well along with the production fluids. These solids are often undesirable and many methods of stopping these solids from flowing into the well whilst producing the fluids are well defined.
A common technique for controlling the production of particulates from a well is known as “gravel packing.” In a typical gravel pack completion, a well screen is lowered into the wellbore and positioned across the interval of the well that is to be completed. Particulate material, collectively referred to as gravel, is then pumped as a slurry down the tubing on which the screen is suspended. The slurry exits the tubing above the screen through a “crossover” tool or the like and flows downward in the annulus formed between the screen and the well casing or open hole, as the case may be.
The liquid in the slurry flows into the formation and/or the openings in the screen that are sized to prevent the gravel from flowing through them. As the fluid is drawn out of the slurry it dehydrates. This results in the gravel being “screened out” on the screen and in the annulus around the screen where it collects to form the gravel pack. The gravel is sized so that it forms a permeable mass which blocks the flow of any particulates produced with the formation fluids.
Gravel packing fills the annular space between the formation and a screen with a clean well-sorted sand or gravel. The gravel pack forms a volumetric filter that prevents fines from plugging the screen and sand from entering the well. It structurally supports the formation, and it prevents flow in the annulus between screen and the open hole. All of these features increase the completion's durability in weak and heterogeneous formations; however, conventional methods for gravel packing vertical wells are not suited for long horizontal wells.
One of the main problems with gravel packing, especially when long horizontal or inclined intervals are completed, is obtaining uniform distribution of the gravel along the entire completion interval and completely packing the annulus between the screen and the casing (in cased hole completions) or between the screen and the wellbore (in open hole completions). Incomplete packing of the interval resulting in voids/unpacked areas in the gravel pack is often caused by the improper dehydration of the gravel slurry into portions of the formation interval. This can occur because the pressure required to pump the fluid slurry into the production interval may exceed the fracture pressure of the formation, which results in the liquid carrier of the fluid slurry leaking off into the formation. Improper dehydration causes the formation of gravel “bridges” in the annulus before all of the gravel has been placed. These bridges block the transport of slurry past the bridge. This results in the insufficient placement of the gravel because gravel fails to fill the annulus downstream of the bridge. Subsequently, the portion of the screen that is not covered or packed with gravel is thereby left exposed to erosion by the solids in the produced fluids or gas and/or that portion of the screen is then easily blocked or “plugged” by formation particulates, that would have been filtered out of the inflow by a properly placed gravel pack.
Consequently, a number of methods for installing sand control in long horizontal (greater than 200 m) or deviated wells (greater than 80° from vertical) have been developed. One technique used to reduce the required pressure for gravel packing a long production interval that is inclined, deviated or horizontal is the alpha-beta gravel packing method described in U.S. Pat. No. 6,311,772 which is hereby incorporated by reference. In this method, the gravel packing operation starts with the alpha wave depositing a bed of gravel on the low side of the wellbore progressing from the near end (heel) to the far end (toe) of the production interval. Once the alpha wave has reached the far end (toe), the beta wave phase begins wherein gravel fills the high side of the wellbore, on top of the alpha wave deposition, progressing from the far end (toe) to the near end (heel) of the production interval. Shunt tubes may optionally be installed to allow an alpha wave to by-pass a bridge or obstruction so that it can continue past the blockage and propagate down the open hole to the toe.
A drawback of the alpha-beta method is that it is sometimes made impractical by logistical considerations including the uniformity of the completion zone, the availability of fluid storage, and the type of carrier fluid used. Gravel packs are more tolerant to non-uniform and heterogeneous completion zones but have installation risks that make them unsuitable for some long horizontal wells in low strength, unconsolidated formations. Additionally, fluid storage and handling volumes are limited for some rigs especially in remote locations. Conventional horizontal alpha-beta methods use low sand concentrations and require large volumes of clean fluid to deploy. The required volumes for alpha-beta packs increase in low fracture gradient environments, where low sand concentrations must be used. Conventional alpha-beta packing uses water-based carrier fluids. In cases where the reservoir section must be drilled with oil-based or synthetic-based drilling fluid, usually the open hole must be displaced to a water based fluid prior installing the screens and gravel pack. This increases the probability of a hole collapse or other hole problems that could result in an incomplete or failed gravel pack job.
Expandable sand screens (ESS) were developed for use in long horizontal wells as an alternative to gravel packs in combination with conventional screens. An example of a method utilizing ESS technology is in U.S. Pat. No. 5,901,789, which is hereby incorporated by reference. When expansion is large enough to eliminate most or all of the annular space between the formation and the expanded screen, annular flow can be limited or prevented. When the expandable screen is in continuous contact with the formation (referred to by those skilled in the art as “full compliant expansion”), it supports the formation and prevents disaggregation of the rock that could release fines and sand particles that might erode or plug the screen.
Because the amount of expansion that is possible with ESS systems, expandable sand screens do not always achieve full compliant expansion leaving an annular space between the screen and the formation. Any significant gap between the screen and open hole defeats some of the perceived benefits of ESS. Additionally, expandable sand screens have features that limit their application to formations with uniform grain sizes where they are most likely to be successful. Other ESS design parameters such as screen aperture sizes, mesh type, unexpanded screen diameters, and expansion ratios are also not robust to uncertainties in rock quality encountered while drilling long lateral sections.
- SUMMARY OF THE INVENTION
Thus there is a need for a reliable method of installing sand control in long horizontal or deviated wells.
The invention includes a method for controlling sand production in a well drilled in a subterranean formation comprising installing an expandable sand screen assembly in the well. The expandable sand screen assembly comprises an expandable sand screen in an unexpanded configuration. A slurry of gravel and carrier fluid is circulated into the annular space between the unexpanded expandable sand screen and the formation or between the unexpanded expandable sand screen and the casing. In one embodiment, a slurry of gravel and carrier fluid is pumped down a tubular inside the expandable sand screen assembly and circulated up through the annular space between the expandable sand screen and the formation. Alternatively, a slurry is pumped through a crossover tool above the sand screen into the annulus between the formation and the unexpanded expandable sand screen, where fluid displaced by the slurry is circulated up a tubular inside the expandable sand screen assembly. The expandable sand screen is expanded, thereby dehydrating the slurry in the annular space. The method further comprises forming a gravel pack behind the expandable sand screen.
The inventions also include a sand control system comprising a well drilled in a formation, an expandable sand screen installed in an expanded configuration, an annular space located between the outer surface of the expandable sand screen and the formation, and a gravel pack located in the annular space. According to one embodiment of the invention, the gravel pack was dehydrated by expanding the expandable sand screen.
BRIEF DESCRIPTION OF THE DRAWINGS
The inventions also include a method for producing oil or gas comprising drilling a well in a subterranean formation comprising, installing an expandable sand screen assembly comprising an expandable sand screen in an unexpanded configuration into the well, pumping a slurry down the well, circulating the slurry through an annular space defined by the expandable sand screen and the formation, expanding the expandable sand screen thereby dehydrating the slurry in the annular space and producing oil or gas from the well.
The present invention is better understood by reading the following description of non-limitative embodiments with reference to the attached drawings, wherein like parts of each of the figures are identified by the same reference characters, and which are briefly described as follows:
FIG. 1 illustrates a well with an expandable sand screen in an unexpanded configuration during circulation of a slurry.
FIG. 2 illustrates the expandable sand screen as it is expanded and being used to dehydrate the slurry.
Referring to FIG. 1, a wellbore 101 is shown drilled in a subterranean formation 102. In the embodiment shown, wellbore 101 is an open hole wellbore; however the invention could theoretically be practiced in a cased wellbore environment.
An expandable sand screen (ESS) assembly 103 is run in an unexpanded configuration into wellbore 101 using a workstring (not shown). The ESS assembly may include any combination of expandable sand screens 104, blank sections of pipe, collapsible centralizers or external packers (not shown). Prior to installing ESS assembly 103, additional tools may have been installed in the well including landing tools (not shown) for a wash pipe 105 and an expansion tool (not shown in this Figure). Wash pipe 105 could alternatively be run simultaneously as part of the ESS assembly 103.
If not already deployed as part of the ESS assembly, wash pipe 105 is run inside expandable sand screen 104. A slurry consisting of gravel pack sand or ceramic proppant suspended in a carrier fluid is pumped down wash pipe 104 and circulated into the annular space 107 between expandable sand screen 104 and the wall of formation 102. The direction of circulation of the slurry is shown by arrows 106. Optionally leading spacers or chemical treatments may be pumped ahead of the slurry to improve open hole displacement and wellbore clean up. The slurry may include internal breakers or other chemicals needed to facilitate the clean up the gravel pack once deployed for oil, synthetic, or water based fluid systems.
After the slurry is circulated, wash pipe 105 is pulled out of the wellbore and may be used to pick up the parts of ESS assembly 103 which are no longer needed. Alternatively, these parts of the ESS assembly may be retrieved on a subsequent trip into the well. In another embodiment, the expansion tool assembly could be parked in an expansion tool-launching sub at the top of the ESS assembly, so that when the lower end of the wash pipe engages the expansion tool. Once engaged, the combined assembly is ready to expand the screen. The gravel pack sand or proppant remains disposed between expandable sand screen 104 and the borehole, forming a gravel pack, albeit one in which significant liquid may be present.
As shown in FIG. 2, expandable sand screen 104 is then expanded using expansion tool 201. Expansion tool 201 may be any conventional expansion tool known in the art known including but not limited to expansion pigs, cones, and mandrels. Expansion of expandable sand screen 104 may be accomplished using a top down or bottom up expansion method. In one embodiment, expandable sand screen 104 is expanded against or into formation 102; however, expandable sand screen 104 may also be partially expanded or expanded to a threshold just before being expanded into or against the formation.
FIG. 2 shows expandable sand screen 104 in an expanded configuration. Expansion of expandable sand screen 104 pushes the outside of the screen toward the wall of the formation. A force is applied in the direction of arrows 210 thereby compressing annular space 107. This properly and uniformly dehydrates the slurry 202 in annular space 107 between expandable sand screen 104 and the wall of formation 102. The expansion force prevents the formation of voids in the gravel pack during the dehydration process. As the slurry is dehydrated, gravel pack 203 is compressed behind expandable sand screen 104, filling voids due to hole irregularities or wash outs.
When the expansion is complete, the work string used to deploy the expansion tool is pulled out of the hole. If needed, the work string may be used to place breakers or other chemicals along the completion as it is pulled back inside the newly expanded screen.
Installation of a gravel pack according to this method limits the necessary fluid volumes needed to deploy the completion. Consequently, this method can be deployed in regions where logistics and fluid storage makes alpha-beta packing impossible or impractical.
This method of installation may also increase the probability of success of an open hole completion in sections that are drilled with non-water-based (non-aqueous) drilling fluids. Unlike gravel packing via the alpha-beta method, this method is compatible with a wellbore in which oil-based or synthetic drilling fluid was used.
Installation of a gravel pack in this method may provide backup insurance of gravel covering screen if the expansion is not sufficient to protect against fines liberation on hole collapse and fines plugging the entire screen. The slurry volume and concentration may be varied to make up for an out of gauge hole if drilling conditions become unstable or difficult.
One of the advantages cited for expandable sand screens that are expanded against the formation is that fines in the unconsolidated formation are “locked” in place because deforming and disaggregating of sand is limited as the well is drawn down. Because open holes are rarely exactly in gauge or circular, the fluid sand slurry can move to fill the space and provide full contact between the expanding screen and formation. Expansion according to this method increases the probability that this “fines locking” stress is applied uniformly along the open hole.
Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials, and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature and elements described separately may be optionally combined.