CA2937488A1 - Sequential re-completions of horizontal wells in unconsolidated sand reservoirs to increase non-thermal primary heavy oil recovery - Google Patents

Abstract

A method of sequentially recompleting a horizontal well, which may have been produced to economic depletion, includes selecting a re-completion site, perforating the liner in a perforation interval in the re-completion site, and producing from the re-completion site with a jet pump until economic depletion, and repeating the process with successive new re-completion sites, moving from toe to heel of the horizontal well.

Description

SEQUENTIAL RE-COMPLETIONS OF HORIZONTAL WELLS IN
UNCONSOLIDATED SAND RESERVOIRS TO INCREASE NON-THERMAL
PRIMARY HEAVY OIL RECOVERY
Field of the Invention [0001] The present invention relates to methods and systems for treating horizontal wells to enhance recovery of oil. In particular, the present invention relates to sequential re-completions of horizontal wells in unconsolidated sand reservoirs to increase non-thermal primary heavy oil recovery, Background

[0002] Horizontal wells were drilled in non-thermal heavy oil reservoirs with the expectation .
that they would recover several times the volume of off-setting vertical wells, because they contact significantly more reservoir than vertical wells.

[0003] However, it has been found that horizontal wells only recover approximately the same volume of oil as a single off-setting vertical well. Horizontal completions typically use a slotted liner, and geomechanical phenomena associated with use of the liner in an effort to prevent sand inflow leads to sand compaction, which prematurely terminates inflow of oil.
Attempts to backtlush the sand from the liner are costly and short lived.

[0004] Attempts to induce sand inflow such as larger slot sizes along the length of the liner or . long sections of perforations with the pump intake landed at the liner top have been unsuccessful. The flow rates and bottom hole pressure are typically too low to carry sand to the pump intake. Sand settles out in the liner leading to costly and repeated sand clean-outs with little to show in incremental recovery. Thus, most horizontal wellbores in a non-thermal heavy oil well do not justify the additional cost of drilling and completion over traditional vertical wellbores.

[0005] In Applicant's co-owned Canadian Patent Application No. 2,899,222, a method of sequential recompletions with perforations is described which has the potential to mitigate many of the difficulties of the prior art. However, with each perforation, there will be a large pressure differential between the reservoir and the inside of the liner at the time of perforating.
There is no way to reduce this differential. With this pressure differential, and the stimulation and fluidization of the sand outside the liner, there is likely to be a large influx of sand. Sand has been known to flow 30 to 50 meters uphole after perforating when there is a large differential. This sand inflow could cause the tubing that transported the perforating gun to become stuck inside the liner.
= [0006] Therefore, there is a need in the art for improved methods of oil recovery from horizontal wellbores. The potential economic benefit of increasing recovery from horizontal wells is significantly greater than with current practices which include existing horizontal well completions, vertical wells, non-thermal flood schemes, and other mechanisms employed to increase heavy oil recovery.
Summary Of The Invention [0007] Implementation of embodiments of the present invention may allow naturally occurring geomechanical phenomena in unconsolidated sandstone to significantly increase recovery of non-thermal heavy oil in a horizontal well. The area drained by production of a vertical well is much wider than the width of the area drained by a horizontal well. This indicates that a horizontal well may increase recovery by re-completing the well to widen the drained area along the length of the well to match the width of the drained area surrounding vertical wells.
[00081 ln one aspect, the invention may comprise a method of sequentially recompleting a horizontal well having a liner, comprising the steps of:
(a) selecting a first re-completion site within the liner, comprising a perforation interval for perforation;
(b) perforating the liner within the selected perforation interval with a perforating gun run on a first tubing string comprising isolation devices, a ported tool and a pump seating nipple;
(c) without pulling the first tubing string, landing a jet pump on a production tubing string onto the pump seating nipple, within the first tubing string; and (d) pumping p.ower fluid comprising a sand dispersion chemical into the j et pump either in the annulus between the first tubing and the production tubing, or within the production tubing, thereby producing fluid, sand and power .fluid to the surface.
Preferably, the method comprises the further step of running in a coil tubing string and unloading the well, causing sand and fluid inflow through the perforations, and extracting the coil tubing string, before landing a jet pump onto the pump seating nipple.

[0009] In one embodiment, the recompletion steps take place after the well has been produced to economic depletion. Alternatively, the recompletion steps may take place to allow first production from a well.
[0010] In one embodiment, once the re-completion site is produced to depletion, the tubing strings are withdrawn, and a new re-completion site comprising a new perforation interval, uphole of the last perforation interval, is chosen and the perforating and pumping steps are repeated. The length of the horizontal well may then be treated from toe to heel by repeating the perforating and pumping steps in sequential re-completion sites.
Brief Description of the Drawings [0011] The following drawings form part of the specification and are included to further = demonstrate certain embodiments or various aspects of the invention. In some instances, embodiments of the. invention can be best understood by referring to the accompanying drawings in combination with the detailed description presented herein. The description and accompanying drawings may highlight a certain specific example, or a certain aspect of the invention. However, one skilled in the art will understand that portions of the example or aspect may be used in combination with other examples or aspects of the invention.
= [0012] Figure 1 shows a cross-sectional schematic of a prior art completion of a horizontal well in an unconsolidated sandstone reservoir.
[0013] Figure 2 shows a cross-sectional schematic view of a configuration of a re-completion after the well has been produced to economic depletion.

[0014] Figure 3 shows the well of Figure 2 after perforation and the ported tool ruptured.
[0015] Figure 4 shows the well of Figure 3 with insertion of a coil tubing string.
[0016] Figure 5 shows the well of Figure 4 after landing of production tubing and a jet pump.
Detailed Description [0017] The present invention comprises methods and systems to continue production of a horizontal well, preferably one that has been produced to. economic depletion.
In one embodiment of the invention, a re-completion site is selected, preferably which is proximal to the toe of the well and in a pay or effective pay zone. In one embodiment, the re-completion site is selected by reviewing well trajectory in effective pay and the drained area diameter of . off-setting vertical wells to maximize recovery from the re-completion.
[0018] As shown in Figure 1, a conventional horizontal wellbore completion with a slotted liner (L) is produced to economic depletion, meaning that the value of the oil inflow into the liner is less than the costs associated with lifting it to surface, processing it, and selling it. At this point, there is no further risk of damaging amounts of sand entering the liner.
[0019] After a horizontal well has been produced to economic depletion, it is likely that there will be sand and sedinient on the bottom of the liner. Open-ended production tubing pushed through the liner will ride over the sediment or plow through it for the most part. However, isolation tools will push the sediment up in front of them until enough has accumulated to prevent forward motion. Therefore, it is preferred to clean out of the length of the liner (L) to the toe of the wellbore, to remove debris and ensure that the liner is undamaged prior to entering it with subsequent equipment. The cleaning step is preferably undertaken with a fluid comprising a sand dispersion chemical. Performing a preliminary clean-out step removes sand, sediment and any other debris. At the same time, the wellbore is backfilled with fluid treated with sand dispersion chemical, which may assist in later trips in and out of the well, [0020] Suitable sand dispersion chemicals are well known in the art and commercially available, and may include water soluble products such as SS5844TM and/or oil soluble, water dispersible products such as SSS6O9TM (Multi-Chem Production Chemicals, a division of Halliburton).
= [0021] In one embodiment, the liner is a slotted liner, or a combination of slotted liner and blank liner, as is well known in the art. However, embodiments of the present invention may be practiced with blank liners throughout the length of the horizontal well.
[0022] After cleaning out the liner, a perforation interval within the re-completion site is Selected and perforated as described below and largely in accordance with conventional perforating techniques, well known to those skilled in the art, The length of perforation interval, perforation diameter, penetration, shot density and phasing are selected based on various reservoir and fluid criteria, which is well within the ordinary skill of one skilled in the art, In one embodiment, consideration -for the pumping equipment's deployment and ability to = remove the sand from the perforations are also factors which are considered. In one embodiment, it is preferred to maintain a relatively short perforating interval, in the range of less than 5 meters, preferably less than 3 meters, more preferably less than about 2 meters. A
= 6 relatively longer perforation interval may increase the risk of smothering the perforations with inflowing sand., [0023] The objective of perforation is to create openings in the liner through which sand and produced fluids may enter the liner. One preferred method of perforating is jet perforating using shaped explosive charges, which is well known to those skilled in the art. Alternative methods of perforation are also well known in the art, and include bullet gun perforation, . abrasive-jetting of openings such as radial or longitudinal slots using high pressure abrasive fluid, and cutting windows.
[0024] In one embodiment, the perforation pattern may comprise 60 degree phasing with relatively more (e.g. 20 to 26) shots per meter with larger holes, rather than 90 degree phasing with fewer shot and deeper smaller holes. This forms a helical pattern of holes off-set about every 2 inches in the entire circumference of the liner for ,sand and oil to flow into the liner Sand has a tendency to settle faster in horizontal pipe than in vertical pipe but inflow from the bottom and sides of the liner, and the increased shot density and hole size may assist in disrupting compaction.
[0025] As is well known in the art, stimulation/fluidization fluid may then be circulated to mobilize the reservoir sand outside the newly created perforations. The stimulation/fluidization fluid preferably contains sand dispersion chemical, and may be in used in a volume of about fifty cubic meters (350 barrels). The intention is that the majority of the sand that will inflow will be treated with sand dispersion chemical. As long as the sand can be kept fluidized it reduces the risk of sand compaction.

=

[0026] In order to avoid the need to trip the detonated perforating gun out of the hole, and provide a means for immediate flowback and clean-up after stimulation is complete, a pump seating nipple is provided with the tubing string conveying the perforating device. The production tubing with the jet pump may be landed a short distance above the pump seating . nipple prior to detonating the perforating gun. Additionally, the accuracy of the location of the pump intake relative to the perforations may be improved.
[0027] This method also avoids the requirement of a sand clean out or prevents sand influx from sticking tubing in the liner after perforating and stimulating, before being able to put the well on production.. If sand inflow is heavy enough during this stage, the cost to remove it could terminate the entire re-completion before getting the well on production. The same can be said of getting the tubing stuck because of the inability to control sand inflow.
[0028] Isolation devices are placed to isolate a perforation interval, and are intended to prevent sand from flowing uphole in the liner outside the first tubing string that transported the perforating gun. The isolation devices will contain and direct the inflowing sand to the inside of the tubing that transported the perforating gun. To reduce the possibility of having to do a sand clean-out inside this tubing, the production string with the jet pump assembly could also be run but not landed in the seating nipple before perforating, rather than run in after perforating and stimulating or fluidizing the sand, Then, immediately after stimulation/fluidization is complete, the production tubing string _may be lowered to scat the jet pump assembly into the pump seating nipple, substantially preventing uncontrolled sand inflow into either tubing string.

[0029] Shortly after the end of the stimulation step, for example, within one hour, a-jet pump can be landed in the pump seating nipple and started up, slowly at first, to commence removing sand inflow. As sand cut stabilizes, the pump may be sped up step-wise to induce more sand inflow and increase overall production rate. This step-wise increase in speeding up the pump would eventually get the well to maximum drawdown where no more sand inflow occurs. In this fashion the pump is both the means of removing the sand and can supply the necessary back pressure to provide the operator the means to control the rate of sand inflow.
[0030] In one embodiment, one significant advantage of this method is that only one trip into the well is required as opposed to multiple trips and it avoids the use of auxiliary equipment.
Thus, the well may be perforated, sand outside the liner may be stimulated and fluidized, and sand inflow may be contained and directed. At the same time, the well is in a position to be = on production shortly after perforation, and sand clean-out may be per-formed using production equipment instead of auxiliary equipment.
[0031] In one embodiment of the method, after an initial sand clean-out to the toe is completed, elements are run into the well to perforate the selected location, as described above and shown in Figure 2. A tubing (10) conveyed perforating gun (12) is deployed between isolation devices (14, 16) at the top and bottom of the gun, which define the perforation interval between them. A ported tool (18) having a rupture disk is placed between the top isolation device (14) and the top of the perforating gun (12). After the perforating gun (12) is fired, fluid is pumped through the tubing (10) at a high enough pressure to rupture the ported = tool (18), causing fluid to wash over the fired perforation gun to wash away sand. The fluid is .9 pumped in large enough volume and high enough rate to enter the formation through the freshly made perforations to further break up and disturb any compacted sand outside the -liner. In one embodiment, the fluid is an aqueous solution comprising a sand dispersion chemical which keeps the sand fluidized, minimizing the risk of getting the perforating gun and tubing stuck in the well by compacted sand inflow. The isolation devices (14, 16) contain any inflowing sand to a relatively short interval. The isolation devices (14,16) also contain the flush fluid to the space covering the perforation gun thereby flushing inflowing sand back through the perforations, as well as direct the sand dispersion fluid into the perforations to disrupt any sand which has compacted in the perforation openings and outside the liner. Once the sand is treated with the sand dispersion chemical there is less likelihood that it will compact under any conditions.
[0032] The tubing (10) is landed in the wellhead prior to detonating the perforating gun (12), but because it also includes a pump seating nipple (24) between the ported tool (1.8) and the upper isolation device (14), it should not need to be extracted again. This ensures that all the important elements necessary for effective production of-the well remain accurately on depth.
[0033] At this stage, instead of tripping out the detonated perforating gun (12) and first tubing (10) and re-entering with concentric tubing, a production tubing string (20) with a jet pump (28) can be immediately landed in the jet pump seating nipple (24) and the well can be placed immediately on production. Alternatively, coil tubing (30) may be run into the landed tubing (10) and into the ported sub. The well can then be unloaded with various fluids and/or gas combinations that will stimulate sand inflow and effect removal of the sand to surface, as is shown in Figure 4.
[0034] If the choice is made to run the coil tubing operation, after the sand in-flow has diminished to a comfortable level, the coil tubing (30) is extracted, and the production string (20) and jet pump (28) arc installed, as is shown in Figure 3, [0035] The jet pump is landed so that the pump intake is above the perforations. While this configuration may result in sand accumulation in the perforations and impeding inflow, certain features of the claimed invention may mitigate this possibility, [0036] The short perforation, for example only a meter long interval, and the placement of the ported tool and pump as close to the perforations as physically possible, about one meter above the perforations, minimizes the length of a potential sand filled section. Flush-by fluid can jet through this and restore flow to the pump intake. Also, the inside diameter of most liners (5 inch) relative to the outside diameter of the perforating gun (4 inch) will create an annular space 0.5 inch to 1.5 inch wide over the length of the perforating gun. Flow rate inside this annular space is an order of magnitude greater than flow rate inside open liner, thus, . allowing better sand fluidization and mobilization in this zone.
[0037] The isolation devices at the bottom of the perforation gun and just above the ported tool not only contain and direct the oily sand inflow into the pump when the well is on production, they contain and direct injected flush-by fluid across the perforating gun and into the perforations' to remove sand build up when the need arises.

[0038] In one embodiment, the jet pump (28) is configured to operate in reverse flow, that is, power fluid will be pumped down the annulus between the first tubing string (10) and the production tubing string (20), and the mixture of produced fluid/sand/power fluid will be produced up the production tubing string (20). Suitable jet pumps which operate on the venturi effect are well-known to those skilled in the art, and are readily commercially available.
[0039] This reverse circulation may restrict abrasive wear from the sand to the inside of the first tubing. Also, in the event of a downhole tubing leak, sand-laden fluid will not spew out into the liner to stick the tubing in the liner. Furthermore, in the event that the inner tubing string (22) does plug up with sand it can be stripped from the well by a service rig to remove the blockage without having to remove both strings simultaneously.
Alternatively, the jet pump (28) can be operated in a forward configuration, where power fluid is pumped down the production tubing string (20) and returns up the annulus between the first tubing string (10) and the production tubing string (20), [0040] Also, the production tubing string (20) can be hoisted by a flush-by rig so that fluid with sand dispersion chemical can be pumped down the first tubing string (10) to displace sand away from the inlet which is now the ported sub, and over the detonated perforating gun which was left in the well, and out the perforation ports into the area outside the perforated liner. The ported tool may be designed to direct injected flush-by fluid to the area where sand might likely be accumulated or compacted, within the area confined by the isolation devices.
Before hoisting, the pump seating nipple bore forms a metal to metal fluid seal with the =

=
outside of the jet pump assembly so that injected power fluid has to circulate back to surface via the production tubing. Lifting the jet pump assembly out of the pump seating nipple = disrupts the seal. When the flushing operation is complete, the Flush-by rig lowers the production tubing replacing the jet pump assembly in the pump seating nipple to restore the seal and production can be resumed. The entire operation may be accomplished in a few hours compared to moving on a service rig and auxiliary equipment for a week long sand clean out operation.
[0041] Treating the jet pump power fluid with sand dispersion chemical is preferred. With methods of the present invention, the horizontal well n-lay produce fluids which are 70% sand by volume. While this sand-laden fluid is diluted by the volume of power fluid when produced, it is still a large amount of sand to be carried over a very long distance.
= Conventional techniques such as "rocking" the well could serve to concentrate the sand, and eventually lead to sand compaction which would require a service job to remediate.
Treatment with a sand dispersion chemical assists in preventing such blockages by keeping the sand fluidized and moveable.
[0042] In one embodiment, each of the first tubing string (10) and the production tubing string (20) comprises jointed tubing, and can be readily extracted by a service rig for clean out or to service the jet pump. With jointed pipe, the pipe can be examined for wear as it is pulled from the well and only the necessary joints are replaced. Furthermore, each successive re-completion requires the tubing strings to be shortened as the move uphole is made to the next re-completion perforation interval. If continuous tubing is used, it has to be cut off and discarded. Discarding cut off sections of continuous tubing, as well as an entire string of continuous tubing, may be costly and difficult. Jointed pipe that is removed from the string during the move uphole can be re-used in the completion of other wells or stored for replacement use when other tubing has worn.
. [0043] The re-completion is then produced by pumping power fluid into the jet pump and producing a mixture of produced fluid, sand and power fluid up the production tubing. Sand dispersion chemical is preferably added to the power fluid to ensure the produced sand in the production tubing string remains fluidized to prevent compaction upon settling.
[0044] When this re-completion reaches economic depletion, the tubing strings (10, 20) are pulled and inspected for wear as they are being pulled. The jet pump downhole components are inspected and serviced at the surface.
[0045] A new re-completion site, uphole of the previous site is selected for a new re-.
completion in the same fashion the first site was selected. In one embodiment, subsequent re-' completion sites may be determined by calculating the diameter of the drained area of the immediately preceding site, and move uphole by approximately the same a distance.
Additionally, or alternatively, data from methods such as 3D seismic surveys may be rendered to show the depleted area, or data from various types of cased hole logging may be used to determine a suitable pay zone for the next re-completion site.
[0046] Once the next site is selected, a perforation configuration and perforation interval is selected, and the well is perforated and flushed as in the first re-completion. The new re-completion is then produced to depletion. In one embodiment, this process is repeated until all space for re-completions in the horizontal wellbore have been exhausted.
In other words, the re-completions are repeated towards the heel of the wellbore, until all available re-= completions have been performed. In a preferred embodiment, the re-completions are performed sequentially, from toe to heel.
Definitions and Interpretation [0047] The description of the present invention has been presented for purposes of illustration and description, bufit is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and. to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
[0048] As used herein, the terms "top", "above", or "upper" and "bottom", "below" or "lower", or similar terms, are used to denote the relative position of an element in the work . string, and not neceSsarily an indication of vertical position. The upper end of the work string is that which is closer to the surface end of the work string, while the bottom end is that which is closer to the toe of the well.
[0049] The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims appended to this specification are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed.
[0050] References in the specification to "one embodiment", "an embodiment", etc., indicate that the embodiment described may include a particular aspect, feature, structure, or . characteristic, but nOt every embodiment necessarily includes that aspect, -feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to combine, affect or connect such aspect, feature, structure, or characteristic with other embodiments, whether or not such connection or combination is explicitly described. In other words, any element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or it is specifically excluded.
= [0051] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or use of a "negative" limitation. The terms "preferably,"
"preferred," "prefer,"
"optionally," "may," and similar terms are used to indicate that an item, condition or step = being referred to is an optional (not required) -feature of the invention.

=

[0052] The singular forms "a," an, and "the" include the plural reference unless the context clearly dictates otherwise. The term "and/or" means any one of the items, any combination of the items, or all of the items with which this term is associated.
[0053] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range (e.g., weight percents or carbon groups) includes each specific value, integer, decimal, or identity within the range.
Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower = third, middle third and upper third, etc. As will also be understood by one skilled in the art, all language such as "up to", "at least", "greater than'', ''less than", "more than, "or more", and the like, include the number recited anC1 such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio, [0054] The term "about" can refer to a variation of IL 5%,, 10%, + 20%, or +
25% of the value specified. For example, "about 50" percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term "about" can include one or two integers greater than and/or less than a recited integer at each end of the range.
Unless indicated otherwise herein, th term "about" is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment,

Claims (11)

Claims

1. A method of sequentially recompleting a horizontal well having a liner, comprising the steps of:
a. selecting a first re-completion site within the liner, comprising a perforation interval for perforation;
b. perforating the liner within the selected perforation interval with a perforating gun run on a first tubing string comprising isolation devices, a ported tool and a pump seating nipple;
c. landing a jet pump on a production tubing string onto the pump seating nipple, within the first tubing string; and d. pumping power fluid comprising a sand dispersion chemical into the jet pump to producing fluid, sand and power fluid to the surface.

2. The method of claim 2 comprising the further step of running in a coil tubing string and unloading the well, causing sand and fluid inflow through the perforations, and extracting the coil tubing string before landing a jet pump onto the pump seating nipple.

3. The method of claim 1 or 2 wherein the liner comprises a slotted liner, a blank liner, or a combination of slotted and blank liner.

4. The method of claim 1 comprising the further steps of choosing a second re-completion site uphole from the first re-completion site, and repeating steps (b) to (e) at the new recompletion site after the previous re-completion site has reached depletion.

5. The method of claim 1, 2 or 3 wherein the second re-completion site is uphole of the first re-completion site by a distance substantially equal to the diameter of a drained area of the first re-completion site, or to use 3D seismic data rendering to show the depleted area, or a cased hole logging technique to determine the drained area.

6. The method.of claim 1 comprising the preliminary step of cleaning out the slotted liner prior to perforating the selected perforation interval.

7. The method of claim 5 wherein the preliminary cleaning step is performed with a wash fluid comprising a sand dispersion chemical, leaving the horizontal well backfilled with wash fluid.

8. The method of claim 1 wherein the perforation interval is less than about 5 meters in length.

9. The method of claim 1 wherein the jet pump power fluid is pumped into the jet pump in the annulus between the first tubing string and the production tubing, thereby producing fluid, sand and power fluid to the surface up the production tubing.

10. The method of claim 1 wherein the jet pump power fluid is pumped into the jet pump in the production tubing, thereby producing fluid, sand and power fluid to the surface up the annulus between the production tubing and the first tubing string.

11. The method of claim 1 wherein the recompletion steps occur after the well has been produced to economic depletion.