Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
  • E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/30—Specific pattern of wells, e.g. optimising the spacing of wells
  • E21B43/305—Specific pattern of wells, e.g. optimising the spacing of wells comprising at least one inclined or horizontal well

Definitions

• the present invention relates to a method for recovering hydrocarbons from a subterranean reservoir through an inverted production well and in one of its aspects relates to a method for recovering hydrocarbons using an inverted production well(s) which has a non- inverted (e.g. vertical with angle building to near 90°) portion, a substantially horizontal portion wellbore which extends into the reservoir, and a tail portion which curves upwardly towards the surface to terminate at or near the top of the reservoir.
• a non- inverted (e.g. vertical with angle building to near 90°) portion e.g. vertical with angle building to near 90°) portion
• a substantially horizontal portion wellbore which extends into the reservoir
• a tail portion which curves upwardly towards the surface to terminate at or near the top of the reservoir.
• thermal secondary recovery operations are routinely employed to recover heavy hydrocarbons, e.g. heavy oil, from subterranean reservoirs (e.g. oil sands) . Due to its high viscosity, the heavy oil must be heated in place to reduce its viscosity so it will flow from the reservoir. Probably the most common of such thermal recovery operations involves "steam stimulation” wherein the heavy oil is heated in place by steam which is injected into the reservoir.
• a steam stimulation or steamflood process can be carried out by either (a) injecting the steam into an injection well and then producing the hydrocarbons from a separate well or (b) injecting the steam and then producing the fluids through the same well.
• steam is injected into one well while formation fluids (e.g. oil) are produced through spaced production wells.
• formation fluids e.g. oil
• production wells normally have substantially vertical wellbores which are cased to at least a depth which lies adjacent the top of the oil sand.
• the lower end of the wellbore is then completed with a gravel pack or the like through the production interval.
• Steam is injected through the injector well for an initial period (e.g. 3 to 24 months) in order to establish thermal communication between the injector well and the production wells.
• each production well may either produce cold oil at a low flow rate or be stimulated by cyclically injecting steam into the producing well, itself. Higher production flow rates normally occur only after thermal communication between wells has been established.
• the production well of the present invention is “inverted” in that at least the terminal portion thereof is inverted, i.e. the terminal end curves upward towards the surface. More specifically, the inverted wellbore of the present invention has a substantially vertical (with angle building to near 90°) , non-inverted portion which extends from the surface to a depth substantially adjacent the top of said reservoir; an integral, substantially horizontal portion which extends into said reservoir; and an integral, upwardly curving tail portion which terminates near the top of the reservoir.
• the production well is cased approximately throughout the substantially vertical, non-inverted portion of the wellbore with the remaining wellbore being completed in accordance with known completion procedures (e.g. cased and perforated, open-hole completions, gravel-packed, etc.).
• a string of production tubing which may include a downhole pump (not shown) on the lower end thereof is positioned in the wellbore and preferably terminates within the non-inverted portion of wellbore.
• the tubing/pump inlet can be repositioned within the wellbore during the life of the production well in response to the actual production of the well.
• the inverted production well of the present invention can be used in different types of steamflood recovery operations.
• a plurality of inverted production wells may be spaced from a central steam injector well in conventional steamflood patterns, e.g. five-spot, nine-spot, in-line, etc..
• Steam when injected through the injector well, will migrate upward to form a "steam chest" across the reservoir.
• the tail portion of each inverted wellbore is deviated towards the injector well and each terminates at or near the top of the reservoir so it will lie in or near the steam chest as it is formed.
• the high-angle horizontal nature of the inverted wellbore of the present invention greatly enhances the length of the completed production interval within the reservoir and can substantially reduce the bottom-water coning within the formation. Further, since the tail or terminus of the wellbore is located near the top of the reservoir (i.e. in or near the steam chest) and since the intake of the production tubing and pump (if used) is located in the non-inverted portion of the well, hot oil and water from the formation are forced to flow from the tail of the wellbore downward through the entire completed length of the wellbore before the heated fluids reach the tubing/pump inlet. These hot fluids provide good conductive heating along this interval thereby enhancing oil production in what would otherwise be a cold interval.
• the steam is entering at the tail of the wellbore and condensing, it will be produced as hot water through the tubing/pump inlet instead of being produced through the well annulus as would be the case in prior art systems thereby substantially eliminating any significant back pressure against the reservoir which, in turn, would inhibit oil production.
• the production of steam through the tail portion can be reduced, if necessary, by setting a bridge plug or the like within the tail portion of the wellbore to block the downward flow of steam through the tail portion. This plug or additional plugs can be repositioned during the life of the production well to compensate for increasing production of steam into the tail portion of the wellbore.
• a single inverted well may be used both as the steam injector well and the production well of a steamflood by positioning a string of injection tubing within the wellbore and extending the injection tubing into the tail portion of the wellbore.
• the injection tubing can be run through the production tubing or it can be run along side the production tubing. Steam is injected through the injection tubing into the tail portion of the wellbore to heat the oil in the top of the reservoir so that it may flow into the lower wellbore to then be produced through the production tubing.
• FIG. 1 is an elevational, sectional view of the lower end of a production well of a steamflood recovery operation which has been completed in accordance with known, prior art techniques;
• FIG. 2 is an elevational, sectional view of the lower end of an inverted production well which has been completed in accordance with the present invention
• FIG. 3 is an elevational, sectional view of the lower end of an inverted production well which has been completed in accordance with the present invention and the lower end of an associated, spaced steam injection well;
• FIG. 4 is a plan view of a typical steamflood pattern in which the present invention can be used.
• heavy oil there are substantial reservoirs of heavy hydrocarbons (hereinafter collectively called “heavy oil”) throughout the world which have such a high viscosity that they can not be economically produced by primary recovery techniques.
• thermal techniques which heat the heavy oil in place to reduce its viscosity to a level sufficient to allow it to flow from the reservoir into a production well.
• steam stimulation One of the best known and most commonly used of such thermal processes is commonly referred to as “steam stimulation” and one which involves injecting steam down the well and into the reservoir to heat the heavy oil.
• FIG. 1 In typical, prior art steam stimulation processes (FIG. 1) , steam 12 is injected down an injection well (not shown) and out into the production formation or reservoir (i.e. oil sand 11) towards a production well 10 (FIG. 1) .
• well 10a has a substantially vertical wellbore which has been cased (casing 13) and cemented (not shown) to a depth approximately adjacent the top 14 of the oil sand.
• the lower portion of wellbore 10a is "gravel- packed" adjacent the production interval of oil sand 11 (i.e. completed with a slotted liner 15 which, in turn, is surrounded by a pack of gravel 16) .
• a production tubing 18 which may have a downhole pump (not shown) on its lower end extends into the wellbore through which the formation fluids are produced to the surface.
• steam 12 Since steam 12 is substantially in the vapor phase, its density is substantially less than that of either the heavy oil or the format on water which causes the steam to rise towards the top of the reservoir as it radiates outward from the well.
• This natural gravity segregation of steam in a typical heavy oil reservoir routinely results the establishment of a "steam chest" 17 which blankets the top of oil sand 11.
• the production well 20 is an "inverted” well in that at least the terminal or tail end of the wellbore is inverted.
• inverted well or “inverted wellbore” is meant to refer to and describe a wellbore which curves or deviates from the vertical towards a horizontal direction and then curves upwardly towards the surface (i.e. "inverted") as the wellbore is being drilled into said reservoir.
• inverted wellbore 20 curves outward from the substantially vertical, non-inverted portion 20a towards the horizontal (e.g. 20b) as it passes into reservoir 11 and preferably continues through a horizontal portion 20b (length of portion 20b depending on a particular reservoir) near the bottom of reservoir 11 before the wellbore begins to curve upward towards the surface.
• the wellbore continues upward to form a tail portion 20c which terminates near the top 14 of reservoir or oil sand 11.
• the drilling of such wells are well within the present state-of -the-art and can be drilled with presently commercially-available equipment (e.g. whipstocks, downhole motors, bent subs, etc.).
• production well 20 is cased (i.e. casing 22) and cemented (not shown) substantially through the non- inverted portion 20a of the wellbore.
• the remaining wellbore (i.e. 20b, 20c) which will form the production interval of the well is then completed in accordance with an appropriate, known completion technique (e.g. cased and perforated, open-hole completions, gravel-packed, etc.).
• a string of production tubing 23 which may carry a downhole pump (not shown) on its lower end is lowered into the wellbore with its inlet (i.e. lower end) being positioned at or near the lower end of the non-inverted portion of wellbore 20 (i.e. within the substantially vertical or horizontal portion of the well) .
• the present inverted production well can be used in a variety of different types of steamflood recovery operations.
• One such operation is shown in FIG. 3 (not to scale) wherein inverted production well 20 is one of a plurality of production wells which are spaced from a steam injector well 21.
• the production wells 20 may be positioned around a central injection well 21 in a typical 5-spot pattern (FIG. 4) or they may be arranged in other well known steamflood patterns (e.g. nine-spot, in-line, etc.) with similar success.
• inverted wellbore 20 is preferably deviated inwardly towards injector well 21 with tail portion 20c terminating at or near the top 14 of reservoir 11.
• Steam 12 is injected through perforations 21a in well 21 and will migrate upward to form steam chest 17 across the top of the formation in the same manner as in prior steamfloods.
• the inversion of wellbore 20 so that it terminates near the top of the reservoir i.e. in contact with steam chest 17
• the high-angle horizontal nature of the inverted wellbore greatly enhances the length of the completed production interval within the reservoir and can substantially reduce bottom-water coning within the formation.
• the tail or terminus of the wellbore is located near the top of the oil sand and in contact with steam chest 17 and since the intake of the production tubing 23 and pump (if used) is located in the non-inverted portion of the well, hot oil and water from the formation is forced to flow downward from the tail portion 20c of the wellbore and along the remaining completed interval of the wellbore before they reach the tubing/pump intake.
• These hot fluids provide conductive heating along this entire interval thereby enhancing oil production from what would otherwise be a cold interval of reservoir.
• an inverted production well Another advantage of using an inverted production well is that the entire completion interval within the wellbore is in contact with hot fluids substantially from the beginning of the steam injection.
• the hot fluids produced from the steam chest region of the wellbore allows heat to be transferred to the otherwise cold, near-wellbore lower reservoir region.
• the heat transfer from the hot produced fluid enhances oil production in what would otherwise be a cold lower wellbore interval.
• an inverted production wellbore allows the inlet of the production tubing/pump to be placed at different points in the wellbore during the production life of the well. For example, the inlet may be placed closer to steam chest region 17 if a large volume of oil is being produced exclusively from that zone.
• the inlet may be placed higher up in the non-inverted portion of the wellbore to establish a fluid level in the wellbore which will inhibit excessive steam production from the steam chest 17.
• the actual position of the inlet of the tubing/pump will be dictated by the changing steam flood dynamics of the well, e.g. steam chest growth, water production, etc..
• a single inverted well 20 may be used both as the steam injector well and the production well. As illustrated in
• a string of injection tubing (shown in dotted lines 30) is run through the production tubing 23 and extends through the wellbore into tail portion 20c. It should be understood that the injection tubing 30 can alternately be ran along side production tubing 23 in the wellbore, if preferred.
• a packer 31 or the like is set to isolate an injection zone within tail portion 20c into which steam is to be injected. The steam heats the oil in reservoir 11 in the same manner as before with the heated fluids flowing downward into the wellbore below the injection zone where it is produced through production tubing 23. The injection of steam through the long tubing string 30 will further enhance the heating of the completed interval of the wellbore.
• inverted production wells can further enhance the steamflood economics by eliminating the lag time normally associated with waiting on thermal communication or response between vertical wells.
• thermal communication in the lateral or horizontal plane is also accelerated significantly.
• the wellbore may be plugged back to shorten its length as the injected steam moves really across the reservoir 11 so that the wellbore remains in contact with the steam chest in both the vertical and lateral or horizontal planes throughout the producing life of the well. This also places the edge of the completion interval in continuous contact with the leading edge of the steam chest. Still further, inverted wells should eliminate the need for cyclic steam, which is typically injected into the production wells of a steam flood during the first few years to stimulate production.
• An added advantage gained from an inverted wellbore is that it provides an improvement in gravel packing horizontal portions of the wellbore.
• the workstring e.g. drill pipe
• the workstring typically used for delivering the gravel slurry during a gravel packing operation can be seated into a shoe on the slotted liner at the tail of the wellbore whereby gravel can flow downward from the tail 20c and into the horizontal portion 20b of the well thereby taking advantage of gravity in the inverted portion to carry the gravel into the horizontal portion of the wellbore.
• inverted production wells in a steamflood operation will increase and accelerate thermal communication between the injection and production wells while at the same time minimizing steam breakthrough at the production wells.
• inverted production wells provide those traditional benefits which are normally derived from more conventional horizontal wells (e.g. long production intervals and reduced bottom water coning) .
• the cost of cyclic steam can be eliminated; the initial hot oil production response may be accelerated by as much as two years in a typical steamflood; heat utilization (both in the reservoir and along the wellbore) to increase oil production will be improved; and steam breakthrough will be reduced and delayed; all of which favorably affect the economics and performance of a steamflood operation by using inverted production wells.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Geology (AREA)
• Mining & Mineral Resources (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)

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• 1996
  • 1996-03-20 CA CA002248757A patent/CA2248757A1/en not_active Abandoned
  • 1996-03-20 EP EP96911343A patent/EP0888489A4/de not_active Withdrawn
  • 1996-03-20 WO PCT/US1996/003718 patent/WO1997035090A1/en not_active Application Discontinuation

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