Method and apparatus for completing a horizontal well

A firing head assembly has a sealed chamber containing a piston, a firing pin, and an impact detonator. The firing head assembly and a perforating charge are installed within a sub and the sub is secured into a string of conduit being lowered into a wellbore. After cementing the conduit, the operator drills out the cement in the conduit, disintegrating the chamber and exposing the sealed chamber to the fluid pressure of the drilling fluid in the conduit. The drilling fluid pressure causes the piston to drive the firing pin against the detonator, which detonates the perforating charge. The operator then pumps down a logging tool to survey the well. Fluid in the conduit below the pump-down head can flow out the displacement perforation into the earth formation while the logging tool is moving downward.

FIELD OF THE INVENTION

This invention relates in general to oil and gas well drilling and in particular to a method of completing a horizontal well that enables a wireline well tool to be pumped down a liner.

BACKGROUND OF THE INVENTION

Highly deviated or horizontal wells are commonly drilled for oil and gas production. As used herein, the term “horizontal” refers to not only wells with truly horizontal sections, but also to wells that are highly deviated. In one type of horizontal well completion, the operator installs and cements a casing or liner that extends to the total depth of the well. Normally, the term “casing” refers to conduit that extends back to the surface wellhead, and “liner” refers to conduit that has its upper end supported near the lower end of a first string of casing. These terms will be used interchangeably herein to refer to a conduit in a well that is cemented in place, whether its upper end extends to the surface or just to the lower end of a first string of casing.

After cementing the casing, the operator perforates through the casing into the producing formation. The operator may then perform other operations, such as hydraulic fracturing or dispensing acid or other chemicals into the producing formation. Normally, the operator installs a string of production tubing in the casing for the production flow.

Even though wells may be fairly close to each other, producing formations often vary in characteristics from one well to another, such as thickness, depth, porosity, water content, permeability and the like. Consequently, it is useful to have a survey or log made of the well before it is cased to provide the characteristics of the producing formation. In highly deviated and horizontal wells, logging can be made while drilling using measuring while drilling techniques.

After cementing, it is also useful for the operator to perform another survey of the well. Because of the casing, the cased-hole log differs from an open-hole survey. By using tools such as ones that measure natural gamma rays emitted by earth formations, the operator will be able to discern the same formations previously noted during the open-hole survey. The operator uses this information to determine precisely where to perforate. Even without an open-hole log, a cased-hole survey provides important information to the operator.

In a vertical or even a moderately deviated well, the operator can run a cased-hole log before perforating by lowering a surveying instrument on a wireline into the casing and making the survey either while running-in or retrieving. Logging a cased horizontal well presents a problem, because gravity won't pull the tool down. One approach has been to mount to the instrument a tractor with motor-driven wheels or tracks. Generally, these logging procedures are expensive and slow. Also, high voltages are typically required, which can be detrimental to the wireline.

Surveying instruments have been pumped down wells in the prior art. An annular piston is mounted to the instrument assembly for sealingly engaging the conduit. This type of operation requires a flow path for displaced fluid below the piston as the instrument moves downward. In the prior art, the flow path typically comprises an open annulus surrounding the conduit containing the instrument. In a cased horizontal well, there is no open annulus surrounding the casing and no place for displaced fluid. Consequently, pump-down logging is normally not performed on horizontal wells.

SUMMARY

In this invention, the operator runs and cements a conduit, such as a liner or casing in a wellbore. The operator then forms one or more displacement perforations through the conduit and surrounding cement and into an earth formation. He then pumps down a wireline logging tool with a pump-down head. The downward movement of the pump-down head causes some of the fluid below the pump-down head to be displaced out through the displacement perforation into the formation. While the logging tool is in the conduit, the operator performs a survey of the well.

Preferably, the operator forms the displacement perforation with a firing head assembly comprising a sealed chamber containing a piston, a firing pin, and an impact detonator. The firing head assembly is mounted within a sub and the impact detonator is linked to a perforating charge. The operator secures the sub to the string of conduit as it is being lowered into the wellbore.

After cementing, the operator lowers a drill bit into the conduit and drills out cement left in the sub and in the lower portion of the conduit. The drill bit ruptures the sealed chamber of the firing head assembly, which exposes the sealed chamber to drilling fluid pressure. The fluid pressure causes the piston to drive the firing pin against the detonator, thereby detonating the perforating charge.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1, the well has a vertical section with a conventional string of casing11that is cemented in place. The operator has drilled an open hole section13below casing11open hole section13having a substantially horizontal portion that may extend thousands of feet. In the embodiment ofFIG. 1, a string of drill pipe15is shown extending into the casing11. A setting tool17is located on the lower end of drill pipe15. Setting tool17is connected to a tieback extension19, which in turn is connected to a packer21. Packer21is connected to a liner hanger23. A liner25is secured to liner hanger23for securing the upper end of liner25to the inner diameter of casing11. Liner25is a string of casing smaller in diameter than the casing11. Rather than having its upper end near the lower end of casing11, liner25could have its upper end at the surface. Liner25is shown in the process of being installed with its upper end a short distance above the lower end of casing11and its lower end near the bottom of the well. Setting tool17, tieback extension19, packer21and hanger23are conventional components used to set liner25.

Liner25has a landing collar27at its lower end for receiving a conventional cement plug (not shown). A displacement sub29constructed in accordance with this invention is secured to the lower end of landing collar27. An extension member31, which may be a section of the same pipe as liner25, extends below displacement sub29. A conventional cement set shoe33is secured to the lower end of extension member31.

After running liner25, the operator pumps cement down liner25, landing collar27, displacement sub29, extension member31and cement shoe33. Cement35flows out cement shoe33and back up the annulus in open hole13surrounding liner25, as illustrated inFIG. 1. After dispensing the desired amount of cement, the operator pumps down a conventional drillable plug (not shown), which lands in landing collar27. Cement35will cure not only in the annulus surrounding landing collar27, extension member31, displacement sub29, and liner25, but also within extension member31and displacement sub29. Immediately after pumping cement35, the operator sets packer21and retrieves the string of drill pipe15and setting tool17.

Referring toFIG. 2, displacement sub29has a tubular steel housing37of substantially the same diameter as liner25. Housing37contains a body39of a drillable material, such as aluminum, brass or composite. Body39is a cylindrical member that is sealingly secured within housing37. Body39has a flow port41extending from its upper end to its lower end for fluid circulation prior to cementing and also for cement35flow. As shown inFIG. 4, flow port41may be crescent-shaped, and it is offset from the longitudinal axis of body39. Prior to pumping the cement through displacement sub29, flow port41is open. As shown inFIG. 5, after pumping cement35, the cement will cure within and block flow port41.

Referring toFIG. 3, a firing head assembly43is secured by threads into the upper end of body39. Firing head assembly43is also of drillable materials and is offset from the axis of body39. Firing head assembly43has a housing45made up of a number of tubular sections secured and sealed together as shown inFIG. 3. A bore47is located within an upper portion of firing head housing45. Firing head housing45has a cap49that encloses the upper end of bore47. A piston51is carried within bore47for movement from the initial position shown inFIG. 3to a lower position (not shown). Piston51is initially spaced with its upper end below cap49. A chamber53at atmospheric pressure is located between the upper end of piston51and cap49. Piston51sealingly engages bore47and is held in the initial position by shear pins55. Piston51has a downward extending rod with a sharp firing pin57fixed to its lower end.

A percussive detonator59is located within firing head housing45a short distance below firing pin57. Detonator59is connected to detonating cord61, which leads to one or more shaped or perforating charges63(only one shown inFIGS. 2 and 3). Detonator59, detonating cord61and shaped charges63are conventional components used in perforating operations. The number of shaped charges63can vary.

Referring toFIG. 2, an optional dye pack housing65is secured by threads to the lower end of body39. Dye pack housing65is also of drillable material and has a sealed chamber that contains a dye. When exposed to well bore fluid, the dye will discolor the fluid circulating back to the surface to indicate that displacement sub29has been drilled through.

Referring toFIG. 6, after cement35is cured and the operator has removed setting tool17(FIG. 1), the operator runs back into the well with a drill bit67on the lower end of drill pipe15. Drill bit67will drill the cement plug (not shown) in collar27, and then began drilling components of displacement sub29. During drilling, the operator pumps drilling fluid through drill pipe15, which discharges from drill bit67and flows back up the annulus between drill pipe15and liner25. Once drill bit67drills through cap49(FIG. 3), the pressure of the drilling fluid will be applied to chamber53, which was previously at atmospheric pressure. The drilling fluid pressure causes shear pins55to shear, pushing piston51and firing pin57downward. Firing pin57strikes and ignites detonator59, which in turn ignites detonating cord61and shaped charges63. The explosion creates perforations69through cement35and into the earth formation as illustrated inFIGS. 7 and 8.

After firing, the operator continues drilling firing head assembly43(FIG. 3) and body39(FIG. 2). When drill bit67reaches dye pack assembly65, the dye is released. The fluid being pumped down drill string15causes dye66to color the drilling fluid returning to the surface, indicating to the operator that he has now drilled through displacement sub29. Tile operator stops drilling substantially at this point, leaving cement35within extension member31and cement shoe33. The operator then retrieves drill pipe15and drill bit67(FIG. 6).

Referring toFIG. 9, the operator may now perform wireline services in the well, using a wireline tool73. Wireline tool73may be any type of conventional wireline service equipment, such as a gamma ray wireline tool, a cement bond wireline tool, perforating equipment or a plug or packer setting tool. Wireline tool73may be attached to a pump-down head71to facilitate pumping down liner25. Pump-down head71is piston-like member that fits closely within tile inner diameter of liner25. Because of their large diameter, some wireline tools73, such as a bridge plug, may not need an additional pump down head71. Pump down head71is located at the lower end of wireline tool73, which is connected to an electrical cable77that leads to the surface.

At the surface, a blowout preventer79will close the well in the event of an emergency. Blowout preventer79may include wireline rams that close around electrical cable77as well as shear rams that will cut it. A manifold81is secured to blowout preventer79for pumping fluid, typically water, into casing11and liner25to force pump-down head71downward. A lubricator83seals around electrical cable77as it moves. Electrical cable77is dispensed by a winch85at the surface. A logging unit87supplies electrical power to electrical cable77and receives signals indicating parameters of the earth formations and cement35.

As illustrated inFIG. 9, fluid89is located below pump-down head71. As pump-down head71moves downward, it displaces some of the fluid89, which flows into displacement perforations69. The exterior of pump-down head71does not form a tight seal with the inner diameter of liner25; rather a small clearance will exist for some of the fluid89to flow around pump-down head71as it moves downward. However, without displacement perforations69, it would not be feasible to pump wireline tool73to the lower end of liner25. Preferably, the operator continues pumping down pump-down head71until it reaches the lower end of displacement sub29.

Subsequently, the operator will retrieve pump-down head71and tool73by winding electrical cable77back onto winch85. The operator may perform the log while retrieving tool73, or while pumping tool73down, or both. The operator then may complete the well by running production tubing and perforating in a variety of conventional manners.

Referring toFIG. 10, in one completion method, the operator perforates to form production perforations93above displacement perforations69. The production perforations93could be made in several ways, one of which could be pumping down through liner25a pump-down perforating gun on wireline, with displaced fluid flowing out displacement perforations69. A bridge plug91could then be set above the displacement perforations69to isolate them from production perforations. The operator may then run a string of production tubing95and set a packer97in liner25above production perforations93. Tubing95is suspended conventionally from a wellhead assembly99for conveying well fluid to the surface.

Alternately, the operator could first set bridge plug91, then run tubing95, then pump down a perforating gun through tubing95with displaced fluid flowing back up the tubing annulus within liner25before setting packer97. The operator could also make the production perforations with a tubing conveyed perforating gun.

The invention has significant advantages. By forming a displacement perforation into the formation, the operator can use a pump-down logging tool, with displacement fluid flowing into the formation. Forming the displacement perforation while drilling out the cement avoids an additional trip just to make the displacement perforation. This method avoids the need for a tractor, thus saving time and expense.

While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.