Patent Application
20100147587
The present application relates in general to wellbore operations and more specifically to methods and apparatus for completing wells and providing fluid communication between the wellbore and the target formations. BACKGROUND
Perforating is a completion operation that provides fluid communication between a subterranean geological formation and a wellbore, which in turn connects the reservoir to the Earth's surface. The goal is to facilitate controlled flow of the fluids between the reservoir formation and the wellbore. Perforating operations are commonly accomplished by running a perforating gun string into the wellbore and firing of explosive charges proximate the desired reservoir formation. The explosive charges deposit significant energy into the reservoir formation within microseconds.
While successfully connecting the reservoir to the wellbore, the perforating event can be detrimental to the formation's localized pore structure (permeability) and, hence, the productivity of the formation. The damage to this shock region is typically mitigated by surge flow, wherein the damaged rock is quickly “sucked” into the wellbore. The surge flow is operationally achieved by underbalanced perforating, wherein the wellbore pressure is set to be less than the reservoir pressure when the charges are detonated. However, underbalance perforating is not always effective. In some instances, the underbalance pressure differential may not be sufficient to overcome the dynamic overbalance caused by the detonation and burn of the perforating charges. In other cases, the underbalance differential may result in collapse of the perforations and or excess inflow of sand.
In many instances, perforation of the well completion is followed with a formation stimulation operation such as fracturing. Fracturing of the formation includes pressuring the desired formation zone, hydraulically or by igniting a propellant.
One embodiment of a wellbore tool includes a perforating charge adapted to create a tunnel in a subterranean formation upon activation; a propellant that provides a pressure cycle when activated; a first delay device operationally connected to the perforating charge to activate the perforating charge; and a second delay device operationally connected to the propellant to activate the propellant in a manner to influence a selected wellbore condition.
An embodiment of a method of influencing a wellbore pressure cycle during a wellbore operation includes the steps of performing a wellbore operation; activating a propellant in the wellbore; and influencing a selected wellbore condition.
An embodiment of a method for performing a wellbore perforating operation includes the steps of detonating a perforating gun in a wellbore to create a tunnel in a target formation; activating a propellant; and influencing a selected wellbore condition.
The foregoing has outlined some of the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages will be described hereinafter which form the subject of the claims.
The foregoing and other features and aspects will be best understood with reference to the following detailed description of a specific embodiment, when read in conjunction with the accompanying drawings, wherein:
Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. In the following description, numerous details are set forth to provide an understanding of the present embodiments. However, it will be understood by those skilled in the art that the present embodiments may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.
As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and “downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate. Moreover, in the specification and appended claims, the term “detonating cord” is intended to include a detonating cord, a deflagrating cord, an igniter cord, or any other cord used to initiate the detonation of another explosive having one or more ignition points.
Tool 10 includes a propellant 20 and a perforating gun 22 having one or more explosive charges 24. Propellant 20 and perforating charges 24 may be connected to a detonating cord 26. A control or delay element 28 may be in operational connection with propellant 20 and/or perforating charges 24 to selectively offset the activation of propellant 20 and perforating charges 24 relative to one another. In the illustrated embodiment, a first delay element 28a is shown connected with perforating gun 22, thus perforating charges 24, and detonation cord 26. A second delay element 28b is connected with detonating cord 26 and propellant 20. In some embodiments, the delay element may be positioned distally from the propellant and/or the perforating gun, for example at the surface. Examples of delay elements include, without limitation, mechanical, electrical, and pyrotechnic devices such as, but not limit to, timers, fuses, processors and electrical circuits. In some embodiments, an activation signal may be provided to activate the propellant separate from the activation signal transmitted to the perforating gun. It is noted that signals for activation of charges 24 and/or propellant 20 may be communicated over an electrical conductor, a fiber optic line, a hydraulic control line, mud pulse, wireless transmission and the like.
Propellant 20 is a pressure generating device. Propellant 20 may be, but is not limited to, a material or a device that when activated creates a pressure cycle that may be identified. The pressure cycle may be referred to herein as a propellant cycle or propellant pressure cycle to avoid confusion with the perforating charge detonation or the wellbore pressure cycle during the wellbore operation being performed. In some embodiments, propellant 20 temporarily generates pressure in a known pressure cycle.
Examples of propellant 20 include, but are not limited to, materials that burn, materials stored under pressure and released upon activation, materials that undergo a pressure inducing chemical reaction, and mechanical pressure generating devices. The pressure cycle represents the high and low pressures over a relevant time period, which in some embodiments may be measured in milliseconds. In the illustrated embodiment, propellant 20 includes a solid propellant material that upon activation or ignition it produces a radial burn that may have a known pressure cycle. Some embodiments of propellant 20 are disclosed in U.S. Pat. No. 7,431,075, the teachings of which are incorporated herein by reference.
Illustrated perforating gun 22 includes a plurality of shaped explosive charges 24 to create perforations or tunnels 30 in formation 16. As is known in the art, tunnels 30 are provided to create or enhance the fluid communication between wellbore 12 and formation 16. In some embodiments it is desired to promote inflow of fluid from formation 16 upon completion of tunnels 30 to remove debris. This is often accomplished by underbalance perforating; wherein the pressure in the wellbore at formation 16 is less than the pressure in formation 16 before the perforating charges are detonated. However, at times a sufficient underbalance differential cannot be established or another pressure environment may be desired. For example, and without limitation, it may be desired to increase the underbalance differential at the point of initiating perforating and/or at the completion of the formation of tunnels 30; to decrease the underbalance differential at various time periods of the perforating operation; to provide an overbalance differential or a balance condition at one or more time of the perforation operation. Examples of some embodiments of wellbore pressure cycles and wellbore conditions that may be desired to be achieved during perforating operations are taught in U.S. Pat. No. 7,428,921, assigned to Schlumberger Technology Corporation, and incorporated herein by reference.
Tool 10 may be utilized to control or influence desired wellbore conditions in the wellbore proximate to the target formation 16 during wellbore operations. One embodiment of a wellbore operation is a perforating operation. It is noted for purposes of description that perforating operations include a period of time prior to detonation of perforating charges 24 and subsequent to the creation of tunnels 30. Wellbore conditions may include overbalance, underbalance and balanced pressure conditions.
A method for performing a wellbore operation is now described. In this embodiment, the wellbore operation is a perforating operation and may include formation fracturing. A propellant 20 and perforating charges 24 are disposed in wellbore 12 and positioned proximate to a target subterranean formation 16. Propellant 20 and perforating charges 24 may be positioned proximate to one another. Propellant 20 and perforating charges 24 may be carried on the same conveyance 18. It is noted, that more than one propellant 20 and or perforating gun 22 may be utilized. Further, the separate propellants 20 and perforating guns 22 may be activated at different times from one another.
In some embodiments, a desired wellbore pressure condition or pressure profile for the wellbore operation may be pre-determined. Activating perforating gun 22 and detonating perforating charges 24 creates tunnels 30 in formation 16. It is recognized that detonated perforating charges 24 have a pressure cycle that create dynamic pressure conditions in wellbore 12. Propellant 20 is activated to influence the desired wellbore pressure condition or conditions. A time delay between the activation of propellant 20 and perforating gun 22 may be selected to influence the wellbore pressure conditions to achieve the desired wellbore pressure condition. The wellbore condition may include a pressure profile of the wellbore operation. Propellant 20 may be activated prior to, simultaneous with, or after the perforating gun is activated.
In one example, propellant 20 may be activated prior to activation of perforating gun 22 so that the pressure low at the end of the propellant pressure cycle corresponds with completion of tunnel 30. This increases the underbalance differential proximate to the time of completion of tunnels 30 and may promote the influx of fluid and cleaning of tunnels 30. Further, activation of propellant 20 may be utilized to increase the pressure conditions during creation of tunnels 30 which may provide a fracturing force to formation 16.
In another example, propellant 20 may be activated relative to activation of charges 24 so that the high pressure of the propellant pressure cycle corresponds with the completion of the formation of tunnels 30. In this manner the wellbore pressure conditions may minimize damage to tunnels 30 and/or sanding of the well.
In some embodiments, propellant 20 is adapted to provide a propellant pressure profile that includes a relatively slow pressure decline. This may influence wellbore conditions and limit the inflow or pressure drop of the inflow of fluid and minimize formation damage and/or sand influx. In some embodiments, one or more propellants 20 may be activated to limit the rate of decline of the pressure cycle from high to low.
From the foregoing detailed description of specific embodiments, it should be apparent that devices, systems and method for timing a pressure cycle of a propellant to influence a wellbore operation that is novel has been disclosed. Although specific embodiments have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects, and is not intended to be limiting with respect to the scope of the claims. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope defined by the appended claims which follow.
