Abstract:
In aspects, embodiments of the present invention provide devices, systems and methods for managing cuttings formed during drilling of a subsea wellbore. By managing, it is meant the processing, storage, transportation and disposal of the cuttings. In an exemplary application, an offshore rig adapted to drill the wellbore uses one or more a selectively buoyant containers to transport the cuttings. The containers are positioned adjacent the offshore rig. In one arrangement, the containers are submerged to a selected depth below the water&#39;s surface. A transfer unit flows the cuttings from the offshore rig to the container via a conduit connected to the container.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. provisional patent application Ser. No. 60/538,810 filed on Jan. 23, 2004, titled “Floatable Drill Cuttings Bag and Method and System for Use in Cuttings Disposal.” 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to devices and methods for the collection, storage and disposal of drill cuttings, particularly during offshore drilling operations. 
   2. Description of Related Art 
   During a drilling operation, drill cuttings and rock are scraped out of the formation being drilled by a drill bit. The cuttings are then circulated to the surface as drilling mud returns up the annulus of the wellbore. The cuttings are commonly separated from the drilling mud by devices such as shale shakers fitted on the drilling rig. The shakers capture the cuttings and large solids from the drilling fluid during the circulation thereof. A screen is fitted on each shale shaker of certain mesh size and is vibrated to facilitate separation of the majority of fluids from the solids. 
   Handling of the drill cuttings following separation is a significant problem, particularly in offshore drilling, where space on a drilling rig is limited. More generally, this limited space can create difficulties in conveying and storing other materials at the drilling rig. 
   SUMMARY OF THE INVENTION 
   The invention provides improved methods and systems for handling, containment, storage, and haulage of liquids and solids-liquids mixtures such as drill cuttings, base oil, brines, drilling mud, potable water to and from a rig site. 
   In one aspect, embodiments of the present invention provide devices, systems and methods for managing cuttings formed during drilling of a subsea wellbore. By managing, it is meant the recovery, processing, storage, transportation and disposal of the cuttings. In an exemplary application, an offshore rig adapted to drill the wellbore uses one or more a selectively buoyant containers to transport the cuttings. The containers are positioned adjacent the offshore rig. In one arrangement, the containers are submerged to a selected depth below the water&#39;s surface. A transfer unit flows the cuttings from the offshore rig to the container via a conduit connected to the container. 
   In accordance with one embodiment of the invention, cuttings are conveyed from the shaker assembly off of the rig by a transfer mechanism and are received within one or more of the containers. In one embodiment, the containers are submersible flexible bags that include one or more storage compartments and flotation chambers. The bags can be anchored to a stationary location such the sea floor and provided with buoys to mark their location. Other suitable locations can include the rig itself, an adjacent facility, or vessel. Sensors positioned in the system can be used to determine the buoyancy condition of the bags. For example, the weight of each of the bags can be monitored by sensors and the buoyancy of the bags is controlled in order to ensure that the bag(s) remain neutrally buoyant during filling operations. The storage bags may be removed from the vicinity of the drilling rig by towing and brought to a remote location for unloading and further processing. 
   In another aspect, the present invention provides methods, devices and systems for conveying a selected material to and from an offshore facility. An exemplary device includes a selectively buoyant container having one or more compartment for storing a selected material such as drill cuttings, base oil, brines, drilling mud, and potable water. The container in one embodiment is a flexible bag adapted to be positioned adjacent a floating facility in a submersed or semi-submersed state. 
   Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing. 
       FIG. 1  is a schematic view of an exemplary offshore drilling rig utilizing a drill cuttings collection and disposal system in accordance with the present invention; 
       FIG. 2  depicts an exemplary ballast control system for floatable drill cuttings bag; and 
       FIG. 3  is a schematic depiction a submersible floating bag filled with cuttings being towed to a facility for processing and disposal. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows an exemplary offshore drilling platform  10  that supports a drilling rig, generally indicated at  12 . The drilling platform  10  is depicted as a platform that floats in the sea  14 , but may also be a tension leg platform or one in which the platform itself has footings that are landed in the sea floor  16 . The drilling platform  10  also supports several shale shakers  18  that receive drill cuttings from the drilling rig  12 , in a manner that is known in the art. As is known, during drilling, a drill bit (not shown) disintegrates an earthen formation. The disintegrated formation are generally referred to as cuttings and can include rock, earth and other such materials. The cuttings captured on the screens of the shakers  18  gravity flow into sloping ditch arms  20  into retaining area  22 . The cuttings are moved from the retaining area  22  by a conveyor  24  that transports the cuttings to a drill cuttings transfer unit  26 . The conveyor  24  may be a moving screw conveyor or a vacuum, auger, or solids progressive cavity pump. Additionally, a reciprocating pump or dense phase pneumatic blower may be used. The transfer unit  26  drives the conveyor  24  and may be located on the drilling platform  10 , as shown, or fitted on jackup, platform, workover, drillship, or a separate semi submersible drilling platform. The transfer unit  26  transmits the cuttings through a flexible conduit  28  (typically 4″ to 6″ in diameter) to a storage bag  30 . 
   In one embodiment, the storage bag  30  is a flexible container that holds a pre-determined quantity of a material at or below the water&#39;s surface. By flexible, it is meant that the bag  30  can deform to accommodate the material. This deformation can include bending, expanding, and/or contracting. Also, in addition to drill cuttings, the material can include slurries, water, drilling fluids and other liquids or solid-liquid mixtures. The storage bag  30  is substantially fluid-tight to prevent leaking of the contents. Additionally, the storage bag  30  is formed or relatively rugged material adapted to withstand extended exposure to the ocean environment and to withstand submerged or surface towing. The storage bag  30  includes a central storage chamber  32  into which the cuttings are received from the conduit  28 . Additionally, the bag  30  includes one or more flotation chambers  34  that allow the bag  30  to buoyantly float in the sea  14 . The bag  30  is secured by a tether  36  to an anchor  38  that rests upon the sea floor  16 . The tether  36  can have an adjustable length to accommodate different water depths. In this manner, the bag  30  is maintained in position with respect to the floating platform  10 . A buoy  40  is secured by a line  42  to the bag  30  in order to mark the position of the bag  30 . Additional bags  44  are positioned alongside the storage bag  30 . These bags  44  are each provided with a tether  36 , anchor  38 , and buoy  40  in the same manner as for the bag  30 . As can be seen from  FIG. 1 , the conduit  28  is interconnected with each of the multiple bags  30  and  44  so that each of the bags  30 ,  44  may be filled by the conduit  28 . Associated with the conduit  28  is a valving system (not shown) that selectively opens and closes valves that permit cuttings to flow into each individual bag. The valving system can be controlled by the controller  48  (discussed below) to provide for such filling. 
   Referring now to  FIGS. 1 and 2 , in one embodiment, a ballast control unit  31  controls the buoyancy of the bag  30 . An exemplary ballast control unit  31  can include one or more sensors for determining the state of buoyancy of the bag  30 , a control unit  48 , an air supply line  50 , and an air supply  52 . It should be appreciated that lighter-than-water buoyant fluids other than air can also be used to provide buoyancy. Additionally, buoyant material such as foam can also be used to provide a preset amount of buoyancy for the bag  30 . 
   In one arrangement, a load cell sensor, shown schematically at  46  in  FIG. 1 , can be incorporated into the tether assembly  36  to sense the strain placed upon the tether from buoyancy of the bag  30 . Load sensors of this type and other types are known in the art for detecting and measuring tensional strain on a line or cable. Other sensor arrangements, such as sensors that measure pressure or depth, can also be used in suitable applications. 
   As illustrated in  FIG. 2 , data supplied by the load cell sensor  46  or other type of sensor is used by a controller  48  to control and adjust the buoyancy of the bag  30 . The flotation chamber (or chambers)  34  of the bag  30  is connected to the air supply line  50  to add air to the flotation chamber  34  and make it more buoyant. The air supply line  50  is interconnected to the air source  52  and includes a fluid control valve  54  that can be actuated to selectively transmit air from the air source  52  into the flotation chamber  34 . Additionally, the flotation chamber  34  is provided with an air outlet  56  having release valve  58  for the selective removal of air from the flotation chamber  34 . Control lines  60 ,  62  are provided from the controller  48  to the fluid control valve  54  and release valve  58 . 
   The controller  48  preferably comprises a programmable logic controller (PLC) that receives data relating to the measured strain from the load cell sensor  46  and, in response, controls the buoyancy of the bag  30 . The controller  48  is preferably preprogrammed to maintain the bag  30  at a predetermined depth within the sea  14 . If the tension on the tether assembly  36  detected by the load cell sensor  46  is positive, this will indicate that the bag  30  has positive flotation. However, if there is excess tension detected (i.e., tension that exceeds a predetermined amount that is programmed into the controller  48 ), the controller  48  will release air from the flotation chamber  34  via control line  62  to actuate release valve  58 . If, however, there is no tension detected on the tether assembly  36  by the load cell sensor  46 , this will indicate that the bag  30  does not have positive flotation. The controller  48  will cause the fluid control line  60  to open and admit additional air into the flotation chamber  34 , thereby causing the bag  30  to become more buoyant. The controller  48  may be preprogrammed to iteratively control the buoyancy of the bag  30  during filling so that a substantially constant floating depth is provided. For example, the controller  48  can be programmed to keep the bag  30  neutrally buoyant, positively buoyant, or negatively buoyant. 
   An amphibious remotely operated vehicle (ROV), schematically shown at  64  in  FIG. 1 , of a type known in the art, may be used to service the bags  30 ,  44 , such as by connecting or disconnecting the conduit  28  or tethers  36  or lines  42 . Alternatively, divers might be used for this purpose. 
   In operation of the cutting handling and disposal method of the present invention, liquid is initially separated from the cuttings by the shakers  18 . Separated cuttings are then transported via conveyor  24  to the transfer unit  26  and, from there into the conduit  28  to the bag  30 . The transfer unit  26  can include one or more pumps for flowing the cuttings to the bag  30 . In one arrangement, the transfer unit  26  is controlled by a control unit  27  that can include programs to control the pumping process. For example, the control unit  27  and adjusting the pump rate in response to measurements from a sensor such as sensor  46  or other sensors  29  measure one or more parameters of interest such as pressure, flow rate, temperature, etc. The first bag  30  is filled with drill cuttings while the controller  48  monitors the buoyancy of the bag  30  and ensures its flotation at a particular depth. When the first bag  30  is filled to capacity with cuttings, subsequent bags  44  are then filled. In order to do this, the ROV  64  disconnects the conduit  28  from the first bag  30  and connects it to an inlet for one of the other bags  44  so that it may be filled in the same way. During this operation, the transfer unit  26  stops pumping cuttings through the conduit  28 . In some applications, simultaneous filling of multiple bags may be accomplished by appropriately programming the controller  48  and utilizing additional flow lines. 
   In one embodiment, the conduit  28  is formed with multiple bores or channels for conveying one or more materials from the transfer unit  26  to the bag  30 . In one arrangement, the conduit  28  can include bores for separately conveying one more liquids, gases, solids, or mixtures. For example, one bore can be adapted to convey the cuttings and another bore can be adapted to convey air. In another arrangement, a bore can be adapted to convey two or more materials either simulataneously or sequentially. In still other arrangements, the bores can provide bidirectional movement of the material. For example, solids or other materials can be conveyed from the bag  30  to the rig  12  as well as from the rig  12  to the bag  30 . Additionally, the conduit  28  can include conductors for conducting power (e.g., electrical power, pressurized hydraulic fluid, etc.) and data signals. 
   It should be appreciated that the teachings of the present invention also include the processing and disposal of the cuttings. Referring now to  FIG. 3 , there is shown a barge  70  towing a bag  30  that has been filled with cuttings. The destination of the bag  30  can be an offshore disposal facility  90  or a land-based disposal facility  100 . In mode of operation, the bag  30  is towed to the offshore facility  90 . The contents of the bag  30  can be removed by methods such as vacuuming or physically tipping the bag  30 . The removed contents are processed as needed to meet environmental regulations and injected via a tubular  92  into a subterranean formation  94  suited to store the processed cuttings. In another mode of operation, the bag  30  is towed to a port or dock  102  wherein the contents are removed and taken to the land-based processing facility  100  for processing and disposal. 
   It should be appreciated that the above-described embodiments are merely exemplary of the teachings of the present invention and that numerous modifications and variations can be made. For example, the bags  30 ,  44  can rest upon the sea floor  16  during filling operations rather than floating above it. Moreover the bags  30 ,  44  can be connected to a relatively stationary location such as the rig or an adjacent facility or vessel. Additionally, any number of bags  30  may be used, not merely the quantity shown in the Figures. 
   In still other embodiments, the bags  30  can be used as a container to transport materials such as base oil, brines, drilling mud, potable water, and chemical additives. These materials can be conveyed into the bags and towed at or below the water&#39;s surface. Moreover, these materials can be tethered adjacent a facility and act as a temporary storage container. It should be appreciated that the bags  30  provide a 154-36748-US convenient method of transporting drilling mud, potable water, and other fluids used to support operations at an offshore hydrocarbon recovery facility. 
   Although the invention has been described in terms of particular embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. Alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.