Cutting boxes are the primary method of transporting waste drilling fluid and cuttings to shore around the world. Cuttings boxes were developed as an easy method of collecting and transporting cuttings given the weight restrictions of offshore cranes on earlier drilling rigs. Cutting boxes are typically placed near the solids control equipment, where cuttings can be moved relatively short distances and collected in the box. When a Cutting boxes gets full, it is removed and an empty Cutting boxes is shuffled into position. When a sufficient number of full Cutting boxes are ready, they are backloaded onto a workboat and returned to shore. Empty Cutting boxes from the dock facility replace the returned cuttings boxes.
In the United States, cuttings boxes (small tanks) must be Coast Guard approved. In other developed areas there are similar requirements. These standards have been developed for safety reasons. Some of the box requirements are:
- Cutting boxes should have a cover that can be locked down and sealed shut. Lid gaskets should be checked frequently.
- The Cutting boxes must be of sufficient strength to survive a drop of 1 meter without leaking or deforming. Skids, frames, and braces should be in good shape. If the Cutting boxes is rusty or shows signs of abuse, it is probably not maintained properly.
- Since the Cutting boxes is sealed, it must have pressure relief to prevent explosion and vacuum relief to allow the lid to be opened when the contents cool and form a vacuum. A rupture disc is usually installed on the lid to allow emergency venting. Check the rupture disc inspection date. A small valve may be used for vacuum venting.
In developing countries, homemade boxes are sometimes encountered. Transporting and emptying boxes is always dangerous. The use of homemade boxes or poorly maintained boxes can be hazardous.
The parameter of cuttings boxes of aipu soilds manuefactured
|6’ 7”||5’ 9”||4’ 4”||2,711lbs.|
Removing settled solids from the box has always been a problem. The cutings boxes have undergone a long period of settling in conjunction with severe vibration (both on the rig and during transport). Typically, the top-filled boxes are lifted and turned over to remove the solids. Sometimes the cuttings boxes have a side-emptying hatch that can be opened, to eliminate turning the box over. Some of the boxes have a sidemounted flushing valve to help flush settled cuttings out of the box. In any event, emptying the box is very dangerous and a nasty, sloppy job.
Cuttings boxes typically come in two sizes: 25 bbl and 15 bbl. The 25-bbl boxes can approach 15 tons when full, especially if highly weighted fluid is being used. The 15-bbl boxes were designed for situations in which the larger boxes could not be handled by the rig crane. The 15-bbl boxes weigh between 7 and 10 tons when full. Boxes can usually be stacked two high when empty, but must not be stacked when full. An area of 4 by 6 feet per box can be used for planning purposes. For larger jobs, as many as 25 to 30 boxes per group (three groups overall) will be used. Rig space needs to be available to accommodate all the boxes.
An alternative to Cuttings boxes use is the use of bulk systems. An example of a bulk system is the collection and transport of inland water cuttings by shale barges. A shale barge typically holds 4000 bbl of fluid and cuttings in four compartments. The compartmentalized tank is basically mounted on a barge. However, shale barges are meant for relatively calm waters and are not intended for offshore use. The forces developed by the heavy cuttings in the barge tanks due to wave action can break the tank walls and/or sink the barge.
Bulk systems for offshore use are basically seagoing vessels. The tanks used for storage are mounted in the hull. The vessels and the tanks are designed to overcome the ‘‘sloshing’’ of the cuttings due to wave action. The problem with putting cuttings in tanks within vessels has historically been that the cuttings settle into a solid mass that is very difficult to remove.
Two relatively new systems have been developed for moving cuttings in larger volumes. The first is a hydraulic-driven submersible pump. The second is a pneumatic system.
The hydraulically driven, modified submersible pump is usually mounted on a movable arm, although it may be fixed in an offshore application. The pump can also be mounted on a tank. A hydraulic motor is used rather than an electric motor. This makes the combination of motor and pump much lighter (and safer for submersible operations). Whereas a 50-hp electric pump is very heavy, a 150-hp hydraulic pump is much lighter. This means that much more power to slurry and pump the cuttings can be applied.
The system is capable of pumping fluid or cuttings, with relatively low liquid content, over considerable distances. The original use of the system was to move cuttings from barges into sealed dump trucks at a dock facility. It was also used to pump fluid and cuttings from earthen pits for downhole injection. One early system was mounted on a 150-bbl tank so that it could be used to collect cuttings and transfer them as well. The pump ran on a track and could be moved to any part of the tank to facilitate slurrying the cuttings, even if they had settled and appeared hard packed. The system is fairly reliable from a technical standpoint. Of course, as with most systems, the state of reliability depends on the operator’s expertise and the maintenance of the equipment.
Typically, for an offshore application, it would be desirable to pump the cuttings from a collection tank to boat tanks. The boat would take The cuttings to shore. Another pump at the shore base would pump the cuttings out of the boat tanks into transport vehicles to be transferred to the disposal site. The boat tanks must have specially designed entryways to allow the pump to be inserted into the tanks and moved around to reslurry the settled cuttings. The shore transportation might be avoided if the disposal site is near enough to the shore base.
In the pneumatic system, a cuttings blower blows the cuttings from the cuttings trough to temporary storage containers. The blower uses pulses of air provided from an air compressor. The units are automated and the pulses controlled by relays and timers. The operator adjusts only the timer, which would vary only if there were a great change in the rate of penetration.
The temporary storage containers are a series of pressure tanks with 95-bbl capacity. The number of tanks depends on the amount of cuttings generated and needing to be stored. In this character the tanks are similar to boxes, except they are larger. A number of tanks are manifolded together and can be located in a variety of locations as space and deck load permit and as required for cuttings storage. The size of each unit is 8×81⁄2×20 feet tall. Each is located on a hydraulic load cell that is used to determine the weight of cuttings produced and when it is necessary to switch to an empty tank. The system can be manually operated or automatic. In automatic mode, a valve closes and directs the flow to a new tank when the original tank is full (by weight). In manual mode, an operator simply changes the hoses.
The system is designed so that tanks are also mounted on a boat. When the boat arrives at the rig site, the cuttings in the rig’s tanks are transferred to the boat’s tanks. The contents of the tanks are removed in less than an hour. The boat returns to shore, where its contents are transferred to shore-based transportation. The tank can also be lifted and moved if crane capacity allows the lift.
Alternatives to Cuttings boxes offer the advantage that larger quantities of waste fluid and cuttings can be transferred, thus reducing the logistical requirements. However, they are fairly new and have limited usage.