Waste Mud Treatment System makes possible to get rid of discharge of drilling waste. Performance of Waste Mud Treatment System was confirmed through the tests sea trials. It was confirmed that treatment capacity of drill drain and waist mud becomes approximately as planed, and there are same items to need improvement. On the other hand, about the treatment of cuttings, the systems were improved to realize necessary performance through the sea trials.
Mud circulation generates drilling waste such as waste mud and cuttings on board. Inthe oil industry, the drilling waste is usually abandoned into the sea. However, in late years the interst for an environment of a drilling waste tends to became severe.
Catagory Of Drilling Waste
The dilling waste is classified three kinds of drilling waste that are drill drain, waste mud and cuttings. The drill drain is thin muddy water contained in the drilling drain tank, such as water used to wash lifted drill pipe, water for washing the circulation equipment etc., or rainwater collected in the drill floor. The waste mud is drilling mud collected in the waste mud tank and reserce mud tank that is degraded, replaced with fressh mud by dilution, or contaminated by cementing. They are separated from mud by shale shakers, mud cleaners, decanter centrifuges and settling solid.
Outline of Drill Waste Treatment Methods
Drilling waste has following characteristic.
- Drilling waste consists of many ingredients (bentonite, balyte, polymer, cattings, etc.)
- A change of the density, composition are big.
- High viscosity.
- Content of oil and hydrogen sufide gas are high.
- mixture of heavy metals.
In consideration of these characteristics, the methods of drill waste treatment are classified roughly 3 kinds of it.
Drill Drain Treatment Process
A processing method of drill drain adopts thickening. Drill drain is heated for thickening by evaporation. It is a point how this method saves thermal energy. It is a key whether you collect energy used for evaporation in the case of the distillation. Before that, a vacuum pump is used to lower the internal pressure of the evaporator in order to accelerate the evaporation of the moisture contents of the drill drain. Evaporated water recovered from drill drain by thickening process shall be filtered and discharged to overboard or transferred to drill water tank. When condenting ratio rise, fluidity of drill drain decreases. Therefore, thickening process is stopped just before that.
Waste Mud Treament Process
Waste mud and thickened drill drain shall be mixed in daily tank. Solid in waste mud and thickened drill drain is cohered and stabilized by chemical process. Cohesive chemical is water-spluble liquid polmer added to promte cohesion. Cohesive additive is inorgnic multivalent salt solution added to cohere solids contained in waste mud. A solids particles is charged with electricity to a negative ion. By adding a positive ion such as the ferric chloride, a solids particles reacts, removes a coloration ingredient and is precipitated. Cohesive waste mud is squeezed out by mechanical process (solids control process). Then waste mud and thickened drill drain shall be separated to sludge and squeezed liquid.
Cuttings and sludge shall be mixed with cement, and stabilized. The calcium hydroxide is formed by hydration from cement. Hereby the hydroxide alkalify strongly. Heavy meatals and toxic substance are absorbed on surface of hydrate. Hereby, stable calciumchloride is formed and is precipitated.
OUTLINE OF DRILL WASTE TREATMENT SYSTEM
Drill waste, including drill drain, waste mud and cuttings are landed outboard for disposal after temporary inboard storage. To facilitate transportation and final disposal of the drill waste, the Drill Waste Treatment System is installed for the volume reduction and stabilization of the drill waste.
Drilling Mud Waste Treatment Design Condition
The requirements of Drill Waste Treatment System;
Incidence of drill drain, waste mud and cuttings depends on drilling plan and stage of drilling operation. Incidences of them are determined according to the experiences of drilling for oil well as follows.
- Drill drain is stored in drill drain tanks and waste mud is stored in waste mud tanks. Average incidence of drill drain and waste mud is determined as follows: Drill drain: 100 m3/day; Waste mud: 40 m3/day. Incidence of cuttings is determined as follows: 1 hour peak: 20 m3/hour at specific gravity 1.5; 1 day peak: 60 m3/day at specific gravity 1.5.
- 24 hours operation (Promotion of automation)
- To use it on the ship (miniaturization, anti-heaving and anti-rolling)
- To be followed the laws.
- Explosion proof.
The mass-balance of the waste mud treatment system is shown in fig. 1.
The Drill Waste Treatment System consists of the following 6 sub-system groups. (see fig.2) (Drill Drain Thickening System; Evaporated Water Filtration System; Cohesion and Dehydration System; Cuttings Transfer System; Drill Sludge Stabilizing System; Big Bag Filling System).
Drill Drain Thickening System
The drill drrain stored in the drill drain tank is transferred to the drill drain thickening system for chcikening bt the drill drain water. The thickened drill drain is transferred to the Cohesion andl Dehydlration System to be treated with waste mud. The evaporated water collected during the thickening process is filtered in the Evaporated Water Filtration System, and then either transferred to the drill water tank or drained out of the vessel.
The Drill Drain Thickening System consists of one heater, one condenser, single effect evaporator and pump assembled on the skid structure (see fig.3). The system is designed for the batch operation. The drill drain is fed to the evaporator and mixed with thickened drill drain. The thickened drill drain is circulated and heated up at the heater before performing the flash evaporation inside evaporator (see photo 3). The vapor newly created by the above flash evaporation is introduced into the steam jet ejector and compressed to raise its temperature so that the compressed vapor could be reused as a heating media at heater. The remaining vapor will be introduced into the condenser and the condensate together with the one from the heater is transferred to the evaporated water tank via the evaporated water discharge pump. Apart of the released vapor is thus effectively recycled in the continuous evaporation! condensation process as a heating media. This unit shall be kept under the vacuum condition by the operation of vacuum pump so that the evaporation could occur at approximate 60 egree. When the thic ening rate reaches the designed value the unit is automatically stopped and start dischar ing the thickened drill drain from evaporator to the thickened drill drain tank via thickened drill drain discharge pump. Thickening capacity is 65m3 per unit per day.
Evaporated Water Filtration System
The Evaporated Water Filtration System consists of one pre-filter, one coalescer, one oil adsorber, one charcoal tower, pumps and tanks (see fig.4).
Evaporated water (including little oil) discharged from Drill Drain Thickening System is stored in the evaporated water tank andl fed to pre-filter and coalescer unit via evaporated water pump. In the coalescer, the pre-filtered oily water firstly enters the gravity separation chamber and the difference in the specific gravity is used to separated and remove the free oil droplets to coalesce. As the diameter of the droplets increase, buoyancy is gained, causing the droplets to rise separately and separate. Microscopic oil droplets which could not be processed with the coalescer are separated with the pleated membrane surface, rise up and are separated. When certain amount of oil collects in the top of separator, asingle from oil level sensor causes the discharge valve to open automatically and discharge the oil from separator. After the oil is removed, the treated water is derived from the bottom of tank and sent to the primary water tank.
The primary treated water is fed to oil adsorber and charcoal tower. At this unit, the fine oil particles passed through the coalescer are removed by the granular oil adsorbent followed by the activated carbon. The secondary treated water is stored in the secondary water tank, and reused as drill water or discharged overboard. The oil content of secondary water is monitored. If the oil content exceeds the value stipulated by the regulation, the treated water is automatically returned to the evaporated water tank with alarming.
Cohesion and Dehydration System
This sub-system coheres and dehydrates waste mud and thickened drill drain. The Cohesion and Dehydration System consists of one waste mud service tank, two kinds consists of one waste mud service tank, two kinds mixer, screw press and pumps (see fig.2).
The thickened drill drain and waste mud is pumped to waste mud service tank. The thickened drill drain and waste mud are agitated evenly by agitator. The agitated waste mud is pumped to the paddle mixer via the static mixer. On its way to paddle mixer, the cohesive chemical is added to the waste mud just before the line mixer, which sufficiently agitates the waste mud and the cohesive chemical. When cement and then the cohesive additive are added in the paddle mixer, the solids contained in the muddy water cohere into soft granular flocks. The moisture-containing flocks and free water are discharged from the downstream of the paddle mixer down into the screw press. The screw press compresses the moisture containing flocks and free water to squeeze moisture from them through the mesh of the screen. The dehydrated solids (hereafter sludge) are discharged from the outlet. The squeezed moisture (hereafter squeezed liquid) is collected into the squeezed liquid tank provide under the screw press, and then transferred to drill drain tank.
Cuttings Transfer System
This system sucks the cuttings from the cuttings chute and transfers them to the drill sludge stabilizing system. Cuttings Transfer System consists of two vacuum units(pump and tank), one bazooka, one vacuum hopper and other pumps (see fig.2).
The Vacuum pump units suck the transfer air from the cuttings chute located in shale shaker room via the bazooka (cuttings suction nozzle provided in cuttings chute, hereafter ‘bazooka'<see photo 12>), the vacuum hopper, and vacuum tank. The cuttings sucked in with the transfer air from the cuttings chute are transferred to vacuum hopper. In the vacuum hopper, the transfer air is sucked from above into the vacuum pump units, while the cutmigs are caugh and separated. The caught and separated cuttings are forced out by the vacuum hopper discharger from the bottom of the vacuum hopper and discharged into the drill sludge stabilizing system. The vacuum tanks are provide between the vacuum hopper and the vacuum pump units in order to catc te solid and liquid carryover un-separated at the vacuum hopper.
The general vacuum suction piping system, which terminates in the following spaces and roos,is used for cleaning the respective rooms and tanks as well as for transferring cuttings.
- drill floor
- drill sludge handling space
- Drill waste treatment room
- Shale shaker room
Drill Sludge Stablizing System
Drill sludge stablizing system uses cement to stabilize sludge and cuttings. Drill sludge stablizing system consists of two cement tanks, two stabilizing mixer, two cement feeder two cyclone separator and two pipe conveyor (see fig.2).
The cement pneumatically conveyed from cement tank unit is fed the cyclone separator provided immediately above the paddle mixer and the stabilizing mixer. The cyclone separator separates the cement from the conveying air. The conveying air returns to the cement tank, while the separated cement is fed through the rotary valve to the mixers under bottom. In the paddle mixer, the waste mud is agitated with the added cement for stabilization. Then, the cohesive additive is added to waste mud stabilized by the paddle mixer to cohere the mud. The stabilized and cohered waste mud dehydrated by the screw press into sludge. The sludge is transferred on the sludge conveyor to sludge stabilizing mixer to further mixed and granulated. In the cuttings stabilizing mixer, the cuttings discharged from the vacuum hopper are agitated with the added cement for stabilization. The stabilized sludge discharged from sludge stabilizing mixer and cuttings stabilizing mixer are transferred with the stabilized sludge conveyor to the big big filling system.
Big Bag Filling System
The system fills stabilized sludge in big bag and transfers the filled bags to below the hatch cover. The Big Bag Filling System consists of main structure frame, 10 cyclic shuttles, sub-hopper, filling device, conveyor and so on.
The filling device has1o0 cyclic shuttles onto which the operator hooks empty big bags. The empty big bags are carried by the shuttle conveyor to the filling section, where they wait to receive stabilized sludge. Meanwhile, the stabilized sludge fed by the stabilized sludge conveyor is dropped into the sub hopper, the stabilized sludge is further transferred by the screw conveyor to filling section, where it is filled in big bags. The stabilized sludge is fed into big bags, while monitored by the weighting instrument, until the bags respectively reach predetermined weight (approximately 2000kg). Then the filled big bags are unhooked from the shuttles and transferred with the conveyors to below the hatch cover. The conveyor can store up to six big bags filled with stabilized sludge. The big bags transferred to below the hatch cover are lifted through the hatch cover by the deck crane.