WO2014171839A1

WO2014171839A1 - Method and system for separation of oil and water from drilling mud

Info

Publication number: WO2014171839A1
Application number: PCT/NO2014/050059
Authority: WO
Inventors: Trond Melhus
Original assignee: Trond Melhus
Priority date: 2013-04-19
Filing date: 2014-04-15
Publication date: 2014-10-23
Also published as: NO20130544A1; EP2986808A1; EP2986808A4; NO342321B1

Abstract

Plant or system for wet cuttings cleaning, comprising a rotatable drying drum, alternatively a dryer, comprising a housing able to operate at overpressure, a closeable inlet for wet cuttings, a closeable outlet for dry cuttings, conduits or channels for heating separate from but in heat exchange with a drum or dryer volume that during operation is to be filled with wet cuttings, distinctive in that the outlet for dry cuttings is connected to at least one vacuum pump-compressor able to reduce the pressure in the drum volume in order to evaporate out water and subsequently oil at reduced pressure and thereby reduced energy consumption.

Description

METHOD AND SYSTEM FOR SEPARATION OF OIL AND WATER FROM DRILLING MUD. Field of the invention

The present invention relates in general to drilling of wells for exploration and production of petroleum fluids or injection of fluids into reservoirs. More specifically, the invention relates to a method and a plant for heating of wet cuttings for separation of oil and water.

The method and plant of the invention is efficient with respect to energy consumption. In general, the invention relates to cleaning of slurries and particulate materials contaminated with liquids. Background of the invention and prior art.

When a well is drilled through rock to reach an oil or gas reservoir, small pieces of rock - called cuttings - are created. These cuttings vary in size and texture, ranging from fine sand to gravel, depending on the type of rock being drilled and the type of drill bit being used. The cuttings are carried back to the surface by a drilling mud, which is pumped down the drill string to lubricate and cool the drill bit and to control the well pressure. The cuttings are separated in the shale shakers. The separated cuttings is termed wet cuttings, and it contains water and oil in addition to rock fragments. Disposal of the wet cuttings cause an environmental problem, and dumping to sea is not allowed unless the oil has been separated out. The remaining mud is treated and can be separated from its fluid constituents in order to control the mud composition before reuse. The mud engineer supervises the reformulation of the mud, which is governed by requirements such as density, viscosity and cooling capacity. Currently, wet cuttings is heated by friction heating devices in order to separate out water and oil by evaporation. The energy used in the process is lost in the cooling water that must be used in order to condensate the water and oil and for cooling the hot, dry solids. Additionally, the labor involved, their health and safety, the weight and space required, are all significant input factors. The required energy is typically not available and must be provided on board or from external sources. Generally 1000 kg wet cuttings contains about 700 kg solids, about 150 kg oil and about 150 kg water. The total energy consumption is about 200 kwh for sufficient heating of this quantity of wet cuttings. If a typical well produces 1400 Ton mud, about 280 Mwh of energy will be required per well for heating the mud. This assumes that the oil evaporation temperature is around 250-270 °C and heating of the mud to 275 °C. The remaining dry solids then have less than 1 % oil by weight and may be dumped to the ocean after cooling.

A demand exists for alternative technology requiring less consumption and waste of energy, less space and weight on board, and less personnel. The objective of the present invention is to meet the above demand.

OBJECTS OF THE INVENTION

The primary object of the invention is to provide a system and a method for energy efficient heating of wet cuttings to separate out oil and water.

Another object of the invention is to provide a closed loop energy-efficient system and method for heating wet cuttings and produce relatively cleaner solids for disposal.

It is yet another object of the invention is to provide a system and method for energy efficient heating of wet cuttings without a friction heating device, involving lesser space, manpower and cost.

It is another object of the invention to provide an energy efficient system and method of heating and treating wet cuttings in an environment friendly manner. How the above and other objectives of the invention are achieved is described in detail hereinafter with the help of the accompanying drawings. SUMMARY OF THE INVENTION

The objects of the invention are met by providing a plant or system for wet cuttings cleaning, comprising a rotateable drying drum, alternativey a dryer, comprising a housing able to operate at overpressure, a closeable inlet for wet cuttings, a closeable outlet for dry cuttings, conduits or channels for heating separate from but in heat exchange with a drum or dryer volume that during operation is to be filled with wet cuttings, distinctive in that the outlet for dry cuttings is connected to at least one vacuum pump-compressor able to reduce the pressure in the drum volume in order to evaporate out water and subsequently oil at reduced pressure and thereby reduced energy consumption.

Preferably, the vacuum-compressor is one unit, alternatively it is two units in parrallel, for operating efficiently at different temperature ranges and/or with different vapours, and/or in series, for operating at reduced suction pressure and/or increased differential pressure over the units. Preferably, the suction pressure can be reduced to below atmospheric pressure, 1 bar, preferably below 0,5 bar, more preferably to below 0,2 bar, providing more energy efficient evaporation in the drum volume, since the underpressure reduces the heating requirement. Preferably, the vacuum-compressor outlet is coupled to the heating channels or conduits, for release of heat of condensation of compressed vapour in the drum volume, preferably only steam, alternatively also oil but then preferably in separate conduits.

The invention also provides a method, using a plant of the invention for separating out water and oil from wet cuttings, distinctive in evaporating water and oil at reduced pressure in the drum.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will be further explained below by some embodiments of the invention and with reference to the accompanying drawings.

In the accompanying drawings:- Figure 1 shows a conceptual diagram of the closed loop heat utilization system according to the invention.

Figure 2 shows the dryer used in the closed loop heat utilization system of the present invention.

Figure 3 shows the schematic diagram of a preferred embodiment of the

Closed loop heat utilization system

Figure 4 shows a graphical representation of the energy consumption in different phases of heating/evaporation method of water and oil used in the closed loop heat utilization system of the present invention

DESCRIPTION OF THE INVENTION

The following is the description of an energy-efficient closed loop heat utilization system and method for heating of wet cuttings for separation into solids, oil and water, at reduced energy consumption This method and system ensures environmentally safe disposal of solids in the sea as well as recovery and recycling of the mixed oil in the subsequent drilling operations.

In the above context, it is hereby clarified that though the present invention has been described with reference to drilling rig_s heating of the wet cuttings, oil and water etc, it can also be used for extraction/purifying solids from unwanted liquids/chemicals. In addition, the method and device according to present invention can also be used for land-based drilling operations.

Figure 1 shows the general concept of the closed loop heat utilization system for heating wet cuttings (sometimes called drilling mud or wet mud) according to the invention. The system comprises a heating drum or dryer 1 and at least one vacuum compressor 9 operably connected downstream to said dryer 1 . At least one closed loop heat exchanger system 12 is provided which includes at least one heat exchanger 12a and at least one condenser 12b. Said condenser 12b is provided downstream to said at least one vacuum compressor 9 at its pressure side. At least one pressure control valve 8 is operably connected downstream to said condenser 12b. The other end of the pressure control valve 8 is coupled with said heat exchanger 12a. At least one fluid outlet valve 5 is provided in the heat utilization system. The condenser 12b also forms a closed loop with the heat exchanger 12a through a fluid line 14 carrying heat media and vacuum pump 13, pressure side thereof being connected to the condenser 12b. The vacuum pump 13 maintains the internal flow of the heat carrying fluid e.g. nitrogen gas, between the heat collection zone and the heat releasing zone of the heat exchanger. In the said closed loop heat utilization system, a non-flammable gas such as nitrogen is preferably used for energy transfer within the system.

Wet cuttings is heated in the dryer 1 to generate steam. Steam is separated from the mud leaving cutting and oil as such. Vacuum compressor 9 pressurizes the steam thereby increasing the temperature further. The heated steam is fed to the condenser 12b of the closed loop heat exchanging system 14 where it gets condensed and discharged through outlet valve 5. The heat exchanger 12a of the closed loop heat exchanging system 12 captures the heat released during the condensation of steam at the condenser 12b by circulation of nitrogen passing from condenser to heat exchanger through line 14. Non-condensable fluid is made to pass through the pressure regulation valve 8 where both pressure and temperature of the non-condensable fluid are reduced. The relatively cooled non- condensable fluid is used to capture excess heat from the heat exchanger 12a and is fed back to the dryer 1 for subsequent cycle of operation. The loss of heat at the heat exchanger 12a makes the heat carrying fluid to become relatively cooler, which is recirculated back to the condenser 12b through the operation of vacuum pump 13 for increased condensing efficiency.

After the separation of water, the temperature of the cuttings and oil is raised further by the recycled heat and evaporation of oil starts at 270° C if at atmospheric pressure. However, the reduction in pressure reduces the temperature of evaporation and thus the heating requirement significantly. The oil vapour is similarly separated from the cuttings, condensed in the heat exchanging system 12 and discharged through outlet valve 5 for recycling in the drilling rig. The drill cuttings, separated from oil and water are then safe to be dumped at sea.

The condensation temperature in the system can be determined either at negative pressure or at positive pressure, depending on what will be most effective in relation to energy consumption. As the heat released during condensation of steam and oil vapour are efficiently captured and utilized in pre-heating the drill cuttings in the subsequent cycles, the overall consumption of energy is substantially reduced.

In order to utilize the energy consumed during the pressure reduction, a turbine (not shown) can alternatively be used to reduce the pressure. The energy from this turbine can be recycled in the compressor(s).

However, most of the energy is consumed by the running of the compressor when water vapour is condensed.

It is well understood that for enhancing the operating efficiency, there can be combination of a plurality of dryers, compressors, vacuum pumps, heat exchangers etc. in the system without departing from the scope of the general concept as described above.

Having described the invention conceptually, the details of a preferred embodiment of the system and the method of the invention will now be described with the help of figures 2 and 3.

Figure 2 shows the dryer 1 comprising of a rotatable drying drum V containing horizontally spaced apart through-going tubes/channels 2. The through-going tubes/channels 2 help in mixing and supplying heat to the cuttings. The tubes/channels are open from A to B, but not the drying drum itself. A closable in- feed opening 3 and a closable out-feed opening 4 are provided at the opposing ends of the drying drum 1 . The dryer 1 is further provided with openings 6 and 7 located on the opposite ends for supply and withdrawal of heat media respectively. Plurality of outlets 5, 8 are provided suitably at the bottom and top surface of the dryer for drainage of condensates and non-condensable fluids respectively. An inlet 1 1 is connected to closable in-feed opening 3 for introducing nitrogen gas to the heat utilization system. The drying drum can withstand high pressure required to increase the temperature of the drill cuttings to the desired levels during the operation, and underpressureure used when evaporating water and then oil. Figure 3 provides a schematic diagram of the preferred embodiment of the inventive system.

The closable out-feed opening 4 of the dryer is connected downstream to a vacuum compressor 9a through valves 4a, 4b. The vacuum compressor at its pressure side, is operably connected back to the dryer through a valve 6a on the heat media carrying line 6. The vacuum compressor 9a is also connected to a condenser 12b through the valve 4c. Said condenser 12b, being a part of the closed loop heat exchanging system 12 , is in turn connected in a closed loop to heat exchanger 12a through pressure reduction valve 8b and vacuum compressor 13 (as shown in figure 1 ). The condenser 12b and vacuum compressor 9a preferably also forms a closed loop through additional vacuum compressor 9b and valves 4d, 4b , 4c.

A compressor/ circulation fan 10 is operably connected to the dryer 1 at its pressure side through valve 6b on the heat media supply line 6 and also downstream through heat media withdrawal line 7 and valve 7a, thereby forming a closed loop with the dryer. As shown in figure 2 and 3 the dryer is provided further with an outlet 8 for non-condensable fluid at its top surface controllable through a pressure reduction valve 8a. The downstream side of the pressure reduction valve 8a is in turn connected to the heat exchanger 12a for recovering excess heat and supplying the same back to the dryer 1 . The above system ensures that the initial heat supplied to the system and/or the heat generated in the process is effectively utilized without significant loss . The wet cuttings is fed to the drying drum 1 through closable in-feed opening 3. Circulation compressor fan 10 is started to feed hot compressed gas or air in the dryer and valves 6b and 7 are opened while valves 4a and 6a are kept closed. Nitrogen is also introduced in the drying drum through line 1 1 and valve 1 1 a. Hot compressed fluid circulates through the dryer as the drying drum rotates. For this initial heating, preferably oil, at low or atmospheric pressure is used in the heater, the oil is circulated from the exhaust gas boiler on the exhaust gas from the main engines or gas turbines for example, which means supply of oil at about 300° C without overpressure. When the temperature of the drilling mud in the drying drum reaches 100 °C and water component of the mud evaporates into steam, the circulating fan 10 and valves 6b and 7 are shut down.

At this point valves 4a, 4b, 6a are opened and the vacuum compressor 9a is started.

With the starting of the vacuum compressor 9a, steam is separated from the cuttings and oil in the mud and evacuated from the drying drum 1 by the suction pressure of the vacuum compressor 9a. Vacuum on the suction side facilitates evaporation. The pressurized steam is pushed back into the dryer through the valve 6a. The sudden expansion of the pressurized steam at the valve 6a makes the steam to lose heat and to condense on the drying drum. The heat recovered from the condensation of steam is supplied to the cuttings for further heating. Condensed water is drained through valve 5a. Non-condensable gases coming into the dryer 1 along with steam through valve 6a are taken out from the top of the dryer by using the pressure reduction valve 8a. This cycle may be repeated a number of times to remove as much water as possible from the wet cuttings.

Vacuum compressor 9a is then stopped and the valves 4a, 4b and 6a are closed marking the end of the first step of the drying method.

In the second step the circulating fan 10 is restarted and valves 6b and 7 are opened and the circulating process again increases the temperature of the relatively dryer cutting and oil mix mud in the drying drum. When the temperature increases to 240-270 °C, the oil portion of the mix gets vapourized. Fan 10 is stopped and valves 6b and 7 are closed.

Once the temperature of the cutting and oil mix mud in the dryer reaches 270° C and evaporation of oil starts, valves 4a, 4b and 4c are opened while valve 6b is closed. The vacuum compressor 9a is started, producing vacuum on the suction side facilitating evaporation of oil, and pushes the oil vapour to the condenser 12b. Vacuum on the suction side facilitates evaporation, allowing a reduced heating temperature. The oil vapour condenses in the condenser and the condensed oil is drained through valve 5b. Non-condensable vapour goes out through the pressure reduction valve 8b and is cooled. The heat recovered during condensation of oil vapour is transported by nitrogen through line 14 (c.f. figure 1 ) and is fed into the heat exchanger 12a. The relatively cooled non- condensable fluid is used to recover excess heat from the heat exchanger 12a and is fed back to the dryer for subsequent cycle of operation. The heat recovered by the non-condensable fluid at the heat exchanger 12a cools the nitrogen which in turn cools the condenser 12b when transported back through the operation of the vacuum pump 13 (c.f. figure 1 ). As a result the efficiency of the condenser is increased.

To make the heat exchanging process more efficient, the process may be repeated number of times through the compressors 9a and 9b and valves 4b, 4c and 4d. Normally, the cycle is repeated till the oil content in the cuttings becomes lower than 1 % by weight and dry cuttings can be safely disposed into the sea.

According to another preferred embodiment, it may be possible that the oil vapour removal cycle can be operated without the heat exchanger/condenser combination. Once the oil vapour is generated at around 270°C at the drying drum 1 ', valves 4a, 4b and 6a are opened and the vacuum compressor 9a is restarted. Oil vapour is sucked out from the drying drum by the vacuum compressor 9a and the pressurized oil vapour is again pushed back into the chamber, where the oil vapour condenses outside the drying drum and drained through valve 5a. The condensation energy is again recovered and used to heat the cuttings. All non-condensable vapour and gases are released through the pressure release valve 8a, thereby reducing the temperature outside the drying drum for further condensation of oil vapour.

In another preferred embodiment, it may also be possible to use separate vacuum compressor(s) for oil vapor capture to avoid any mixing of water and oil in the process. This embodiment is particularly useful because of high temperature of the oil vapour and also because of the fact that as compared to water, oil has much lower expansion from liquid to vapour. The process can be fully automated by using a Programmable Logic Controller (PLC). Figure 4 is a graphical representation of the energy consumption in different phases of heating/evaporation of water and oil as per the currently prevailing technologies.

Assuming that 1000 kg of drilling mud consists of 700 kg of cuttings, 150 kg of water and 150 kg of oil then from the graphical representation of figure 4, it is seen that in the existing systems, about 339000 kJ of energy is consumed to evaporate the water in the return sludge. In comparison, this amount is only 4500 kJ for evaporating the same quantity of water in the invented process. For higher efficiency, condensed water/oil/cuttings can also be used to heat an identical circuit and about 130605 kJ of energy can be recovered from the condensation of water and oil, which is sufficient to heat about 1000 kg of drilling mud (mixture of cuttings, oil and water). By cooling the solids from 275 °C to 100 °C additional energy is released and this energy can be used for heating of a parallel running circuit from 100 °C to 275 °C.

Because of the efficient management of energy, the actual consumption of energy reduces substantially and comes down to 15% - 20% of the original energy consumption.

The plant and method of the invention can be used not only for wet cuttings, but also for mud cleaning, cleaning of sewage from humans or animals, and other slurries.

Another advantage of the present system is that as no cooling water is necessary, the plant is less cumbersome and manpower requirement is also less. The closed loop heat exchanging system of the present invention can also be used in other methods/plants for heating of wet cuttings for separating the oil from the drill cuttings for better energy efficiency. The present invention has been described with reference to some drawings and preferred embodiments purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described herein before and claimed in the appended claims.

Claims

PATENT CLAIMS

1 .

Plant or system comprising a rotateable drying drum, alternativey a dryer, comprising a housing able to operate at overpressure, a closeable inlet for wet mud, a closeable outlet for dry mud, conduits or channels for heating separate from but in heat exchange with a drum volume that during operation is to be filled with wet mud, c h a r a c t e r i s e d i n that the outlet for dry mud is connected to at least one vacuum pump-compressor able to reduce the pressure in the drum volume in order to evaporate out water and subsequently oil at reduced pressure and thereby reduced energy consumption.

2.

Plant or system according to claim 1 , wherein the vacuum-compressor is at least two units in parrallel, for operating efficiently at different temperature ranges and/or with different vapours, and/or in series, for operating at reduced suction pressure.

3.

System according to claim 2, wherein the suction pressure can be reduced to below atmospheric pressure, 1 bar, preferably below 0,5 bar, more preferably to below 0,2 bar, providing more energy efficient evaporation in the drum volume.

4.

System according to any one of claim 1 -3, wherein the vacuum-compressor outlet is coupled to the heating channels or conduits, for release of heat of condensation of compressed vapour (steam) in the drum volume.

5.

System according to any one of claim 1 -4, wherein the system comprises:

at least one dryer connected to at least one vacuum pump/compressor at its suction side, at least one condenser located downstream and operably connected to the pressure side of the said vacuum pump/compressor, at least one heat exchanger being coupled the said condenser in a closed loop and capable of receiving heat from the condensate of the condenser, the closed loop being filled with a non-combustible, evaporable heat carrying media, at least one pressure control valve operably connected downstream to said condenser and to the pressure side of the said vacuum compressor, the other end of the pressure control valve being engaged to said heat exchanger and connected to the dryer and adopted to pick up heat from the heat exchanger and supply it to the dryer for subsequent operational cycle, thereby forming a further closed loop, a control valve operably connected to the pressure side of the vacuum compressor and the dryer for carrying pressurized fluid from the vacuum compressor to the dryer completing another closed loop and at least one condensate drainage valve.

6.

System according claim 5, wherein the heat carrying media is nitrogen gas.

7.

System according to claim 1 cha racte ri sed i n that the dryer comprises a drying drum, horizontally spaced apart through-going tubes/channels on the drying drum, a closable in-feed opening and a closable out-feed opening are provided at the opposing end of the drying drum , plurality of openings located on the opposite ends for supply and withdrawal of heat media , a plurality of outlets at the bottom and top surface adapted to drain out condensates and non- condensable fluids respectively and an inlet introducing nitrogen gas to the system.

8.

System according to claim 1 cha racteri sed i n that the condenser is connected to at least one additional vacuum compressor at its suction side, the pressure side of the additional vacuum compressor 9b being connected the vacuum compressor 9a at the suction side completing a closed loop for repeated condensation process.

9.

System according to claim 1 cha racteri sed i n that a compressor fan (10) is operably connected to the dryer for supplying initial heat, the compressor fan (10) completes a closed loop with the dryer through openings for supply and withdrawal of heat media.

10.

Method, using a plant or system according to claim 1-9, for separating out water and oil from wet mud, ch aracteri sed by evaporating water and oil at reduced pressure in the drum.

11.

Method according to claim 10, cha racte ri sed i n the steps as follows: arranging a closed loop for heating the mud, the closed loop comprising at least one dryer , at least one vacuum pump/compressor, at least one condenser, at least one pressure control valve, at least one heat exchanger, the heat exchanger is coupled to receive energy from the condensate from the condenser, the closed loop is filled with a non-combustible, evaporable heat carrying media such as nitrogen,

-heating the mud to generate steam, compressing the steam and returning the steam to the dryer through a valve causing expansion and pressure drop of the steam, thereby condensing it and returning the heat gained from condensation to the dryer for further heating of mud,

-heating the mud again to generate oil vapour, compressing the vapour and flowing it through the condenser, draining out the condensate, causing the heat gained during condensation to be transported to the heat exchanger by the heat carrying media, transporting the additional heat of the heat exchanger with a depressurized non-condensable gas to the heating cycle and transporting back the cooled heat carrying media to the condenser for better efficiency, and preferably, the steam and oil vapour removal cycle is repeated for maximum cleaning of the drill cuttings.

12.

Method according to claim 10-11, cha racteri sed i n the steps as follows:

arranging a closed loop for heating the mud, the closed loop comprising at least one dryer ,one vacuum pump/compressor, at least one control valve, the closed loop being filled with a non-combustible, evaporable heat carrying media such as nitrogen,

-stepwise heating the mud to generate steam and oil vapour at suitable temperature and pressure, stepwise compressing the steam and oil vapour and stepwise returning the compressed steam and oil vapour to the dryer through a valve causing expansion and pressure drop, thereby condensing it and returning the heat gained from condensation to dryer for further heating of mud.