Methods for treating wastewater from oil drilling.

Abstract

DEPCT66 The method of treating water from oil drilling involves the steps and treatments performed. It is allowed to settle by agglomerating the watery material obtained from oil drilling and separating it. The clear water and sediment are treated in a concentrated manner by boiling and evaporating the remaining water. The water is clear and contains condensed water that can be drained out, as well as concentrated water that resembles the oily portion. The trees, for example, have been treated rigorously. -----------------------------------------------------------

Description

Treatment method for produced water from oil drilling

[0001] The present invention relates to a method for treating water produced by oil drilling.

[0002] When oil is drilled at an oil drilling site, groundwater is pumped up along with the oil. The pumped oil drilling produced water (sometimes referred to as "produced water" in this invention) contains COD components such as oil, suspended solids (mud) derived from the soil, and inorganic salts. Furthermore, the amount of produced water is large, said to be several times more than the amount of oil pumped up, and it is a waste product that is difficult to treat. Furthermore, for purposes such as protecting the drill, drilling mud is supplied to the drill while it is drilling. This drilling mud also mixes with the produced water and becomes part of the produced water.

[0003] Currently, many oil drilling sites are located in remote areas with poor infrastructure, and one possible way to properly treat produced water is to transport it to a plant with appropriate wastewater treatment facilities and treat it there, or to install such wastewater treatment facilities on-site and treat it there. However, the former is not realistic in terms of transportation costs.

[0004] Furthermore, although treated and purified water is discharged into rivers, the residues that result from the treatment require further treatment processes such as solidification and landfilling. Therefore, reducing the amount of residues (concentrating them) is also an important factor in treating produced water.

[0005] Regarding the above-mentioned on-site produced water treatment method, Patent Documents 1 and 2 disclose a method in which the produced water is treated with a reverse osmosis membrane (after prior precision membrane filtration), and the resulting concentrated water is then evaporated and concentrated.

[0006] WO2013 / 153587 publication WO2012 / 008013 publication

[0007] However, according to the inventors' investigations, the methods proposed in Patent Documents 1 and 2 for performing separation treatment on produced water using a reverse osmosis membrane have the following problems. First, produced water exhibits large fluctuations in composition, particularly with respect to oil content. That is, when the drill is excavating a water layer, the produced water is relatively clean and contains very little oil. On the other hand, when the drill approaches an oil layer, the produced water contains a large amount of oil. There are also times when the produced water is neither of these, and the drill is simply excavating soil. Furthermore, produced water contains substances derived from the soil and components derived from the drilling mud, making it a complex mixture of composition.

[0008] The reverse osmosis membrane used in the method described in Patent Document 1 and the like has excellent separation performance, and therefore is excellent at purifying produced water. However, as described above, produced water is a complex mixture, and the membrane is subjected to a high load, quickly becoming unusable. For this reason, membrane replacement is frequent in actual operations for treating produced water from oil drilling, and considering the amount of produced water generated, the cost of treating the produced water becomes enormous. This problem becomes particularly pronounced when the produced water contains a large amount of oil and other components (especially mud that can clog the membrane and protective agents derived from drilling mud (polymeric compounds such as polysaccharides, e.g., guar gum)).

[0009] The present invention was made under these circumstances, and the problem that it aims to solve is to provide a treatment method that can concentrate oil and other contaminants at low cost and purify produced water to a level that can be discharged, even if the water is heavily contaminated with oil and other contaminants.

[0010] In order to solve the above-mentioned problems, the present inventors have conducted extensive research and have found that by subjecting contaminated produced water to coagulation and sedimentation treatment and then subjecting the resulting clarified water to evaporation and concentration treatment, it is possible to obtain, at low cost, condensed water that has been purified to a level that can be discharged and concentrated water that can be treated appropriately, and have thereby completed the present invention.

[0011] That is, the first invention to solve the problems is a method for treating oil drilling produced water, comprising the steps of subjecting the oil drilling produced water to a coagulation and sedimentation process to separate it into clear water and a sediment, and subjecting the clear water to an evaporation and concentration process to obtain condensed water and concentrated water. The second invention is a method for treating oil drilling produced water according to the first invention, in which the oil concentration in the oil drilling produced water is 100 to 5,000 ppm, the COD is 10 to 20,000 ppm, and the inorganic salt concentration is 200 to 35,000 ppm in terms of TDS. The third invention is a method for treating oil drilling produced water according to the first or second invention, further comprising the steps of measuring the oil concentration in the condensed water, and if it is found to exceed a predetermined value, removing the oil from the condensed water using an oil separation membrane. A fourth invention is a method for treating oil drilling produced water according to any one of the first to third inventions, further comprising a step of measuring the nitrogen concentration in the condensed water and, if it is found to exceed a predetermined value, removing nitrogen from the condensed water. A fifth invention is a method for treating oil drilling produced water according to any one of the first to fourth inventions, in which the oil concentration in the clear water is 5 to 1,000 ppm. A sixth invention is a method for treating oil drilling produced water according to any one of the first to fifth inventions, in which the oil concentration in the condensed water is 5 to 100 ppm, the COD is 5 to 200 ppm, and the inorganic salt concentration is 10 to 100 ppm in terms of TDS. A seventh invention is a method for treating oil drilling produced water according to any one of the first to sixth inventions, in which the evaporative concentration treatment is carried out using an evaporative concentration apparatus that can be transported by vehicle or an evaporative concentration apparatus that can be separated into two to four units that can be transported by vehicle. An eighth invention is a method for treating oil drilling produced water according to any one of the first to seventh inventions, in which a treatment for removing organic components from the oil drilling produced water is carried out before the coagulation and sedimentation treatment.

[0012] According to the present invention, even if the produced water is highly polluted, it is possible to purify the produced water at low cost by concentrating oil and other components and purifying the water to a level that makes it suitable for discharge.

[0013] 1 is a diagram showing an operation flow of a method for treating oil drilling-derived water according to the present invention and an example of a treatment device.

[0014] As described above, the present invention is a treatment method for concentrating and purifying, at low cost, produced water (which also contains drilling mud) that is groundwater pumped up along with oil during oil drilling at an oil drilling site and contains oil, COD components, suspended solids (mud) derived from soil, and inorganic salts, to a level that makes it suitable for discharge.

[0015] The method for treating oil drilling produced water according to the present invention comprises a coagulation-sedimentation process for subjecting the produced water to a coagulation-sedimentation process to separate it into clear water and precipitate, and an evaporation-concentration process for subjecting the clear water to an evaporation-concentration process to obtain condensed water and concentrated water. The method for treating oil drilling produced water according to the present invention may also optionally include an oil removal process for removing oil from the condensed water, or a denitrification process for removing nitrogen from the condensed water. Furthermore, optionally, an organic component removal process may be included before the coagulation-sedimentation process.

[0016] The present invention will be described below with reference to FIG. 1, which shows an example of an operation flow of a processing method and a processing apparatus according to the present invention.

[0017] As shown in Figure 1, the present invention includes a coagulation and sedimentation treatment process [1] in which produced water (10) from which organic components have been removed as needed in an organic component removal process [1'] is received and coagulated and sedimented to obtain clarified water (11) and a precipitate (12), and an evaporation and concentration treatment process [2] in which the clarified water (11) is received and subjected to an evaporation and concentration treatment to obtain condensed water (21) and concentrated water (22). The condensed water (21) is returned to the environment, for example, by being discharged into a river or the sea, while the concentrated water (22) is appropriately treated, such as by being transported to a disposal site and solidified. For convenience, the produced water received in the organic component removal process [1'] is referred to as "produced water (10)" in Figure 1.

[0018] However, if the condensed water (21) contains oil or nitrogen at levels equal to or greater than a predetermined standard, it is preferable to provide an oil removal step [3] for removing oil from the condensed water (21) and / or a denitrification step [4] for removing nitrogen from the condensed water (21).

[0019] The present invention will be described below in the following order: [1'] organic component removal process, [1] coagulation and sedimentation treatment process, [2] evaporation and concentration treatment process, [3] oil removal process, [4] denitrification process, and [5] treatment of precipitate and concentrated water.

[0020] [1'] Organic Component Removal Step If the produced water (10) contains a large amount of organic components, a step [1'] for removing organic components may be carried out before carrying out the coagulation and sedimentation treatment step [1]. In this case, it is preferable to provide a biological treatment tank (17) before the coagulation tank (15) in which the coagulation and sedimentation treatment step [1] is carried out. The organic components are decomposed by aerobic treatment / anaerobic treatment. A preferred example of the biological treatment tank (17) is an SBR tank, which allows selection of aerobic and anaerobic conditions and has high solid-liquid separation stability.

[0021] [1] Coagulation-Sedimentation Treatment Step In the present invention, if necessary, the produced water (10) is subjected to an organic component removal step [1'], followed by a coagulation-sedimentation treatment step [1]. As described above, the produced water (10) received in this step is a mixture of complex composition and is typically black to brownish-red. Its oil concentration typically ranges widely, from about 100 to 5,000 ppm. This is because, as described above, the composition of the produced water (10) varies significantly depending on whether the drill is drilling near an oil reservoir, near a water reservoir, or neither. Specifically, the oil content is high when the drill is drilling near an oil reservoir. The COD of the produced water is typically about 10 to 20,000 ppm, and the concentration of inorganic salts, as TDS, is typically about 200 to 35,000 ppm. The present invention can treat produced water (10) without any problems even if the oil concentration in the water is high, and is preferably applicable to produced water (10) having an oil concentration of 120 to 5000 ppm, and more preferably applicable to produced water (10) having an oil concentration of 150 to 5000 ppm.

[0022] If the oil concentration is so high as to exceed 5,000 ppm, the oil will float on the surface of the produced water, and it is preferable to scoop it out to bring the concentration within the above range before carrying out the coagulation and sedimentation treatment step [1].

[0023] The coagulation and sedimentation treatment step [1] aims to remove soil-derived suspended solids (mud) from the produced water (10) by coagulation treatment using a coagulation tank (15) followed by sedimentation treatment to obtain clear water (11). This coagulation and sedimentation treatment is often preferable because it can also remove part of the COD and oil content from the produced water (10).

[0024] In the coagulation and sedimentation treatment step [1], a coagulant is first added to a coagulation tank (15) containing produced water (10), and substances that can be captured by the coagulant (such as the above-mentioned suspended solids) are coagulated. Examples of the coagulant include inorganic coagulants (13) and polymer coagulants (14). Preferred examples of the inorganic coagulant (13) include polyiron sulfate, polyiron chloride, polyaluminum chloride, and polyaluminum sulfate. Preferred examples of the polymer coagulant (14) include anionic coagulants, cationic coagulants, and nonionic coagulants.

[0025] Among these flocculants, polyferrous sulfate has the following excellent features: it excels in oil removal, it can form precipitates with calcium and other scale-causing components and can remove them, and the precipitates do not redissolve even if the pH fluctuates during the treatment of the produced water (10) (especially when the pH reaches about 10). These features are preferable from the viewpoint of maintaining stable operation of the subsequent evaporation concentration treatment step [2].

[0026] In the coagulation-sedimentation treatment step [1], the produced water (10) containing coagulated material due to the coagulation described above is separated into clarified water (11) and precipitate (12) by solid-liquid separation using a solid-liquid separator (16) (specific examples include centrifugation using a centrifugal separator, sedimentation using a thickener or the like, filtration using a hollow fiber membrane, decanting from a coagulation tank, etc.). If necessary, the clarified water (11) is temporarily stored in an evaporation and concentration raw water tank (20).

[0027] The oil concentration in the clarified water (11) obtained in the coagulation and sedimentation treatment step [1] is typically about 5 to 1,000 ppm, and the COD is typically about 10 to 5,000 ppm, which are often reduced compared to the starting produced water (10). The inorganic salt concentration is typically about 200 to 35,000 ppm in terms of TDS. Furthermore, the suspended solids (mud) contained in the produced water (10) have been significantly removed from the clarified water (11), and the clarified water (11) is colorless, transparent, or translucent white, or has a color derived from the chemicals used in this step.

[0028] [2] Evaporative Concentration Treatment Step In the evaporative concentration treatment step [2], the clarified water (11) obtained in the coagulation-sedimentation treatment step [1] is subjected to an evaporative concentration treatment using an evaporative concentration apparatus (23). This evaporative concentration treatment produces condensed water (21) and concentrated water (22). If the target of evaporation contains coarse substances such as mud, these will be transferred to the concentrated water (22), causing problems such as clogging the piping of the evaporative concentration apparatus, making continuous operation impossible. This leads to increased operating costs. However, in the present invention, the produced water (10) is first subjected to a coagulation-sedimentation treatment to substantially remove the coarse substances, so the above-mentioned problems do not occur, continuous operation is possible, and operating costs can be kept low.

[0029] The evaporative concentration apparatus (23) used in the evaporative concentration treatment step [2] is not particularly limited. For example, the steam compression brine distiller (steam compression brine distiller equipped with a horizontal heat transfer tube and a steam compressor) described in JP-A-59-26184, the self-evaporative compression concentrator (concentrator capable of two-stage compression using two compression means) described in JP-A-10-57702, the vacuum evaporator (vacuum evaporator equipped with a Roots blower) described in JP-A-2011-185192, etc. can be used as the evaporative concentration apparatus in this step. However, considering that many oil drilling sites are located in remote areas, building an evaporative concentration apparatus on-site from scratch would require a long construction period and would be expensive.

[0030] The inventors have now come to the conclusion that it is preferable to transport the evaporative concentration apparatus (23) as a finished product or as a plurality of separate units to the oil drilling site and install it there, or to perform final assembly before installing and operating it. Such an evaporative concentration apparatus (23) is either small enough to be transported by vehicle such as a truck, or can be separated into two to four units, each of which is small enough to be transported by vehicle. Furthermore, the inventors have come to the conclusion that the evaporative concentration apparatus disclosed in JP 2018-126680 A is particularly suitable as an apparatus for use in the evaporative concentration treatment step [2] of the present invention, because the apparatus can be separated into two storage containers (the first storage container and the second storage container in claim 1 of the publication), each of which can be transported by vehicle such as a truck.

[0031] Regarding the evaporation conditions in the evaporation concentration treatment step [2], it is preferable to set the liquid temperature in the evaporator of the evaporation concentration apparatus (23) to 60 to 80°C and the pressure in the evaporator to 5 to 50 kPa abs from the viewpoint of reducing operational costs. The concentration ratio of the concentrated water (22) obtained in this step (the volume ratio of the clarified water (11) to the concentrated water (22)) is preferably 2 to 20 times by volume from the viewpoints of concentrating the produced water (10) and reducing operational costs.

[0032] When a quality check is performed on the condensed water (21) obtained by the evaporation and concentration process, the oil concentration is typically about 5 to 100 ppm, the COD is typically about 5 to 200 ppm, and the inorganic salt content is typically about 10 to 100 ppm as TDS. Since the condensed water (21) is composed of the volatile components in the clear water (11), the oil content (excluding volatile oils) and other components are significantly reduced. If the oil content, COD, and inorganic salt content of the condensed water (21) are low enough to comply with environmental standards, the condensed water (21) can be directly discharged into a river or the like, recycled as service water at an oil drilling site, or returned underground.

[0033] By carrying out the coagulation-sedimentation treatment step [1] and evaporation-concentration treatment step [2] described above, condensed water (21) that can be returned to the environment, and precipitate (12) and concentrated water (22) to be treated by an appropriate method can be obtained from the produced water (10). According to the present invention, a concentration ratio (produced water / (precipitate + concentrated water)) of preferably 3 to 15 times by volume of the produced water (10) to the total of the precipitate (12) and concentrated water (22) can be achieved. Moreover, since neither the coagulation-sedimentation treatment step [1] nor the evaporation-concentration treatment step [2] requires the use of expensive chemicals or equipment and can be operated continuously, the method for treating oil drilling-derived water of the present invention can be carried out at very low cost.

[0034] [3] Oil Removal Step The oil removal step [3] is a step in which, if the quality check (oil concentration measurement) of the condensed water (21) reveals that the oil content in the condensed water (21) exceeds a predetermined value, the condensed water (21) is subjected to, for example, gravity separation using an oil separation membrane (33) installed in an oil separation device (32) to obtain treated water (31) and oil (34). The method for measuring the oil concentration will be described later in the Examples section. The predetermined value is a value determined by wastewater standards, such as environmental standards, of each country, and will be described in detail in the section on the denitrification step [4] below.

[0035] The produced water (10) targeted by the oil drilling produced water treatment method of the present invention described in the "Coagulation and Sedimentation Treatment Step [1]" generally has a very high oil content. For this reason, if an attempt is made to separate oil from the produced water (10) using a reverse osmosis membrane or the like, as per the prior art typified by Patent Document 1, the load on the reverse osmosis membrane or the like is high, necessitating frequent replacement, and thus increasing treatment costs. The suspended solids (mud) contained in the produced water (10) also clog the reverse osmosis membrane (or the microfiltration membrane used before the reverse osmosis membrane), increasing the need for frequent replacement.

[0036] The reason why reverse osmosis membranes are used in conventional technology is that the previous precision membrane filtration method cannot remove ultrafine-sized substances such as inorganic salts on the single nanometer order or smaller. In contrast, in the present invention, ultrafine-sized substances such as inorganic salts are substantially removed by evaporation and concentration (removal focusing on boiling point rather than size), resulting in condensed water (21) composed essentially of water and volatile oil (34) with very little other impurities. The oil (34) exists in the condensed water (21) as micron-level droplets. Removal of such oil (34) does not require an ultrafine reverse osmosis membrane with a pore size of less than 1 nm; instead, oil removal can be achieved using a less expensive oil separation membrane (33). Furthermore, because the condensed water (21) is essentially composed of water and volatile oil (34), the load on the oil separation membrane (33) is light, eliminating the need for frequent replacement of the oil separation membrane (33), resulting in low processing costs.

[0037] As described above, the oil separation membrane (33) does not need to be an expensive one with a pore size of the single nanometer order or less, as in a reverse osmosis membrane. In the present invention, a coalescer-type membrane can be suitably used as the oil separation membrane (33). This type of oil separation membrane (33) is a membrane composed of fibers with a thickness (diameter if the cross section is circular) of approximately 0.1 to 10 μm. Water is first passed through the membrane to wet the fibers. Subsequently, condensed water (21) (containing a predetermined amount of oil or more) is passed through the membrane. The water permeates the membrane, but the oil (34) repels the wet fibers and does not permeate the membrane. As the condensed water (21) continues to flow, the oil accumulates and coalesces on the fibers, growing larger and then separated according to its relative specific gravity to water (specific gravity separation). In this way, oil can be removed from the condensed water (21) using a simple and inexpensive method. Note that, if strict standards for oil content are to be met, further advanced treatments, such as oil removal using activated carbon, may be performed as necessary. Such a process is also inexpensive to implement.

[0038] As a result of a quality check of the treated water (31) obtained through the oil removal step [3], if the concentration of oil contained in the treated water (31) is found to be equal to or less than a predetermined value, the treated water (31) can be discharged into a river or the like, recycled, or returned underground.

[0039] [4] Denitrification Step The denitrification step [4] is a step in which the nitrogen concentration in the condensed water (21) or the treated water (31) obtained in the oil removal step [3] is measured, and if the nitrogen concentration exceeds a predetermined value, the denitrification step is performed using a known denitrification method. This is because a high nitrogen content in the condensed water (21) (or the treated water (31)) can cause environmental loads. As a known denitrification method, the chloramine denitrification method, which has low operating costs, is preferred. The method for measuring the nitrogen concentration will be described later in the Examples section. The predetermined value is a value determined by wastewater standards, such as environmental standards in each country. Examples are shown in Table 1 below, along with the predetermined value for the wastewater standard for oil content in the oil removal step [3]. For both the oil content and the nitrogen content, the predetermined value may be set to a value between 5% and 100% of the wastewater standard value by multiplying the wastewater standard value by a safety factor.

[0040]

[0041] If the quality of the treated water (31) obtained through the denitrification step [4] is checked and the nitrogen concentration in the treated water (31) is found to be below a predetermined value, the treated water (31) can be discharged into a river or the like, recycled, or returned underground. When both oil removal and denitrification are required for the condensed water (21), it is preferable to perform oil removal first. This is because if chloramine denitrification, a typical denitrification method, is performed first, the oil in the condensed water (21) is oxidized and becomes water-soluble, making oil removal difficult.

[0042] [5] Treatment of Sediment and Concentrated Water The sediment (12) described in the "Coagulation and Sedimentation Treatment Step [1]" and the concentrated water (22) described in the "Evaporation and Concentration Treatment Step [2]" are preferably transported to an appropriate disposal site for disposal. Considering that many oil drilling sites are located in remote areas, the cost of transporting the sediment (12) and concentrated water (22) to the disposal site is high. Therefore, it is important to minimize the amount of transport, i.e., to achieve a high concentration rate from the produced water (10). From this perspective, when considering the method for treating oil drilling produced water according to the present invention, as described above, the sediment (12) and concentrated water (22) are concentrated and reduced in volume to a total of approximately 3 to 15 times the volume of the produced water (10). This volume reduction through concentration is considered to be sufficiently effective in terms of reducing transportation costs.

[0043] The present invention will be described in more detail below with reference to examples. In the examples, the oil concentration was determined by adjusting the pH of a sample to 4, extracting it with normal hexane, heating it to 80°C to evaporate the normal hexane, and measuring the weight of the residue. The inorganic salt concentration was determined as TDS using Orion TM Versa Star Pro TM A pH / conductivity desktop multi-parameter meter was used to measure total dissolved solids and nitrogen concentration was measured as ammonia nitrogen (NH ３ -N) concentration was measured by the ion electrode method (Orion TM Versa Star Pro TM The pH was measured using a HORIBA pH meter F-16. If the sample temperature during measurement was 25°C, the actual measured value was used. If the sample temperature was not 25°C, the pH value at 25°C was calculated using the built-in calibration function of the pH measuring device. COD was measured in accordance with JIS K 0102:2013 using the dichromate method (COD Ｃｒ ) was measured.

[0044] (Reference Example) When the oil concentration of oil drilling produced water (produced water 1 and 2) produced at different times at an oil drilling site was measured, the oil concentration of produced water 1 was 3010 ppm, and the oil concentration of produced water 2 was 198 ppm. This result shows that there is a large variation in the oil concentration of oil drilling produced water. Note that both produced waters contained a polymer compound as a protective agent. The same applies to the following examples.

[0045] Example 1: The produced water from an oil drilling site was used as the raw water for the treatment of oil drilling produced water according to the present invention. The following describes the steps in this order: 1. coagulation and sedimentation treatment process, 2. evaporation and concentration treatment process, and 3. oil removal process.

[0046] 1. Coagulation and sedimentation treatment process The produced produced water was introduced as raw water into a coagulation tank, where polyferrous sulfate (registered trademark: Polytetsu, manufactured by Nittetsu Mining Co., Ltd.) was added as a coagulant at a rate of 2 g per 1 L of produced water. The produced water contained suspended solids (mud) and was brown in color.

[0047] The mixture was then stirred and mixed at 250 rpm for 0.1 hour using a stirrer attached to the coagulation tank. The resulting slurry was centrifuged at 4,500 rpm using a centrifugal separator, a solid-liquid separator, to separate it into clear water (supernatant) and a precipitate. The clear water was pale orange in color. The amount of precipitate was approximately 1 to 5% by volume of the produced water.

[0048] 2. Evaporative concentration process The separated clarified water was temporarily stored in an evaporative concentration raw water tank, and then introduced into an evaporative concentration device (registered trademark: Mobile Evaporator VVCC-40) manufactured by Sasakura Co., Ltd., where an evaporative concentration process was carried out. Note that this evaporative concentration device can be separated into two units (the first storage container and the second storage container disclosed in claim 1 of JP 2018-126680 A), and each unit can be transported by truck or the like.

[0049] The operating conditions for the evaporative concentration apparatus were a degree of vacuum in the evaporator of 20 kPa abs and a temperature of the retained liquid of 65°C to 70°C. While the boiling point increase due to the concentration of the components contained in the retained liquid was controlled to within 8°C, volatile components were evaporated and condensed from the retained liquid to generate condensed water, which was then removed from the evaporative concentration apparatus. Meanwhile, the specific gravity of the retained liquid in the evaporator was monitored, and when the specific gravity reached 1.1 kg / L, it was determined to have become concentrated water and was discharged from the evaporative concentration apparatus, thereby performing a continuous evaporative concentration process. The concentration rate was approximately 3.7 times the volume.

[0050] 3. Oil Removal Step Because the oil content in the condensed water obtained in the above-mentioned evaporation concentration treatment step was as high as 52 ppm, an oil removal step was carried out using an oil separation device equipped with an oil separation membrane (registered trademark: Eutec TH-80, manufactured by Asahi Kasei Corporation), and treated water was obtained. This oil separation device was a coalescer type device, and oil was removed from the condensed water by gravity separation to obtain treated water.

[0051] The pH values, inorganic salt concentrations (as TDS), ammonia nitrogen concentrations, COD values, and oil concentrations of the produced water, clarified water, condensed water, concentrated water, and treated water in the above operations are shown in Table 2 below.

[0052]

[0053] The oil concentration of the treated water can be further reduced by further treating it with activated carbon, for example. Although not performed in this example, if the treated water is subjected to a denitrification process, the ammonia nitrogen concentration can be easily reduced to 1 ppm or less.

[0054] Example 2: The raw water was produced from an oil drilling site different from that of Example 1. 1. A coagulation and sedimentation treatment process and 2. an evaporation and concentration treatment process were carried out in the same manner as in Example 1. The pH values, ammonia nitrogen concentrations, COD values, and oil concentrations of the produced water, condensed water, and concentrated water obtained through the above operations are shown in Table 3.

[0055]

[0056] If the produced water is subjected to the evaporation and concentration treatment process without undergoing the coagulation and sedimentation treatment process, the piping of the evaporation and concentration apparatus may become clogged, causing the apparatus to quickly break down.

[0057] 1': Organic component removal process 1: Coagulation sedimentation process 2: Evaporation concentration process 3: Oil removal process 4: Denitrification process 10: Produced water 11: Clarified water 12: Sediment 13: Inorganic coagulant 14: Polymer coagulant 15: Coagulation tank 16: Solid-liquid separator 17: Biological treatment tank (SBR tank) 20: Evaporation concentration raw water tank 21: Condensed water 22: Concentrated water 23: Evaporation concentration device 31: Treated water 32: Oil separation device 33: Oil separation membrane 34: Oil

Claims

DEPCT661. A treatment method for oil drilling water consisting of a sedimentation step to agglomerate the oil drilling water, separating it into clear water and sediment, and a concentration step to evaporate the clear water, yielding condensate and concentrated water.

2. A treatment method for oil drilling water specified in Relativity 1 where the oil concentration in the oil drilling water is 100 to 5,000 ppm, the COD is 10 to 20,000 ppm, and the concentration of inorganic salts is 200 to 35,000 ppm as TDS.

3. A treatment method for oil drilling water specified in Relativity 1 or 2, which includes an additional step to remove oil from the condensate using an oil separation membrane if the oil concentration in the condensate exceeds the specified values. 4.Treatment methods for oil drilling water specified in any of Claims 1-3, which include additional treatment procedures that remove nitrogen from such condensate water if the concentration of nitrogen in such condensate water is measured and found to exceed the specified value.

5. Treatment methods for oil drilling water specified in any of Claims 1-4, where the oil concentration in such clear water is 5 to 1000 parts per million.

6. Treatment methods for oil drilling water specified in any of Claims 1-5, where the oil concentration in such condensate water is 5 to 100 parts per million, the COD is 5 to 200 parts per million, and the concentration of inorganic salts is 10 to 100 parts per million as TDS. 7.

8. Any of the oil drilling water treatment methods specified in Reputations 1-6, which perform such concentrated evaporation treatment using a vehicle-transportable evaporation concentrater unit or a vehicle-transportable evaporation concentrater unit of 2 to 4 units.

9. Any of the oil drilling water treatment methods specified in Reputations 1-7, which perform treatment that removes the organic components present in the oil drilling water prior to such coagulation treatment.