Hits:Updated:2020-04-09 13:04:32【Print】
The development of the Misang Oilfield produces a large amount of high-temperature produced water. In order to meet the requirements of oilfield production and environmental protection, it is necessary to build a produced water treatment system with a treatment scale of 20,000 m / d. The oil content of the incoming water of crude oil dehydration system ≤ 1 000 mg / L, suspended matter ≤ 500 mg / L, and hydrogen sulfide ≤ 200 mg / L. In view of the physical properties of produced water, the process adopts the pressure regulation process of "adjustment and storage buffer + coalescence degreasing + coagulation sedimentation + gas stripping desulfurization + two-stage filtration". Water injection in oil fields. The project has been put into operation for more than two years, and the operation effect of the device is stable, which has a good engineering reference.
01 Water quality
The temperature of the incoming water from the Misang Oilfield is about 80 ℃, the H2S concentration is close to 200 mg / L, the salinity is 220 g / L, the Cl-mass concentration is 136 g / L, the pH is 5 ~ 7.6, and the water quality is weakly acidic. It belongs to high-sulfur and high-mineralization calcium chloride water type and is extremely corrosive. Sewage contains more HCO3-, SO42-, CO32- and Ca2 +, Mg2 +, Sr2 + and other scaling ions. When the working conditions change, it is easy to cause corrosion and scaling of process pipes and equipment containers.
02 Design difficulties and characteristics
1 Water quality stability and purification
The produced water in the Misang Oilfield has the characteristics of "high mineralization, high chloride ion, high hydrogen sulfide, high water temperature, low pH", four high and one low. This type of produced water generally has poor chemical reaction kinetics, poor flocculation effect, and difficulty in purification and stabilization of water quality. The highly mineralized water greatly accelerates the primary battery reaction in the water, and accelerates the corrosion rate of equipment and pipelines.
In view of the physical properties of the produced water, in order to solve the problems of high salinity in the water that are easy to corrode and scale, and the effect of poor water purification, the whole system pressure treatment process is used for the produced water treatment, and the micro-positive natural gas sealing process is used to treat the treatment device and other containers The facility conducts airtight oxygen isolation and develops new pressure-type produced water purification equipment, which improves the chemical reaction effect and avoids the strong corrosion problem caused by dissolved oxygen in the "four high and one low" water type.
2 Scaling control of gas stripping desulfurization process
The project adopts natural gas stripping desulfurization technology to reduce H2S content in water. Oilfield produced water contains high scale-forming ions such as HCO3-, SO42-, Ca2 +, and Mg2 +. Under normal circumstances, produced water has the following chemical balance:
Under normal circumstances, CaCl2 water-type produced sewage calcium carbonate has a low tendency to scale. However, under the action of purified natural gas, the produced sewage has a reduced partial pressure on the surface of the sewage, soluble CO2 overflows, and HCO3- in water is easily decomposed into CO32-. The calcium carbonate precipitates generated by CO32- and Ca2 + intensify the decomposition of HCO3-, and eventually generate calcium carbonate precipitates, which leads to serious scale formation inside the gas stripping desulfurization tower.
Aiming at the problem of easy scaling in the gas stripping desulfurization tower, the "micro-positive pressure natural gas stripping + acid injection + alkali injection" desulfurization process technology was adopted to adjust the pH of the produced water in and out of the tower to solve the scaling problem of the desulfurization tower and the problem of acid water corrosion. In order to improve the desulfurization efficiency, the hydrogen sulfide index of sulfur-containing sewage is ≤20 mg / L. At the same time, it ensures that the purified sewage has good stratigraphic compatibility and low scaling tendency. By using Aspen HYSYS 9.0 and PRO II software to simulate the desulfurization process of the gas stripping tower, the process parameters and internal structure of the gas stripping tower are optimized. In order to ensure that the removal of hydrogen sulfide in the sewage reduces the tendency of sewage scaling due to the increase in the alkalinity of the sewage and the impact on the post-treatment facilities, the gas stripping tower is provided with acid injection at the front end and alkali injection at the rear end. The feed, cascade and proportional control loops are applied to the multiple feed ends, acid injection mixing point and alkali injection mixing point of the parallel stripping tower, thereby solving the problem of unbalanced distribution of multiple raw materials and minimizing the upstream and downstream The impact of process flow.
3 Research on efficient produced water treatment equipment
Domestic pressure coalescing degreasing equipment usually uses random packing or structured packing, and the filling method is a section of coalescence structure. The packing of this type of equipment is easy to block, the coalescence separation efficiency is low, and the single processing capacity can only reach 250 m / h. According to the project construction owner's requirements for large-scale equipment, developed efficient pressure coalescing degreasing equipment, using a segmented coalescing degreasing filler structure, effectively solved the problems of coalescence filler clogging and low removal rate, single processing capacity It reaches 350 m / h.
4 Anti-corrosion technology and material selection
The produced water in the Misang Oilfield is extremely corrosive. In addition to taking technical measures to reduce the corrosivity in the process design process, the project design also studies material selection as an important technical control factor, and uses professional software for different water conditions The corrosiveness of the material is simulated and verified. In the end, duplex stainless steel was selected as the lining material for equipment and valves. Duplex steel was used for internal pipelines, non-metallic materials were used for buried underground and overhead pipelines, and internal corrosion protection + sacrificial anode blocks were adopted for equipment containers.
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