Preparation method of water used for oilfield flooding, water flooding and water gathering

Abstract

The invention belongs to the technical field of oil field development and relates to a preparation method of water used for oilfield flooding, water flooding and water gathering. Firstly seawater is subjected to sterilization and algae killing and then filtered by virtue of an electrolysis chlorine producing device and then is subjected to heat exchange by virtue of a primary preheater and a secondary preheater, then the seawater is conveyed into an ultrafiltration device to be filtered, so as to obtain ultrafiltration producing water; one part of the ultrafiltration producing water is conveyed into a nanofiltration device by virtue of a high pressure pump, the rest of the ultrafiltration producing water enters into an energy recycling device, is subjected to energy exchange together with concentrated water of the nanofiltration device and then is conveyed into the nanofiltration device; then nanofiltration producing water is subjected to heat exchange together with produced water by virtue of a heat exchanger; and the nanofiltration producing water is deoxidized and then is directly taken as injected water to enter into a water injection system or a matching and gathering device, polyacrylamide is added to prepare a polymer mother solution, and finally the polymer mother solution is diluted and injected underground to displace oil. The preparation method provided by the invention is easy to operate, low in cost, low in energy consumption, low in oxygen corrosion rate and beneficial to popularization of waterflooding and polymer flooding techniques.

Description

Technical field: [0001] The invention belongs to the technical field of oilfield development, and relates to a method for softening seawater based on nanofiltration seawater softening technology, deoxidizing based on membrane degassing technology, and producing water for offshore oilfield water injection and preparation of oil displacement polymer solution, especially a method A method for preparing oilfield water injection and polymer injection water. Background technique: [0002] Most onshore oilfields in China use water injection or polymer injection to drive oil. The water volume provided by the produced sewage treatment is often difficult to meet the water volume requirements for reinjection water. Therefore, other water sources are needed as supplementary water. Generally, clean water (river water or pumped water) is used shallow groundwater) for supplementary water injection, water injection development and polymer flooding are also important enhanced oil recovery me...

AI Technical Summary

Problems solved by technology

[0002] Most onshore oilfields in China use water injection or polymer injection to drive oil. The water volume provided by the produced sewage treatment is often difficult to meet the water volume requirements for reinjection water. Therefore, other water sources are needed as supplementary water. Generally, clean water (river water or pumped water) is used shallow groundwater) for supplementary water injection, water injection development and polymer flooding are also important enhanced oil recovery measures for offshore oilfield development, both of which require suitable water sources, especially polymer flooding Technology has high requirements on the hardness and salinity of the water used to prepare polymer solutions; however, one of the challenges currently faced by offshore oilfield development is the lack of fresh water resources. The commonly used water source is obtained by digging water source wells to extract formation water. However, the cost of drilling water source wells is generally high, and the water volume is generally not easy to guarantee; using high-salt and high-hardness seawater directly as water injection is not compatible with formation water, and will interact with formation clay and formation water, resulting in scaling and clay migration. If seawater is used for direct polymerisation, because of the high salinity and high content of divalent ions in seawater, the viscosity of the polymer solution prepared by conventional polymers is very low, which cannot achieve flooding. If the salt-resistant polymer is used, the cost is relatively high and the amount of polymer used is large. Therefore, one of the technical keys for the development of offshore oilfield water flooding and polymer flooding is to find a large amount of water that is compatible with formation water as an injection Water or as water for preparing polymer solutions

[0003] At present, the application of nanofiltration seawater softening technology in oilfield water injection development is mostly for the purpose of removing divalent sulfate ions in seawater that are easy to scale and then directly use it as oil injection water for oilfield production. The company's patent US2004007358 (A1); Chinese patent ZL200910016067.3 (the applicant) discloses a method of using nanofiltration membranes for seawater softening and advanced treatment of produced water, and through cleaning and mixed injection, it can reduce oil production gathering and transportation systems in oilfields. In terms of nanofiltration technology used in polymer injection development, Chinese Patent Application No. 200710113282.6 discloses a method for using seawater or brackish water in oilfield water injection and polymerization process, using cyclone and membrane separation integration technology, This method has the inherent disadvantage that the cyclone cannot remove low-density particles

None of the above patents considers the deoxidation of water injection or polymer blending water. Whether it is water injection or polymer blending flooding, the oxygen content must not exceed 0.1mg / L, otherwise it will easily cause severe corrosion of the oil production pipeline. one of the main problems

At present, thermal or supergravity deoxygenation methods are mostly used, which need to consume more energy

The presence of oxygen in the polymer solution can also easily cause polymer oxidation and chain scission, resulting in polymer degradation and viscosity drop, reducing the oil displacement effect

In addition, in the process of membrane application, every time the water temperature drops by one degree, the membrane flux will drop by about 3%. Therefore, the membrane flux will drop sharply in winter, only half or one-third of that at 25 degrees, while oilfield water injection development and The amount of water needed for polymer injection development will not change because of this. In order to ensure the normal supply of sufficient water in winter, the membrane device needs to have a very wide operating flexibility, which is very difficult for the design and operation of the membrane process.

Generally, the only way to increase the membrane area is to greatly increase the occupied area, which is very expensive for the limited space of offshore oil production platforms and offshore floating production storage and storage vessels (PFSO)

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