Plunger pump and pump material selection:
At present, the number of wells using rod pumps in domestic oil fields is a large proportion, most of which are plunger type pumping pumps, and conventional plunger pumping pumps have become one of the main oil recovery methods.
Most of the domestic oilfields have entered the high water-bearing development period, coupled with the high-sand, high-temperature steam heavy oil mining, polymer injection mining and strong corrosive media environment and poor well conditions, the pump barrel of the plunger pump The wear, corrosion and scratching of the plunger are becoming more and more serious. The average inspection cycle of the oil well is getting shorter and shorter, and some even require less than 30 days to check the pump, which seriously affects the comprehensive economic benefits of oilfield development. Many institutions at home and abroad have invested a lot of effort to study the failure causes and protective measures of the pump. One effective method is to optimize the material and surface treatment of the pump barrel and plunger.
The pump barrel and plunger friction pair and the surrounding working environment and conditions constitute a tribological system. The corrosion wear of this system is determined by the sum of the corrosion wear of the pump barrel and the corrosion wear of the plunger. The corrosion wear of the pump barrel and the plunger is determined by factors such as the physical and mechanical properties of the constituent materials, the mutual motion relationship, the working environment and conditions. Ultimately, from the perspective of the pump, the choice of material and surface treatment of the pump and plunger is the determining factor in determining the amount of corrosion and wear in this tribological system.
The purpose of selecting and optimizing the pump and plunger materials and surface treatment process is to minimize the amount of corrosion wear in this tribological system. Due to the large number of influencing factors, there is still no theoretical guidance on the material selection of the pump barrel and the plunger. The most work done by the researchers is to select the material and surface treatment process of various pump barrels and plungers, and then to corrode certain corrosion. The indoor friction and wear test is carried out under the condition of wear, and the results of the test are used to determine what kind of pump plunger material should be selected under the test conditions. Here are two test results:
The first result: pump material and surface treatment process are 45 steel surface electroless nickel-phosphorus alloy, 303 steel surface chrome plating, 4%-6% chrome steel pressure nitriding, etc.; plunger material and surface treatment process It is made of carbon steel chrome plating, carbon steel laser treatment, naval brass electroless nickel-phosphorus alloy, and Monel alloy chrome plating. The above materials were individually paired for the abrasion resistance test, and the friction pair for the test consisted of a ring and a block. The medium is clean water, the temperature is 60 ° C, and the viscosity is 0.000653 Pa / s. The test machine is a MG-200 high-speed high-temperature friction and wear tester. The applied load is 1kN, and the total friction stroke of the test piece is 20km. Through the paired wear resistance test of different pump and plunger materials and surface treatment process, and sorted according to the plunger failure principle, the optimal matching materials for the pump cylinder and plunger friction pair are respectively carbon steel chemistry. Nickel-plated phosphorous alloy and carbon steel are chrome-plated.
The second result: the pump material and surface treatment process are chrome plating on carbon steel surface, electroless nickel-phosphorus alloy on carbon steel surface and 38CrMoAl nitriding; plunger material and surface treatment process are chrome plating on carbon steel surface, electroless nickel plating on carbon steel surface Phosphorus alloy, carbon steel surface spray-welded nickel-based alloy and 38CrMoAl nitride, respectively combined into 9 pairs of friction pairs. The test friction pair consists of a ring and a column. The test medium is oily sewage, which contains 5% oil; the mineral content in water: chloride ion 11000mg/1, carbon dioxide 25mg/1, calcium ion 25mg/1, bicarbonate ion 30mg/1, magnesium ion 13mg/1, total iron 8 mg / 1; sand containing 0.4%; temperature is 60 ° C. The same use of domestic MG-200 high speed high temperature friction and wear testing machine. The test load is 100N and the total friction stroke is approximately 6km. Based on the comprehensive analysis of the test results, it is considered that the carbon steel spray-welded plunger is optimally matched with the carbon steel chrome-plated pump cylinder, and the 38CrMoAI nitride plunger is matched with the carbon steel chrome-plated pump cylinder.
As can be seen from the above, the laboratory test results are obtained under the set conditions. If different test conditions are changed, the workload is huge, and even if the conditions are different, it is not necessarily consistent with the downhole conditions of the oilfield site, so the experimental results are limited. Due to the different test conditions and the shape of the friction pair, there is no comparability between the test results.
It can be seen that it is determined by the test that the matching between the pump barrel and the plunger material is insufficient, and the test has no theoretical guidance, so the test workload is large. The materials selected for the test are only known materials, and it is difficult to propose other materials that are not used on the pump but may perform better.
With the development of materials engineering and the emergence of new material surface treatment processes, many materials and surface treatment processes are likely to be applied to the pump and plunger surfaces, and the friction and wear tests of pure laboratory matching materials are used to determine the far-off. It is far from meeting the current urgent requirements for improving the life of pumping cylinders and plungers. How to design the pumping and plunger pairing materials with the principles and techniques of materials science and other disciplines is an urgent problem to be solved.
