Summary At present, many oil fields in China have entered the high-water-cut production period, and the water cut of oil wells has continued to rise. Therefore, how to reduce the water cut of the produced liquid, reduce the amount of surface water treatment, shorten the ineffective water circulation, and reduce the comprehensive production cost have become the key problems restricting the sustainable economic exploitation of a high-water-cut oil field. To this end, the development model of circular displacement and the oil-recovery technology of a downhole oil/water-separation system with sucker-rod pump (DOWS-SRP) are proposed. The technology system consists of downhole oil/water-separation devices, an injection/production pump-string system, a sealing system, and downhole data-test system, mainly applied to separating the oil and water in the well through the separation device. The separated water is then directly injected into the formation and the separated concentrated liquid is lifted to the ground so the water injection and oil recovery are completed simultaneously in the same wellbore. The field-test data show that after the implementation of injection/production technology in the same well, the surface liquid-production volume decreased by 90%, the water-cut decreased by 27%, and the water/oil ratio decreased by 93%. In addition, the liquid volume of lifting, gathering, and treatment was greatly reduced, as well as the surface infrastructure investment, to achieve the purposes of cost saving, energy saving, and consumption reduction. At the same time, the downhole reinjection replaces surface water injection, transforming ineffective surface water circulation into effective internal displacement power in the reservoir and improving the yield and recovery rate. The successful application of the quaternary-oil-recovery block has made it possible to redevelop a large number of abandoned oil reservoirs, providing a potential basis for quaternary oil production. In addition, the preliminary energy-saving effect and economic-benefit analysis are performed. The data show that the energy-saving effect of this technology is obvious and good economic benefit is obtained.
The difficulty in directly determining the failure mode of the submersible screw pump will shorten the life of the system and the normal production of the oil well. This thesis aims to identify the fault forms of submersible screw pump accurately and efficiently, and proposes a fault diagnosis method of the submersible screw pump based on random forest. HDFS storage system and MapReduce processing system are established based on Hadoop big data processing platform; Furthermore, the Bagging algorithm is used to collect the training set data. Also, this thesis adopts the CART method to establish the sample library and the decision trees for a random forest model. Six continuous variables, four categorical variables and fault categories of submersible screw pump oil production system are used for training the decision trees. As several decision trees constitute a random forest model, the parameters to be tested are input into the random forest models, and various types of decision trees are used to determine the failure category in the submersible screw pump. It has been verified that the accuracy rate of fault diagnosis is 92.86%. This thesis can provide some meaningful guidance for timely detection of the causes of downhole unit failures, reducing oil well production losses, and accelerating the promotion and application of submersible screw pumps in oil fields.
To address the common issues of low-production oil wells like unbalanced supply and output, low pump efficiency and system efficiency and high energy consumption, a small-displacement oil pump has been developed. The pump has an enhanced structural strength with solid plunger and the mobility of the pumping oil with offset outlet valve. The outlet valve is located at the highest point of pump chamber when the plunger is at the bottom dead center, which is preferable for the discharge of gas and high gas-liquid and pump efficiency improvement. Combined with the distribution law of oil and gas in vertical pipe flow, it is assumed that the dissolved gas is linearly distributed from the oil inlet valve to the bottom end of the plunger after the pump is introduced. According to the position of the oil pumping valve of the oil pump, the efficiency calculation formula is derived. Then through reasonable matching of working conditions, the influence of various factors on pump efficiency is analyzed. The pump’s pump efficiency is about 10% higher than the API minimum pump diameter (32 mm), which is important for energy saving in oil fields.
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