Abstract

Hailar Oilfield is a new block of Daqing Oilfield developed from the end of last century. In the beginning of the development, beam pumping unit was the only lifting method of the Oilfield. Due to the low pump efficiency and higher rod failure rate as well as the 2000m lift, beam pumping system was not as economic as other in blocks of Daqing Oilfield. As the result, PCP was put into production from 2005. Though all the four wells had a good performance with high pumping efficiency in the beginning, after several month's operation, rod strings suffered from severe oscillation and resulted in fatigue failures in a short period. Theoretical and experimental study indicated that, high working temperature (85 centigrade) and special oil characteristics caused much higher swelling degree of elastomer than in other blocks, which led to the increment of interference fit and friction force between rotor and stator.

In the initial application, although pump parameter and elastomer formula were adjusted before treatment to reduce the swelling effect, these adjustments didn't take into effect as predicted. In that case, a personalized PCP design was brought forward which gave an integrated methodology for PCP application in Hailar Oilfield. In this design, all the lifting parts from surface to downhole equipments were considered as a whole system. FEM analysis was applied to make a detailed description of the pump for different operating temperature. Based on deeper adjustment of elastomer and pump's structure parameters, the optimum design of rod and other equipments were take into consideration as well. In the end of 2006, 4 new personalized design pumps were put into production. In the following year, despite of small oscillation in the first few days due to the influence of treatment water, all PCP systems performed stably with high efficiency.

Background

Hailar Oilfield located in the northeast of Inner Mongolia Autonomous Region, near the frontier of China and Mongolia. It was a continental facies deposit basin which was developed from 1980s. See Fig. 1. Till the mid of 2007, the oil production rate has reached 250,000 tons. In the beginning, the lifting methods of the oilfield were beam pumping system and bailing lift system. The production rate per well was around 10 m3/day, and many of them were under 5 m3/day. The lift of producers ranged from 1600m to 2500m, and temperature was from 70 to 90?. Due to the low displacement and higher lift on the average, beam pump system and bailing lift system wasn't so economic. In the beginning of 2005, one PCP well (Well#0) was put into production with 1400m lift. The system operated stably and was pulled out till the mid of 2006 due to the new development requirement of the block. According to the good performance of this case, PCP lifting technology was recommended to be applied in higher lift wells (above 1800m) in Hailar basin.

Pilot Test of PCP Lifting System

In 2006, a pilot test was implemented including 4 PCP wells in Hailar Oilfield from August to November. The pump efficiency was very high up to 90% in the beginning of the operation. But several weeks later, high flunctuate of operating loads were found in all the wells. See Fig. 2. Obvious oscillation could be observed from the surface polished rod and abnormal sound could be heard clearly, which indicated the pumps weren't operated in the constant speed. Under this abnormal operating condition, rod and pump failures were frequent in the following several months. Up to April, 2007, Well#1 has a rod failure after one month operation. Well#2 has three rod failures in five months. Well#3 has two rod failures in two months. Except that Well#3 operated normally, all the other three well's average running life was around two months.

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