Abstract After large scale polymer flooding in the field, due to the high elasticity and viscosity of the fluid, the efficiency and effective life-span of the producers (and injectors) decreased significantly, new technologies were developed.
After polymer is produced, severe eccentric wear on sucker rods occur. To solve the problem, on the basis of theoretical and lab studies, techniques to reduce the normal force on sucker rods and control its eccentric wear were developed. Field practice shows that this technology has increased the average life span of pumping wells by 3 times.
The effective time of conventional fracturing and acid stimulation of polymer injectors is less than 3 months. Therefore, technologies of resin-coated sand tail-in fracturing and surfactant stimulation were developed. These 2 new technologies have increased the effective time of injector stimulation by about 5 times.
The above techniques are all used in a mass scale in the field with significant results; they can and are also used on conventional wells.
Introduction Commercial polymer flooding has commenced in Daqing Oil Field since 1996, resulting in oil recovery over 50%OOIP. At present, the annual oil output by polymer flooding has reached 1.2×10t, accounting for a quarter of the total oil output of the oilfield. With the wide application of polymer flood, there are also many problems that adversely impact the injection and production of polymer flooding. These problems are as following:Severe eccentric wear on sucker rod and tubing has occurred on a large number of pumping wells and the increase in wells that have wear problems has reached 3000%, which has increased workover frequencies and production cost as well. The problem of eccentric wear has greatly affected oil production.
On approximate one third of the polymer injection wells, injection pressure is close to the formation fracture pressure, the injection rate is low also. The effective time by conventional fracturing treatment can only last about three months.
Acid fluids react with the injected polymer solution. Therefore, conventional acidizing cannot be used on polymer injection wells.
Some novel techniques, including eccentric wear control, resin sand fracturing and surfactant stimulation were developed to solve the above problems.
Technology for Controlling Eccentric Wear of Pumping Wells Mechanism of eccentric wear of pumping rod. The constitutive equation describing viscoelastic fluids is set up and the flowing equation under the condition of discrete state can be calculated, then velocity distribution of flow field can be obtained. The distribution of velocity contour line and normal stress is shown in Fig 1. As seen in Fig.1, when the distance between the inner axis and outer tubing is small, its corresponding velocity gradient will be higher than that of larger distance. And the resultant force of normal stress points to the side of which the distance between the inner axis and outer tubing is smaller.