Nonlinear Mechanical Analysis And Life Forecast Of Horizontal Well Rod String

Most of oilfields in our country are being in the period of waterflood development, and along with further development of oilfields, water content ratio of the fluid increases unceasingly which brings many difficulties and problems to the process of oil extraction, storage, transplantation and oil-water separation. The economic limit between foreign countries and ours have great differences. They don't exploit the oilfields which are in late high water-cut stage. Therefore, we have no experience to utilize. As is known to all, Daqing oilfield has come into late exploited stage, water content ratio is getting higher and higher. Using the technology of horizontal well and transforming old oil well to horizontal well are effect measures to raise the oil well's output. But the mechanical behavior of the sucker rod in the process of the horizontal well's production is not clear at present.Comparing with the gravity of the sucker rod itself, the force of friction between sucker rod and tubing is small in the vertical well. But in the slanting section of slant wells and horizontal wells, the sucker rod moving in slanted condition, under the function of its gravity, the friction force and abrasion are much bigger than those in the vertical wells. In order to change this situation, centralizers are needed, turning the friction between sucker rod and tubing wall to the friction between centralizers and tubing wall, and the kinetic resistance also has big changes. With dissimilar lubricants between sucker rod and tubing, the friction and abrasion characteristics are different. To the horizontal well, the principal problems are tubing leakage and rod parting. This topic has done some researches on the nonlinear mechanical analysis to the sucker rod, and the friction and abrasion characteristics between sucker rod and tubing have been found, so the service life of sucker rod can be forecasted.Through the theoretical analysis to the operation behavior of the horizontal well, the mechanical model of the horizontal well's sucker rod has been established. By defining the model's boundary condition, exerting the load, carrying on nonlinear mechanical analysis and numerical solution, the variation law of the normal pressure at the contact place of the sucker rod and tubing in horizontal wells are obtained.According to actual conditions of the horizontal well pumping system, the experiment apparatus are transformed. Friction pairs are formed, using the field used tubing and sucker rod with normalizing treatment. The friction and abrasion characteristics in various proportions of oil-water mixture as well as oil-polymer mixture under different pressures and velocities are summarized and analyzed. Conclusions have been obtained that friction coefficient on the spot decreases with the increasing of velocity and load, the abrasion losses of the friction pairs have no relation with velocity and the abrasion losses between the centralizers and the tubing sample increase along with the increasing of load.According to the Holm-Archard abrasion law of metal sliding friction, the abrasion period of the sucker rod coupling (centralizer) has been calculated, and the forecast service life of sucker rod is got. The conclusions have been got that the abrasion period can be lengthened effectively by using centralizer, changing the material of sucker rod to be glass fiber reinforced plastic, making the hole drift angle to be 30 degree to 40 degree at the maximum pump location. The analysis and computation to this model has an important academic value to improve the oil's output, the scientific management level and to lengthen the pumping inspection period.