Ground-driven Single-screw Pump Lifting System Process Design

The surface-driven single progressing cavity pump(PCP) lifting system is one artificial lift of well reliability,low running charge and cost, adapting to the exploitation of shallow wells,viscous crude wells,sandy wells and gas wells. Scarce of the sophisticated theory of technological design, the capacity of well is not given full play to, and system resources as well as energy source is seriously wasted. Therefore it is very significant for comprehensive application to increase the design technology of PCP.On the basis of analyzing profoundly the PCP recovery mechanism and the flow rule of the fluid in annular, the expressions of velocity and flow rate of helical flow of viscous fluid between rod strings and tubing has been obtained by using helical flow in a vertical annular space as a simplified flow model. And built upon mass, momentum, energy conservation and the theory of well-bore radius heat transmission, this paper establishes the mathematical model for predicting accurately the profile of helical flow pressure,temperature of the fluid in annular. The model allows for Joule-Thomson effect,the structure of the well,different heat transfer medium in annular and changes of the physical properties with the depth. Furthermore, it proposes a numerical solution that deals with the wellhead temperature as an unknown quantity by means of iterative computation, which avoids errors caused by the inaccurate estimation of the wellhead temperature, and takes the influences of the rising of flow temperature through PCP.Depending upon breakaway lapse form,cause and dynamics of spindly rod in the well-bore, it proposes a mathematical model reposed on the wave differential equation for rod strings and its finite difference solutions through divergent analysis under the condition of initial and boundary factors. This model can be used to calculate and predict the change in torque of rod string located at pump and any locations in well-bore according to the change in torque of polished rod measured on the surface, vice versa. The results of the study provide a theoretical basis for the study of kinematic behavior and working conditions for the surface-driven single progressing cavity pumping system.Grounding on the working characteristics of PCP lifting system, the pump can be considered as a functional nodal, and the way of technological design is brought forward. Incorporation the power of lifting fluid and PCP characteristic curve, it optimizes pump for the sake of its paramount efficiency. And setting depth of pump is sensitively analyzed to make sure the reasonable position. Rod strings are designed by computing compound stress with the fourth strength energy on the condition of torque and axial force. And the horsepower of surface motor is ascertained through anticipating the operating power of motor shaft according to the power of lifting liquid and rotational speed of PCP.According to the energy loss of surface and down-hole segments of the lifting system, including the motor,reducer box and strap,rod strings,pump and tube pillar, system efficiency analytical model is proposed, and every factor of affecting system efficiency is researched fully.The case history calculation is done with the basic data of well Ba18-55 in Erlian Oil Field of North China and He 8 in Shunan Gas Production Division, pumping power and total stages are calculated under the production condition such as output and tubing pressure, and then pump,rod strings and the horsepower of the electric motor are designed, and it is analyzed that sensitivity parameters such as produced gas-oil ratio and water cut affects lifting efficiency as well as torque and axial force of rod strings in the well-bore.