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Home / Issue Archive / 2009 / March #3 / New PCPs Provide More Economical Well Development

№ 3 (March 2009)

New PCPs Provide More Economical Well Development

The progressing cavity pump (PCP) is a standard lift system for oil production as well as sucker rod pumps and EPS pumps. The application of PCPs has been limited for decades only to the vertical wells to handle oil fluids featuring high viscosity and high sand cut.

By Article supplied by Netzsch

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   The improved and new developed material and further developed pump accessories increased the application conditions for PCPs. This development process of a relative new pump system can only be successful if the manufacturer and operator closely cooperate. A representative example for PCP installation is to decrease the fluid level in gas wells.

Project Description

   Reducing the reservoir pressure in the reservoirs featuring intensive water drift causes a high water inflow. Due to the water inflow the bottom flow pressure increases at the perforation.  Thus the gas inflow from the producing horizons decreases or ceases. Lifting water decreases the dynamic level and reduces the bottom flow pressure.

   The completion for such wells is designed to remove the water through the tubing and free gas through the annulus (Fig. 1).
In the early 90’s RAG (Rohoel-Aufsuchungs AG Austria) installed sucker rod pumps in several gas wells with high water content, which were considered to be the optimal lift system at that time; there were no appropriate options for lifting gaseous water available.

   During the continuous operation the high operating costs were caused by the short life-time and frequent pump replacing. The main failure causes were gas lock and sanding of the pump plunger. Yet the mid-90’s, most sucker rod pumps were shut down, because an economically justifiable dewatering method based on the pump system did not exist. In 2004 RAG started a project in cooperation with NETZSCH to try, for the first time, PCP for dewatering of gas wells. The gas well Weizberg 1 (Fig. 2) was chosen for the pilot project.

Description of the Pilot Project Weizberg 1

   The well Weizberg 1 in the oilfield Weizberg (Upper Austria) is ca. 1700 m deep and is cased with a 7” production casing.

   On the basis of the production rate produced by a sucker rod pump in the mid-90s PCP NTZ 350 * 180 ST 25 was designed for a production rate of ca. 30 cu. m/day. The material selection was based on the experience with PCPs in different oil wells with high gas content. The pump assembly consists of rotor, stator, stop pin, torque anchor and gas separator.

   The drive-head assembly consists of drive head NDH*045KW*15T with a pressure-capsulated three-phase motor (motor power 22 KW). A suitable motor pulley combination enables a speed reduction of 5:1. The pump speed was controlled by a frequency converter. The frequency regulation was required by RAG for system automation.

System Automation and Defining the Optimum

Operating Range

   There are several parameters that have to be monitored to guarantee optimum operation of the PCP. The most important parameters are torque (calculated from electrical power consumption), gas rate on the casing outlet and water rate on tubing outlet.

   In addition to that the liquid level in the annulus has to be measured manually in defined time intervals to determine the optimum production rate and avoid liquid build up or depletion in the annulus. These parameters should be measured daily for the first two weeks and the interval can be decreased to 1 to 3 times per month once the dynamic fluid level in the annulus has stabilized. 
   The dynamic liquid level in the annulus is measured manually with acoustic fluid level measurement and is correlated with the measured torque on the motor. Using these two parameters the movement of the dynamic fluid level can be predicted. A drop of the fluid level results in an increase of torque whereas an increase of the fluid level causes a decrease of torque. Based on these observations a torque graph is derived. This torque graph is used to program the electric control panel.

Summary and Outlook

   Changing from sucker rod pumps to NETZSCH PCPs for the deliquification of gas wells was a very successful step at RAG (Fig. 3). With the use of PCPs, wells can now be produced more economically than before.  

   Besides optimum completion, and redesigning the pump, the main issue for optimisation is the automation of the whole system. However, the most important aspect in the process is the close cooperation between the pump supplier and the operator.

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