Summary
The traditional means of artificial lift production for vertical and deviated wells in the Orinoco oil belt in eastern Venezuela used to be rod pumping and top-drive progressive cavity pumps (PCPs), particularly for wells with production rates ranging from 200 to 600 barrels of oil per day (BOPD) of extra-heavy oil (8°API gravity and viscosities of 2,000 cp at a reservoir temperature of 133°F). After 1995, with the implementation of horizontal drilling technologies for the construction of wells in unconsolidated sandstones, electrical submersible pumps (ESPs) became an alternative to handle higher production volumes (Ramos and Rojas 2001). More recently, top-drive PCPs have also been installed to produce extra-heavy oil at high rates.
Hybrid artificial lift technologies, such as bottom-drive progressive cavity pumping, which combine features of the ESP and the PCP systems, have recently been successfully evaluated in the Orinoco belt to exploit extra-heavy oil reserves economically. A typical completion assembly includes a multisensor gauge to obtain downhole pressures, temperatures, and vibration amplitudes of the system, and to detect power-cable current leaks; a four-pole motor; a protector; a 4:1-ratio gear box; and the PCP. The functional design of the bottom-drive PCP facilitates the handling of viscous and abrasive fluids, increases the flow rate, and diminishes the operational costs. Further advantages of this application include the complete elimination of tubing wear by eliminating the need for a rod string, greater torque capacity, lower surface maintenance cost, lower load and horsepower requirements, and lower frictional losses.
The application of bottom-drive PCPs in the Cerro Negro area has resulted in production rates of up to 1,000 BOPD of extra-heavy oil with 50% lower horsepower requirements in comparison to those of conventional top-drive PCP systems.
Introduction
The Orinoco oil belt is located on the northern side of the lower Orinoco River in eastern Venezuela. It covers an area of approximately 20,850 square miles and contains the country's largest deposits of extra-heavy oil, estimated to be 1.2´1012 barrels of oil in place (OIP). The Cerro Negro area is located in the eastern part of the Orinoco belt; it covers 70 square miles, with an estimated OIP of 18.5´109 barrels of extra-heavy oil (Fig. 1).
The extra-heavy oil that is currently being produced in the area has gravity values ranging between 6 and 10°API, with an average value of 8.5°API, and viscosities of 2,000 to 5,000 cp at a reservoir temperature of 130°F.
To exploit these extensive extra-heavy oil reserves economically, new drilling and production technology implementations have been significant over the last 10 years, particularly the use of horizontal and multilateral wells and the development of artificial lift systems, resulting in new production targets of 2,000 BOPD per well compared to the former 200 BOPD per well.
Wells with productivity potentials greater than 1,000 BOPD are typically completed with either ESPs or conventional PCPs. To achieve the advantages of both ESP and PCP production methods and to reduce the lifting cost, a bottom-drive PCP system was evaluated for the production of extra-heavy oils. A discussion of the applicability of this artificial lift method and a comparison with the top-drive PCP system are presented in this paper.
