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.

The diluent-gas method is an artificial lift system for heavy oils (as low as 8.5 °API), where a light crude is used as diluent and it is injected into the well along with natural gas in order to reduce the viscosity of the crude oil therefore increase oil production. This method is unique in the world and has been long used in Venezuela. Due to high maintenance costs, 20,000 US$ annually, incurred in replacing and repair diluent pumps (reciprocating pumps), which are used to inject at 900-1,000 psig the diluent (28-35°API) into the well, those pumps are considered as a critical system, basically, because of high operational pressures and oil production deferred, which is estimated in 2,500 barrels per year. This project was based on analyzing a novel way to pump the Diluent and Gas down the well. The equipment designed is denominated Gas Displacement Pump and utilize the same gas lift (900 – 1,000 psig) as a driving force to inject the Diluent into the well. The system is made up of a vessel, a group of valves, pipes, level control systems, etc. This novel design will allow minimizing; deferred oil production, environmental damage and maintenance costs, OPEX is reduced considerably (85%), as the Gas Displacement Pump will not have moving parts thus maintenance expenses would be low, generating this significant savings to the company. Finally, it was demonstrated that there is no slug flow formation using this new system and that the flow regime governing the system is stratified.

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Recent experimental studies on intermittent gas lift have shown that the lift efficiency of this method decreases drastically as the viscosity of the fluid to be lifted increases. As the viscosity increases more gas is needed to keep the fallback losses at a minimum. One way to get around this problem and eliminate fallback losses is to implement the use of Gas Chamber Pumps (GCP's). GCP's are highly appropriate for shallow wells producing heavy oil in places where high-pressure injection gas is available. That is the case of some wells in Lake Maracaibo and in some places in the eastern oil fields in Venezuela that are currently producing oil of 14 to 23°API from reservoirs located at depths between 2000 and 3500 ft. A variety of different GCP configurations can be found in the literature, from highly complex and compact units to simple types of completion that can be implemented with minor changes of current gas lift completions. The advent of simple and highly reliable programmable surface controllers is making it possible to simplify subsurface completion. The simplicity of these new completions implies a new and economical way of implementing GCP's where they are appropriate. A description of how different GCP's work and the most popular configurations are given in this paper. It is also explained in detail a new and simple engineering procedure to estimate the liquid production and gas consumption of a well producing with a GCP. This procedure takes into account the inflow capability of the well and couples this capability with the pressure losses across the different parts of the completion and the flow and pressure capacity of the gas lift system. Introduction Even though in many operational situations GCP's are more efficient than sucker rod pumps, currently they are not widely in use. One reason for this to happen might be the lack of injection gas in areas where sucker rod pumps are being used. The early methods, such as the one depicted in Fig. 1, consisted in alternately injecting gas into a down hole accumulation chamber and bleeding it off to allow it to refill. In Fig. 1, surface valve # 1 is open and surface valve # 2 is closed while gas is being injected. For this type of completion, during the gas injection stage the liquids are forced into the well annulus through a down hole valve installed in a standard side pocket mandrel. This valve is equipped with an internal check valve that does not allow the liquids to return to the tubing chamber. Once the liquid level has reached a minimum, which is at the down hole valve depth or above it, surface valve # 1 would close and surface valve # 2 would open allowing the injection gas to be vented to the surface flow line. The pressure in the tubing chamber then drops to a pressure close to the separator pressure so that the liquids can flow from the formation to fill the tubing chamber again. There are many different types of gas chamber pumps that are explained below. The advantages of using GCP's over other types of artificial lift methods are as follows:They are able to manage sand production with fewer problems.They can lift gassy or viscous fluids better and high fluid temperatures will not affect the subsurface completion.Some types of completions can be very simple. More complicated pumps can be wireline retrievable which is ideal for offshore installations.Their use reduces the changes of creating emulsions.Compared to gas lift, GCP's can significantly increase the drawdown on the formation. They can also be combined with gas lift to get maximum formation drawdown at maximum production rate.GCP's can provide full pump stroke at any depth or cycle rate.They can be installed in deviated wells and can be run and pulled with wireline equipment.

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