State-of-the-Art Summary

The other components of the installation include the controller, which opens and closes the valves based on time or pressure, the downhole assembly to cushion and hold down the plunger if the well is flowing, and the lubricator installed on top of the wellhead that cushions the plunger when it arrives at the wellhead and holds it.

There are several specialized tools, including multi-stage tool, "smart" plunger, and casing plungers. Chandler Frost (PCS) presented information on the multi-stage (usually two) plunger. It costs about $2,500 more than the conventional plunger system, but works with a lower gas-to-liquids ratio. Essentially the multi-stage tool is set between two plungers, allowing the movement of fluid in two stages. It is a candidate where running the conventional plunger is difficult or has long shut-in times, in packer or slimhole wells, liner wells and wells with tapered production strings. Becoming recently popular, there are more than 400 installed in the Midcontinent and Permian basins.

The PCS Smart Plunger™ is a specialized test tool used in wells equipped for a conventional plunger to measure downhole pressure and temperature. According to Kyle Stell (PCS), it leases for $500/day, less for longer periods. It has an internal pressure and temperature gauge that gathers the data, which are then downloaded into a PC when returned to surface, requiring no wireline. It will provide a flowing gradient, allowing a single technician to run a buildup test without needing a rig or crew. It can also be used as an optimization tool for measuring travel time, fluid levels and other information used to optimize the conventional plunger. (Figure 2) Finally, it can be used as a surveillance tool to detect and locate tubing leaks.

The casing plunger is a relatively new technology. Information presented by Robert Moore (PAAL) showed that, in certain cases, it can be utilized to lift fluids in lieu of the standard rods and pump, without the expense of running the pump and motor. At 50 pounds and 4 ˝-inch diameter, it requires more gas than a standard plunger, ideally a gas/liquid ratio of 12,000 scf/bbl or greater at depths up to 7,500

Figure 2:  Pressure and Temperature vs. Delta Time, courtesy PCS

feet. Where the application replaces the conventional rod pump, the installation involves laying down the rods and tubing, converting the wellhead and preparing the casing.

The cost of the plunger itself is $11,500. The cost of periodic maintenance runs under $100 monthly. The technology has shown to be effective even with moderate amounts of paraffin in the produced oil.

Rod Pumps

When there is insufficient gas energy to lift the fluid, a common solution is the standard rod pump and jack. Even this established technology must be sized and maintained properly to minimize expenses. In his presentation, Norman Hein, Jr. (Oil and Gas Optimization Specialists) discusses key design factors, including the type and diameter of the pump, stroke lengths and pumping speeds that in turn affect the size and type of surface pumping system. After analyzing the rod-string and pumping-unit limitations, he concludes that the free fall speed of the rods and the pumping-unit stroke length determine the maximum pumping speed. He further analyzes current fatigue life and concludes that the modern equipment fatigue life to failure is on the order of 50 million cycles, five times greater than assumed in the past and sufficiently so that corrosion and operating practices become the limiting factor, essentially taking

simple fatigue out of the design equation. While the acceptable range of stroke and speed is modest, his analysis concludes that the use of sinker bars will reduce the load range for shorter/faster operation, which in turn will save capital and operating costs with less moving mass.

It is necessary to understand how the pump works to properly diagnose pump problems and avoid unnecessary work and expense. Mark Mahoney (Harbison-Fischer) discussed some problems and misdiagnoses of those problems. The basic rod pump is a fairly simple device with only three moving parts: the reciprocating plunger or barrel, and two check valves, stationary (standing valve) and moving (traveling valve) that are opened by pressure differential and closed by fluid flow. The standing valve is opened when the pressure in the pump chamber drops below the pump intake pressure on the upstroke. On the downstroke, fluid flow closes the standing valve and the pump chamber pressure builds until it overcomes the hydrostatic pressure on the top of the traveling valve and the traveling valve opens. The fluid is displaced from the pump chamber by the travel of the plunger during the downstroke and on the next upstroke after the traveling valve closes, a column of fluid the diameter of the plunger is lifted up the tubing to the surface. This sounds simple until symptoms appear indicating a problem. These problems can include gas lock, gas interference, fluid pound, sand problems, scale, paraffin, corrosion and wellbore deviations.

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PTTC

3rd Quarter 2006