Producing High GLR Stripper Wells With an Automatic Casing Swab
Authors: Haynes C.D. , Johnson P.W. , Carlson E.S. 
Published: March 2010

An automatic casing swab system has been developed and tested over a two-year period in high gas/liquid ratio (GLR) stripper wells in the Appalachian Basin. Wells in the Basin typically produce lesser amounts of liquids in their later productive lives. These amounts are usually too small for efficient operation of the rod pumps or tubing plunger systems that were originally installed. Normal practice has been to periodically remove the liquid with a wireline casing swab or to plug and abandon the well. The system described herein is capable of prolonging the economic producing lives of these wells.

This system consists of a cylindrical swab tool configured to seal against the casing wall when moving upward, but capable of falling through wellbore fluids when released from a specially-designed wellhead. A "stop "in the casing prevents the swab from falling into the perforations and closes the liquid bypass valve. The cycling frequency of the swab is dependent on the strength of the individual well.

The automatic swab system is usually less expensive to purchase, install, and operate than sucker rod pumps or tubing plungers. It can operate unattended for extended periods, can frequently increase gas output, and provide a smoother orifice meter chart for easier integration. In addition, the system is suitable for operations in remote locations.

Field experimentation has shown the ideal candidate well for this system to have a GLR over 900 std m3/st m3, a bottomhole pressure between 1.4 and 6.9 MPa, low fines production, and modest paraffin output.

Introduction

The typical stripper oil and gas well is characterized by low total liquid output, low reservoir pressure, and a relatively high gas-liquid ratio (GLR). Wells of this type are plentiful throughout the world, but are predominantly located in the United States and Canada. Because of the relatively poor output from these wells, they are first to face abandonment at times of low product prices.

Beam pump-sucker rod (pumpjack) and tubing plunger (rabbit) systems are ordinarily found in use on these stripper wells. They were typically installed when the well had greater reservoir pressure and liquid output. Once the well declines in pressure and output each of these systems becomes inefficient. The pumpjack may tend to pump-off the well even though it may operate only a few hours each month or gas lock and fluid-pound from the scarcity of liquid entering the wellbore. The tubing plunger will become less efficient because of slow plunger movement to the surface, liquid fallback, and the necessity of "blowing-down" the well to atmospheric pressure periodically in order to bring the plunger to the surface.

A common practice is to convert these wells to "swab wells, "where all downhole equipment is removed and the wells are produced by periodically removing accumulated liquids by a wireline swabbing unit. Gas production continues for a certain period of time before the well "loads-up" and requires swabbing once again. Even though it may appear simple and inexpensive, this practice can be even more expensive than before when factoring in the cost of the swabbing unit and the frequent need for it.