Lease Pumper's Handbook Published
by the Commission on Marginally Producing
Oil and Gas Wells of Oklahoma, First
Edition 2003 Written by Leslie V. Langston
Table of Contents Introductions A. Cover
Sheet Book Title B. Publishing Information
First Edition, 2003
The Lease Pumper's Handbook
Published by the Commission on Marginally Producing Oil and Gas Wells of Oklahoma, First Edition 2003 Written by Leslie V. Langston Table of Contents Introductions A. Cover Sheet Book Title B. Publishing Information First Edition, 2003
Written by Leslie V. Langston
Publishing Information. First Edition, 2003. C. Foreword. Rick Chapman, Executive Director (1996-2000) Commission on Marginally Producing Oil and Gas Wells, State of Oklahoma. D. Dedication. John A. Taylor, Chairman (1992-1998) Commission on Marginally Producing Oil And Gas Wells, State of Oklahoma. E. Author’s Introduction. Leslie V. Langston, Author, First Edition F. Commission Introduction. Liz Fajen, Executive Director, Commission on Marginally Producing Oil and Gas Wells, State of Oklahoma.
The Lease Pumper’s Handbook Chapter 18 Gas Wells Section C GAS DEHYDRATION Figure 1. An glycol dehydration unit. C-1. Gas Dehydration. Gas, as it leaves the separator, will probably be saturated with distillate and water vapor. Gas in this condition is referred to as wet or rich gas. The purpose of the dehydration unit (Figure 1) is to reduce the level of the water and distillate remaining in the gas. After these vapors have been removed, it is referred to as dry or lean gas. The field glycol dehydration unit has other popular names such as the stack pack or thermo pack. As the gas leaves the dehydrator, it will still contain some moisture and distillate, but it will have a lower dewpoint, the temperature at which the gas will form condensation. 18C-2 C-2. Operating the Dehydration Unit. The dehydrator is part of the separator unit (Figure 2) and may use either ethylene glycol or tri-ethylene. In the following paragraphs, glycol is referred to but the same principles apply to a system using triethylene. Figure 2. A separator unit with dehydration unit, a knee tub, and the water and distillate tank battery. The inlet scrubber. The two-phase inlet scrubber (Figure 3) is the first vessel in the dehydration unit that the wet gas enters. The wet gas is divided into drier gas and liquid. The gas is diverted into a circular action, passes up through a stainless steel wire mesh mist extractor, then flows on toward the contact tower. The condensate (and water) that is stripped out of the gas is dumped to the distillate stock tank. The contact tower. The contact tower (Figure 3) is the vessel that is designed to dry the gas. The gas enters the contact tower near the bottom through a chimney tray. The gas works its way up through bubble-type trays filled with ethylene glycol, which has a natural attraction to water. The glycol absorbs the water contained in the gas, and the gas passes up and out the top of the tower. Figure 3. Note the inlet scrubber and contact tower in this view of a dehydration unit. As the gas returns to ground level through the down-comer line, it passes through the glycol-gas heat exchanger where the outgoing gas cools the glycol coming into the contactor. The dry gas leaves the dehydration unit to be compressed and measured as it leaves the location. The glycol pump. Glycol is pumped into the contact tower by a dual-purpose pump (such as the Kimray glycol energy exchange pump), which moves glycol up through the cooler or heat exchanger and into the top of the contact tower. The glycol trickles down through the contact trays where it collects water and condensate and flows to the bottom of the contact tower. 18C-3 The dual-action pumps. The dual-action glycol pump pulls the wet glycol out of the bottom of the contact tower through a highpressure strainer, where it is pumped along with a little gas through the bottom section of the reboiler. The heat exchanger surge tank. The wet glycol is circulated through the heat exchanger surge tank and into a three-phase gas, glycol, and condensate separator. The three-phase gas, glycol, and condensate separator. As the fluid enters the end of the three-phase separator, the fluid stratifies into three layers. The gas comes to the top and fuels the reboiler and supplies it with stripper gas. The second layer formed is the condensate, which is controlled by an indiscriminate float. The float directs the fluid into a tank for distillate and condensate at the tank battery. The water-laden glycol is directed toward the reboiler for water removal. The reboiler. The purpose of the reboiler is to boil off the water that was removed from the contact tower but leave the glycol. This is done by raising the temperature to a level that will cause the water to evaporate but which is below the boiling point of glycol. Figure 4. A small reboiler. The reboiler operates at a temperature of approximately 350° F. If the reboiler has a back-up temperature control, this second control is set 20° higher. Water boils at 212° F, but, if it is under pressure or contains any contaminants, it requires more heat. Glycol boils at a temperature higher than this temperature setting. The water vapor rises in the stripping still and condenser. It trickles down an angled pipe and is collected in a foot tub (Figure 5). This tube has to be insulated to prevent the water from freezing in cold weather. Figure 5. A water collection tub. The water collects in these short, small volume tanks, and vacuum trucks come by periodically to remove the accumulated water to prevent overflow. C-3. Tank Batteries for Gas Wells. Tank batteries for gas wells, as a rule, are less imposing than tank batteries for oil wells. Most gas wells will produce distillate and water. Distillate has such a high API gravity that these two fluids flash separate almost instantly. Since they separate usually in a matter of seconds, no treating vessels are necessary. This means that there is no need for heater/treaters, gun barrels, free water knockouts, or flow splitters. 18C-4 There are, however, a host of support vessels and equipment designed just to take care of the needs of gas wells. The tank battery for a gas well (Figure 6) is basically just like any other tank battery with one exception. Condensate has a very high gravity and acts as a penetrating liquid so that seep leaks that lose a small amount of liquid may develop unless the fittings are made up properly. With time, the installation becomes stained and looks bad. Because the produced fluids will be a little different from each well, the vessels to be considered in new construction are the two- and threephase separator, the condensate storage tank, the water disposal tank, and possibly a chemical injector. Figure 6. A gas well tank battery. Note the two loading lines—one for condensate and one for water. The dehydration unit has either one or two small separators that produce condensate, according to how much is contained in the gas. The small tank shown in Figure 7 was set up just to serve the needs of a dehydration unit because for fire safety, the tank battery was a long distance away. Because of the high gravity of the distillate in the tank battery, the tank vent valve is of considerable importance. Evaporation out of this vessel can be so great that in the heat of summer, the evaporation can be several barrels a day. A higher back pressure may be required, and if smaller loads or split loads are sold, income from the distillate may be dramatically increased. Careful accounting and measurement will indicate the lease needs in sales of liquids. Figure 7. A small tank used to store condensates.