There are various reasons why fluid should be removed from an oil or gas well thus necessitating the need for swabbing operations. A few of the most common reasons are listed below:
Unload a producing well:A producing gas or oil well may load up with fluids causing the well to quit flowing. These fluids may be water, hydrocarbons or a combination of both and it is necessary to remove these fluids to allow the well to return to a flowing state. Usually when a well begins loading up, it is time to consider secondary or artificial lift. Additionally, it may be necessary to swab a well in after it has been worked over and has kill weight fluid in the well.
Apply an underbalanced pressure on a well prior to perforating: When it is desired to perforate a normally pressured well underbalanced, or with a pressure less than the formation pressure, it may be necessary to remove fluid from the wellbore prior to perforating. The amount of fluid removed from the well is determined by the weight of the fluid in the wellbore, the formation pressure and the desired underbalanced pressure. An underbalanced condition prior to perforating allows a well to flow into the wellbore immediately upon perforating and helps clear the perforation tunnels of damage and debris. Swabbing a well down to an underbalanced condition prior to perforating can be done quickly in as few runs as practical. After the final run, the fluid level should be tagged and the line flagged so that after perforating it can be determined if there was any formation feed in to the wellbore.
Swab test a well: As a well depletes, either by a declining formation pressure or an increasing water cut, it is necessary to consider artificial lift methods such as rod pumps, jet pumps, gas lift, plunger lift or electric submersible pumps. It may be necessary to determine a well's productivity to properly design the artificial lift system. Swabbing is a good method to determine this productivity. Inflow rates and oil cuts can be determined with swab runs and allow for accurate artificial lift design and economic analysis.
A swabbing operation should be designed based on well conditions. What size is the tubing in the well? How much fluid volume is between the packer and the perforations? It is important to check the casing prior to swabbing. Is there pressure on the casing? Is the casing on a vacuum? It may be necessary to pull the gauge and double check the casing conditions as often times a casing pressure gauge may be "frozen" in a position and may not be reading accurately.
Poor swabbing methods can create problems with a well. A well can be swabbed too hard which may cause sand to enter the wellbore. A well may produce sand while swabbing even under the best of circumstances. A gas bubble coming up while swabbing can actually force the swab line out of the well quicker than it can be spooled up. Well conditions need to be monitored closely and taken into consideration on each run to prevent these problems from happening. Always start a swab operation slowly with 300'-500' fluid pulls. Determine if the fluid level is returning to the same level after swabbing, rising from the original level or if the well is swabbing down. Is the well blowing after a swab run? Is the casing staying full? It is important as well to note the fluid that is being removed from the well. If water, what is the weight? Is it load water or formation water? Is there any oil cut? Is the well making any gas? All of these important observations will lead to the decision of the next pull. Should you give more time between runs? Should you pull a little more fluid or stay with the same amount you started with?
A swabbing operation can be used to gather important information about a well or bring a dead well back to production. Using all information available during a swab operation will lead to a safe and effective operation which hopefully will extend the economic producing life of the well.
