Soap Stick 101

Why Soap Sticks?

• First Choice – Based on the simplicity of use and ready availability, soap sticks are the first choice for de-watering a gas well;

• Least Cost – Soap sticks are reasonably cost effective at restoring gas production from those locations that are declining do to loss of gas velocity;

• Large Bore - Suitable and effectively used in casing only completions;

• Stop-Cocking – Soap sticks and stop-cocking, correctly combined, can be effective on low rate locations. Stop-cocking alone can de-water but at the ‘cost’ of lost production;

• Trial Ready – Ease of use and readily available, the operator can conduct a test run;

• Counter Indications – Although long term use of surfactants in a well bore that produces oil or condensate predominately is discouraged, short term use is not harmful;

What Are Soap Sticks?

Soap sticks range in size from 5/8 inch to 2 inch in diameter (16mm to 50mm). The composition is either a hard, wax-like stick or a soft-core gel in a water-soluble polymer tube. A thin, water-soluble paper-shell jacket is also available. The paper-shell is popular because the stick is cleaner and does not break as easily. The most common size soap stick available is 1.25 inch in diameter and measures 16 inches long.

Suppliers

There is an abundance of soap stick manufacturers in the United States. No doubt some products work better than others. Our experience is that prior to abandoning the idea of using surfactant in a particular well, the operator should contact his current supplier or a new supplier and ask for help in selecting the optimum surfactant composition. The supplier will typically request basic information including accurate liquid rates, and water samples to determine chloride levels.

Suppliers can provide surfactants for brine or fresh water as well as varying percentages of hydrocarbons. Some users, with a higher hydrocarbon cut, achieve outstanding results by loading the Soap Stick Launcher with a surfactant foamer stick then alternately with an oil foamer stick. It should be noted that gauging the performance of a particular formula is made easier by the Soap Stick Launcher because it reduces the human factor during the test period. 

Pro-Seal Lift Systems’ automatic Soap Stick Launchers can accommodate from 1 to 18 sticks (.625 inch to 1.625 inch diameter depending on the model) in either hard or paper shell. The Launcher will accommodate the smaller sizes, which are especially suited for those wells that require frequent application but with only a small amount of surfactant. Such a well will exhibit low bottom hole pressure and minimal water production. The operator should beware of dropping too much soap in a low water-production well. An alternative to using small diameter sticks is to use one-half of a hard stick in the Launcher.

How Soap Sticks Work

Surfactant dissolved within formation water reduces the surface tension of the water molecules – promoting the formation of mist within the tubing. This mist is more easily carried to the surface by the up-flowing gas stream. The more quickly a de-watering program is initiated the better the ultimate recovery will be from a given well bore. A well that has begun to ‘slug’ is overdue for surfactant treatment.

Some operators choose to drop multiple soap sticks into the well bore and then shut-in the well for up to 24 hours prior to re-opening the location to flow. In this scenario, the formation responds positively, as a rule. However, the positive response is due more to the pressure and volume build-up and less attributable to the soap sticks. 

This phenomenon can be explained: When one or more soap sticks fall into a non-flowing well bore, the soap sticks simply drill through the accumulated liquid located within the lower end of the tubing and sink into the rat hole without properly dissolving - just as a bar of bath soap in a bowl of water will remain undissolved for a long, long time. In addition to a waste of soap sticks, during this extended shut-in period, the well is not contributing to the bottom line. Clearly defined toe-up horizontals are the exception to this rule.

The preferred way to introduce a soap stick into the well bore is as the well is flowing. Dropped while flowing, the soap stick will encounter the top of the water column where it will be dissolved by exposure to a bubbling, agitated, wet environment at an elevated temperature. By these three methods – mechanical action, chemical reaction, and temperature degradation – the stick will be entirely dissolved in short order.

One soap stick contains sufficient active ingredients to dilute one barrel of produced water only. Yet, it is common for one soap stick to result in the flow of 4 or 5 barrels of liquid to the surface. How so? 

When introduced into the well bore correctly, the soap stick will dissolve and mix with only a limited amount of water – that water at the top of the water column – as opposed to the water lower in the tubing. The water at the top of the water column is considered to be the ‘low hanging fruit’ meaning that it is the easiest water to be blown to the surface – in mist form. Once this uppermost volume of water is discharged, the formation – thus lightened – will spit out additional barrels of water in slug form. As proof of this concept, a water analysis of this tail water will show almost no dissolved surfactant. The weight of that uppermost barrel of water – pushing down against the formation – is the equivalent of 100 psi (in 2-3/8” tubing). With that 100 pounds of back pressure out of the way, the formation pressure will spit out several more barrels of liquid before the new liquid inflow retards the gas rate. A review of the flow rate chart will indicate when it is time to drop another soap stick.

Launch While Flowing

Dropping a soap stick, whether manually or with the Launcher is best done while the well is flowing. That way, the stick will free-fall within the up-flowing gas until it encounters water in the tubing column. If the water is scattered and gas cut, the stick will slow down a little, and dissolve a little but the soap stick will not stop until it encounters enough water and loses enough mass to pause and suspend in the column. Gas bubble agitation is a critical factor in the dissolution process – that’s why we prefer flowing conditions for launching the stick.

Avoid the Rat Hole - If the well is shut-in (closed) during the stick drop, the soap stick will fall, find and sink below the surface of the water column. While sinking through a quiescent water column, the soap stick will begin dissolving but not rapidly. If the well is shut-in, there will not be enough gas bubble agitation to dissolve the soap stick prior to the stick’s arrival at the bottom of the well.  A deviated well bore is not as problematic but launch-while-flowing is still preferable for removing the uppermost part of the water column.

The Target-The water down around the perforations is the most difficult water to remove.The water nearest the surface of the water column is our target. It is the easiest water to remove from the tubing. If we can place the soap stick within the upper reaches of the water column, then we can move more water - up and out - with less surfactant (soap sticks).

Flow Rate Discussion - A problem arises when the gas rate from the tubing exceeds a known maximum during the soapstick launching process. Under higher flow rate conditions, the well should be shut-in for a brief period, somewhere between 20 to 120 seconds, while the soapstick is transiting to a point below the wing block. Thereafter, the well may be re-opened to flow. A soapstick falls at 3000 feet per minute until it encounters the top of the water column. Don’t shut-in too long else the stick will overshoot the target. The maximum suggested gas rate for dropping a soapstick without a brief shut-in is 250 MCFD in 2-3/8″ tubing. At rates above 250 MCFD, it is possible that the soapstick will be captured at the wing block outlet. The wing block is the cross-shaped transition piece on the christmas tree where the flow changes from vertical to horizontal. If the wing block is larger than 2-3/8 inch, then the maximum flow rate for free-falling a soapstick increases accordingly.

The maximum gas flow rate against which a soap stick will clear a 2-7/8” wing block is 500 MCF rate. If the well is flowing above 500 MCF, the well should be shut-in during the moment that the soapstick is transiting the wing block. Because of the greater area of a 3-1/2” wing block, a flow rate of 760 MCF or less will not cause the soapstick to hang up at the wing outlet. 

Flow Control Valve– If the flow rate is higher than specified in the paragraphs above, then the well should be shut-in prior to launching the soapstick – either manually or automatically. Click here to view the Flow Rate Limitations Chart for additional information.