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Colloids and Surfaces A: Physicochem. Eng. Aspects 309 (2007) 177–181

Foam for gas well deliquification

Jiang Yang ∗, Vladimir Jovancicevic, Sunder RamachandranBaker Petrolite, Sugar Land, TX 77478, USA

Received 31 July 2006; received in revised form 4 October 2006; accepted 5 October 2006Available online 10 October 2006

bstract

Foam is used to remove liquid loading up in gas well and increase gas production. The experimental methods were developed to stimulate

he foam deliquification process. Effects of temperature, hydrocarbon, brine and particle on foam were studied. Foam height was reduced withncreasing temperature, presence of hydrocarbon, brine, particles and demulsifier. A foam model was also developed to predict the foam unloadingpplication for gas well with consideration of reduction of surface tension and fluid density by the foam. 2006 Elsevier B.V. All rights reserved.

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eywords: Foam; Gas wells; Deliquification; High temperature; Brine; Hydroc

. Introduction

Foams have many applications in oil and gas field. They aresed in drilling fluids, fracturing fluids and enhancing oil recov-ry [1]. Foam is also widely used in deliquifying gas wells. Gasecomes more important energy since the demand for naturalas as a clean hydrocarbon source has grown worldwide. Asatural gas is extracted, reservoir pressures decline, resultingn, reduced gas flow rates. Gas wells normally have associatedater. When velocities are low enough, liquid holdup is higher

n this flow regime. The gas production will decrease. There areeveral ways to solve this problem, i.e. mechanical or chemicalethods [2]. For mechanical method, artificial pump lift may be

sed. For chemical method, foam can be used. The foam is theasiest and most economic method to try firstly. The addition ofurfactant leads to decrease of the surface tension and forma-ion of foam that has much lower density than the bulk liquid.s demonstrated below, both of these factors facilitate the deli-uification of the gas wells. The foam is effective in transportinghe liquid to the surface in gas wells with very low gas rates.

Hydrocarbon condensate, brine and high temperature in down

ole have negative effect on foam generation. Hence, laboratoryest of actual produced fluid is needed to evaluate the effec-iveness of foamer. Studies have been done on the foamer and

∗ Corresponding author. Tel.: +1 281 276 5494.E-mail address: jyang98@yahoo.com (J. Yang).

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927-7757/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2006.10.011

orrosion inhibitor combination [3]. No systemic studies of var-ous experimental conditions have been done yet. In this paper,arious factors, such as temperature, brine, hydrocarbon, demul-ifier and particles were studied. A modified model was used toredict the possibility of foam unloading liquid in down hole.

. Experimental

.1. Materials

Anionic surfactant, sodium dodecyl sulfate (SDS) andationic surfactant, dodecyl trimethyl ammonium chlorideDTAC), from Aldrich were used as model surfactant.MO2327 is a demulsifier from Baker Petrolite Co. Heptane,ecane and cyclohexane were purchased from Aldrich Co. Fieldondensate and brine from various gas wells of US were usedn testing. Aqueous phase was either de-ionized water or 0.5 MaCl brine solution.

.2. Foam measurements

The foam test apparatus is shown in Fig. 1, which is a modifiedet up of US Bureau of Mines [4]. A volume of 100 ml of fluid atarious hydrocarbon/water ratio was added into a thermo jacket

olumn (77 cm × 5 cm) with medium fret. The nitrogen was useds gas to create the foam at a fixed flow rate of 15 ft3/h (i.e..425 m3/h). The amount of liquid unloaded by foam at 5 minas used to quantify the effectives of the foam.

178 J. Yang et al. / Colloids and Surfaces A: Physico

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Fig. 1. Dynamic foam testing apparatus for gas well deliquefication.

Foam density was determined by measuring the height ofhe foam after agitation of the mixture in a blender. One hun-red millilitres of synthetic or produced fluid at a desiredater/condensate ratio of the well was agitated at a low speed formin at room temperature. The volume of total fluids and foamas immediately measured. The time at which the foam reduced

o half its initial height was recorded as the foam half-life.The high temperature foam test was conducted in a spe-

ial foam generation apparatus under high pressure as shown inig. 2. Temperature of the column was maintained inside oven.he foam was generated in a quartz column in room tempera-

ure (20 ◦C) and high temperature (120 ◦C). Heptane as model

Fig. 2. Foam testing apparatus in high temperature and pressure.

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chem. Eng. Aspects 309 (2007) 177–181

ydrocarbon and 0.5 M NaCl as brine solution were used. Theatio of hydrocarbon and brine was 10/90. Nitrogen gas for gen-ration foam was used for 10 s under pressure of 3 MPa. Fifteenillilitres solution was used as test fluid. The foam height and

alf-life was observed visually through window of the oven.

.3. Dynamic surface tension measurements

Dynamic surface tension is a function of the diffusion ratef the surfactant and is dependent upon the method of measure-ent. For this paper, the maximum bubble pressure method was

sed due to its ability to function in a dynamic regime with aubble rate chosen to simulate the conditions encountered in gasroduction.

Dynamic surface tension instrument was made by SensaDynenstrument, AZ, USA. In the maximum bubble pressure tech-ique, a small glass capillary (0.25 mm diameter) is immersednto the fluid of interest kept at a constant temperature. Nitrogens bubbled into the solution at a fixed flow rate and the pressureor bubble detachment is measured. To correct for differences inmmersion depth, a larger glass capillary (4.0 mm diameter) islso immersed in the solution and the detachment bubble pres-ure is used as a reference. In this work, the surface tensioneasurements were reported when the flow rate of the nitrogen

s kept at a precise mass flow rate of 10 bubbles per second.

. Results and discussion

The foam column test (Fig. 1) was used to stimulate the foameliquification process in the gas well. Although actual gas wellas much longer tubing length and higher velocity, it is the eas-est and feasible apparatus to stimulate the foaming process inhe lab. The reasonable fast and controllable flow rate of 15 ft3/hi.e. 0.425 m3/h) was used to compare the performance of foamnder various conditions. Gas flow at lower rate will not simulateeal dynamic condition.

.1. Effect of surfactant concentration

In order to generate foam from liquid, surface tension must beowered, and the foam film must show a surface elasticity. Theurfactant molecule can give both properties. The amount of liq-id unloaded by foam increases with increasing concentrationnd reaches the maximum around critical micelles concentra-ion (cmc) as shown in Fig. 3. The surface tension reaches theowest at or above cmc. Foam generation and removal of liquidre related to the depletion of surfactant in solution, and lowerurfactant concentration reduces the availability of surfactantn the solution. Hence, the higher surfactant concentration inolution is, the more foam will be generated and more liquidill be unloaded. The concentration of surfactants at air–water

nterface will reach to maximum at cmc. Above cmc, surfactantill go to solution phase and forms micelle aggregate. In pres-

nce of oil, the situation will be different since the oil/water willorm emulsion and consumes more surfactants. The amount ofxcess surfactants absorbed at oil–water interface is dependedn emulsion droplet size and amount. Hence, more surfactants

J. Yang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 309 (2007) 177–181 179

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ig. 3. Amount of liquid unloaded by foam and dynamic surface tension reduc-ion vs. concentration for SDS at 25 ◦C in DI water.

re needed. However, excess surfactant is undesirable since itill form high viscose and stable foam, which creates problemn surface separator and decreases the unloading efficiency.

.2. Effect of brine

The amount of liquid unloaded in brine solution (0.5 M NaCl)as reduced by 30% as compared to that of liquid unloaded inI water. Maximum unloading water is attained when the num-er of bubble formed is equal to the number of broken bubbles.he sodium chloride brine solution has two effects on foamnloading of water. Firstly, it reduces thickness of foam filmy compressing electrically double layer of ionic surfactants.ence, it decreases the volume of plateau borders and decreases

he volume fraction of water in the foam. In addition, it sup-resses electrostatic stabilization and makes the film easier toupture. Secondly, it forms denser adsorption layers. Outflow ofurfactant with the generated foam is faster, and exhaustion ofhe surfactant in the cylinder is also fast, which results in filmupturing.

.3. Effect of hydrocarbon condensate

Hydrocarbon reduces the foam amount as shown in Fig. 4.he oil acts as antifoam and also forms emulsion which will

educe the effective of surfactants as foamer. The mechanismf oil as antifoam has been studied by Denkov [5]. There are

ig. 4. Effect of condensate (from east Texas gas well) on foam unloading ofDS surfactant (1000 ppm) at 70 ◦C.

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ig. 5. Illustration of oil droplet in foam thin film and move toward plateauorders.

wo mechanisms, one is fast antifoam and one is slow antifoam.n some of gas field condensate, even 1% of hydrocarbon con-ensate could completely destroy the foam. It is related to fastntifoam mechanism. Fast antifoams rupture the foam films athe early stages of film thinning. Hence, the foam was destroyedompletely in less than a minute by “bridging” mechanisms,hich forms oil bridges between the two surfaces of the foam

hin film. The phenomena can be explained by capillary theory.he slow antifoams are unable to enter the surfaces of the foamlms and are first expelled into the plateau borders as shown

n Fig. 5. When it is compressed by the narrowing walls ofhe plateau borders, oil dropet of the slow antifoams will enterhe solution surface and destroy the adjacent foam films. Therocess of foam destruction by slow antifoams requires muchonger time. The barrier preventing the emergence of emulsifiedntifoam oil droplet on solution surface is important for foamestruction. For major component of gas condensate studied,he amount of liquid unloaded by foam was shown in Table 1elow. In this case, it is obviously a slow antifoam process forhe light hydrocarbon. Hence, foam can carry over the oil dropletontaining liquid thin film to the top of column.

A very high percentage (>80%) of condensate is also possiblen certain gas wells. In such case, special surfactants, such asuorocarbon surfactant can be used.

.4. Effect of demulsifier

Formation of emulsion is undesirable during the oil and gasroductions. Emulsion increases viscosity of produced fluid, androhibits the refining of hydrocarbon. Hence, demulsifiers areften added. In this work, presence of demulsifier was studiedo see its effect on foam. The phenolic resin alkoxylate demusi-er, DMO2327, was used. Hydrocarbon condensate from an eastexas well was used. The results of foam unloading are shown

n Table 2, the presence of demulsifier has negative effect on

oam. This is because the demusifier as surface-active agentlso adsorbs at air–water interface. However, the packing ofemulsifier on surface is not condensed, and it increases inhe intermolecular distance between foamer molecules in the

able 1iquid unloaded by foam in model hydrocarbon/0.5 M NaCl (10/90) by DTAC

odel hydrocarbon Liquid unloading% by foam

eptane 53ecane 49yclohexane 57

180 J. Yang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 309 (2007) 177–181

Table 2Effect of demulsifier on foam by 1500 ppm SDS

Hydrocarbon/0.5 M NaCl solution (10/90) Liquid unloading% by foam

No demulsifier 5013

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dsorbed film. The surface viscosity and elasticity resulting isignificantly decreased. In addition, formation of bigger dropletn the presence of demulsifiers breaks the foam thin film andlateau borders. Hence, the foam generation and stability isreatly reduced in the presence of demulsifier.

.5. Effect of particle in produced fluids

The undissolved particle (0.2–1 �m) also affects foam gen-ration. In a lab experiment with water/condensate (1/1), foamannot be unloaded from produced water containing just 1%lay particles. After removing the particle by filtering the waterhrough 0.2 �m membrane, foam can be generated and unload0% water. The mechanism of particle antifoam is similar to oilroplet antifoaming mode. The particle forms bridge on foamlm, and results in rupturing of the thin film. This is related

o wettability contact angle. In presence of hydrocarbon, oilroplets containing particle easily enter and spread on foamurfaces, making it easier to breaks the foam film. Althought is unusual to have particles presence in the produced fluid, itould be handled by selecting different surfactants to alter theettability of the particles and still maintains the foam.

.6. Effect of temperature

Bottom hole temperature of gas well can be very high. Hence,erformance of foamer was studied at high temperature. The lab-ratory test has to be under high pressure to prevent evaporationt high temperature. The stimulation of liquid removal by foams difficulty to run in such closed high pressure system, hencenly foam height and half time was determined. The resulting

oam height was shown in Fig. 6. It can be seen that foam heightecreases at higher temperature. The half-life is especially shortompared to lower temperature one. This could be due to theast desorption of surfactant from thin film at high temperature,

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Fig. 7. Illustration of liquid droplet model from Turner et

ig. 6. Effect of temperature on foam height and half-life with DTAC surfactant.

nd the stability of foam was drastically decreased. Some sur-actants under such high temperature could also be chemicallyecomposed. In such case, foaming ability and surface activityas also lost.

.7. Foam unloading model

Taitel et al. [6] developed a simple Eq. (1) to characterize theransition to annular flow.

USGρ1/2G

σg(ρL − ρG)1/4 = 3.1 (1)

n the equation above, USG is the gas superficial velocity, ρGhe gas density, ρL the liquid density, σ the gas liquid surfaceension and g is the acceleration due to gravity. This equations a modification to Eq. (2) by Turner et al. [7] and Coleman etl. [8] used to estimate the critical velocity, νgc, at which gasnloads liquid from a gas well.

gc = 1.912σ1/4(ρL − ρG)1/4

ρ1/2G

(2)

The symbols are the same as in Eq. (1). All parametersbove can be measured by experiment. The equation was further

odified by Ramachandran and co-workers to account for the

resence of foam [9]. The basis of the modification was to treathe foam in a gas well as modified liquid phase. A schematiciagram showing the foam flow in a gas well is shown in Fig. 7.

al. [7] and modified model for surfactant foamers.

J. Yang et al. / Colloids and Surfaces A: Phys

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ig. 8. Plot of velocity, Vg, vs. SDS concentration, calculated with Eq. (2).

Using surfactants can modify the flow regimes in a gas wello allow the annular flow regime to occur in a well at lower gasuperficial velocities.

It is well known that the surface tension of liquid in the pres-nce of surfactant is lower than pure liquid, in addition densityf foam is also lower than liquid. Hence, the required minimalritical velocity to remove the liquid is reduced with foam, oth-rwise, large liquid accumulation in gas well tube will occurnd high multiphase flow pressure losses. The example of foamnloading liquid predicted by the equation was shown in Fig. 8.t can be seen that actual gas well velocity (22 ft/s), measuredy flow meter, is lower than critical velocity (29 ft/s) requiredo unload the liquid without surfactant. In the presence of sur-

actant foamer (SDS), the critical velocity required is lower, andelow the actual gas well velocity at addition of 360 ppm foamer.ence, above this surfactant concentration, the gas well liquid

an be unloaded at that “unloaded point”.

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icochem. Eng. Aspects 309 (2007) 177–181 181

The modified foam model predicts the feasibility of foamero unload the specific gas well with foamer treatment.

. Conclusions

Dynamic foam column test was used to stimulate the foameliquification process. Foam height was reduced with increas-ng temperature, brine, presence of hydrocarbon, demulsifier andarticle. Foam model can be used to predict the foam unloadingpplication for gas well.

cknowledgement

The authors acknowledge the help of Professor Ying Li ofhangdong University, China for experiment of foam at high

emperature and pressure.

eferences

1] L. Schramm, Foams: Fundamentals and Applications in the Petroleum Indus-try, ACS, Washington, DC, 1994.

2] J. Lea, H. Nickens, M. Wells, Gas Well Deliquification, Gulf ProfessionalPublishing, Burlington, 2003.

3] M. Pakulski, R. Martin, SPE International Symposium on Oilfield Chem-istry, Houston, Texas, February 13, 2001.

4] H.N. Dunning, J.L. Eakin, C.J. Walker, Using Foaming Agents for Removalof Liquids from Gas Wells, Monograph 11, Bureau of Mines, Am. GasAssoc., New York, NY, 1961.

5] N. Denkov, Langmuir 20 (2004) 9463.6] Y. Taitel, D. Bornea, A.E. Duckler, AIChE J. 26 (1980) 345.7] R.G. Turner, M.G. Hubbard, A.E. Dukler, SPE Paper 2198, J. Pet. Technol.,

Trans. AIME, 246 (November 1969) 1475.8] S.B. Coleman, H.B. Clay, D.G. McCurdy, H.L. Norris, J. Pet. Technol. 3

(1991) 329.9] S. Campbell, S. Ramachandran, K. Bartrip, SPE Production and Operations

Symposium, Oklahoma, OK, 2001 (SPE paper 67325).