What Is Foam Cleaning Of An Oil Well

Hydraulic fracturing fluid systems

Hoss Belyadi , ... Fatemeh Belyadi , in Hydraulic Fracturing in Unconventional Reservoirs (Second Edition), 2019

Foam quality

Foam quality is the ratio of gas volume to foam volume (gas + liquid) over a given pressure level and temperature. Nitrogen or CO _ii can be used to create foam in liquid status, just nitrogen is typically preferred considering CO₂ can be extremely harsh and eroding when water is existent.

(5.2) $FQ = \frac{Gas book}{Gas volume + liquid volume}$

where FQ is the cream quality, %; gas book = BBLs or gallons; and liquid book = BBLs or gallons.

When cream quality is between 0% and 52%, gas bubbles do non contact each other and are spherical. Cream viscosity is too low because at that place is a lot of gratis fluid in the system, which in plow will affect the fluid-loss capability. When foam quality is between 52% and 96%, the gas bubbles are in contact with each other and every bit a result, an increase in viscosity will occur. Foam qualities of 52% and sixty% do not take the proppant-break adequacy. Finally, when foam quality is more than 96%, the cream will degenerate into mist and as a event, there will be a loss in viscosity. Annotation that higher foam quality has a higher viscosity and is better able to append proppant. As foam quality increases, more hydraulic horsepower will be needed. This is because an increase in foam quality will decrease the hydrostatic pressure and in turn will increase the surface-treating pressure. An increase in surface-treating pressure level will cause an increase in hydraulic horsepower. The nearly oftentimes used foam quality is typically 70%–75%.

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Foam Drilling

Neb Rehm , ... Amir Paknejad , in Underbalanced Drilling: Limits and Extremes, 2012

four.36 Foam Quality

Foam quality is the volumetric ratio of gas-phase to gas/liquid-phase. The foam quality index Γ can be defined equally

(4.17) $Γ = \frac{V_{grand}}{5_{yard} + V_{50} + {Five}_{f}}$

where

V_g = Gas book

V_l = Liquid volume

Five_f =Formation fluid influx volume

The foam quality is a office of the pressure in the annulus. About foams are stable when cream quality is between 0.6–0.97. Depression-quality foam contains more liquid than a high quality cream. The cream bubbles of depression-quality foam, besides known as "wet foam," are plant to be spherical and evenly dispersed. The foam bubbling of loftier-quality foam, too known as "dry foam," have a polyhedral construction with thin separating films.

In stable cream drilling operations, the lower limit of foam quality is ordinarily establish at the lesser of the annulus and the college limit at the top of the annulus.

The cream quality at the lesser of the annulus is controlled past a valve placed on the flow line at the top of the annulus. Since the dorsum pressure upstream of the valve tin can be set to a desired value, the control of the foam quality at the tiptop enables usa to determine the foam quality at any position in the annulus (particularly at the bottom of the annulus).

Qualities greater than 0.97 cause the continuous cellular foam construction that entraps the gaseous stage to become unstable, and the foam to turn into mist. When quality is less than 0.6, gas forms isolated bubbling that are independent of the liquid-phase and two phases can motion with different velocities which breaks downward the cream structure. To make the Eq. (iv.17) more applicable, the ideal gas law is used as

(4.xviii) $\frac{P_{s} V_{s}}{T_{s}} = \frac{P 5}{T}$

where

P = Pressure at whatever betoken, psi

P_southward = Force per unit area at surface, psi

T = Temperature at whatsoever point, °R

T_s = Temperature at surface, °R

Five = Gas volume at whatever point, ftⁱⁱⁱ

V_southward = Gas book at surface, ft³

Which can be rearranged equally

(4.19) $V = \frac{P_{south} T}{P T_{s}} V_{s}$

Substituting Eq. (iv.19) into Eq. (four.17) yields

(4.20) $Γ = \frac{\frac{P_{s} T}{P T_{south}} Q_{g s}}{\frac{P_{s} T}{P T_{southward}} Q_{thou south} + Q_{fifty} + Q_{f}}$

where

Q_gs = Gas injection rate

Q_l = Liquid injection rate

Q_f = Formation fluid influx rate

Gas-liquid ratio (GLR) is defined as

(4.21) $Thou L R = \frac{Q_{k s}}{Q_{l}}$

In gild to maintain the surface cream quality at the desired value, we need to set an appropriate gas-liquid injection ratio at the surface. Based on the maximum commanded foam quality at surface without backpressure, the GLR is calculated every bit

(4.22) $1000 L R = \frac{Γ_{\max}}{ane - Γ_{\max}} [\frac{one}{vii.48} + \frac{5.615 Q_{f}}{60 Q_{l}}]$

Past substituting Eq. (4.21) and Eq. (iv.22) into Eq. (four.twenty), the correlation for foam quality at whatsoever point can be expressed as

(4.23) $Γ = \frac{\frac{P_{s} T}{P T_{due south}} G 50 R}{\frac{P_{south} T}{P T_{south}} M L R + \frac{1}{7.48} + \frac{five.615 Q_{f}}{60 Q_{l}}}$

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Task simulation and design

Gunnar DeBruijn , in Practical Well Cementing Engineering, 2021

vii.13.v.1 Foam cement design

Foamed cement has variable density and foam quality in a well as downhole temperature and pressure change. To blueprint a cream job, one will determine a schedule of nitrogen loading ratios together with pumping rates of liquid fluids. Given a temperature contour in the well, required nitrogen loading ratios during pumping can be calculated based on terminal fluid positions and foamed slurry densities or functioning methods such as constant nitrogen charge per unit, constant density or "hybrid" (a combination of both). The time dependent foam density during the entire job at any depth tin can be predicted in a computer simulation. Fig. 7.46 shows an case of constant density design generated by a figurer program. Computer programs can give profiles of the pressure, cream quality, and nitrogen ratio distribution in the annulus and help engineers make up one's mind whether the blueprint objective is met.

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Evaluating Drilling Fluid Performance

Ryen Caenn , ... George R. , in Composition and Properties of Drilling and Completion Fluids (Seventh Edition), 2017

Rheological Backdrop of Foams

The rheological beliefs of foams depends on foam quality (ratio of gas volume to total volume). In the quality range of interest in oilfield operations the flow model of foams is that of Bingham plastic and the parameters yield stress, PV, and effective viscosity are used to describe foam consistency curves. A multispeed viscometer, and capillary viscometers accept been used to determine these parameters ( Marsden and Khan, 1966). Mitchell (1971) used a capillary viscometer in which the flow velocity was measured by the transit time of a dye betwixt two photoelectric cells, and the pressure drib beyond the capillary was measured past means of a differential transducer or a high-force per unit area manometer. Further data on foams can exist found in Air and Gas Drilling Manual (Lyons, 2009).

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Equipment and Procedures for Evaluating Drilling Fluid Operation

Ryen Caenn , ... George R. Grey , in Composition and Backdrop of Drilling and Completion Fluids (6th Edition), 2011

Rheological Properties of Foams

The rheological behavior of foams depends on foam quality (ratio of gas volume to total volume). In the quality range of interest in oilfield operations the flow model of foams is that of Bingham plastic (see Affiliate 7), and the parameters yield stress, plastic viscosity, and constructive viscosity are used to describe foam consistency curves. The Fann V-G meter, the Bendix Ultra-viscoson, and capillary viscometers accept been used to make up one's mind these parameters (David and Marsden 1969; Marsden and Khan 1966). Mitchell (1971) used a capillary viscometer in which the menstruum velocity was measured by the transit time of a dye between 2 photoelectric cells, and the force per unit area drop across the capillary was measured by ways of a differential transducer or a loftier-pressure manometer.

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Hydraulic Fracturing Fluid Systems

Hoss Belyadi , ... Fatemeh Belyadi , in Hydraulic Fracturing in Unconventional Reservoirs, 2017

Foam Stability

There are several factors that affect foam stability. Foam quality, surfactant type/concentration, and polymer type/concentration are some examples. I of the well-nigh of import aspects of foam fracturing is to keep the cream in motility. If cream is not in motion, it volition exist unstable. When foam stops moving, gravity will cause the free fluid in the foam to drain. This drainage can cause foam instability problems. The charge per unit of cream drainage will depend on many factors such equally temperature, viscosity of the liquid phase, and foaming-amanuensis concentration. An increase in temperature can potentially crusade a reduction in the viscosity of the fluid. As temperature increases, more foaming agents must be used. Gelling agents are as well very important because they can be used to add together stability to the fluid. Gelling agents volition increase the viscosity (not considerably), but volition improve proppant transport and fluid-loss control. Gelling agents must be used in moderation considering higher fluid viscosity will be harder to foam and pump, and every bit a result, will require more than hydraulic equus caballus power.

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Apply OF FOAM TO DELIQUIFY GAS WELLS

James F. Lea , ... Mike R. Wells , in Gas Well Deliquification (2d Edition), 2008

8.ii.three Foaming Agent Pick

An effective FAL program must have a foaming agent suitable for completion of the chore. Testing must be conducted on fluid from each well in social club for a program to achieve a sustainable and/or substantial increment in production. Foaming agents are not still—they will perform differently on fluid of varying compositions. A production that works on a given well may or may not be effective on wells within a reasonable proximity. Yous should ever utilize a product that has been specifically tested on fluid from the applicative well.

Experience has demonstrated that selection of a foaming amanuensis cannot be completed in a lab under all circumstances. Field testing and selection of foaming agents is necessary to obtain accurate results. At that place are several well-documented factors for this phenomenon:

•: Components of the water oxidize as the sample ages. This leads to solids nowadays in the water that can accumulate at the gas/liquid interface and impact foam quality. Oxidized water will likewise have a different interfacial surface tension, thus impacting the performance of surfactants used in foaming agents.
•: Dissolved gases dissipate, leading to pH changes in the fluid. Changes in pH bear upon the functioning of the products.
•: Oil/condensate volition oxidize as the sample ages. Volatile components of the sample will exist lost to flashing. Naturally occurring surfactants that may be nowadays in the hydrocarbons will likely be altered by the oxidation process and tin can have an impact on product selection.

In all cases, we recommend that fresh field fluids exist utilized for selection of the foaming agent. Constructed fluids do not accurately reverberate the organic content of field samples and probable will not be fully representative of the complete inorganic content. Testing on constructed fluids will probable lead to erroneous results and the increased likelihood of application failure.

There have been several methods of testing recommended by various companies involved in FAL programs. These methods include blender testing, malt mixer testing, sparge column testing, or well simulators. All the various methods have claim and the methodology for each method can be verified for given circumstances. Information technology has been our experience that malt mixer testing works best with our selection and application methodology. This method has proven to be reliable and delivers results that tin exist correlated to application performance.

Beyond the option of product based on performance as a foamer, it is also important to consider other product related concerns prior to applying the foaming agent. Items that should be addressed are:

•: Compatibility with produced fluids (solubility/dispersibility)
•: Incorporation of other treating chemicals
•: Production compatibility with metals and elastomers in the injection organisation and product components
•: Temperature stability of the product in relation to temperatures encountered in the application
•: Residence time of the production in the injection system and related production components

In many cases, foaming agents are formulated for specific fluids and/or specific applications. Having the correct production in place volition increment the likelihood that favorable results will be achieved from the FAL program.

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Reducing Density: Polyolefin Foams

Michael Tolinski , in Additives for Polyolefins, 2009

Publisher Summary

This affiliate focuses on how Polyolefin (PO) foams are made and what blowing agents are used. The advantages these foams bring in specific product sectors are also elaborated. The factors and additives that meliorate foam quality or control cream cell size are likewise discussed. Reducing the mass of a PO or plastic part is helpful in efforts to "lightweight" various applications and for reducing resin content as well. Making products thinner is merely one arroyo for reducing mass; foaming is some other selection for low-cal part designs with high property-to-mass ratios. Foaming is besides useful for creating insulating or daze-arresting properties that solid resin parts cannot supply. These backdrop accept already made POs useful in the automotive sector, for example. Too in this sector, the foaming of already low-density PO materials will likely abound as an important approach for creating a new generation truly lightweight, fuel-conserving automobiles. Many other PO applications do good from foaming, including the most mutual packaging and consumer appurtenances, since foaming allows significant raw material savings without major losses of aesthetics or key backdrop. Bravado agents, or materials that cause foaming in a plastic, tin can be added to the polymer as an internal additive (chemical blowing agents) or injected as gases or liquid during cook processing with special equipment (concrete blowing agents). These agents create and expand bubbling throughout the polymer matrix, forming an internal cellular network of open or closed cells.

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Hydraulics design

Boyun Guo , ... Na Wei , in Practical Gaseous Fluid Drilling Engineering science, 2022

6.iii.one Gas injection rate

It has been observed in laboratories that foams are stable when their gas contents are between 55% and 97.5% (Sanghani, 1982 ). The gas content is also called foam quality index, or simply foam quality, in foam drilling. It is defined as:

(6.16) $Γ = \frac{Gas volume}{Total foam volume}$

(half dozen.17) $Γ = \frac{\frac{4.07 T}{P} Q_{g o}}{\frac{4.07 T}{P} Q_{g o} + \frac{1}{7.48} Q_{50} + \frac{v.615}{60} Q_{f ten}}$

where T=temperature, °R, P=pressure, lb/ft^two, Q _become=gas injection rate, scfm, Q _fifty=liquid injection rate, gpm, and Q _fx=formation fluid influx rate, bbl/h.

Plainly foam quality drops equally the pressure level increases with depth. Foam drilling operations are normally designed with the maximum foam quality at top hole existence equal to 0.95 and the minimum cream quality at lesser pigsty being equal to 0.60. Even so, these conditions are not maintained when the depth is beyond a certain value. For deep drilling operations with foams, it is vital to use high enough liquid-injection rate for hole-cleaning purpose considering foam stability is not guaranteed in the lower department of annulus. Guo et al. (2003) presented methodology for foam stability command past adjusting injection gas-liquid ratio (GLR) and backpressure.

Dividing the numerator and denominator of the right-hand side of Eq. (6.17) by Q _l gives

(6.xviii) $Γ = \frac{\frac{iv.07 T}{P} G L R}{\frac{4.07 T}{P} G Fifty R + 0.09358 \frac{Q_{f x}}{Q_{l}} + 0.13369}$

If backpressure is not applied, at surface (flow line) condition, the foam quality reaches its highest value. In social club for the foam quality non to exceed its maximum allowable value of Γ_max, the injection GLR should be controlled. Setting P and T to the atmospheric pressure level and temperature, respectively, the maximum commanded injection GLR can be solved from Eq. (6.18) as:

(6.19) $G L R_{\max} = \frac{Γ_{\max}}{(i - Γ_{\max})} (0.09358 \frac{Q_{f x}}{Q_{l}} + 0.13369)$

Fig. half-dozen.vii presents a chart to make up one's mind the GLR _max for different values of Γ_max and $Q_{f 10} / Q_{50}$ . Information technology reveals that for Γ_max=0.95, the maximum commanded GLR without backpressure is less than 3 scf/gal. If this GLR _max results in a foam quality less than the minimum commanded value of foam quality Γ_min at bottom hole, a GLR value of higher than the GLR_max should be used to achieve the minimum allowable value of foam quality Γ_min at bottom pigsty. In this situation, a backpressure should exist applied to reduce the foam quality within its maximum allowable value of Γ_max at surface. The minimum required backpressure tin exist solved from Eq. (half dozen.18) as:

(six.xx) $P_{\min} = \frac{4.07 T (1 - Γ_{\max}) G L R}{Γ_{\max} (0.09358 \frac{Q_{f ten}}{Q_{50}} + 0.13369)}$

Assuming T=520°R and Γ_max=0.975, the minimum required backpressures are calculated and plotted in Fig. 6.8 for different values of $Q_{f x} / Q_{l}$ . Information technology indicates that with the help of backpressure up to 70 psia, the maximum commanded GLR can be extended to 20 scf/gal.

For a given foam drilling operation, there is always a limitation for gas injection rate and thus GLR. With this constraint of GLR, the foam quality at bottom hole will decrease to its minimum commanded value of quality Γ_min when the lesser-hole pressure increases to a disquisitional value. This critical bottom-pigsty force per unit area is called the maximum allowable pressure for stable foam drilling. This maximum allowable pressure level tin can exist solved from Eq. (half dozen.xviii):

(half-dozen.21) $P_{\max} = \frac{4.07 T (1 - Γ_{\min}) 1000 L R}{Γ_{\min} (0.09358 \frac{Q_{f x}}{Q_{50}} + 0.13369)}$

Assuming T=520°R and Γ_min=0.55, the maximum pressures are calculated and plotted in Fig. 6.9 for different values of $Q_{f 10} / Q_{l} .$ This figure indicates that the maximum allowable pressure is less than 2000 psia even with a GLR value of 20 scfm/gpm. This does not hateful that wells cannot be drilled with foams when the bottom-hole pressures are greater than 2000 psia. In fact, many wells take been drilled with foams at bottom-hole pressures higher than 2000 psia. The explanation is that although the foams may not be stable at bottom hole, pigsty cleaning can still be achieved with adequate mixture flow velocities in the annulus.

With the constraint of GLR, the foam quality at lesser hole volition decrease to its minimum allowable value of quality Γ_min at a critical depth. This critical depth is called the maximum depth for stable cream drilling. This maximum depth can be solved from Eq. (3.79) in Affiliate 3 equally:

(vi.22) $L_{\max} = \frac{1}{a (1 + d^{2} e)} {\begin{cases} b (P_{\max} - P_{southward - \min}) + \frac{1 - ii b m}{2} \ln | \frac{{(P_{\max} + m)}^{2} + northward}{{(P_{s - \min} + m)}^{2} + n} | \\ - \frac{m + b n / c - b {one thousand}^{two}}{\sqrt{n}} [\tan^{- 1} (\frac{P_{\max} + g}{\sqrt{n}}) - \tan^{- i} (\frac{P_{s - \min} + grand}{\sqrt{n}})] \end{cases}}$

where all variables are defined in Chapter 3 except

P _max=force per unit area at the maximum depth, lb_f/ft²;

P _s−min=minimum required surface pressure level at asphyxiate, lb_f/ftⁱⁱ.

Assuming T=520°R, Γ_min=0.55, and 12.25″×6.325″ annulus, the maximum depths and corresponding equivalent circulation densities (ECDs) are calculated and plotted in Fig. half-dozen.10 for $Q_{f 10} = 0 .$ This effigy indicates that the maximum depth is less than 5000 ft even with an farthermost GLR value of twenty scfm/gpm. The ECD at this depth is 7.4 ppg. Again this does not hateful that wells cannot exist drilled with foams at depths greater than 5000 ft. In fact, many wells have been drilled with foams at depths deeper than 5000 ft. The explanation is over again that although the foams may non be stable at bottom pigsty, pigsty cleaning can withal be achieved with acceptable mixture menstruum velocities in the annulus.

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The Surface Chemistry of Drilling Fluids

Ryen Caenn , ... George R. , in Composition and Properties of Drilling and Completion Fluids (Seventh Edition), 2017

Foams

When water is encountered in air or gas drilling, foaming agents are added to facilitate its removal. Cream formation is quite a simple matter: it only requires the injection into the airstream of a surfactant that sufficiently lowers the surface tension of the h2o. Foams, however, tend to collapse in a short time because the surface gratis energy of the system is thereby reduced. In drilling, foam longevity must exist considered when selecting a foamer.

Foams and Mists

Foams and mists are colloidal systems in which the 2 phases are a gas and a liquid. Distribution of the two phases depends on the relative amounts of each present. This ratio is commonly expressed as either the book fraction of the gas (cream quality) ( David and Marsden, 1969) or the volume fraction of the liquid (LVF) (Beyer et al., 1972). In the foam quality range from 0 to about 0.54 the foam consists of independent bubbles dispersed in the gas (see Fig. eight.12); in the range from 0.54 to 0.96 the system is coordinating to an emulsion with gas as the internal stage and the liquid every bit the external phase. Above a quality of 0.96 the organisation consists of ultramicroscopic aerosol of water dispersed in the gas, and is termed a must or an aerosol.

The factors governing the germination and stability of foams is not well understood. Obviously, since foaming involves a huge increase in expanse, the reduction of surface tension by the addition of a surfactant is essential. Withal, reduction of surface tension is non the simply pertinent gene. The molecular structure of the surfactant likewise appears to be pregnant. One theory is that the anions are oriented normal to the surface of the film, and the cations are distributed in the solution betwixt the walls (Bikerman, 1958b). Thus, the walls carry an electrostatic charge, and repulsion between these charges hinder coalescence. Considering of the lack of basic theory, foaming agents must be evaluated by empirical tests (meet Chapter 3, Evaluating Drilling Fluid Performance).

Foams are used for iii purposes in the drilling industry: (1) to remove formation water that enters the borehole when drilling with air; (2) every bit a depression-density fluid to remove drill cuttings and other solids when completing or working over wells in depleted reservoirs (Anderson et al., 1966); and (3) equally an insulating medium in Arctic wells (Anderson, 1971).

If a water-bearing sand is encountered when drilling with air, the inflowing water accumulates in the bottom of the hole and creates a back pressure that increases air book requirements and reduces the rate of penetration. In addition, information technology causes cuttings to brawl up and adhere to the bit and drill string. Injection of a suitable foamer into the airstream enables the air to deport the water and the cuttings out of the hole as a cream. Maximum efficiency is achieved when all the inflowing water is converted into foam as information technology enters the pigsty, and the foam remains stable but long enough to reach the surface. The pick of surfactants depends on the salinity of the h2o and on whether or not oil is present. Suitable surfactants include anionic soaps, alkyl polyoxyethylene nonionic compounds, and cationic amine derivatives, all of which are commercially available.

The cutting-carrying chapters of foam depends on the foursquare of the annular velocity and on the rheological properties of the foam. The rheological properties depend mainly on the viscosity of the air and the liquid, and on the quality of the foam (Mitchell, 1971) (see Figs. 8.12 and 8.thirteen). When the foam quality is betwixt 0.threescore and 0.96, cream behaves as a Bingham plastic (Beyer et al., 1972; Krug and Mitchell, 1972). Buckingham's equation (encounter Eq. (6.12) in Affiliate vi, The Rheology of Drilling Fluids) may be used to decide flow pressure/menstruum rate relations if modified to allow for slippage at the pipe wall and for changes in air/h2o ratios (and hence in foam viscosity) with pressure. Beyer et al. (1972) take adamant the human relationship betwixt slippage, shear stress at the wall, and LVF, and between viscosity and LVF, by means of pilot-calibration experiments. From these relationships and Buckingham'due south equation, they developed a mathematical model that describes the flow of foam in vertical tubes and annuli. Computer programs based on this menstruum model may be used to decide optimum gas and liquid flow rates, pressures, apportionment times, and solids lifting capacity in prospective workover jobs (Millhone et al., 1972). Detailed analysis should be made whenever jobs in new fields or under new conditions are being undertaken (Figures viii.14–8.18).

The rheological properties of the cream in normal air-drilling operations are of no great concern because annular velocities sufficient to clean the hole are economically viable. However, high annular velocities are undesirable when completing hands erodable formations in workover wells where minimum bottomhole pressures are advantageous, and in very large diameter holes. Under these circumstances, a preformed stiff cream, made from a surfactant plus bentonite or a polymer, is used (Anderson et al., 1966; Hutchison and Anderson, 1972).

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