GB2390861A - Solution of ethoxylated propoxylated alcohol used in downhole cementing operations - Google Patents

Abstract

A chemical wash comprises an alcohol ethoxylate propoxylate as surfactant for use in well treatment, particularly for removing invert emulsion mud deposits from a well prior to cementing. The alcohol is preferably 2-ethylhexanol. The surfactant is biodegradable and acceptable for aquatic organisms. It can be used to formulate a chemical wash by dispersing it at a concentration of about 1% - 10% by weight in water or brine. The solution may also be used as a spacer fluid, separating the drilling fluids and the cement slurry.

Description

239086 1

CHEMICAL WASH

The present invention relates to chemical washes. Chemical washes arc fluids. in particular surfactant compositions, for use in removing or displacing materials in well 5 operations. This invention is particularly useful for removal of invert emulsion muds (drilling fluids having diesel oil, mineral oil or synthetic fluid as continuous phase and water or brine as an emulsified phase) from a well prior to a cementing operation or the like. The chemical wash of the invention can be used to remove oil- based materials from well bore walls, including pipe surfaces and to improve the surface 10 wetting of cement slurry components for enhancement of bonding to such surfaces.

Still further, the present invention also provides test methods for a better and complete evaluation of the efficacy of surfactant compositions for mud removal applications.

In the drilling of a well such as oil or gas well, a drilling fluid, often called "mud" is 15 used to transport drilled material back to the surface and to provide support to the well and to balance the pressure of fluids in the formation through which the well is drilled. These fluids are typically suspensions of solid particulate materials including clays such as bentonite and heavy minerals such as barite in a liquid continuous phase, usually water or brine. A solid layer will often form on the formation from the 20 drilling fluid solids (bentonite, barite, drilled materials, etc.) and is called "mudcake".

In many cases' gelled mud deposits can also form on the walls of the well (or on top of the mudcake), or on casing in the well.

From time to time in the drilling of a well, it may be necessary to cement a casing into 25 the well to provide physical support for the well and to provide isolation between the various fluid-containing zones of the formation penetrated by the well. In order to do this, the casing is positioned in the well and cement pumped down the inside of the casing and allowed to rise up the outside and fill the annulus between the outside of the casing and the wall of the well. In order to provide effective zonal isolation, it is 30 necessary that the cement makes a good bond with the wall and the presence of mudcake can interfere with, or completely prevent this from occurring. Therefore, it is necessary to make sure that as much of the mudcake and gelled deposits as possible are removed from the wall before the cement is placed. Scratchers or other such tools run on the outside of the casing can be used to remove mudcakc if required. Gelled

: r l l l 4: fluid deposits can be removed using a"chemical wash" fluid. Washes are fluids, typically with a density and a viscosity very closed to that of water or oil. They are pumped into the borehole ahead of the cement slurry and act by thinning and dispersing the mud, and leave the casing water-wet and receptive to bonding with the 5 cement. Other fluids such as spacers are also pumped to ensure removal of drilling fluids before a cementing job. Chemical washes and spacers are also acting as buffers between mud and cement slurry to avoid contamination of the cement by the mud with consequent degradation of properties.

10 Oil- or synthetic-based drilling fluids (oil-based muds or "OBMs'' and synthetic-based muds or "SBMs,') are often used to drill the most watersensitive shales in areas with difficult drilling conditions because the clays and shales do not hydrate or swell when coming; into contact with the continuous phase. In cases where the well is deviated from vertical and contact between the drill string and the wall of the well is extensive, 15 these drilling fluid also provide the required lubrication. OBMs and SBMs provide particular problems in cementing since removal of mud deposits can be difficult. As cement slurries are usually aqueous, a good cleaning is important to ensure water-wet surfaces in the well to allow a good bond with cement. Moreover, most of these drilling fluids are incompatible with aqueous cement slurries and their contact can 20 results in the formation of an unpumpable viscous mass at the drilling mud/cement interlace. This may lead to fluid channelling of the displacing fluid and contamination of the cement by the mud. Contamination of the cement by mud in particular can result in unpredictable thickening time (flash set) or set properties of the cement that in the worst case may lead to a major operation failure (MOE). It can also cause high 25 friction pressures, which can fracture the formation, and lead to lost circulation problems. As with water-based muds, some of the problems associated with the use of invert emulsion muds can be addressed using a chemical wash, a fluid with a density and a 3() viscosity close to that of water or oil. Chemical washes assist mud removal by thinning, dispersing and emulsifying the mud when pumped ahead of spacer or cement slurry. These chemical washes often contain a mixture of dispersants, surfactants and solvents to assist in their operation. The presence of surfactant is necessary when dealing, with invert emulsion muds as the surfactant also helps in

1 ' I t14..

:' l::l' leaving the casing water-wet and receptive to bonding with cement. One type of surt:actant that has been proposed for use in such wash fluids is an alkylpolyglucosidc in a mutual solvent. Examples of such surfactants and their use in well applications can he found in European Patent Application No. 01401524.2.

SIt is an object of the present invention to provide a chemical wash composition that is suitable for well-related applications, particularly with invert emulsion muds (OBMs.

SBMs) in well cementing operations.

10 A chemical wash according to the invention comprises a solution of a non-ionic surfactant in an aqueous solvent, the surfactant comprising an alcohol ethoxylated propoxylated. The wash preferably comprises a short chained synthetic alcohol. One particular 15 example is 2-ethylhexanol ethoxylate propoxylate, although other similar surfactants can be used within the scope of the invention. Such surfactants are also relatively non-

toxic and biodegradable compared to older, previously-used non-ionic surfactants such as nonyl phenol ethoxylate (NPE).

20 The surfactant Carl be used to formulate a chemical wash by dissolving it at a concentration of about 1% - 10% (e.g. 5%) by weight in water or brine. This wash can be used before placement of cement in a well to remove mud deposits from the wall of the well. The washes are applicable to various types of invert emulsion muds, e.g. linear a-olefins, low toxicity oils and esters. A surfactant of this type can be used in 25 spacer fluids.

The present invention also provides test methods for each zone identified in a phenomenological description of mud removal mechanism. A compatibility test

determines the degree of compatibility of wellbore fluids. A reverse emulsion test 30 determines the capability of a chemical wash to invert OBM/SBMs and then, to achieve quick mixing and viscosity decrease. Both of these tests mimic a mixing zone. A grid test determines the efficiency of a chemical wash in removing a gelled mud cake by tangential flow as in a tangential erosion zone. casing water-wetting

i l; l I test shows the capability of a chemical wash to remove an oily film left by an invert mud at a casing surface so as to allow a good cement bond to form.

The present invention will now be described by way of examples, with reference to 5 the accompanying drawings, in which: Figure I shows a conceptual diagram of chemical steps required for an efficient cleaning of an invert emulsion mud, relevant mechanism and potential test methods; Figures 2-4 show the efficacy in mud removal for three different surfactants fair different types of invert emulsion muds, 10 Figures 5-7 show the efficacy in inverting mud emulsion for three different surfactants for different types of invert emulsion muds; Figures 8-10 show the efficacy in inverting wettability of casing coupon's surface for three different surfactants for different types of invert emulsion muds; Figures 11-13 show the efficacy in mud removal for a chemical wash according to an 15 embodiment of the invention in various solutions (water and seawater) for different types of invert emulsion muds; Figures 14-16 show the efficacy in inverting mud emulsion for a chemical wash according to an embodiment of the invention in various solutions (water and seawater) for different types of invert emulsion muds; 20 Figure 17 shows the efficacy in inverting wettability of casing coupon's surface for a chemical wash according to an embodiment of the invention in seawater solution for different types of invert emulsion muds; and Figures 18-19 show the effect of temperature on the efficacy in mud removal and in inverting mud emulsions for a chemical wash according to an embodiment of the 25 invention in water solution and an ester mud.

Referring now to Figure 1, three successive phases are clearly distinguished during displacement of a drilling mud in a well by a chemical wash prior to a cementing operation. At the leading edge LE of the wash fluid CW, in the middle of the flow 30 conduit C-F, wash CW and mud M are mixed together. 'I'his is called the "Mixing iLone" MZ as this is the region of stronger turbulent flow that ensures mud mixing, dilution and thinning. The chemicals present in the wash CW help wash CW and mud M to mix together as quickly as possible and reduce the viscosity of the mixture.

Behind this front LE, the wash CW occupies the middle of the conduit but thick mud

I layers MC remain on the walls. These layers MC are removed by tangential flow of the wash CW through an erosion mechanism. This zone is called "Tangential Erosion Z.onc" FEZ. Further downstream, only a wetting oil film remains on the walls. The wash CW must remove it and watcr-wet the surt:aces for the cement to optimally bond 5 to the surt;accs. This zone is called "Water-wetting Zone" W7,.

The following four methods were used to test the surfactant compositions to obtain the data for Figures 2 - 19: 10 'line cleaning efficiency of the surfactants/solvents are tested using invert emulsion muds prepared according to standardized procedures including aging by "hot rolling" at 1 85 OF (85 C) during 16 hours using pressurized mud "bombs".

The first method is the compatibility test.

The test determines the degree of compatibility of the well bore fluids (mud, chemical wash, cement slurry). Compatibility is defined as "the ability of firming mixure.s; that d> not undergo undesirable chemical and/or physical reactions".

20 Two fluids are mixed in various volume ratios using a spatula until the mixture is homogeneous. The suggested volume ratios for two fluids are 95%15%, 75%/25%, 50%/50%, 25%/75% and 5%/95%. The rheology of each mixture is monitored across the full range of rotation speeds (from 600 to 3 rpm).

Refer to the API Recommended Procedure 1 OB, section 16.

The second method is the reverse emulsion test (RET).

This test determines the capability of a chemical wash (COO) to invert oil-based mud or synthetic-based mud emulsions. This method is used to evaluate the effectiveness 30 of the wash fluid in achieving quick mixing in the mixing zone MZ (Figure I).

Mud and CW are preheated in two cells in an atmospheric consistometer. The Waring blender bowl is preheated with warm water and dried. In order to observe emulsion inversion properly, the preheated CW is placed in the heated Waring blender Ad the s

r l l ':d l conductivity is set at 2 mA, when possible. CW is replaced into consistometer to keep it warm. The bowl is cleaned and preheated with warm water if needed, then dried.

175 mL of mud is poured in the preheated Waring blender bowl. IOO ml, of CW is 5 added at once in the heated bowl. Mixture is agitated at low speed (3()0() rpm) for 2 min. The conductivity value of the mixture is read. CW is then added by small volume increments while agitating for 2 min and the conductivity value recorded. CW is added in the same way until the mud emulsion inversion is complete.

10 This stage can be detected by the following: The conductivity of the mixture suddenly increases to 2 mA. No change in the 3 following conductivity value readings.

The mixture in the Waring blender becomes thinned. Barite settling is observed in the Waring blender while the oil and water float on the surface.

For the interpretation, two features need to be considered, the volume of fluid required to reach a given current value and the shape of the curve. Interpretation is easy when the curves show a sudden and sharp increase together with no visible incompatibility in the bowl: the system that leads to the minimum volume of wash 20 at similar surfactant concentration - is the best candidate for inverting the mud emulsion. The third method is the grid test, as described in A metallic grid is used to cover the normally smooth surface of a Chan 35 rotor and to create a rough surface to which the mud can adhere. The rotor and metallic grid are weighed The Chan 35 is set up as normally done for an API standardized rheology measurement except that the "bob" is not used.

The rotor with the metallic grid is lowered into to the mud and left under static condition. When taken out' a smooth and homogenous layer of mud covers the metallic grid. The rotor, grid and mud are weighed too.

:::l:::. The rotor with the metallic grid, now covered by a smooth mud layer is placed in a preheated test cup containing the test solution. 'I'he rotor is rotated at 100 rpm for 5 minutes and then taken out of the test solution. The rotor is taken off the Chan 35 and weighed. 'I'he rotor is now replaced in the test solution and run in an exactly same 5 way as described above for another 5 minutes to obtain the weight value at 10 minutes. The process is repeated until values at 15, 20 and 30 minutes have been obtained. The mud removal (%) is then calculated.

The fourth method is the casing water wetting test (CWWT).

This test shows the efficiency of a chemical wash on removing an oily film, left by an invert mud (OBM, SBM) or an oil-contaminated water-based mud (WBM), at casing's surface.

15 Two standard casing corrosion coupons are used as substrate and dipped completely in mud for 10 minutes, to obtain a film of mud on the coupon's entire surface. The convex face is cleaned from the mud with paper and the coupons placed and fixed inside the Chan cup containing the CW, with the mud-covered face facing the inside of the cup.

The Chan 35 is set up as normally done for an API standardized rheology measurement except that the "bob" is not used. The heated cup containing the coupon is positioned so as to be 2/3 immersed in the CW. Rotate at 100 rpm. After 30 minutes, remove the steel coupons. Observe the surface state and note if there is any 25 visible trace of mud left.

Take the first coupon. Place a drop of distilled water with a pipette on the surface that has been totally immersed in the CW. Observe whether it spreads or not. Monitor the diameter of the drop (D 1) Run a comparison test with an oil-wet surface: Place a piece of Teflon tape on the coupon and place a drop of the same water with the same pipette on it. Teflon tape represents a perfectly oil-wet (hydrophobic) surface. Monitor the diameter of the drop (D2)

4 I, [ d t t d t, d e t I..

As the coupon was not totally immersed in the CW, a part of the coupon is still covered by the mud, and is oil-wet. Place a drop of the same water with the same pipette on it and compare.

Take photographs to allow easy drop measurements and comparison.

Take the second coupon and clean the washed surface of' any mud residue with a wiping towel. Place a drop and make a comparison test with an oilwet surface. Take photographs. 10 For a quantitative evaluation of waterwetting, contact angle calculation is recommended (Dl and D2 determination) For drops that spread, the measured diameter is the one corresponding to the contact circle between the drop and the steel.

If the drop does not spread too much (contact angle > 90 degrees), the 15 measured diameter corresponds to the larger one and not to the contact surface's one (this being much less).; I'he ratio of drop radii, D1/D2, is calculated. There is a rigorous mathematical expression between this ratio and the value of the contact angle. Due to the limited accuracy of the measurement of diameters, the numerical values of the contact angle 20 is not used as such but rather expressed as one of three -or more categories: Poor wetting Fair wetting and Good wetting The boundaries of these domains are suggested below: 25 Contact angle = 0 degree means perfectly water-wet (clean glass surface).

Contact angle - 180 degrees means perfectly oil-wet (Teflon) I'he minimum wetting required for an efficient chemical wash is "good wetting".

In the test data listed below, Product A is GT 2624 a non-ionic surf'actant, comprising; 30 an alcohol ethoxylate propoxylate (2ethylhexanol ethoxylate propoxylate) obtained from Akzo Nobel Surface Chemistry AB of Stenungsund, Sweden, i.e. a surfactant forming part of the invention; A is biodegradable in freshwater (>60% after 28 days) and seawater (40% after 28 days) and acceptable to aquatic organisms (Acartia tonsa: LC50 (48h)=29.2 mg/L, Corophiurn volutator: LC50 ( I Odays)=25 I mg/L'

Be f d 1, Skeletonema costatum: EC50 (72h)=44 mg/L, Sheepshead minnow: LC50 (96h)=55 mg/L). P rod uct B is a formulation containing a nonyl phenol ethoxyl ate (N P. E) as surfactant (see US 4,767,460); this product is a reference concerning; its cf'ficiency for well 5 cleaning but is not environmentally friendly: its biodegradability in seawater is very low (5% after 28 days) and it is more toxic to aquatic organisms (Skeletonema costatum: EC50 (72h)=3.5mg/L).

Product C is a formulation containing an APG as surfactant, see European Patent Application No. 01401524.2. C is biodegradable in seawater (>6()% after 28 days) 10 and acceptable to aquatic organisms (Acartia tonsa: LC50 (48h)=89.7 mg/L, Corophium volutator: LC50 (lOdays)=252 mg/L, Skeletonema costatum: EC50 (?2h)= 18.2mg/L) but is not very efficient for well cleaning.

In each case the product is tested at a concentration of 2 gal/,bbl of chemical wash, 15 that is as a 5% by weight solution in water, according to the different methods described above.

Table I shows the various compositions evaluated with the grid test to provide that data of Figures 2 - 4: Fig. Product Invert emulsion mud solution Temp.

A()' B(u), C() Low toxic mineral oil Water 85 C 3 A(), B(a). C() Ester Water 85 C2 A(), B(u). C() Linear a-olefin Water 85 C 20 Table I

As can be seen from figures 2 and 3, the CW with Product A is at least as effective or better than those with Products E3 or C. While the performance is slightly less than that of Product B in Figure 4, the results are close and Product A has much better 25 biodegradability and toxicity.

I'able 2 shows the various compositions evaluated with the reverse emulsion test to provide that data of Figures 5 - 7: Fig. Product Invert emulsion mud Solution Temp.

5 A(), B(a)' C() Low toxic mineral oil water 50 C

.. . 1..DTD: | 6 A(). B()'C() | F:ster | Water | 50"C | 7 1 /()7 B(n), C( ) | Linear (x-olefin I Water 1 50"(: | Table 2

As with the results of' the grid test above, Product A performs at least as well as the established surfactant Product B. I'able 3 shows the various compositions evaluated with the casing water-wetting test to provide that data of Figures 8 - 10 (CWWT). All tests are performed at 85"C in a water solution: Fig Product Mud Comment Wettability Low toxic mineral oil The picture presents 3 drops: the Good middle one is representative of the coupon's part that was in the CW for 30 minutes. On the left, it is the reference: a drop on a Teflon band. On the right, the coupon was covered by mud but has not been immerged in the CW. The surface's wettability inversion is good: the drop spreads totally.

8 B Low toxic mineral oil The picture presents 3 drops. The left Fair one is representative of the coupon's part immerged in the CW.

The surface's wettability inversion is not perfect as the drop does not spread totally and is still bulging.

8 Low toxic mineral oil The picture presents 3 drops. The left Poor one is representative of the coupon's part immerged in the CW.

The surface is still oil-wet: the drop does not spread at all.

9 A Ester The picture presents 3 drops: the left Good one is representative of the coupon's part that was in the CW for 30 minutes.

In the middle, it is the reference: a drop on a Teflon band. On the right, the coupon was covered by mud but has not been immerged in the CW.

The surface's wettability inversion is _ good: the drop spreads totally.

9 B Ester The surface's wenability inversion is Good good: the drop spreads totally.

9 C Ester The surface's wettability inversion is Good _ good: the drop spreads totally.

10 A Linear a-olefin The picture presents 3 drops: the right Good one is representative of the coupon's part that was in the CW for 30 minutes.

_ In the middle, it is the reference: a drop

d l on a Teflon band. On the left, the coupon was covered by mud but has not been immerged in the CW.

The surface's wettability inversion is good: the drop spreads totally.

10 B Linear a-olefin The picture presents 3 drops. The air middle one is representative of the coupon's part immerged in the CW.

The surface's wettabiiity inversion is not perfect as the drop does not spread totally and is still bulging.

1() Linearac-olefin The picture presents 3 drops. The left Poor one is representative of the coupon's part immerged in the CW.

The surface is still oil-wet: the drop does not spread at all.

Table 3

Table 4 shows Product A in various solutions (water and seawater) evaluated with the grid test to provide that data of Figures 11 - 13: Fig, . Solution Invert emulsion mud Product Temp.

I I W(), SW() Low toxic mineral oil A 850C 12 W(). SW() Ester A 85 C We). SW() Linear a-olefin A 85 C 5 Table 4

l able 5 shows Product A in various solutions (water and seawater) evaluated with the reverse emulsion test to provide that data of Figures 14 - 16: Fig. Solution Invert emulsion mud Product Temp.

W(), SW( A) Low toxic mineral oil 50"C _ W(), SW( A) Ester A 50"C 16 W(), SW() Linear or-olefin A 50 C Table 5

As can be seen from these tests, Product A is effective in both water and seawater (brine). Table 6 shows Product A in seawater solution evaluated with three invert emulsion 15 muds (low toxic Mineral oil, Ester and linear a-Qlefin) with the casing water-wetting test to provide that data of Figure 17 (CWWT): Table 6

,,, r , I. ' ' ',

l Fig Product Mud Comment Wcttability 17 A Low toxic mineral oil The picture presents 3 drops: the Icft (food one is representative of the coupon's part that was in the CW for 30 minutes.

In the left. it is the reference: a drop on a Teflon band. On the right' the coupon was covered by mud but has not been immerged in the CW The surface's Nettability inversion is good: the drop spreads totally.

_ 17 A Ester The surface's Nettability inversion is Good good: the drop spreads totally.

17 linear a-olefin The surface's Nettability inversion is Good good: the drop spreads totally.

Table 7 shows Product A evaluated with an ester mud at various temperature with the grid test and the reverse emulsion test to provide that data of Figures 18 - 19: Fig. Temperature (C) Test method Invert emulsion mud Solution Temp. | 18 27(-), 50(). 85() Grid test Ester Water 85 C l 19 27(-)' 50(), 65( ) Reverse emulsion test Ester Water 85"C l Table 7

The tests described above demonstrate that a simple aqueous solution of the alcohol ethoxylated propoxylated non-ionic surfactant is highly effective as a chemical wash for use in oilfield well cementing operations. While particular examples have been

described' other similar compounds may be used as surfactants.

1() In use, the chemical wash is pumped into the well after the mud has been displaced and before the cement is pumped down the casing and back up in the annulus. Plugs can be provided between the chemical wash and the preceding and succeeding fluids' if required. Also, a series of chemical washes can be pumped into a well prior to 15 cementing, either consecutively, or interspersed with other chemical washes or well treatment fluids.

Claims (1)

1. l CLAIMS

   I A chemical wash comprising a solution of a non-ionic surfactant in an aqueous solvent, the surfactant comprising an alcohol ethoxylated propoxylated.

   2 A chemical was as claimed in claim l, wherein the non-ionic surfactant comprises a short chained synthetic alcohol.

   3 A chemical wash as claimed in claim 2, wherein the surfactant comprises 2 10 ethylhexanol ethoxylate propoxylate.

   4 A chemical wash as claimed in claim 1, 2 or 3, wherein the surfactant is dissolved in the aqueous solvent at a concentration of about 1% - 10% by weight. A chemical wash as claimed in any preceding claim, wherein the aqueous solvent comprises water or brine.

   6 The use of a chemical wash as claimed in any of claims I - 5 to remove mud 20 deposits from the wall of a well or from the surface of casing.

   7 The use of a chemical wash as claimed in claim 6 to remove invert emulsion muds. 25 8 The use of a chemical wash as claimed in claim 6 or 7 prior to placement of a cement slurry in the well.

   9 A well cementing operation, comprising pumping through the well a chemical wash comprising a solution of a non-ionic surfactant in an aqueous solvent, 30 the surfactant comprising an alcohol ethoxylated propoxylated so as to remove mud deposits, followed by pumping a cement slurry into the well and allowing it to set.

   t, I 1 () A spacer fluid comprising a solution of a non-ionic surfactant in an aqueous solvent, the surt:actant comprising an alcohol ethoxylatcd propoxylated.