MXPA01008495A - Cementing compositions and application of such compositions to cementing oil wells or the like - Google Patents

Abstract

The invention provides a method of cementing an oil well or the like comprising injecting a cement slurry comprising a surfactant, and foaming said slurry before allowing the cement to set. The water content of the slurry used is very low (less than 50%by volume for systems based on an ordinary cement and less than 72%by volume for systems based on a micro-cement).

Description

CEMENTATION COMPOSITIONS AND APPLICATION OF SUCH COMPOSITIONS TO CEMENT OIL WELLS OR THE LIKELY The present invention relates to cementing techniques used in civil engineering, in the construction industry and more particularly in the drilling of oil wells or similar. More precisely, the invention relates to cementing compositions of very low Density There are many applications for which a lightweight cement would be appropriate. In civil engineering and construction industries, a low density cement would allow less bulky lower structures to be produced that would not need to be reinforced to support the weight of the cement. However, the properties of lightweight cements currently available are generally lower, in particular with respect to compressive strength, and the permeability is too high and thus are only rarely replaced by ordinary cement, particularly co to guarantee He worked for the desired service life. In oil wells, the selection of a suspension density depends on a number of criteria The main purpose of the cement placed in the housing and the paced well is to isolate the different geological layers that are traversed and reinforce the housing mechanically. The cement also protects the corrosion alloy steel, passivating In order to avoid any blasting cranes the density of the cement must be used so that the pressure at the bottom of the well is at least equal to the pore pressure in the formations crossing geology Clearly, the longer the column, the cement suspension needs to be dense. In addition to this lower limit, there is a higher limit on the density of the pressure exerted on the rock (due to the hydrostatic pressure generated by the cement column and the pressure drop associated with the circulation of fluid during pumping) must be lower than the pressure with which That rock can tolerate without fracturing. That pressure increases with the length of the cement column. In general, the length of the cemented section will be so marked by the density of the cement suspension that can be used. a minimum density in order to have acceptable mechanical properties the length of the cemented section is often very limited by the fracture pressure if it is not limited due to other reasons such as pressure inversions between the geological layers, each new section must be drilled with a smaller diameter than the previous section to allow the drilling tool and the housing to be lowered through the sections already provided with a housing, a section that was too narrow to accommodate the finishing tools would be useless. Due to this reason, if the number of sections is high, drilling should be started using large diameter sections at the top of the well, resulting in extra high costs due to an increase in the volume of rock to be drilled and to the greater weight of the housing sections due to their larger diameter. Of course, it is known how to cement a section in a plurality of steps to prevent the well from contracting. This technique involves high supplementary costs and the equipment required for multiple stage cementation is often not safe. A cement of reduced density in this manner would be desirable, to increase the length of each section while maintaining the mechanical properties of the cemented cement sufficient to ensure the long-term isolation. The present invention provides particularly lightweight cementation formulations with good mechanical properties, of impermeability, and adhesives For oil well cements, the most frequently used technique to reduce the density of a cement suspension is to add a larger amount of water and spreaders which are intended to prevent the particles from separating and / or to prevent the formation of free water on the suspension surface. This technique greatly reduces the strength Cement copulation increases its permeability and reduces the cement's ability to adhere to the supports. Due to these reasons, the technique can not be used to produce densities less than the order of 1300 kg / m3 and keep the geological layers isolated., as well as providing sufficient housing strength. An additional routine technique for lightening a cement is to formulate a suspension containing a surfactant and introduce a gas such as air or nitrogen to the cement before it sets. The amount of gas added it is such that the required density is obtained. The quantity can be such that foamed cements are formed. A "foam quality" can be defined for such systems as the ratio of the volume of gas to the volume of foamed product, likewise, the "swelling" as the ratio of the increase in volume due to foaming to the volume of the foam. This technique is a little less powerful than the prior art, since the density of the gas is lower than that of the water and thus less has been added. However, density is the practice limited to densities of more than 1100 kg / m3 in petroleum industry applications even when starting from a suspension that has previously been made light with water. Above a certain "foam quality". the stability of the foam decreases very quickly, the compressive strength of the cured foam becomes too low and its permeability becomes too high which compromises its service life in hot aqueous media, including ions that are aggressive towards cement up to a greater or lesser degree. In this regard, the United States patent US-A-5 696 059 should be consulted, since it describes a foamed cement with a density of 1170 kg / m3, obtained with a foam quality in the range of 30% to 35% and that, after 24 hours, it has a compressive strength of only 4.2 MPa (60? pounds per square inch) while the setting temperature is greater than 100SC and the system comprises a microcement and silica The authors of the present invention have discovered that foams of excellent quality, very light, are obtained by dense, strongly foaming suspensions with a low water content to produce good mechanical functioning and very low permeability, contrary to current practice and to that which at first sight seems to be more rational, to say, using suspensions that are already low density, extended with water These denser suspensions withstand higher "foaming qualities" while forming stable foams Fi Finally, for an identical foam density, the mechanical properties of the foam of the invention are better with lower permeability, and the ability of the cement to adhere to the housing and the geological formulations are improved in a variation of the invention carried out with suspensions based on ordinary cement, before foaming, the initial suspension must comprise a surfactant to stabilize the foam and is characterized by a low water content in general the initial water content should not exceed 50% by volume of the suspension non-foamed, and preferably less than 45%, more preferably around 40% In some cases, the water content can be reduced again but in general, a suspension with a water content of less than 33% is no longer used that then it becomes very difficult to obtain the correct rheology The fluid portion of the additives when they are liquids or solid additives that are lubles are counted as part of the volume of liquid together with the mixing water In contrast if the liquid additives comprise more soluble particles in suspension the volume of those particles is counted as part of the other solids The term "ordinary cement" means a cement with an average particle diameter that is generally cei at 20 um, with a maximum particle size that can reach 100 u and a specific surface area per unit weight determined by the test d? air permeability [Fineness Bldine] typically in the escape from 0 2 mVg to 0 4 m2 / g All commercially available Portland cements for oil well applications (categories A to H) can be used, but the lase O cements are preferred in the present invention The goal of a lower water content combined with good rheology can be achieved by adding coarse particles the term 'coarse particles' ? 5 J means particles with a size typically in the range of 5 to 50 times the size of ordinary Portland cement used in oil well cements, or in other words, particles with a size on the scale of 100 μm to 1 mm These thick particles preferably light particles such as spheres or hollow particles produced from a plastic or elastic material However, to obtain a foam with a density of more than 900 kg / m3 for reasons of economy and better resistance to compression it is possible to use coarse particles solid with dimensions less than one millimeter, composed, for example, of silica or carbonates of natural lime or any other mineral product of low solitude which may or may not be reactive in the water of the suspension The dense suspensions of high performance with a reduced content of water which, however, have sufficient fluidity to be pumped without a pressure drop ex is? v? This is described in European patent EP-A-621 47 or PCT application PCT / FR98 / 02429 which, in addition to cement, comprise a group of "thick" oarticles with a typical diameter on the scale of 200 um a 800 um, and a group of fine particles "with a typical diameter on the scale from 0 5 ura to 5 um, and optionally other groups of coarser or finer particles, each group of particles having a scale of grain sizes that it is different from the other groups, with an average particle diameter differing by a factor of 5 to 20, and the respective proportions of the particles of the different groups being such that the compact quality of the mixture is a maximum and at least Typically the solid fraction of said suspension of reduced water content will be constituted by 35% to 65% (by volume) of coarse particles, 20% to 45% of Portland cement, and 5% to 25% of micronic particles In a variation of s particularly preferred, the solid fraction will consist of 55% fine sand with an average size d? 300 μm, 35% Portland cement, and 10% fine silica It is also possible to initiate from multimodal suspensions analogous to those described in EP-A-621 247 by omitting particles with a size exceeding the particles of the function. of the "coarse" particles being carried out by the buroujas in the foam In a second variation of the invention, the dense suspensions of preference are obtained as described in EP-A-G 748782 or the application d? French patent FR-98 15570 These suspensions, which are particularly suitable for tightening operations, to plug or reinforce low-consolidated geological formations, are based on a product and not on an ordinary cement. The term "my crocement" means a cement with a maximum particle size on the scale d? 6 um at 12 um, preferably on the scale from 8 um to 11 um, with a mean diameter of a few microns typically 4 um for the commercially available micro-cores tested, and the specific surface area per unit weight, determined by the air permeability test [Fineness Blaine] plus d? 0 6 m2 / g, preferably more than 0 7 rVg, and more preferably about 0.800 m2 / g Most applications of the petroleum industry using a crocement use compounds formed from slag comprising 45% lime, 30% silica 10% alumina, 1% iron oxides, and 5% -6% manganese oxide (only the principal oxides are mentioned here, these quantities, of course, may vary slightly depending on the supplier) microcements with a composition that is that of a Class G Portland cement are also commercially available, typically comprising about 65% lime, 22% silica, 4% d? alumina 4% iron oxides and less than 1% manganese oxide The two types of materials or mixtures of the two ee can be used in this second variation of the invention For suspensions based on microcement, the amount of water used is necessarily more high that for a suspension based on an ordinary cement In this way for the sispensionee of the invention the volume of water will be less than 72%, preferably in the scale of 58% to 70% Clearly, a surfactant can also be added to stabilize the foam This 3S water content significantly higher than in the case ie a suspension based on ordinary cement but the volume of liquid however, is notoriously low compared to that used for suspensions based on my friction normally used for the operations of tamped, in particular to inject into cracks, and that has ur water content of more than 75% (the amount of water added being a At least 100% with respect to the weight of the cement, and usually close to 80% by volume This is the inventive step of the invention to say foaming of a "dense" suspension For suspensions based on a micro-cement, prepared as desired IDT in the European patent application EP-A-0 748 X 2 or in the French patent application FR-98 1557) (density of 1650 kg / mJ to 1800 kg / m1, compared to 1400 kg / m3 for suspensions of Conventional tamping), in addition to the points described above, the foam has the advantage of not penetrating into highly porous media such as reservoir rocks. Surprisingly, the authors of the present invention have found that despite a higher yield point due to foaming, these foams have a much greater ability to penetrate into porous fissures compared to non-foamed tampon suspensions, conventional, and only slightly smaller than the non-foamed suspensions described in the patent applications EP-A-621 246 and FR-98 15570 These suspensions are constituted by a water-based fluid a dispersing agent in solution in the aqueous phase and optionally other liquid additives, a microcement, that is, a cement constituted by micro-sized particles, and a first additive constituting it by particles 5 to 100 times, preferably of the order of 10 times smaller than the microcement particles. Typically, the Average particle diameter in this way is on the scale of 0 05 3 0 5 my chemistry such as a latex, a condensate of s fumed silica type silica, a condensate of manganese oxides of pigment smoke, certain fine soot, carbon black or certain microgels of polymers such as a fluid loss control agent; and optionally, a second additive consisting of ultrafamous particles, 5 to 100 times, preferably of the order of 10 times less than the particles of the first additive, such as dispersed colloidal silicas or aluminas (average dimension 3-60 nanometers, preferably 15- 40 nanometers) or a nanolatex The preferred compositions known from EP-A-621 247 advantageously comprise 10% to 40% of the first additive and 5% to 30% of "ultra-fine" particles, the percentages being indicated with respect to the total volume of solid particles in the composition. More particularly preferred are compositions comprising 50% to 75% microcement, 15% to 40% d? "very fine" particles, and 5% to 20% of "ultra-fine" particles. Preferred known compositions of FR-98 15570 comprise an aqueous phase, a micro-cement, and an aqueous suspension comprising a polymer of the vinyl acetate type obtained by chemically cross-linking, in a controlled stirring reaction, a polyvinyl compound (PVA) in solution with bl-or poly-crosslinking agents. functionalities that crosslink the alcohol groups (secondary or tertiary primary), the molar concentration of said crosslinking agent with respect to the monomer residue of PVA being from the scale of 0 1% to 0.5%, a nanolatex and an ammonium surfactant With a cloud point of more than 80 ° C Whatever the variation, it should be noted that the presence of very fine particles such as ST described in the earlier patents contributes to stabilizing the foam and can achieve higher "qualities" than conventional foaming additives and foam stabilization additives It is also possible to start from suspensions produced by a suspension ion of solid particles (mineral particles cements my crocements, organic particles such as latices or polymer microgels), for which the graph of the size distribution of the particle mixture shows the logarithm of the cumulative frequency of the particles co or a function of the logarithm of the particle size is substantially linear as long as they contain micro particles, even though they are less preferred than the previous compounds because the "compact quality" of the solid fraction is lower, that is, the minimum volume occupied by the solid fraction of the suspension is higher than in the previous case, which means that a greater amount of water is used. In this way the foams with a density of less than 660 kg / m3 can be obtained that have mechanical properties. waterproofing and adhesion properties suitable for applications in the petroleum industry. The thermal insulation of these foams with a high "quality" of foaming change is greatly improved due to the greater incorporation of iaire gas or nitrogen being generally preferred due to the greater ease of use in the field, and e. cost) as well as greatly reduced heat release during setting due to the small amount of cement and the dilution by the gas a particularly advantageous phenomenon when cementing in gelatin type zones Good qualities of thermal insulation are also advantageous in the case of very deep wells, in particular when the sections in the well that are closest to the surface nc have been cemented with cements that comprise silica and yet must tolerate a crude circulating at an elevated temperature. The known tensioac t ive agents indicate to form and stabilize cement foams Other additives can be agitated such as any of the normal cements, mortars and concrete additives except, of course, antifoam additives. Examples with dispersing agents (also known as superplasticizers and antifouling agents). Igellation, water retainers, retarders (intended to control the ti setting times at temperatures of more than 60 ° C) or accelerators (intended to control the setting time at cold temperatures). The techniques for producing the foam, which are also well known, do not form part of the invention as claimed. existing techniques The "quality" of the foam is adjusted as a function of the density of the starting suspension to obtain the desired foam density. However, the quality of the foam should not exceed 65% over whose limit the stability of the foam and its properties quickly degrades, becoming too low (resistance to compression impermeability) The conditions to operate the ap > Arate to generate the foam AND the amount of surfactant are adjusted so that the bubble size does not exceed 7 millimeters, preferably 3 millimeters The present invention is illustrated by the following examples EXAMPLE 1 The properties of four suspensions were compared Suspension A (according to the invention) A mixture of powders was prepared, comprising 55% by volume of fine sand with a size average of 300 microns, 35% by volume of Poitland Class G cement, and 10% by volume of fine silica with an average size of 3 microns Water and additives (retarder based on purified lignosulfins (D801, sold by Schlumberqer Do ell ) in an amount of 4 5 ml / kg of solid mixture (0 05 gallons per bag of mixture ie 3,785 liters per second of 42 637 kg of mixture, in other words, 1 gps = 0 0888 liters of additive per kg mix) AMPS polymer based on water retainer (D158 sold by Schlumderger Dov / ell) in an amount of 13 3 ml / kg of solid mixture (0 15 gp and a superplasticizer based on polmaf sulfonate (D80 sold by Schlumberger D owell) in an amount of l-8 ml / kg of solid mixture (0 02 gps) were mixed with this powder so that the volume percentage of liquid in the suspension was 40%. The density of this suspension was 2115 kg / m3 (17 6 pounds per gallon) The rheology of a suspension is characterized by its PV plastic viscosity (in cP or mPa s), the conversion factor being 1) and the Ty performance point (in pounds per 100 square feet) , lbf / 100ft?), conversion to Pascal multiplied by 0.478803), assuming that the suspension was a Bingham fluid For the suspension At the yield point was 5 3 Pa or 11 lbf / 100ft2 and the plastic viscosity was 159 mPa s The thickening time at 852C was 5 hours 40 minutes There was no free water or sedimentation using conventional API (American Petroleum Institute) tests Suspension B (according to the invention) A mixture of powders was prepared Comprised 55% by volume of hollow spheres from cenoesfßras c on an average size of 170 microns, 35% by volume of Portland Ciase G cement, and 10% by volume of fine silica with an average size of 3 microns. Water and additives (water retainer based on AMPS polymer (D159, sold by Schlumberger Dowell) in an amount of 8 ml / kg of mixture (0 09 gps) and a superplasticizer based on polyphenylene sulphonate (D80) in an amount of 4 5 ml / kg of mixture (0 05 gps) is They mixed with this powder so that the percentage by volume of liquid in the suspension was 40%. The density of this suspension was 1465 kg / m3 (12.2 pounds per gallon). There was no free water or sedimentation using conventional API tests Suspension C ( example of comparison) This Example corresponded to the current technology for average densities Water and additives (retarder based on purified lignosulphates (D801) in an amount of 4 5 ml / kg of cement (0 05 gallons per bag of cement) water retainer Based on polymer AMPS (D158) in an amount of 13 5 ml / kg of mixture (0 15 gps) and a superplasticizer oasado in polinaf alene sulfonate (D80) in an amount of 1 78 ml / kg of mixture (0 02 gps)) were mixed with Fortland cement class G so that the density of this suspension was 1900 kg / m3 (15 8 pounds per gallon) that is 58% n volume of liquid fraction Suspension D (comparison example) This suspension corresponded to the current technology for densities Low A mixture of powders was prepared. It comprised a class G cement with added bentonite constituting 10% by weight of cement. Water was added to the previous mixture of powders so that the density of the suspension was 1575 kg / m3 (13 lbs. gallon), ie 73 d% by volume of liquid fraction For foaming these suspensions conventional surfactants sold by Schlurnberger Dowell under the reference D139 (an aqueous solution of alkoxylates, methanol and polyglots) and F052.1 (a agent t? nsioa based on ethanol, propylene glycol and ammonium salts of fatty alcohol sulfate) were added in proportions of 1 1 The amount depended on the quality of the foamWas more added to obtain superior foaming quality? 46 ml per kg of solid mixture (0.084 gallons per sack dp solid mixture) were used to obtain a 50% foam quality.

D Deennssiiddaaddeess 1 1220000 ((10) 1080 (9) 960 (8) 840 (7) 720 (6) Suspension AQ 43% 49% eDc-jo /, or CS 27 6 24 20 6 (4000 3500) (3000) P 0.8 1 1 5 S Suussppeennssiióónn BB 0Q 3 355 %% 4 433 %%? L% CS 16 13 5 11 (2300) (2000 1? I 00 P 1 1 22 1 6 2 4 Suspension C 0 37% cs 20 (00) P 6 Suspension D 0 31% 39% cs 5 5 4 8 (800) (700) P 50 70 Densities are expressed in kg / m3 with pounds per gallon in brackets Q designates the Foam quality, expressed in% by volume, CS denotes the compressive strength after 24 hours of setting, expressed in egaPascals, with psi in parentheses. P designates the permeability of the cured cement expressed in icroDarcy. It can be seen that for the foamed suspensions of the present invention, the compressive strength was substantially higher and the permeability was considerably lower than for conventional foamed suspensions with an equal density of suspension, EXAMPLE 2 In this Example, submicron particles were introduced into the suspension, in this case latex-type particles containing 50% by volume of particles of 150 nanometers suspended in water. It should be noted that? The latex can be replaced by mineral particles (silica fume, or suspended pigment smoke) or constituted by microgels of a crosslinked polymer as described in EP-A-0 705 850 or International application WO 98/35918. Suspension F The mixture of powders was exactly the same as for suspension A Water, latex in an amount of 0.4 gallons per bag and mixture, and additives (retarder based on purified lignosulfonates (D800) in an amount of 0.15% and weight with With respect to the solid mixture and a superplasticizer based on sulphonate of pol-inafta-wood (D80) in an amount of 0-12% by weight with respect to the solid mixture) were mixed with this powder so that the volume percentage of liquid in the suspension was 40%. The density of this suspension was 2090 kg / m3 (17 4 pounds per gallon) Its rheology was as follows Performance point 32 pounds per square foot and plastic viscosity of 8 centiPoises, using a fluid model of Bingha Thickening time at 1029C was 4 hours 00 minutes There was no free water or sedimentation using conventional API tests Densities 1320 (11) 1080 (9) 960 (8) Suspension EO 35% 49% 55% (invention CS A 2 13 1 11 (2 00 (1900) (1600 P 0 2 0 3 0.5 Units and symbols are the same than those previously used It may be that the compressive strength was a little lower than in Example 1 but still highly acceptable In contrast, the permeability was substantially lower which is advantageous with respect to the resistance of the cement to chemical attack by means of fluids for example groundwater or acdic treatments carried out during the life of the well to increase the total production EXAMPLE 3 In this Example the base suspension corresponded to a composition as described in earlier patents more particularly adapted to very low temperature cementation, which without requiring a reduced thickening time and a rapid development of the compressive strength. The composition of the powder mixture was the same as for the B subjection, with the exception that the fine silica was replaced by the same amount in microcement volume Dyckerhoff Mikrodur PU, say 10% by volume Water, microgels of polymer ret In a quantity of 0 1 gallons per bag of mixture and additives (a superplastifit based on polymelane sulfonate (D145A) in an amount of 0.15 gallons per bag of solid mixture) were mixed with this powder so that the percentage in volume of the liquid in the suspension outside 42% The density of the suspension was 1480 kg / m3 (12 3 pounds per gallon) Thickening time at 10SC was 5 hours 30 minutes There was no free water or sedimentation using conventional API tests Densities 960 (8) 745 (6 2) 660 (5 5) 0 35% 50% 55% CS at 24 h 5 2 3 9 3 5 (760) (56 n) (500) CS at 43 h 12.1 9 0 7 9 (1760) (1300) (1150) CS at 89 h 15 11 9 6 (2200) (1600) (1400) P 0.3 0 6 0 7 The units and symbols were the same as those used in the previous example. The compressive strength was recorded at 24 hours, 48 hours and 39 hours. The resistance measurements were carried out at 10 ° C. The development of compressive strength - 2! It was much slower than in the previous examples. This was due to the very low temperature that reduced the hydration rate of the cement and the extremely low cement densities. These ruspensicnes are particularly suitable for very deep water cementation where the temperature is very low and the geological formations of the maritime soil are highly unstable. The density of the cement for drilling in very deep water must be even lower than for other wells, since the depth of the maritime soil means that there is a great depth of suspension of cement in the housing and in this way the pressure exerted on the bottom in low-set formation is high It can be seen that despite all the resistance to compression after 24 hours was atable, meaning that the drilling tool could be inserted again, and the resistance continued to develop values that would guarantee good value You can also see that the permeabilities were very low EXAMPLE 4 In this Example, the ICLO component? The powder of the suspension G was identical to that of the suspension F Loe organic additives were different since it was subjected to a temperature of 143aC to place it under conditions comparable to those of US-A-5 696 059 of Example 2 called U '059 in Table Suspension G The composition of the powder mixture was the same as for the suspension F A polinaf sulfonate dispersion agent in an amount of 0 01 gallons per bag of solid mixture and a cement setting retarder, D161 , in an amount of 0 06 gallons per sack of solid mixture were added. The retarder was added to control the setting of cement at 143SC The surfactants used to produce the foam were the same as those in all previous examples Quality 0% 35% 50% Suspension F Density 2030 1350 1040 (17 4) í 11 3) (8 7) (invention) Time of 5h 4 thickening to 12? EC Rheology 25/87 T (lbl / lOOf t2 ¡Pv ícP ) CS to 24 ha 60 30 22 143BC (8800) (4400) (3200) Density suspension 1800 1170 S '059 (151 (9 8) Time 6h 14 thickening at 1 79C Rheology 114/92 t and (lbf / 100ft2j / Pv (cF) CS at 24 h at 4 2 143BC (607) The units and symbols were the same as those used in the previous example. You can see that the rheology of the F - 2 suspension! non-foamed was substantially lower than that of the suspension of US '059 even though the density was higher. The compressive strength after 24 hours for the suspension F was much higher than that of the suspension of US' 059, even though the made] in comparison with an identical foam quality or the same foam density In particular, the compressive strength after 24 hours of foamed 50% F suspension should be combined with that of the suspension of US '059 It was substantially aliñen higher even when the density was lower than 1 p 0 kg / m3 as opposed to 1170 kg / m3 EXAMPLE 5 This Example covered applications without coarser particles than the cement in the suspension. Foam bubbles acted in place. For the Example we selected a suspension produced in accordance with EP-A-621 247 Suspension H The cement used was a Spinor A12 microcement. 2 4 gallons per bag of cement were added to an additive in accordance with FR-98 15570 A dispersion agent based on polymelamine sulfonate (PMS) D1454 was added in an amount of 0.52 gallons per bag of cement The additives used for foaming the suspension and stabilizing the foam were like those described in all previous examples D13 '> and F052 1, which were each added in an amount of 0.1 gallons per bag of cement. Foaming quality was 53% Quality 0% 43% Suspension H Density 1690 960 (invention) (14.1) (8) Rheology 2 6/44 2 Pv í rnPa e) Ti me of 5 h espesam i en t o a? 7 SC CS at 24 h 4. 1 (600 The units and symbols were the same as those used in the previous Example. This type of suspension was intended, inter alia, for tampering, blocking cracks, filling volumes with a very small opening for injection, and plugging porous walls to retain the gels in place in a porous medium With non-foamed suspension lae, which have a amazing penetration capacity even in a permeable medium, in certain cases it can be feared that they would also penetrate towards the porous geological formation if the permeability exceeded 1 Darcy, and would damage it. It is known that the foams considerably reduce the penetration towards pores due to its high point of performance In this way it could be feared that penetration into permeable cracks would also be reduced. The apparatus described in EP-A-621 247 was used to check this point. Most surprisingly, the penetration was excellent. The foam advanced the full length (23 cm) of a slot of 150 μm to exit at the other end of the slot. foam was still well expanded at the exit of the groove and thus exerted a pressure on the walls This phenomenon is extremely important to ensure an excellent seal

Claims (1)

1. - A method for cementing an oil well or the like, comprising: a) forming a cement suspension comprising: i) cement; ii) a surfactant: and iii) water; b) foam the suspension by introducing 9a: and c) * inject the suspension into the well allowing it to set; characterized in that the water content of the suspension is less than 50% by volume before foaming. 2, - A method according to claim 1, comprising forming a cement suspension having a water content of 33% to 45% by volume before foaming. 3 - A method according to claim 1 or 2, wherein the step of forming the suspension comprises providing a solid fraction constituted by a) 35% to 65% by volume of particles with an average diameter on the scale of 200 um a - 3: 600 um b) 20% to 45% by volume of Portland cement, and c) 5% to 25% by volume of particles with an average diameter on the scale from 0 5 um to 5 urn 4 - A method for cementing an oil well or the like which comprises forming a suspension comprising i) a microcement having a maximum particle size in the bone The one from 6 um to 12 um with a particle diameter equal to a few microns and a specific surface area per unit weight , determined by the air permeability test [Fineness Blame] of more than 0 6 m2 / gn) a surfactant and m) water b) frothing the suspension by introducing a gas and c) injecting the suspension into the well and allowing it to It is characterized in that the water content of the suspension before frothing is less than 72% by volume. 5. A method according to claim 4 which comprises forming a suspension having a water content before foaming. on the esca that of 58% to 70%, in volume 6.- A method according to claim 4 or 5, which comprises forming a suspension having a solid fraction from 50% to 75% by volume of microcement, 15% to 40% in volume of particles with an average diameter in the scale of 0.05 micrometers to 0.5 micrometers, and 0 to 20% in volume of particles with an average dimension in the scale 3 nanometers to 60 nanometers. 7. - A method according to any of the preceding claims, comprising introducing gas to the suspension so that the quality of foaming is in the range of 30% to 65%. 8. A method according to any of the preceding claims, comprising including in the suspension one or more additives of the following types: a dispersing agent, an antifreezing agent, a water retainer, an accelerator or setting retarder of cement, or a defoaming stabilizer.