FR2689562A1 - Plugging well filled with fluid - by injecting soln. off polymerisation material with adjustment of bulk wt., viscosity and solidification rate of soln. - Google Patents

Abstract

In placing a plug in a well (1) filled with a fluid (3) by pumping a soln. (10) through pipes (4) in the well, where the soln. contains a polymerisable substance and a Lewis acid catalyst, and is adapted to form a solid plug by polymerisation at the temp. and pressure at the lower end of the pipes (4), the physio chemical properties of the soln., esp. the bulk wt. and the viscosity, are adjusted so that the vol. injected remains in place in the fluid, close to the injection level (2) and that dilution and/or solubilisation between the soln. and the well fluid is low. and the proportions of the components of the soln. are controlled to give a delay before the start of solidification at least equal to the time of positioning in the well. The polymerisable material is pref. an aq. mixt. of melamine-HCHO resin and the viscosity is controlled to be at least equal to that of the fluid by addn. of a polysaccharide viscosifier, e.g. xanthane or scleroglucane, the bulk vol. is brought to about equal to that of the fluid by addn. of an inert filler, e.g. fly ash, and the delay in solidification is controlled by varying the amt. of catalyst, comprising NH4Cl, p-toluene sulphonic acid, tartaric acid, formic acid and/or oxalic acid. The plug obtd. after polymerisation pref. has a mechanical resistance to compression of 5-15 MPa. The fluid (3) is pref. sea water. A liq. in which the polymerisable substance is not soluble, e.g. a mixt. of organic fluids with bulk wt. close to that of the fluid, is injected before the soln. A cement slag may be injected above the (partly) polymerised plug of soln. USE - For plugging of very permeable geological formations which may be crossed by a well, with the soln. penetrating into the permeable zones. The plug can be destroyed by drilling, while preserving the plugging of the well walls at the level of the formations.

Description

 The present invention relates primarily to a method for placing in a well, a plug of solid material. The solid material constituting the plug results from the polymerization of a solution injected into the well at the level where it is desired to put in place a plug of solid material.

 In the field of well drilling, it is common to wish to set up solid plugs for the permanent or temporary abandonment of drilled wells. These plugs must isolate, including aquifers, other geological formations or the surface, fluids that can come from the underlying formations drilled.

 Well plugs can also be used as a base for deviated drilling operations called side track.

 Such plugs are placed in the wells to consolidate the walls of a borehole or to partially or completely plug the permeable walls causing leaks or losses in the formation of the fluids contained in the well.

 The industrial technique consists in injecting slags based on cement, the solid plugs being obtained after the reaction of setting the cement in the well.

Many parameters complicate and sometimes call into question the feasibility of setting up cement plugs:
- poorly controlled effects of the geological environment of cement slag,
- influence of pressure, temperature,
- the density of the slag, too high compared to that of water gives a tendency to slag down to the bottom of the well and to flee in the formation,
dilution of the slag by the fluid filling the well, etc.

 The technical solutions to overcome these disadvantages, for the most part, have a negative effect on the mechanical strength of the plug material.

 Of course, the problems mentioned above are exacerbated when the well is open, that is to say not unconscious by tubes cemented to the ground.

 Patent US Pat. No. 3,447,608 discloses a technique for placing a cement plug including the preliminary placement of a temporary plug of sufficient consistency to support a plug of cement slurry until it is set. There is no use of polymerizable substance and catalyst.

Also known by the application FR-90/07916 and the patent
US-5005648, the use of in situ polymerizable resin for consolidating or sealing permeable geological formations in which said resin is injected. In contrast to the present invention, the polymerizable resin solution is adapted to be easily moved to penetrate the formation to be treated. These types of solutions can not be suitable for the installation of well plugs.

 The present invention relates to a method of setting up a closure cap of a well filled with a fluid and into which a volume of a solution is injected, by pumping through tubulars lowered into the well, said solution comprises a polymerizable substance and at least one catalyst of Lewis acid character, said solution being adapted to turn into a plug of solid material, by a polymerization reaction steffectuant substantially at the temperature and pressure prevailing at said level of the lower end of said tubulars.

 In this process, the physicochemical characteristics of said solution, in particular the density and the viscosity, are adapted so that the injected volume remains substantially in place in said fluid, close to the injection level, and for dilution and / or or the solubilization between said solution and said well fluid are low, and the proportions of the various components of said solution are adjusted to obtain a delay before the onset of solidification at least equal to the duration of introduction into the well.

 The polymerizable substance may be an aqueous mixture of melamine-formaldehyde resin. The viscosity of said solution may be adjusted so that it is greater than, or at least equal to, that of said fluid by adding viscosifiers of the polysaccharide type, for example xanthan or scleroglucan.

 According to the invention, it is possible to adjust the density of said solution with respect to the density of said fluid, by adding an inert filler, for example fly ash, the density of the solution possibly being substantially equal to that of the fluid. .

 It is also possible to adjust the delay before the onset of solidification of said solution by varying in particular the proportion of catalyst selected from the group consisting of ammonium chloride, ptoluene sulphonic acid, tartaric acid, formic acid, oxalic acid and mixtures thereof.

 The injected solution can be adapted in order to obtain, after polymerization, a closure plug made of solid material having a compressive strength of between 5 and 15 MPa.

 In this process, said fluid can be seawater.

 A volume of liquid in which the polymerizable substance is not soluble, for example a mixture of organic fluids having a density close to that of the fluid, can be injected beforehand into said solution.

 It is also possible to inject a cement slurry into the well, above the partially or completely polymerized solution plug.

 The invention also relates to a solution intended to be injected into a well filled with a fluid, comprising a polymerizable substance and at least one Lewis-acid catalyst, said solution being adapted to form a plug in the well by transforming into a - A solid material, by a polymerization reaction taking place substantially at the temperature and at the pressure prevailing at the injection zone in said well. The solution comprises an inert filler, preferably fly ash, adapted to give said solution a density substantially equal to that of said fluid and the catalyst content is adapted so that the solidification starts after the introduction of said solution in the well.

 The solution may comprise viscosifiers, preferably polysaccharides, for example xanthan or scleroglucan, adapted to give a viscosity of said solution substantially greater than that of said fluid.

 The polymerizable substance of the solution may be an aqueous solution of melamine-formaldehyde resin and the catalyst may be selected from the group consisting of ammonium chloride, ptoluene sulfonic acid, tartaric acid, formic acid oxalic acid and mixtures thereof.

 The solid material resulting from the polymerization of said solution may have a compressive strength of between 5 and 15 MPa.

 The method or the solution according to the invention will be applied to the clogging of geological formations of high permeabilities that may be traversed by a well. In this application, the solution penetrates substantially into areas of high permeabilities.

 The plug of polymerized solid material can then be destroyed by drilling in the well while maintaining the clogging of the walls of the well at the level of said formations.

The invention will be better understood and its advantages will appear more clearly on reading the examples which follow, which are in no way limiting, and in particular illustrated by the appended figures, among which:
FIG. 1 schematically represents a well in which a stopper is placed,
FIG. 2 shows a variant of the invention,
FIGS. 3A and 3B show an application of the invention to the consolidation and clogging of the walls of a well.

 Figure I shows a well 1 filled with fluid 3 to level 8.

 The fluid 3 is most often the fluid used for drilling if the drilling operation of the well is in progress. The worst case for the plugging operation in the well is when the fluid 3 is forming water or sea water whose density is close to 1.025. Indeed, the static level 8 of the liquid 3 represents the hydrostatic pressure prevailing in the pores of the formation containing salt water. If a certain volume of fluid 3 is replaced by the same volume of fluid of greater density, there is then hydrostatic imbalance in the well. The new equilibrium will be obtained by lowering the level 8, until the new hydrostatic column, including the initial fluid and the heavier fluid of the plug, provides a hydrostatic pressure identical to the origin. There is therefore necessarily injection penetration of a certain volume of liquid 3 in the most permeable formation.

 The higher density fluid volume will thus be displaced in the well relative to its injection level.

 There is therefore a great difficulty in setting up precisely a cement plug or the like whose density is often significantly greater than the fluid present in a well.

 In addition, the pressure drops induced during the circulation of the various fluids come to accelerate the pressure imbalance.

 Most often, injection into such a formation can destabilize the most fragile formation and increase its permeability. The volume of fluid injected into the well can be fully absorbed by the formation. There will be no plug in the well.

 In Figure 1, there is shown by reference 2 the area in front of which it is desired the presence of a solid plug to have either a resistant base or a seal to isolate the upper part of the well of the part lower than zone 2.

 Tubulars 4 are lowered into the well, at zone 2, preferably according to the rules of the art substantially at the lower level of zone 2. The end surface of the tubes is connected by an injection head and a nozzle. injection line to a pumping means 6. The volume of liquid solution for making the cork is prepared in the tray 7.

 This solution 10 is injected at the zone 2 by the internal channel 9 of the tubes 4. The direction of displacement of the solution in the well 1 is represented by the arrows 11.

 The volume of solution is calculated taking into account the diameter of the well at the level of the zone 2 and the height thereof. The pumping means 6 pushes this volume through another fluid, generally the same as that present in the well. However, it is possible to use another fluid or a separator plug between the solution and the pusher fluid.

 To avoid the imbalance problem described above, the density of the fluid 10 is adjusted to that of the fluid 3 by adding lightening or weighting products as the case may be. The solution plug 10 thus put in place in front of the zone 2 does not undergo displacement by gravity or drive.

 Of course, the present invention is particularly suitable when the fluid 3 is seawater.

By way of example, a formulation of a solution adapted to constitute a plug in a well filled with seawater of density 1.025 is given below:
* 100 parts hydrosoluble thermosetting resin melamineformol Madurit MW 815 manufactured by HOECHST, density about 1.2,
* 50 parts of fly ash of density about 0.7,
35 parts of aqueous catalyst solution, 20% solid catalyst, density about 1.

 The solution obtained has about the following characteristics: a density of 1.025, a pumpability time of 4 hours, hardening in 20 hours and a mechanical strength between 10 and 15 MPa.

 The presence of seawater does not interfere with the setting that is done at ordinary temperature. The setting time can be adjusted by varying the level of catalyst.

 A difficulty in using water-soluble resin lies in the possible dilution between the seawater filling the well and the solution. The dilution ratio changes the setting time and the mechanical strength of the material once polymerized.

 The present invention solves this difficulty by showing the possibility of strongly viscosifying the solution with respect to the viscosity of the water. Indeed, the viscosity of the solution comprising the polymerizable substance has the effect of limiting the mixture between the fluid present in the well and the injected solution volume.

The following laboratory tests focused on the viscosity of the melamine-formaldehyde resin in the presence of polymers:
- Products used:
* Madurit MW 815 resin,
* Polymers: Xanthane (Rhodopol 23 manufactured by Rhône
Poulenc) and Scleroglucane (CS 1 1 manufactured by SANOFI),
* Solvent: distilled water with or without 20 g / liter of sodium chloride.

- Experimental conditions:
The products are mixed in the weight ratio of 100 g of resin and 35 g of water. Polymer solutions in the presence or absence of 20 g / l of NaCl are prepared at the study concentration before addition to the resin. The polymers, in powder form, are used as such without any other preparation. The polymer concentrations are expressed in grams of product per kilogram of total mixture.

The viscosity, expressed in centipoise, is evaluated from a conventional viscometer (Low Shear Contraves) and measured at 30 ° C. at a shear rate of 0.15 sl.The results are given in the table below.
COMPOSITION OF THE MIXTURE

<tb><SEP> PRODUCTS <SEP> Concent. <SEP> Water + NaCl <SEP> Water <SEP> pure <SEP> Resin <SEP> Visco
<tb><SEP> in <SEP> polym. <SEP> (20 <SEP> g / l) <SEP> sity
<tb><SEP> (g / kg) <SEP> (g) <SEP> ~ <SEP><SEP> (g) <SEP> (g) <SEP> (cp)
<tb> Resin <SEP> 0 <SEP> 0 <SEP> 2.6 <SEP> 7.4 <SEP> 25
<tb> Sckeroglucan <SEP> 0.3 <SEP> - <SEP> 10 <SEP> 0 <SEP> 8
<tb><SEP> 0.3 <SEP> - <SEP><SEP> 2.6 <SEP> 7.4 <SEP> 46
<tb><SEP> 1.1 <SEP> 2.6 <SEP> - <SEP> 7.4 <SEP> 170
<tb><SEP> 2.5 <SEP> 2.6 <SEP> - <SEP> 7.4 <SEQ> 870
<tb> Xanthan <SEP> 0.3 <SEP> - <SEP> 10 <SEP> 0 <SEP> 25
<tb><SEP> 0.3 <SEP> 10 <SEP> - <SEP> 0 <SEP> 7
<tb><SEP> 0.3 <SEP> - <SEP> 2.6 <SEP> 7.4 <SEP> 194
<tb><SEP> 0.3 <SEP> 2.6 <SEP> - <SEP> 7.4 <SEP> 31
<tb><SEP> 1.3 <SEP> 2.6 <SEP> - <SEP> 7.4 <SEP> 35
<tb><SEP> 2.2 <SEP> 2.6 <SEP> - <SEP> 7.4 <SEP> 370
<Tb>
These results call for the following comments:
The resin is significantly viscosified as soon as polymer is added, even at low concentrations.

 Xanthan is less viscosifying in the presence of salt.

 The viscosifying power of scleroglucan is not affected by the presence of salt.

 It should be noted that the viscosity measurements of the various mixtures were made just after mixing the various constituents.

 It has been possible to note a significant change in the viscosity of the resin over time, in the direction of increase. This can be explained by a slow solubilization of the polymer in the resin and / or a beginning of crosslinking of the resin.

 In the context of this invention, it will be possible to limit the dilution or the solubilization of the solution 10 in the fluid 3, by replacing the fluid 3 at the zone 2 by a fluid of the same density, but in which the resin is insoluble. This may be, for example, an organic mixture of oil and trichloroethane.

 Figure 2 illustrates a variant of the invention, particularly advantageous in the case where it is mandatory to have a high cap. Indeed, the volume of polymerizable solution is important when applying the method according to Figure 1. The cost of the resin is relatively high compared to cement. It is therefore advantageous to set up a first plug 10 according to the invention, of a height and a sufficient strength to serve as a seat for the main plug 12, which is conventional in its composition, that is to say The cement plug 12 may have a high mechanical strength because, thus being freed from the problems of falling down a cement slurry of high density relative to the fluid contained in the well, the composition of the cement this slag is optimized to obtain a determined mechanical strength.

 The introduction of the second plug 12 is made after sufficient solidification of the first cap 10 polymerizable material to serve as support.

 FIGS. 3A and 3B illustrate an application concerning the clogging of a zone 13 having unstable walls when a well passes through it. Zone 13 can also be a formation with significant losses. The introduction of a plug 10 according to the invention makes it possible firstly to consolidate the walls and / or to seal the zone 13. The viscosity of the solution 10 will be such as to limit the introduction of the solution into the formation and its complete disappearance of the zone considered. When the resin is solidified, the central portion of the plug can be removed by drilling.

 FIG. 3B shows the process of reforging the plug using a tool 14 fixed to a drill string 16.

 After this operation, only a sheath 15 of solid products will remain, consolidating and / or clogging the walls of the well. Drilling or exploitation operations may resume without being threatened by the presence of the critical zone 13.

 It will not be departing from the scope of this invention if the process and the liquid solution use other thermosetting resins, other viscosifiers or other products that are lighter than those mentioned in the examples, insofar as these are used for the same purposes and have equivalent functions.

Claims (14)

 1) A method for placing a closure cap of a well (1) filled with a fluid (3) and into which a volume of a solution (10) is injected, by pumping through tubulars (4) descended into the well, said solution comprises a polymerizable substance and at least one Lewis-acid catalyst, said solution being adapted to turn into a plug of solid material, by a polymerization reaction taking place substantially at the temperature and the pressure at said level of the lower end of said tubular (4), characterized in that ::  the physicochemical characteristics of said solution, in particular the density and the viscosity, are adapted so that the injected volume remains substantially in place in said fluid, close to the injection level (2), and for the dilution and / or the solubilization between said solution and said well fluid (3) is weak,  the proportions of the various components of said solution are adjusted to obtain a delay before the onset of solidification at least equal to the duration of placement in the well.  2) Process according to claim 1, characterized in that the polymerizable substance is an aqueous mixture of melamineformaldehyde resin and in that the viscosity of said solution is adjusted so that it is greater, or at least equal to that of said fluid, by adding viscosifiers of the polysaccharide type, for example xanthan or scleroglucan.  3) Method according to one of the preceding claims, characterized in that the density of said solution is adjusted relative to the density of said fluid, by adding an inert filler, for example fly ash, the density of the solution being preferably substantially equal to that of the fluid.  4) Method according to one of the preceding claims, characterized in that the time before the onset of solidification of said solution is adjusted by varying in particular the proportion of catalyst selected from the group consisting of ammonium chloride, the ptoluene sulfonic acid, tartaric acid, formic acid, oxalic acid and mixtures thereof.  5) Method according to one of the preceding claims, characterized in that the injected solution is adapted to obtain, after polymerization, a closure plug of solid material having a compressive strength between 5 and 15 MPa.  6) Method according to one of the preceding claims, characterized in that said fluid (3) is seawater.  7) Method according to one of the preceding claims, characterized in that before injecting said solution, a volume of liquid in which the polymerizable substance is not soluble, for example a mixture of organic fluids having a density close to from that of the fluid.  8) Method according to one of the preceding claims, characterized in that injected into the well a cement slurry (12) above the solution cap (10) partially or completely polymerized.  9) Solution (10) intended to be injected into a well (1) filled with a fluid (3), comprising a polymerizable substance and at least one acid Lewis catalyst, said solution being adapted to form a plug in the well by transforming into a solid material, by a polymerization reaction taking place substantially at the temperature and pressure prevailing at the injection zone (2, 13) in said well, characterized in that it comprises an inert filler, preferably fly ash, adapted to give said solution a density substantially equal to that of said fluid and in that the catalyst content is adapted so that the solidification starts after the introduction of said solution in the well.  10) Solution according to claim 9, characterized in that it comprises viscosifiers, preferably polysaccharides, for example xanthan or scleroglucan, adapted to give a viscosity of said solution substantially greater than that of said fluid (3).  11) Solution according to one of claims 9 or 10, characterized in that the polymerizable substance is an aqueous solution of melamine-formaldehyde resin and in that the catalyst is selected from the group formed by ammonium chloride, the p-toluene sulfonic acid, tartaric acid, formic acid, oxalic acid and mixtures thereof.  12) Solution according to one of claims 9 to 11, characterized in that the solid material resulting from the polymerization of said solution has a compressive strength between 5 and 15 MPa.  13) Application of the process according to one of claims 1 to 8 or the solution according to one of claims 9 to 12 for sealing the geological formations (13) of high permeability that can be traversed by a well, characterized in that said solution (10) penetrates substantially into areas of high permeabilities.  14) Application according to claim 13, characterized in that the plug of polymerized solid material is destroyed by drilling in the well while maintaining the clogging of the walls of the well at the level of said formations (13).