Earth boring – well treating – and oil field chemistry – Earth boring – Contains organic component
Reexamination Certificate
1999-05-14
2002-02-19
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains organic component
C507S104000
Reexamination Certificate
active
06348436
ABSTRACT:
The present invention relates to fluids used in the presence of water, which are applied in the field of petroleum extraction, either for the operations for installing wells, with the drilling operations, the so-called “work-over” operations and the completion operations, or for the actual exploitation of the petroleum deposit.
Drilling operations consist in drilling a hole using a tungsten carbide drill bit in particular, fixed to hollow drillpipes screwed end-to-end. Usually, mud comprising additives in aqueous solution is injected into the drillpipe string. This mud then rises via the probe hole, outside the drillpipes, and entrains components of rocks detached during the drilling operation. At the same time, the rock-laden mud establishes a counterpressure which consolidates the hole. The mud is then extracted from the drilling hole in order to be freed of the rocks it contains, before being reinjected into the hollow drillpipes.
Under such working conditions, it is essential that the additives added to the mud give it specific rheological behaviour. The reason for this is that when it is subjected to very high shear stresses and high temperatures, as is the case on the drill bit, the fluid must be of sufficiently low viscosity to facilitate its evacuation out of the hollow drillpipes. On the other hand, this same fluid, laden with rocks, must have a viscosity which is high enough to keep in suspension the cuttings entrained during the drilling.
The use of high molecular weight polysaccharides, for example such as xanthan gum, as an additive for drilling muds or fluids in order to give the said fluid the specific type of rheological behaviour described above, which is referred to as shear-thinning behaviour, is well known.
However, although xanthan gum has undeniable advantages in this type of application, it nevertheless remains limited since the rheological properties of the drilling fluid degrade over time, and this occurs all the more quickly when the temperature to which it is subjected is in the region of or exceeds 120° C. Now, in petroleum drilling operations, it is quite common for such temperatures to be reached. Firstly, there is considerable heating of the mud caused by the movement of the drill bit. Furthermore, the depth of the deposit and its geographical location (hot well) also have consequences on the temperature to which the fluid is subjected. Thus, temperatures of this order of magnitude can be reached without difficulty at the bottom of the well since the depth reached during the drilling operations is in the region of a kilometre or more. In addition, there are wells in which the temperature of the earth's crust is already at a higher level than elsewhere (hot wells) which further accentuates the effect of the increase in the temperature of the subsoil as the depth increases.
In a normal cycle, the effect caused by such temperatures is not systematically detrimental, or at any rate not at the start of use of the additive, since the duration for which the fluid is at these high temperatures is limited. However, it should be appreciated that it is not rare to have to stop the drilling operations in order to replace one of the tools, for example the drill bit. Now, in such a case, the drilling fluid remains under high temperature conditions for a relatively long period.
When the fluid is subjected to high temperatures, its viscosity degrades considerably and the role of suspending the cuttings torn out during the drilling operation is no longer maintained. This may thus be one of the causes of a blockage of the well by deposition of rocks at the bottom of it.
European patent application EP 134,084 describes the use of cellulose microfibrils as an additive for a petroleum drilling fluid. However, although the heat resistance of this additive is better than that of xanthan gum, it nevertheless remains limited to 160° C. when it is used as sole viscosifying agent.
The aim of the present invention is thus to propose a drilling fluid additive which has better thermal stability than the polysaccharides employed, better thermal stability than the cellulose microfibrils discussed above, while at the same time retaining the advantages of these microfibrils.
Thus, the object of the present invention is to propose a fluid comprising a compound which can give the said fluid quite specific flow behaviour.
In addition, on account of its improved heat stability, the additive according to the invention makes it possible for the fluid to conserve these rheological properties, even at very high temperatures, i.e. at least equal to 180° C., or even up to 200° C.
Moreover, the additive according to the invention is stable in aqueous media comprising salts or additives of any other type commonly used in this type of application for controlling or adapting the fluid characteristics, such as oxygen scavengers, filtrate reducing agents, rheology modifiers, such as fillers and soluble or insoluble weighting materials.
In addition, the additive used according to the invention has the characteristic of conserving its particular viscosifying properties over a very wide water composition range, thus making it suitable for uses in the presence of highly mineralized waters or sea waters.
The fluid according to the invention is moreover entirely suitable, on account of its stable shear-thinning properties, for uses close to the petroleum production zone, or during deviated drilling operations in which, for reasons of flow and of damage to the formation, the fluids must preferably be formulated with few or no solids.
An additional advantage of the additive according to the invention is that it is easier to filter than polysaccharides of the xanthan gum type, which reduces the risks of damaging the drilling site by avoiding the formation of a plug in the well. Moreover, this can contribute towards making it easier subsequently to process the drilling muds, i.e. to separate out the cuttings, before recycling the muds into the well.
These aims and others are achieved by the present invention, which consists of a petroleum drilling fluid comprising cellulose nanofibrils containing at least about 80% of cells with primary walls and charged with carboxylic acids and with acidic polysaccharides, alone or as a mixture.
However, other advantages and characteristics of the present invention will emerge more clearly on reading the description and the examples which follow.
Before describing the fluid according to the invention, it should be pointed out that this fluid is particularly suitable for use as a drilling fluid.
However, its rheological properties, its filterability and its compatibility with numerous components make it just as suitable for subsequent applications to the actual drilling and/or applications associated with the actual exploitation of the deposit.
Thus, by means of adapting its characteristics, in particular such as the viscosity, the fluid can be used in so-called “work-over” operations. It is similarly possible to use the fluid, again after adapting its rheological characteristics, for the assisted recovery of petroleum.
For reasons of simplicity, mention will only be made in the text hereinbelow of the application of the fluid according to the invention in drilling operations, bearing in mind that the use of such a fluid is not limited to this sole application.
As has been mentioned above, the drilling fluid according to the present invention comprises quite specific cellulose nanofibrils as additive, which, in contrast with the standard microfibrils, such as those described in particular in the abovementioned European patent application, have particularly interesting and surprising advantages.
Thus, the cellulose nanofibrils forming part of the drilling fluid composition contain at least about 80% of cells with primary walls, and are charged, at the surface, with carboxylic acids and with acidic polysaccharides, alone or as a mixture.
The term “carboxylic acids” is intended to refer to simple carboxylic acids and their salts. These acids are preferably chosen from
Benchimol Joël
Cantiani Robert
Guerin Gilles
Langlois Bruno
Senechal Alain
Rhodia Chimie
Seugnet Jean-Louis
Tucker Philip
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