Process for consolidating geological formations

This process comprises injecting into the formations a liquid organic mixture containing at least one polymerizable chemical compound and a catalyst. The organic mixture reacts with a limited amount of a injected oxidizing gas to give a solid product which consolidates the formations without substantially reducing their permeability. The catalyst is characterized by the combination of lead and of at least an element of the group constituted by nickel, copper and zinc.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for consolidating geological 
formations, this process being in particular applicable to oil and gas 
reservoirs, to prevent sand from flowing into a well traversing 
unconsolidated, or insufficiently consolidated, sand formations. 
More generally, this process can be used to locally consolidate permeable 
formations. 
Various methods have been proposed to prevent sand from flowing into new 
boreholes, or to treat wells liable to be subjected to sand flowing during 
exploitation of oil or gas deposits. 
A first type of method consists of maintaining the sand by mechanical 
means, using artificial screens with calibrated apertures or packs of 
gravels having a well-defined size distribution, depending on the size of 
the sand particles or grains of the geological formation traversed by the 
borehole. Such a method is very often applied to new wells, but is 
difficult to put into operation. 
A second type of method consists of injecting into the geological formation 
a liquid resin which by polymerization creates a bound between the sand 
grains. 
The efficiency of a chemical method of this second type is uncertain, since 
the reaction of polymerization of the injected resin depends essentially 
on the conditions prevailing in the borehole at the level of the 
formation, and on the characteristics of the latter. Thus such a method 
does not permit control of the extent of the chemical reaction. 
There is thus the risk either of an insufficient consolidation of the 
formation if the degree of polymerization of the resin is not sufficient, 
or of an excessive reduction of the permeability of the geological 
formation, or even of complete plugging thereof, if a too large an amount 
of polymer is retained in some of the pores of the formation. 
Another method, which is described in British Pat. No. 975,229, consists of 
successively introducing into the formation a material consisting 
essentially of an unsaturated fatty acid, then an oxygenated gas, with a 
view toward obtaining a resinification of said material. 
However, a proper consolidation is obtained by this method only if the 
formation to be consolidated is at a temperature comprising between 
150.degree. and 300.degree. C., or is heated to such a temperature which 
is much higher than the normal temperatures of oil or gas reservoirs. 
It has been contemplated in this prior art patent to add a catalyst made of 
cobalt naphthenate or manganese naphthenate. 
Even in this last case, the so-obtained consolidation is satisfactory only 
if the temperature of the formations is sufficiently high. 
U.S. Pat. No. 3,388,743 also discloses a consolidation method wherein 
injection of a drying oil into formations surrounding a borehole is 
followed by the injection of an oxidizing gas. 
The partially oxidized oil constitutes a good binding material for the sand 
particles. 
By using an oxidizing catalyst, such as lead or cobalt naphthenate, it is 
possible to shorten the time required for oxidizing the oil. 
However, the consolidation obtained by application of this method is 
generally insufficient for the object at which it is aimed. 
French Pat. No. 1,409,599 teaches a process for consolidating the grounds 
wherein these grounds are treated by oily polymers containing siccative or 
drying catalysts which are hardened by air drying on the surface of the 
ground to be consolidated. 
This treatement which produces hard, impermeable ground masses is however, 
not suitable for consolidating subterranean formations whose permeability 
must be preserved. 
SUMMARY OF THE INVENTION 
The object of the present invention is accordingly to provide a simple and 
reliable process for consolidating a geological formation without 
substantially reducing its permeability, this process being applicable to 
ground formations whose characteristics may vary within a rather wide 
range. 
This method is particularly suitable for treating oil or gas wells were 
sand flowing is liable to occur. 
This result is obtained, according to the invention by controlling the 
chemical alteration of a polymerizable material. 
This process comprises injecting into the formation a liquid mixture of 
organic products of which is achieved in situ a moderate chemical 
alteration by contacting this liquid mixture with a determined quantity of 
an oxidizing gas, so as to transform said liquid mixture by an exothermic 
reaction into a substance which binds the unconsolidated elements of the 
formation, the injection of oxidizing gas permitting avoidance of any 
substantial reduction in the permeability of this formation relative to 
oil or natural gas. 
The composition of the liquid mixture, as well as the oxygen content and 
the quantity of oxidizing gas are adjusted so as to enable the reaction to 
start at the normal temperature of the formation, and so as to control the 
extent of the oxidizing reaction of polymerization of the liquid mixture. 
More particularly the invention provides a method for consolidating a 
geological formation comprising the following two successive steps: 
a-Injecting into the formation a liquid organic mixture containing at least 
one polymerizable chemical compound and a catalyst, this mixture being 
capable of being subjected in situ, at the contact of an oxidizing gas, to 
chemical reactions, starting at the normal temperature of the geological 
formation and producing a solid product which consolidates the formation 
without substantially reducing its permeability, and 
b-Injecting a sufficient quantity of an oxidizing gas to achieve 
substantially complete solidification of said organic liquid, this 
quantity being however, so limited that the temperature reached in the 
formation during said reactions does not exceed 350.degree. C. and is 
preferably comprised between 150.degree. C. and 250.degree. C. 
The process according to the invention is characterized in that said liquid 
organic mixture contains a catalyst comprising in combination lead and at 
least one element of the group formed by nickel, copper and zinc. 
The process according to the invention is efficient even if the temperature 
of the formation (which is in particular dependent on its depth) is low, 
since the reaction of oxidation of the organic material causes a 
sufficient heat release in the treated zone so as to reach the thermal 
level enabling the organic mixture to be efficiently polymerized, and 
providing a proper cohesion between the grains of the geolical formation. 
Moreover, the oxygen content of the injected oxidizing gas and the amount 
of oxygen introduced into the formation are controlled so as to not exceed 
the maximum temperature which would lead to degradation of the polymerized 
material. 
The organic mixture used in the process according to the invention may be 
advantageously constituted by a drying oil, optionally diluted by an 
organic solvent, a catalyst as above defined being added to this oil. 
The utilized drying oil will advantageously be linseed oil, tung oil (wood 
oil), safflower oil, or more generally vegetable oils having a high 
content of polyethylenic compounds. 
The employed solvents will be constituted, for example, by hydrocarbons 
such as benzene, toluene, xylene, or by a petroleum cut; the solvent 
content will advantageously comprise between 0 and 50% to limit the 
reactivity decrease resulting from dilution. 
The components of the catalyst will be used in the form of salts, such as 
carboxylates, naphthenates, sulfonates, octoates etc., soluble in the 
basic components of the organic mixture. The content of each of the metals 
used in the catalyst in the solution will be smaller than 3 percent by 
weight, preferably comprised between 0.007 and 2 percent by weight. The 
exact composition of the catalyst (selected metals and respective contents 
thereof) will depend on the nature of the surrounding medium and on the 
conditions prevailing in the deposit (pressure, temperature, etc.). 
The amount of the injected organic mixture will be preferably smaller than 
500 liters per meter of thickness of the geological formations, however, 
larger quantities will not decreasee the efficiency of the method 
according to the invention. 
In the application of the method to oil reservoirs, the injected oxidizing 
gas will be preferably oxygen or air, optionally diluted with nitrogen, 
carbon dioxide or another gas which is chemically inert under the 
operating conditions. In the application of the method to gas reservoirs, 
the use oxidizing gaseous mixture will preferably be oxygen or air diluted 
by nitrogen, another inert gas or dry natural gas; however, the content of 
natural gas must be such that the gaseous mixture remains outside the 
limits of its explosive range during the test conditions. 
The volumetric oxygen content of the gaseous mixture will be advantageously 
comprised between 0.5 and 100%, and preferably between 1 and 21%. The 
oxygen content for a given composition of the organic mixture will 
preferably be reduced as the injection pressure increases. The presence of 
water in the gaseous mixture will be avoided by a suitable drying 
treatment, if necessary. 
Proportioning of the oxidizing mixture will be effected at the ground 
surface, the components of the mixture being either supplied from 
compressed gas, or cryogenic gas bottles, or delivered by compressors. 
The oxygen volume in the injected gas, measured under standard temperature 
and pressure conditions, will preferably be smaller than 200 liters per 
liter of injected organic mixture; excellent results are obtained by using 
between 10 and 80 liters oxygen per liter of organic mixture.

DETAILED DESCRIPTION OF THE INVENTION 
In the enclosed FIG. 1, which diagrammatically illustrates an embodiment of 
the process according to the invention, reference 1 designates a sandy 
geological formation traversed by a well 2, which comprises a casing 3 
provided with apertures 4 at the level of the formation 1 from which a 
fluid, such as oil or natural gas, must be extracted. 
In this embodiment the process according to the invention is carried out by 
successively injecting into the treated formation 1, predetermined 
quantities of an organic material 5 such as a drying oil to which a 
catalyst (as above-defined) has been added, optionally in admixture with 
another organic liquid, such as a solvent or a petroleum cut, and an 
oxidizing gas 6 such as air or oxygen diluted as above indicated. 
The organic liquid mixture and the gas may be injected one after the other 
through the same production tubing 7, which opens at its lower end 
substantially at the lower level of the apertures 4. 
Packer means 9 provides for sealing of the annular space between the casing 
3 and the production tubing 7, above the formation 1. 
In the tubing 7 the oxidizing gas is separated from the organic mixture 
through a plug 8 of a material which is little or not oxidable, this plug 
being, for example, constituted by a small volume of solvent or of a 
petroleum cut in an oil well, or of natural gas in a gas well. 
It is thus possible to prevent reactions of the organic mixture from 
occurring in the production tubing itself. 
Obviously the above-described embodiment is by no way limitative and other 
embodiments may be contemplated. 
Generally speaking, the liquid injected at 5 is an organic mixture which at 
the contact of an oxidizing gas is capable of participating in a chemical 
alteration starting at the temperature of the formation 1 which leads to a 
consolidation of the formation in the vicinity of the well. 
The liquid 5 is more easily alterable by the oxidizing mixture than the 
hydrocarbons contained in the formation, and than the basic organic 
compounds which do not contain any catalyst, thus resulting in the 
consolidation of the formation. 
In the case of oil deposits, it will be advantageous before injecting the 
liquid 5 to inject fluids such a xylene, or a petroleum cut and an 
alcohol, such as isopropanol, in order to drive away oil and water present 
in the vicinity of the well, since excessive quantities of such oil and 
water may be detrimental to the efficiency of the consolidation of the 
medium. 
The quantity of injected oxidizing gas will be determined so as to obtain 
complete solidification of the organic liquid 5, while preventing the 
temperature reached in the formation from exceeding 350.degree. C., as a 
result of the evolved heat. Burning of the organic liquid 5 is avoided 
thereby, thus preventing any degradation of the polymerization product and 
providing for the protection of the well equipment, particularly of the 
casing 3. 
The efficiency of the process according to the invention is illustrated by 
the following tests, the characteristics of the operating mode during 
these tests being by no way limitative. 
TEST NO. 1 
An intimate mixture of quarry sand (grain size comprised between 150 and 
300 microns), and of linseed oil is packed at ambient temperature in a 
vertical tube having a thin wall, 20 cm in diameter and 15 cm in height. 
Heating collars are positioned around the tube over the height occupied by 
the mixture, so as to control lateral heat losses. In the case of a 
temperature increase, the electric power delivered to the collars adjusted 
so that the temperature measured within the mixture does not differ by 
more than 10.degree. C. from the temperature measured at the same level 
against the wall of the tube. 
The solid mass obtained by packing a mixture of 7.2 Kg sand and 0.63 Kg 
linseed oil has a porosity of 38% and a degree of saturation with linseed 
oil equal to about 40% of the pore volume. Its initial temperature is 
20.degree. C. 
An air flow rate of 1.55 liter/minute is injected under atmospheric 
pressure through the upper end of the tube during 7 hours. 
No decrease in the oxygen content of the gaseous effluent and no 
temperature increase of the impregnated porous medium could be 
ascertained. 
At the end of the test, it appeared that solid mass remained 
unconsolidated. 
It is thus apparent that under the selected operating conditions no 
reaction occurs in the solid mass impregnated with linseed oil without 
catalyst. 
TEST NO. 2. 
An intimate mixture of a mineral support and of a liquid organic mixture is 
packed at ambient temperature in a vertical thin walled tube 12.5 cm in 
diameter which constitutes the inner housing of a high pressure 
cylindrical cell. The inner tube is provided with heating collars and with 
a thermal insulating coating to compensate for temperature losses during 
the thermal increase of the solid mass. 
The utilized organic mixture is linseed oil with the addition of 1.68% 
weight of lead in the form of naphthenate, and the mineral support is 
quarry sand with the addition of 5% kaolinite. The test is effected under 
a relative pressure of 10 bars with an air flow rate of 3 liters/minute 
(measured under standard temperature and pressure conditions). 
During the test which lasted 6 hours the temperature rised from 20.degree. 
C. to a maximum value of 48.degree. C., and the low extent of the reaction 
did not permit consolidation of the solid mass. 
TEST NO. 3 
A test was performed under operating conditions identical to those of the 
test No. 2, but using as the organic mixture linseed oil with the addition 
of 0.3% weight of nickel octoate. 
Neither a temperature rise nor a consolidation of the medium could be 
ascertained. 
TEST NO. 4 
Negative results were also obtained when operating under conditions similar 
to those of TEST NO. 2 but with an air flow rate of 1.5 liter/minute 
(measured under standard conditions) and using as an organic mixture 
linseed oil with the addition of 0.06 weight % of copper naphthenate. 
TEST NO. 5 
A test similar to the TEST NO. 2 was effected using this time linseed oil 
with the addition of 1.68 weight % lead in the form of naphthenate and 0.3 
weight % Nickel in the form of octoate. 
The test was performed under a relative pressure of 10 bars with an air 
flow rate of 3 liters/minute (standard temperature and pressure 
conditions). 
The reaction caused a temperature rise up to 195.degree. C. 
After the test it was ascertained that the medium had kept its permeability 
and was properly consolidated: its resistance to compression was 90 bars. 
Thus the utilized catalyst gives excellent results in the consolidation of 
the solid medium. 
TEST NO. 6 
A test similar to the TEST NO. 2 was effected using this time as an organic 
mixture linseed oil with the addition of 1.68 weight % lead and 0.12 
weight % copper, both in the form of naphthenate. 
The test was performed under a relative pressure of 10 bars with an air 
flow rate of 3 liters/minute (measured under standard conditions) during 7 
hours 40 minutes. The reaction caused a temperature rise from 20.degree. 
to 260.degree. C. 
At the end of the test it was ascertained that the medium has kept its 
permeability and was perfectly consolidated. Its resistance to compression 
was 92 bars. 
TEST NO. 7 
A test was performed under operating conditions similar to those of test 
No. 2, but using this time as an organic mixture linseed oil with the 
addition of 1.68 weight % of lead and 0.2 weight % of zinc. In the course 
of the test which lasted 7 hours, it a temperature rise from 20.degree. to 
240.degree. C. was observed in the solid mass. 
After the test it appeared that the medium has kept its permeability and 
was perfectly consolidated. Its resistance to compression was 74 bars.