WO1998028044A1

WO1998028044A1 - Method for oxidising pre-treatment of drillings contaminated by olefin based sludge

Info

Publication number: WO1998028044A1
Application number: PCT/FR1997/002354
Authority: WO
Inventors: Frédéric Perie; Alain Rabion; Christian Zurdo; Anne Basseres
Original assignee: Elf Exploration Production
Priority date: 1996-12-23
Filing date: 1997-12-18
Publication date: 1998-07-02
Also published as: FR2757408B1; FR2757408A1

Abstract

The invention concerns a method for the pre-treatment of drillings containing sludge, recuperated at ground level, particularly olefin based synthetic sludge characterised in that it comprises at least an oxidising step using an oxidising agent with an acid pH.

Description

OXIDIZING PRETREATMENT PROCESS FOR OILFINE-BASED DRILL CUTTINGS CONTAMINATED

The present invention relates to a process for the pretreatment of drill cuttings raised from the well by mud, and more particularly the large cuttings removed by sieving and which remain impregnated with mud. It relates more particularly to cuttings impregnated with sludge containing olefins.

During drilling, mud plays an essential role; it ensures the removal of the cuttings from the ground dug at the bottom of the well, their lubrication by coating, and the cooling of the drilling tool. At the outlet of the well, the fragments of mineral rock constituting these cuttings are separated from the mud by successive sieving and decantation. The mud thus sieved and decanted can be recycled in the well for a new drilling cycle.

In addition to this recycling of the mud, there is the problem of recovering and storing the cuttings. If it is already delicate on a production field, it is much more difficult to solve on an oil platform, because the constraints in terms of environmental regulation are much more strict, especially since it is economically more viable to dump them into the open sea.

In addition, this dumping of spoil at sea will depend essentially on the nature of the mud used which is more or less toxic or biodegradable. Different types of mud are used for drilling. These are, first of all, water sludges whose majority organic fraction is based on cellulose, cellulose derivatives and acrylic acid derivatives. These sludge is easily biodegradable and does not cause potential environmental degradation.

Oil sludge is economically preferred to them; they essentially consist of a stabilized reverse emulsion of water in oil, generally hydrocarbons of the diesel type, and their rheological properties are adjusted by means of viscosifying, densifying and other additives. However, they represent a very great risk of pollution because organic and toxic.

A third type of sludge, called substitution sludge, is used mainly to replace oil sludge containing aromatic molecules, but they are still considered too polluting by their organic load. They are formulated either from esters in stabilized emulsion or from mixtures of esters and olefins or polyalphaolefins, branched or linear.

If this sludge exhibits part of the performance close to oil sludge, it is nonetheless slowly and / or weakly biodegradable.

To improve the biodegradation of these muds, enzymatic treatments starting from a lipase modifying chemically the mud, were envisaged to improve the biodegradation of the muds containing esters, but such a pretreatment is ineffective for the muds containing bases olefins or polyolefins.

The aim of the present invention is therefore to accelerate the biodegradation of substitution olefin-based sludges by a specific pretreatment of the olefins and polyolefins used, a prerequisite for accelerated biodegradation. Its purpose is to chemically modify the mud in order to accelerate its subsequent bacteriological degradation.

In the context of the present invention, the term “mud” means any pure synthetic organic phase containing in particular olefins or polyalphaolefins and used as drilling mud, the formulated drilling mud, all cuttings made up of rocks impregnated with mud, and the raw sludge obtained after sieving the cuttings, still containing the rock fines.

The present invention therefore relates to a process for the pretreatment of drilling muds recovered from the soil surface containing hydrocarbons comprising at least one olefinic bond for the purpose of their biodegradation, characterized in that it comprises at least one oxidation step of said mud using an oxidizing agent at acidic pH.

By acid pH is meant a pH below 4 and preferably between 0 and 1. The treatment process according to the invention can be carried out at room temperature. However, it may be favorable to increase this temperature from 20 to over 100 ° C to increase the kinetics of the reaction. In the context of the present invention, the oxidizing agent will preferably be chosen from the group consisting of nitrates, sulfates, chlorates, perchlorates, persulfates, nitrogen oxides and peracetates. Similarly, to reach a pH of less than 4 for the oxidizing aqueous solution, the oxidizing agent is mixed with at least one strong mineral or organic acid such as hydrochloric acid, sulfuric acid, perchloric acid, l nitric acid, phosphoric acid, trichloroacetic acid. In a preferred embodiment of the invention, the oxidizing agent is the nitrate anion and the preferred acid is nitric acid. This choice is particularly favorable in that the traces of nitrogen products resulting from the oxidation by these compounds can constitute a source of nitrogen assimilable by the bacteria used during the subsequent biodegradation.

In the context of the present invention, the sludge to be treated consists of any organic phase comprising at least one olefinic bond, the rocks impregnated with this organic phase and the sludge recovered after sieving the cuttings. Generally, this sludge to be treated contains

1 to 10% by weight of hydrocarbon compounds comprising from 8 to 30 carbon atoms, preferably 12 to 20 carbon atoms, and at least one olefinic bond. The preferred oxidizing solution contains a dilute nitric acid solution with a concentration of 300 g / l or less.

After oxidation of the mud, the treatment according to the present invention comprises the following steps in the particular order given below. Thus, after oxidation, the sludge is separated (for example by centrifugation) from the aqueous oxidizing solution which can thus be recycled. The solid fraction of the mud is then neutralized by a basic compound chosen from the group consisting of lime and alkaline or alkaline-earth salts, in particular sea salts or even simply sea water. The last pretreatment operation consists to reject the oxidized mud in the sea, the oxidized organic compounds still present in the mud being biodegraded by the bacteria present in the ocean. These oxidized organic compounds are in the form of easily biodegradable carboxylic acids, ketones or alcohol.

In the case of an acid treatment, the treated sludge will only contain a limited quantity of limestone, preferably not more than 15% by weight, to avoid significant dissolution of the cuttings leading to significant gas evolution, in particular of carbon dioxide. .

A second object of the present invention is the device necessary for the implementation of the method characterized in that it comprises an oxidation capacity (1) into which are introduced respectively by two conduits (2) and (3), the sludge to be treated, the aqueous solution of oxidizing agent of pH less than 4, the said capacity comprising a third line (4) for discharging the gases formed by oxidation and a fourth line (5) for discharging the oxidizing solution / mixture oxidized sludge to a separation unit (6) comprising a line (7) for recycling the oxidizing aqueous solution to the line (3) and a line (8) directing the oxidized sludge recovered in the neutralization unit (9) supplied as a neutralizing agent by at least one line (10). In a preferred embodiment of this device, the gases formed at the time of oxidation are recovered and directed through the line (4) to a gas treatment unit (12). When the recovered gases are loaded with nitrogen oxides (NOx), this treatment consists in manufacturing, according to techniques known per se, from these gases nitric acid which is recycled in the oxidation capacity of the device for avoid evaporation of toxic gases.

Of course, this method and this device according to the invention apply to the treatment of substitution sludges containing olefinic compounds recovered at the surface, in particular those collected on the high seas.

To illustrate the process of the invention, various figures are given. Figure 1 corresponds to the diagram of a device for implementing the invention.

FIG. 2 represents a curve showing the efficiency of the process of the invention as a function of the temperature and of the concentration of the oxidizing solution. Figure 3 shows two curves showing

1 influence of the process on the rate of subsequent biodegradation, between pretreated cuttings and untreated pretreatments.

In FIG. 1, the device according to the invention comprises an oxidation capacity (1) comprising two conduits (2) and (3) respectively for the introduction of the sludge to be treated and for the aqueous solution of oxidizing agent of pH lower than 4. This oxidation capacity comprises a third line (4) for evacuating the gases formed by oxidation and a fourth line (5) for evacuating the oxidizing solution / oxidized slurry mixture to a separation unit (6) for example a centrifuge, comprising a line (7) for recycling the aqueous oxidizing solution to the line (3) and a line (8) directing the oxidized sludge recovered in the neutralization unit (9) supplied with neutralizing agent by minus one pipe (10). As neutralizing agents, lime or simply seawater can be introduced. The gases formed at the time of the oxidation are recovered and directed via the line (4) to a gas treatment unit (12) where the gases loaded with nitrogen oxides (NOx) are transformed into nitric acid in a known manner in itself, this acid being recycled via line (14) into the supply line (3) of oxidizing agent.

The examples given below are given by way of illustration of the invention, without wishing to limit the scope thereof.

EXAMPLE I:

The present example aims to illustrate the oxidation of mixtures of olefins by an acid oxidizing compound.

Two mixtures of olefins were tested. These are two base oils used for the formulation of the corresponding drilling muds:

- the isoteq, marketed by Baker Hughes which is a mixture of internal olefins (I.O.) in Cι_g (50%) and Cτ_g

(50%) containing a double bond in position C7-C8 and optionally a methyl group in position Cg.

- Ultidrill, marketed by Dowell / IDF which is a mixture of olefins called "Linear Alpha Olefine" (LAO) containing an unsaturation in the Cι_ position. Several mixtures of synthetic LAOs have been patented by Dowell (Patent WO 9506695). The base oil used in this study consists of C _] _2 olefins (1%), Cη_4 (57%) and

Cτ_g (41%), which would correspond in the Dowell patent to the fluid referenced "C ₁ 4-C ₁ g LAO".

The base oil (Ultidrill or Isoteq) is emulsified in a dichloroethane: water mixture. The reaction mixture consists of 7 ml of water, 3 ml of dichloroethane, 250 mmol / l of base oil (0.75 ml of Isoteq or 0.68 ml of Ultidrill), and 36 mg of cetyltrimethylammonium bromide (CTAB ) as a phase transfer agent. The reaction is started by adding various amounts of oxidizing agent. At the end of the reaction, the two phases are separated by decantation after extraction solid liquid using dichloromethane containing as an internal standard dodecane in a 1/1000 ratio, and analyzed by gas chromatography on a BPX column (apolar) 50m x 0.25mm ID with temperature gradient. The reactivity of these mixtures of olefins was tested for different oxidizing acid mixtures after 24 hours contact at 80 ° C. The activity of the chemical treatment is estimated by comparing the quantity of non-oxidized olefins at the end of the reaction with the quantity of olefins introduced before the oxidation. The results are given in Table I below.

TABLE I

It can be seen from Table 1 that the internal olefins contained in the Isoteq mixture and the terminal olefins contained in the Ultidrill mixture react with nitric acid (lmol / 1) at 80 ° C. This activity does not come from a simple electrophilic addition of a strong protonic acid, HZ, to the double bond, since hydrochloric acid H-Cl under the same reaction conditions does not cause any degradation. The activity observed for nitric acid can be reconstituted by an HC1 / NaN0 ₃ mixture. EXAMPLE II:

This example describes the influence of temperature and dilution of olefins on oxidation. The dilution operating conditions and the analyzes after extraction are identical to those described in Example I. The tests are carried out on the Isoteq base oil only: only the dilution rates of the oxidizing solutions change. The results obtained are given in Table II

TABLE II

The attack of olefins by dilute nitric acid needs to be activated by a high reaction temperature (80 ° C). For lower temperatures, the reaction rate decreases sharply.

EXAMPLE III

The present example aims to compare the treatment efficiency of dilute nitric acid and well-known oxidants such as oxygen peroxide (H ₂ 0 ₂ ) and sodium chlorate (NaOCl), even in the presence of catalysts. oxidation. Table III below summarizes the reaction conditions as well as the results obtained. TABLE III

^a mixture of dichloroethane / acetonitrile / water, 5: 4: 1; 250 mmol / 1 olefins, 10 mmol / 1 CTAB, T = 40 ° C or 70 ° C, 24h.

^ same conditions as, TPA = tris-N- methylpyridine-amino. ^c dichloroethane / water mixture, 10:10; 250 mmol / 1 olefins; pH = 3; T = 70 ° C; 24h.

^ same conditions as ^c , Fe (II) = Fe (S0 ₄ ) ₂ (NH4) ₂ . ^e Conditions of Example I.

It is found that these oxidants are not effective compared to dilute nitric acid.

EXAMPLE IV:

The present example aims to illustrate the oxidation of olefins trapped in drill cuttings, these cuttings having been impregnated with drilling mud and more particularly with a mud containing isoteq oil sold by Baker-Hugues.

In the present example, cuttings A are used, drilled in an argillaceous layer of mineral matrix consisting of quartz, barite, albite, pyrite, microcline and kaolinite, impregnated with 6% isoteq oil. The cut A, after having been finely ground with a pestle, is suspended in water at a rate of 35% by weight, corresponding to a rate of 2% by weight of impregnated isoteq oil. The stirring is carried out by means of a magnetic bar, then the temperature of the suspension is brought to 80 ° C. The addition of the oxidizing solution marks the start of the reaction; after addition, the stirring at 80 ° C. is maintained for two hours.

TABLE IV

The results of this table IV confirm that the olefins trapped in the cuttings are degraded by the action of dilute nitric acid (lmol / 1.6%) at 80 ° C. As in Example 1, the action of strong acids such as hydrochloric, sulfuric or perchloric acids alone is zero under the reaction conditions. The activity observed for nitric acid can be reconstituted by a mixture of HC1 / NaNO3. Note that these results are significantly better than in Example I. EXAMPLE V

The present example aims to illustrate the effect of temperature on the efficiency of treatment with nitric acid of olefins trapped in drill cuttings, in particular cuttings A impregnated with isoteq oil as described in Example IV.

TABLE V

^a Diluted nitric acid solution, doped by bubbling N0 _X nitrous vapors.

The results of this table show that the degradation of the olefins impregnated in the cuttings (suspension containing 2% by weight of olefins) is effectively carried out at room temperature for a nitric acid concentration of 3 mol / l (20%). It is therefore found that it is possible to degrade the olefins even at room temperature but with a higher concentration of nitric acid. In addition, when the 3 mol / 1 nitric acid solution is doped by bubbling nitrous vapors, the degradation of the olefins is more extensive.

If these results are compared with those of Example I concerning the degradation of the oils, the operation is carried out at a much lower temperature for almost identical reaction kinetics.

In terms of kinetics, Figure 2 shows the efficiency of the process of the invention as a function of time. Each point listed was obtained by stopping the reaction at the required time. This reaction stop is obtained by immersing the reaction mixture in ice then extraction of the residual olefins with dichloromethane and analysis by gas chromatography as described in Example I. It can be seen from this figure that the treatment with dilute nitric acid is very effective since qu 'after thirty minutes of reaction more than 80% of the starting olefins are degraded.

EXAMPLE VI:

The purpose of the present example is to compare the treatment efficiency according to the invention compared to conventional oxidizing treatments on impregnated cuttings, in particular cuttings A impregnated with isoteq oil as described in Example IV.

The operation is carried out according to the invention as described in Example IV. The results are collated in Table VI below.

TABLE VI

^a T = 70 ° C, reaction time = lh b T = 50 ° C, reaction time = lh ^c T = 50 ° C, reaction time = lh, the iron complexes tested being Fe (S0) ₂ (NH ₄ ) ₂ , TPA-Fe, iron oleate

^ conditions of Example IV.

This table shows that the two conventional oxidants, even in the presence of catalysts, do not allow to oxidize olefins impregnated in cuttings, unlike nitric acid.

EXAMPLE VII

The present example aims to describe the effectiveness of the method according to the invention for different types of drill cuttings.

In addition to the cuttings A described in Example IV, two other types of cuttings B and C were studied.

The cuttings B are drilled in a clay layer with a composition similar to that of the cuttings A but also comprising calcite.

The C cuttings are drilled in a mineral layer containing more than 80% by weight of limestone.

The results of these tests for different types of impregnation of these cuttings are given in Table VII below.

TABLE VII

a Suspension of cuttings B, impregnated with 3.5% by weight of isoteq and to which 3.5% by weight of ultidrill oil has been added relative to the quantity of cuttings b Suspension comprising 35% by weight of cuttings constituted by 50% by weight of cuttings B, impregnated with 3.5% by weight of isoteq and 50% by weight of cuttings C impregnated with 6% by weight of ultidrill oil.

The process according to the invention, with nitric acid is also effective with regard to the degradation of olefins impregnated on two cuttings from two different clay layer holes. On the other hand, on limestone cuttings, the method according to the invention is not as effective due to the rapid rise in pH. It is preferable to have the lowest possible level of lime in the mineral matrix, less than 30%.

EXAMPLE VIII

The present example aims to illustrate the effectiveness of the process according to the invention for accelerating the biodegradation operations of olefinic hydrocarbons trapped in cuttings.

Two cuttings A samples containing 6% isoteq oil were compared. The first, Al was treated by the process of the invention as described in Example 5 (Temperature 20 ° C, HN0 ₃ 3M), then neutralize with sea water. The second, A2 was not subjected no oxidation.

Several reactors with a capacity of 1.51 are filled with sediments containing an unsuitable bacterial flora (10 ⁹ bacteria / g of sediment) having a micro-aerophilic layer 1 to 2 mm thick, below which they are anaerobic. A1 and A2 are buried to a depth of 2 cm in these sediments and are kept in incubation for twenty days. In these reactors, the cuttings are therefore both in the micro-aerophilic layer and in anaerobic conditions. They undergo degradation by bacteria mainly denitrifying and sulphate-reducing, then methanogenic. Samples were taken every five days to measure the quantity of oxidized olefins. The results are given in Table VII below and the oxidative degradation curves of the cuttings A _χ and A ₂ are given in FIG. 3. TABLE VIII

The rate of biodegradation corresponding to the slope of each of the curves in FIG. 3, it clearly appears that the cuttings A ₁ having undergone the oxidative pretreatment according to the process of the invention are more easily biodegraded than the cuttings A ₂ not having been subjected to this pretreatment.

Claims

R VF.NnTCΑTTON.q

1 - Process for the pretreatment of synthetic organic drilling muds recovered from the ground surface, in particular muds containing hydrocarbons having at least one olefinic bond, characterized in that it comprises at least a first oxidation step of said mud using an oxidizing agent at acidic pH.

2 - Process according to claim 1 characterized in that the oxidation step is carried out at a pH less than 4 at a temperature between the ambient and more than 100 ° C.

3 - Method according to one of claims 1 and 2 characterized in that the oxidizing agent is selected from the group consisting of nitrates, sulfates, chlorates perchlorates, persulfates, nitrogen oxides and peracetates.

4 - Method according to one of claims 1 to 3 characterized in that the oxidizing agent is mixed with at least one of the strong mineral or organic acids, chosen from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and trichloroacetic acid.

5 - Method according to one of claims 1 to 4 characterized in that the oxidizing agent is 1 nitrate anion and the acid is nitric acid.

6 - Method according to one of claims from 1 to 5 characterized in that the oxidizing solution consists of a solution of nitric acid diluted in water to a concentration less than or equal to 300g / l.

7 - Method according to one of claims from 1 to 6 characterized in that the sludge belongs to the group consisting of any organic phase containing hydrocarbons comprising at least one olefinic bond, the rocks impregnated with this organic phase and the sludge recovered after sieving the cuttings.

- Method according to one of claims 1 to 7 characterized in that the sludge contains from 1 to 10% by weight of olefinic compounds from the group consisting of olefins of carbon chain length varying from 8 to 30 carbon atoms, and preferably from 12 to 20 carbon atoms.

- Method according to one of claims 1 to 8 characterized in that the molar ratio of the oxidizing agent and the olefin is greater than or equal to 5/1 (mol / mol), preferably equal to 10/1 (mol / mol).

- Method according to one of claims 1 to 9 characterized in that it comprises, in addition to the oxidation step of the mud, several treatment steps consisting in: separating the oxidized cuttings in suspension from the oxidizing solution which is recycled ,

- neutralize the oxidized cuttings with a basic compound chosen from the group consisting of mineral salts such as the salts present in sea water, and with lime, - finally, reject the oxidized cuttings.

- Device for implementing the method defined by one of claims of 1 10 characterized in that it comprises an oxidation capacity (1) into which are introduced respectively by two conduits (2) and (3), the crushed cuttings to be treated, the aqueous solution of oxidizing agent of pH less than 4, said capacity comprising at its base a third pipe (4) for discharging the gases formed by oxidation and a fourth pipe (5) for discharging the mix solution oxidant / oxidized cuttings to a separation unit (6) comprising a pipe (7) for recycling the oxidative aqueous solution to the pipe (3) and a pipe (8) directing the cuttings recovered in a neutralization unit (9) supplied as a neutralizing agent by at least one line (10).

- Device according to claim 11 characterized in that the gases recovered by the line (4) are directed to a gas treatment unit (12).

- Application of the method according to one of claims 1 to 10 to the treatment of substitution sludge loaded with drill cuttings, recovered from the ground surface, more particularly those collected at sea.