OA17346A - Hydrocarbon dosage method. - Google Patents

Abstract

The invention relates to a method for measuring hydrocarbons in a composition comprising hydrocarbons and water, comprising: adding a chemical agent to the composition to form an emulsion of water and hydrocarbons; taking a sample of the emulsion and dissolving this sample in a common solvent of the water and hydrocarbons to form a solution; measuring the quantity of hydrocarbons in the solution. The invention also relates to an installation suitable for implementing this method.

Description

The present invention relates to a method for assaying hydrocarbons in a composition comprising hydrocarbons and water as well as an installation suitable for carrying out this method.

TECHNICAL BACKGROUND

In order to optimize the extraction of hydrocarbons from a subterranean formation, it is known practice to take samples of material in the subterranean formation (cores) or else to use so-called “analogous” porous materials, consolidated or not, and to saturate them with water and hydrocarbon thus simulating the composition of an oil reservoir. We can then test different means of extraction on these samples: water, water vapor, surfactants, polymers, gas, etc. Fractions comprising essentially hydrocarbons mixed with water are recovered during each experiment. and solid minerals. The precise dosage of the quantity of hydrocarbons present in each fraction makes it possible to obtain a simulation of the production history and thus to evaluate the efficiency of the extraction means tested.

Accurate dosing of the amount of hydrocarbons mixed with water and possibly mineral solids is also useful when producing deposits.

When dealing with conventional crude oil with low viscosity, simple decantation or centrifugation can separate these hydrocarbons from the water and thus perform the necessary dosage. However, even with low viscosity oils, persistent emulsions may form and prevent accurate counting of the hydrocarbon produced. When we are in the presence of heavy oils, the situation is even more difficult: indeed large quantities of water can be trapped with the hydrocarbons, and the proximity of the densities of the water and of the hydrocarbons makes the separation gravity inoperative. In addition, the hydrocarbons tend to adhere to the walls of the containers used and / or to incorporate water.

ORIGINAL

Different methods, long and tedious, are currently used to allow such an assay:

- heating and evaporation of water at atmospheric pressure or under vacuum, which does not solve the problem of the dosage of water which may remain trapped with the hydrocarbons;

- X-ray counting, which requires very heavy equipment;

- dilution of the hydrocarbons in a solvent such as toluene, then centrifugation to separate the water / oil emulsion: the quality of the water / oil separation is however very poor, and the visualization of the position of the interface is difficult .

The article "No-solvent" Oil-in-Water Analysis, A Robust Alternative to Conventional Solvent Extraction Methods, by Brost et al., Available on the Turner Designs website, describes a method for the determination of crude in water. , in which surfactant is added to the mixture in order to produce a microemulsion of the crude in water, then a fluorescence measurement is carried out on this microemulsion. However, this method requires a large amount of surfactant and is limited to measuring small amounts of oil (less than 1%). The calibration curve is non-linear, and the surfactant itself generates fluorescence which must be subtracted, resulting in significant background noise.

There is therefore a real need to develop an improved and simplified method for measuring hydrocarbons mixed with water, capable in particular of being applied reliably to heavy oils, and without limitation to a measurement of small quantities. of hydrocarbons.

SUMMARY OF THE INVENTION

The invention relates firstly to a process for the determination of hydrocarbons in a composition comprising hydrocarbons and water, comprising:

- adding a chemical agent to the composition to form an emulsion of water and hydrocarbons;

- taking a sample of the emulsion and dissolving this sample in a common solvent of water and hydrocarbons to form a solution;

- measuring the amount of hydrocarbons in the solution.

According to one embodiment, the measurement of the quantity of hydrocarbons in the solution is carried out by UV spectrometry.

ORIGINAL

According to one embodiment, the chemical agent is a solution comprising a base, preferably sodium hydroxide, or one or more surfactant compounds, or a mixture thereof.

According to one embodiment, the method comprises a step of diluting the system with distilled water, in particular a dilution to a concentration of the aqueous phase in salt of less than or equal to 20 g / l.

According to one embodiment, the common solvent for water and for hydrocarbons is tetrahydrofuran or dimethyl sulfoxide.

The invention also relates to a process for the production of hydrocarbons, comprising:

- the extraction and recovery of a production stream from an underground formation containing hydrocarbons;

- taking a composition comprising hydrocarbons and water from the production flow;

- the determination of the hydrocarbons in said composition according to the process described above.

The invention also relates to a method for simulating the recovery of hydrocarbons, comprising;

- the supply of a block of porous material containing hydrocarbons;

- the injection into the block of porous material of a hydrocarbon recovery agent;

- the recovery of one or more fractions comprising hydrocarbons and water leaving the block of porous material; and

- The determination of the hydrocarbons in each fraction according to the process described above.

The invention also relates to an installation for metering hydrocarbons in a composition comprising hydrocarbons and water, comprising, upstream to downstream:

- means for adding a chemical agent to the composition, the chemical agent being suitable for forming an emulsion of water and hydrocarbons;

- a collection line for an emulsion sample;

- means for adding a common solvent for water and hydrocarbons to the emulsion sample;

- a solution collection line;

- means of measuring the quantity of hydrocarbons in the solution.

According to one embodiment, the means for measuring the quantity of hydrocarbons in the solution comprise a UV spectrometer.

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ORIGINAL

According to one embodiment, the means for adding chemical agent are means for adding a solution comprising a base, preferably soda, or one or more surfactant compounds, or a mixture thereof.

According to one embodiment, the means for adding a common solvent for water and hydrocarbons are means for adding tetrahydrofuran or dimethyl sulfoxide.

According to one embodiment, the installation comprises a first chamber adapted to mix the chemical agent with the composition to form the emulsion, and a second chamber adapted to mix the emulsion sample with the solvent to form the solution.

According to one embodiment, the installation comprises a sampler suitable for providing the composition.

The present invention overcomes the drawbacks of the prior art. More particularly, it provides an improved and simplified method of dosing hydrocarbons mixed with water. This method can be reliably applied to heavy oils and is not limited to the measurement of small amounts of hydrocarbons.

This is accomplished through the use of an emulsification step, resulting in a homogeneous mixture of hydrocarbons and water; a step of taking a sample of emulsion, which is representative of the composition as a whole, taking into account its homogeneity; and a step of dissolving in a solvent, making it possible to obtain a solution in which the hydrocarbons and water are dispersed in the solvent at the molecular level, which makes it possible to perform a direct measurement of the amount of hydrocarbons in this solution.

According to certain particular embodiments, the invention also exhibits one or preferably more of the advantageous characteristics listed below.

- The method according to the invention can be implemented manually or by using integrated equipment (installation according to the invention), which is optionally portable. The whole process can be automated.

- The process according to the invention is rapid (typically about 5 minutes).

- The method according to the invention overcomes the difficulties associated with the heterogeneity of the composition dosed, and in particular the presence of trapped water or gas bubbles.

- The process according to the invention does not require large quantities of chemicals or complex and expensive equipment. In particular, the actual measurement of the hydrocarbon content can be

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ORIGINAL performed with commercially available devices (eg UV spectrometer).

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 provides the correspondence between the UV absorbance measurement (on the ordinate, without units) and the mass concentration of crude oil (abscissa, in%) in tetrahydrofuran. The square symbols represent the calibration of crude oil without water, and the circle symbols represent the calibration of crude oil in the presence of water. The water-crude ratio varies from approximately 9 to 1. See example 1 below.

Figure 2 is a schematic representation of one embodiment of the installation according to the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in more detail and in a non-limiting manner in the description which follows.

The invention is applicable to any composition comprising non-gaseous hydrocarbons and water. The composition can also optionally comprise gaseous hydrocarbons, but these are intended to be evacuated during the process and are therefore not measured.

The invention is particularly useful for the assay of so-called heavy oils. Consequently, according to one embodiment, the (non-gaseous) hydrocarbons of the composition have an API degree (density measured according to the API method) less than or equal to 10 and / or comprise a mass proportion of molecules comprising at least 12 atoms. of carbon greater than or equal to 80%, preferably greater than or equal to 90% or 95%.

The hydrocarbon / water mass ratio can vary from 5 * 10 ' ⁵ (dosage of crude dispersed in water) to 10.

The composition can also contain other compounds, and in particular solid mineral particles. At least part of the solid mineral particles can be separated from the composition by settling or filtration before the step of adding the chemical agent.

As a first step, the invention therefore provides for adding a chemical agent to the composition to form an emulsion of water and hydrocarbons. The chemical agent can be a solution comprising one or more surfactant compounds. But it can also be, according to a particularly simple embodiment, an alkaline solution, such as a sodium hydroxide solution. Indeed, a base (such as soda) is capable of reacting with the naphthenic acids present in the

ORIGINAL hydrocarbons to form surfactant compounds in situ. The soda can be replaced by another base such as potash, ammonia, or soda ash etc.

If, on the other hand (or in addition) a contribution of surfactant compound is used, in particular for low-acid oils, the surfactant compound (s) must be chosen so as not to disturb the final step of measuring the quantity of hydrocarbons. For example, when measuring UV absorbance, the surfactant compounds should be essentially non-absorbent in the UV spectrum.

The chemical agent should be mixed with the composition until the emulsion is obtained, manually or preferably using mechanical mixing means (paddle stirrer, magnetic stirrer, vortex or other).

The nature and amount of the chemical agent are adapted according to the nature of the composition, to allow the formation of a homogeneous emulsion. The concentration of chemical agent can vary between 0.05% and 3% by mass. The emulsion formed must be of the oil-in-water type, and therefore have good fluidity. Visual observation under agitation then makes it possible to appreciate its homogeneity.

Secondly, the invention provides for taking a sample of the emulsion, which is representative of the overall emulsion, and then dissolving this sample in a common solvent of water and hydrocarbons to form a solution. Sampling makes it possible to limit the amount of solvent used while obtaining a sufficiently dilute hydrocarbon solution to be able to measure the concentration of hydrocarbons, while avoiding saturation of the measuring device. Depending on the sample, the solvent dilution rate can vary from 1 to 10.

A product is considered to be a solvent for water and for hydrocarbons when, at ambient temperature and at ambient pressure, the solubility of water in this product is greater than or equal to 30% by volume and the solubility of the hydrocarbons in this product is greater than or equal to 30% by volume.

If the water contains salt, at a concentration typically greater than 20 g / L, the solubilization of the water in the solvent may become insufficient and phase separation may occur. The method requires an additional step to be adapted to the situation. This additional step consists of diluting the system with distilled water so as to reduce the salinity to a value below 20 g / L.

ORIGINAL

The method of the invention may also include a step of dosing the amount of salt in the aqueous phase prior to the step of dilution with distilled water.

A very effective common water and hydrocarbon solvent is tetrahydrofuran, but, without this list being exhaustive, it is possible to use other solvents such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide etc.

If solid mineral particles are still present in the solution, they generally settle easily due to the disappearance of the aqueous phase in which these particles are generally suspended and are therefore no longer troublesome for the measurement. Alternatively, filtration can be provided if necessary. Any gas present is generally also evacuated during this step.

The third step is to take a direct measurement of the amount of hydrocarbons in the solution. A particularly simple method is to measure the absorbance of the solution in the UV range, using a spectrometer. This requires pre-calibration of the spectrometer with samples of hydrocarbons in the solvent, at various concentrations. The complete analysis of the UV spectrum of the hydrocarbon allows selection of wavelengths that produce different absorbances. Depending on whether the samples are highly concentrated or highly diluted, one can choose wavelengths producing low or high absorbances, respectively, allowing improved accuracy.

It is remarkable that the presence of water in the solution on which the measurement is carried out does not disturb said measurement. This is confirmed by Figure 1, which shows an overlay of calibration curves of crude oil in tetrahydrofuran at a wavelength of 408 nm, with and without water (see Example 1).

In addition, the calibration curve is linear over a wide range of concentrations if the dilution of the emulsion in the solvent has been correctly adjusted, allowing a particularly reliable measurement to be made.

The method of the invention is particularly useful for the determination of hydrocarbons in the fractions obtained during a simulation experiment of recovery of hydrocarbons in a block of porous material. It can also be applied to the dosage of hydrocarbons in a production flow.

The method of the invention can be implemented by means of a plant according to the invention.

ORIGINAL

With reference to FIG. 2, this installation may comprise means for supplying the composition comprising hydrocarbons and water 1, which may for example comprise means for manually supplying the composition or means for sampling and sampling in a production flow or in fractions recovered during a simulation experiment of recovering hydrocarbons in a block of porous material.

It also includes chemical agent addition means 7, connected to a chemical agent reservoir.

The composition supply means 1 feed a first chamber 2 (or emulsification chamber), advantageously provided with mixing means 3. The chemical agent addition means 7 can be connected either to the first chamber 2 or to the means for supplying composition 1 upstream thereof.

At the outlet of the first chamber 2, an emulsion sample collection line 9 is provided, provided with sampling means, which supplies a second chamber 4 (or dissolution chamber). Means 8 for adding solvent feed either the second chamber 4 or the emulsion sample collection line 9 upstream thereof. The second chamber 4 is advantageously provided with mixing means (not shown).

At the outlet of the second chamber 4 is provided a solution collection line 10, which supplies means for measuring the quantity of hydrocarbons in solution 5 (for example a UV spectrometer). A computer 6 is used to acquire the measurement and possibly to control the entire installation. The installation is advantageously provided with a set of valves, drain means and cleaning means, not shown.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1

Viscous crude oil P1 (10,000 cP at room temperature) is dissolved in tetrahydrofuran (THF) at a concentration of 0.15% by weight. The absorption spectrum is determined in the wavelength range 190 - 1100 nm. A secondary absorption peak appears at 408 nm, which wavelength is used for the assay.

A range of crude solutions in THF are prepared in the concentration range 0.1% - 0.3% by weight. The absorbance A, measured at 408 nm, is plotted as a function of the concentration Cb in Figure 1. The absorbance varies <2 ^

ORIGINAL linearly with concentration (regression coefficient 0.9989). The straight line thus obtained, with equation A = 7.00119 Cb (1), constitutes the calibration for the dosage of the crude considered.

The effect of the presence of water in the crude + THF mixture was studied. Table 1 gives the results of absorbance A measurement in the presence of water compared to the absorbance calculated from equation (1) above in the absence of water. It shows that the absorbance measurement is not significantly affected by water (<3%) and therefore that equation (1) can be used to calculate the crude concentration. The representative points of these calculations are shown (red circles) in Figure 1.

Gross h ₂ o THF H ₂ O / Crude Absorbance Absorbance measured calculated % weight % weight % weight weight / weight 408 nm 408 nm 0.1279 1.17 98.71 9.1 0.9220 0.8968 0.185 0.75 99.06 4.1 1.3230 1.2972 0.2038 0.48 99.32 2.3 1.4652 1.4290 0.2398 0.25 99.51 1.0 1.7213 1.6815

Table 1

An experiment to recover this oil trapped in a core of porous medium was carried out by injecting water and chemical additives. The fluids produced (crude + water) are collected in a fraction collector. In each collecting tube, a mass of 2 g of 0.4% aqueous sodium hydroxide solution is previously placed so as to limit the adhesion of the crude to the walls of the tube and to facilitate subsequent emulsification of the mixture. The whole is weighed.

After collecting the effluents, the tubes are weighed and a known mass of 0.4% sodium hydroxide solution is added. The tubes are then shaken manually and a fluid emulsion is formed. By way of example, Table 2 gives the masses of the effluents collected in a few tubes, as well as the total amount of added sodium hydroxide solution. A fraction of the emulsion is then taken from each tube and poured into new test tubes containing tetrahydrofuran. The whole is weighed again. After stirring, a clear solution is obtained, which is assayed by UV spectrometry at 408 nm. The crude concentrations are calculated using the calibration line in Figure 1 (Equation (1)). The bitumen content in the initial collection tube is then calculated taking into account the dilution factors by the sodium hydroxide solution and the tetrahydrofuran.

ORIGINAL

Collection tube AT B VS D Mass of effluents + initial soda (g) 9.8267 10.2201 9.9678 10.2573 Mass of soda added (g) 5.2000 5.1800 5.2350 5.1716 Emulsion mass taken (g) 0.2985 0.3661 0.5361 0.8167 Emulsion mass + THF (g) 44.5247 44.6915 44.6146 44.5103 Absorbance measured (408 nm) 1.5662 1.0456 0.7683 0.6219 Crude concentration in collected tube (% weight) 75.39 39.59 20.59 10.54

Table 2

Example 2

A solution of low viscosity P2 crude oil (3 cP at room temperature) at 0.15% by weight in tetrahydrofuran was studied by spectroscopy between 190 and 1100 nm. An absorption peak appears at 263 nm, for which the absorbance is around 1.9.

In order to be able to measure more concentrated solutions without additional dilution, the calibration was carried out by also measuring the absorbance at 3 other different wavelengths: 325, 350 and 375 nm.

A range of crude solutions in THF, varying in concentration from 0.01% to 1% by weight, resulted in 4 calibration curves at selected wavelengths.

The results are given in Table 3.

C% W / W At 263 nm At 325 nm At 350 nm At 375 nm 0.011 0.1522 0.0437 0.0263 0.015 0.0468 0.6093 0.1815 0.1137 0.0702 0.0853 1.0496 0.3041 0.1885 0.1128 0.1556 1.8776 0.5611 0.3496 0.2098 0.3313 1.1671 0.7305 0.4404

ORIGINAL

0.5178 1.7951 1.1354 0.6833 0.973 2.0665 1.2595

Table 3.

The absorbance A varies linearly with the concentration of crude Cb: 5 A = <xCb, with Cb in% by weight (Table 4).

Wavelength (nm) 263 325 350 375 OC 12.186 3.494 2.1472 &, 3037 Regression coefficient 0.9986 0.9996 0.9994 0.9997

Table 4

I

Instead, the 263 nm calibration line is used for concentrations below 0.15%. For higher contents, the other straight lines can be used, taking care to remain at absorbance levels below 2. Otherwise, an additional dilution must be carried out.

An emulsion of crude in brine (10 g / l NaCl and 4 g / l NaOH) was prepared for various samples in a water phase / crude mass ratio of 10/1. The measured absorbance was measured and compared to that predicted from the data in Table 5. It can be seen that the presence of water disturbs the measurement of the hydrocarbon concentration by less than 3%.

ORIGINAL

C% W / W 0.0468 0.0801 0.1577 Measured 263 nm 0.58 1.0078 1.8895 Calculated 0.57 0.976 1.92

Table 5 "Measured" = in the presence of water;

“Predicted” = from data in Table 4.

Example 3

A synthetic sample was produced by mixing sand and an emulsion in water of low viscosity crude oil P2, at a concentration of 5.35% crude by weight relative to the mixture, and 2.15% water. .

Two samples were taken and dispersed in THF. After stirring, the sand decanted and the supernatant was determined by the previous method, at the wavelength of 375 nm.

Concentration measured in sample 1: 5.48% (relative to the mixture).

Concentration measured in sample 2: 5.43% (relative to the mixture).

The presence of solid does not disturb the measurement of the hydrocarbon concentration.

Example 4

A low viscosity crude emulsion of Example 2 in salted water at 35 g / L NaCl and 6 g / L NaOH is prepared with a 1/1 aqueous phase / crude mass ratio. To 0.4 g of this emulsion are added 1.2 g of distilled water. Dilution with 40 g of THF leads to a homogeneous solution.

The calculated absorbance at 325 nm is 1.677. The measured absorbance is 1.722, in very good agreement with the predicted value.

Dilution of the emulsion sample with distilled water therefore allows the method to be applied to systems in which the water electrolyte content is high (typically greater than 20 g / L). At these salinities in fact, direct dilution with THF leads to a separation of the phases of the system, and not to the homogeneous solution allowing measurement of the crude oil concentration by UV.

Claims (12)

1. Method for the determination of hydrocarbons in a composition comprising hydrocarbons and water, comprising: - adding a chemical agent to the composition to form an emulsion of water and hydrocarbons; - taking a sample of the emulsion and dissolving this sample in a common solvent of water and hydrocarbons to form a solution; - measuring the amount of hydrocarbons in the solution. 2. The method of claim 1, wherein the measurement of the amount of hydrocarbons in the solution is performed by UV spectrometry. 3. The method of claim 1 or 2, wherein the chemical agent is a solution comprising a base, preferably sodium hydroxide, or one or more surfactant compounds, or a mixture thereof. 4. Method according to any one of claims 1 to 3 which comprises a step of diluting the system with distilled water, in particular a dilution to a concentration of the aqueous phase in salt of less than or equal to 20 g / l 5. Method according to one of claims 1 to 4, wherein the common solvent for water and hydrocarbons is tetrahydrofuran or dimethyl sulfoxide. 6. A process for the production of hydrocarbons, comprising: - the extraction and recovery of a production stream from an underground formation containing hydrocarbons; - taking a composition comprising hydrocarbons and water from the production flow; - the determination of the hydrocarbons in said composition according to the method of one of claims 1 to 5. 7. Method for simulating hydrocarbon recovery, comprising: ORIGINAL - the supply of a block of porous material containing hydrocarbons; - the injection into the block of porous material of a hydrocarbon recovery agent; - the recovery of one or more fractions comprising hydrocarbons and water leaving the block of porous material; and - the determination of the hydrocarbons in each fraction according to the method of one of claims 1 to 5. 8. Installation for dosing hydrocarbons in a composition comprising hydrocarbons and water, comprising, upstream to downstream: - means for adding a chemical agent (7) to the composition, the chemical agent being adapted to form an emulsion of water and hydrocarbons; - a collection line for an emulsion sample (9); - means for adding a common solvent of water and hydrocarbons (8) to the emulsion sample; - a solution collection line (10); - means for measuring the quantity of hydrocarbons in the solution (5). 9. Installation according to claim 8, wherein the means for measuring the amount of hydrocarbons in the solution (5) comprise a UV spectrometer. 10. Installation according to claim 8 or 9, wherein the means for adding chemical agent (7) are means for adding a solution comprising a base, preferably sodium hydroxide, or one or more surfactant compounds. , or a mixture of these. 11. Installation according to one of claims 8 to 10, wherein the means for adding a common solvent for water and hydrocarbons (8) are means for adding tetrahydrofuran or dimethyl sulfoxide. 12. Installation according to one of claims 8 to 11, comprising a first chamber (2) adapted to mix the chemical agent with the composition to form the emulsion, and a second chamber (4)