WO2014058332A1 - Hydrogeochemical method for determining accumulations of shale gas - Google Patents

Description

 HYDROGEOCHEMICAL METHOD FOR DETERMINING CLUSTERS

 SHALE GAS

Technical field

 The invention relates to organic petroleum geology and can be used to predict the accumulation of shale gas during geological exploration within local oil and gas areas without environmental risks.

State of the art

 Known methods for the search for hydrocarbon deposits, based on the study of underground (formation) water samples, which are extracts from the aqueous medium of a mixture of polyaromatic hydrocarbons (arenas), namely, for the forecast of hydrocarbon accumulations.

 So in the document US 2767320 describes a method of searching for hydrocarbon deposits, which consists in determining the quantitative content of aromatic hydrocarbons in groundwater samples by spectral UV analysis. It involves the separation of organic from inorganic components, then the separation of organic components into fractions in order to separate benzene from naphthalene, i.e. performing multiple operations to separate interfering components. The next step in the analysis is the registration of the ultraviolet spectrum. The presence of benzene in the spectrum judges the presence of a hydrocarbon deposit. However, the known method requires the mandatory separation of naphthalene, the analytical maximum of which masks the maximum of benzene, which leads to losses in the quantitative content of benzene and thereby reduces the reliability of the results.

SU 1695249 discloses a method for determining aromatic hydrocarbons in formation waters when searching for hydrocarbon deposits, including treating samples with a solvent matrix, freezing the arenas extract and solvent mixture with liquid nitrogen or liquid hydrogen, followed by fine-structure luminescence analysis. As the matrix solvent, a mixture of normal hexane and carbon tetrachloride in a mass ratio of 1: 1 with the addition of 0.33 ml of ammonia is used. However, this method does not allow to make an unambiguous conclusion about the presence of accumulations of shale gas.

 There is also a hydrochemical method for searching for hydrocarbon deposits according to the copyright certificate SU 913316, based on the spectral determination of the quantitative content of benzene in groundwater, according to which groundwater samples are treated with cyclohexane, simultaneously with the spectrum of benzene, the quasilinear luminescence spectrum of naphthalene, obtained cyclohexane extract and the amount of benzene and naphthalene or naphthalene judge the presence of hydrocarbon deposits.

 This method allows to detect the presence of hydrocarbon deposits in small quantities in the extract at the same time naphthalene and benzene, which are direct hydrochemical indicators of oil and gas. However, like the above method, this method does not allow to reliably determine the presence of accumulations of shale gas.

 The objectives of the invention is to increase the reliability of identifying accumulations of shale gas, simplifying the technology of their search, as well as reducing environmental risks.

Disclosure of invention

 These problems are solved in the hydrogeochemical method for determining accumulations of hydrocarbons, including the steps at which groundwater samples are taken, the samples taken are treated with an organic solvent, obtaining an extract of organic compounds in this solvent, the obtained extract is separated from the aqueous medium; the resulting extract is frozen; performing a fine-structured spectral analysis of the indicated frozen extract by recording the quasilinear luminescence spectrum of benzene; measure the intensity of the analytical line of benzene in the spectrum, which is used to judge the presence of accumulations of hydrocarbons.

According to the invention, surface water samples are additionally taken; normal hexane is used as a solvent for each sample; the intensities of the analytical lines of benzene in the spectra of groundwater and surface water samples are compared, and if the intensities of the analytical lines of benzene in the spectra of groundwater samples are exceeded, the presence of shale gas accumulations is judged. Advantageously, the extract of organic compounds in normal hexane is frozen using liquid nitrogen or liquid hydrogen.

 The method according to the invention allows to avoid errors in the determination of benzene in organic matter (OM) of ground and surface waters, which is a direct (local) hydrochemical indicator of gas content, saves time and money, and also increases the reliability of detecting accumulations of shale gas by its small amounts in groundwater samples .

 Features and advantages of the present invention will be more apparent from the following detailed description with reference to the drawings.

Brief Description of the Drawings

 In FIG. 1 shows a flow chart of operations with water samples in a method according to the present invention;

 in FIG. 2 - quasilinear fluorescence spectrum of benzene in a normal hexane extract from an underground water sample in the presence of gas accumulation.

An embodiment of the invention

 Within the studied oil and gas bearing area, groundwater samples are taken in several places. Groundwater samples are taken, for example, using auger drilling from a depth of 20-30 m.

 Samples of surface waters are also taken, for example, from puddles, ponds, etc.

 Each of the water samples is placed in a glass flask.

 Then, with each of the water samples (both underground and surface), the following actions are carried out, schematically shown in FIG. one.

 In step 1, normal hexane is added as an organic solvent to a glass flask with a sample of water. The resulting mixture of water with a solvent is thoroughly mixed (step 2), for example, using an apparatus for shaking liquids, sedimented and then the obtained benzene extract with other arenas in the solvent is separated from water, placing this extract in a quartz cuvette (step 3).

Then, the separated extract is frozen (step 4), placing the indicated quartz cuvette with the extract in a Dewar vessel with liquid nitrogen (~ 77 ° K), until formation of a crystalline solution. Liquid hydrogen (~ 20 ° K) can also be used for freezing.

 The resulting frozen extract was examined in a fluorescence spectrophotometer.

 When using a fluorescence spectrophotometer, for example, a Hitachi F7000 with a low-temperature attachment, a quartz cuvette with frozen extract is transferred to the Dewar vessel of the low-temperature attachment of this device (step 5).

 The study of the frozen extract is carried out in a device with registration of a quasilinear spectrum (step 6).

The spectrum of benzene in complex with other arenas is _recorded upon excitation of benzene with light with a wavelength of λ _{Β 03} 6. ^~ 255 nm with the yield of the analytical maximum of benzene fluorescence at _ι6 ιχ ^- 292 nm.

 A search feature of a gas deposit is the concentration of benzene in groundwater that exceeds the concentration of benzene in surface water (background concentration).

 The spectra of all samples (surface and groundwater) are recorded under the same conditions to obtain comparable results.

 In FIG. Figure 2 shows the quasilinear fluorescence spectrum of benzene in a normal hexane extract from an underground water sample of a gas reservoir.

The dashed line shows the fluorescence spectrum quasilinear spectrally pure normal hexane, analytical whose maximum (X _vk = 255 nm) is spaced from the highest analytical line benzene (λ _ΒΜΧ = 292 nm) at 37 nm, and therefore the maximum benzene analytical line is not masked.

The method allows to determine the presence of accumulations of shale gas in clay shales of Carboniferous age (Barnett formation) by very low concentrations of benzene (10 ^"6 mg / ml) in the OM of groundwater.

 A direct study of an underground water sample avoids the errors in determining benzene, saves time and money, and also increases the reliability of identifying accumulations of shale gas by its small amounts using a highly sensitive, selective, rapid method of quasilinear fluorescence spectra without environmental risks.

Claims

CLAIM 1. A hydrogeochemical method for determining accumulations of hydrocarbons, comprising the steps of:  - take samples of groundwater,  - process the samples taken with an organic solvent, obtaining an extract of organic compounds in this solvent,  - separate the obtained extract from the aqueous medium;  - the resulting extract is frozen;  - carry out a fine-structured spectral analysis of the specified frozen extract, registering a quasilinear luminescence spectrum of benzene;  - measure the intensity of the analytical line of benzene in the spectrum, which is used to judge the presence of accumulations of hydrocarbons,  characterized in that  - additionally take samples of surface water;  - use normal hexane as a solvent for each sample;  - compare the intensities of the analytical lines of benzene in the spectra of samples of groundwater and surface water;  - if the intensity of the analytical lines of benzene in the spectra of groundwater samples is exceeded, the presence of shale gas accumulations is judged.  2. The method according to p. 1, characterized in that the extract of organic compounds in normal hexane is frozen using liquid nitrogen or liquid hydrogen.