METHODS FOR DETECTING AND MAPPING THE SPATIAL DISTRIBUTION OF ORGANIC COMPOUNDS IN RESERVOIR ROCKS AND THE USE THEREOF

Abstract

The present invention relates to a method for detecting and mapping the spatial distribution of organic compounds aiming to understand how such organic compounds are distributed on the surfaces of reservoir rocks subjected to injection fluids for oil recovery purposes. The DESI and LAESI techniques may be used in the analysis of rocks from trials of oil recovery in small or large scale. Furthermore, both techniques may be applied in the analysis of compounds present on the surfaces of minerals from aquatic environments.

Claims

1. A method for detecting and mapping the spatial distribution of organic compounds in reservoir rocks, comprising a combination of DESI and LAESI techniques for analyzing reservoir rock surfaces.

2. The method of claim 1, wherein the DESI technique comprises desorbing and ionizing analytes of the surface of the reservoir rock through a spray of charged droplets, wherein the spray is generated by an internal silica capillary that emits a solvent or a mixture of solvents, and an external silica capillary that emits an inert gas; and pneumatically directing the spray towards the sample surface.

3. The method of claim 1, wherein the LAESI technique comprises irradiating the sample surface through a laser beam on the infrared wavelength to desorb the analytes from the surface of the reservoir rock and ionize them through a spray of charged particles located above the sample surface.

4. The method of claim 2, wherein the electrolytic spray solvent is methanol or a 1:1 methanol/toluene mixture.

5. The method of claim 2, wherein the electrolytic spray solvent presents a flow of 2 μL/min.

6. The method of claim 2, wherein the inert gas is nitrogen gas with a pressure of 150 psi.

7. The method of claim 3, wherein the electrolytic spray solvent is methanol or a 1:1 methanol/water mixture.

8. The method of claim 3, wherein the electrolytic spray solvent presents a flow between 1.5 and 2 μL/min.

9. The method of claim 1, wherein the DESI technique is applied to analyze polar compounds.

10. The method of claim 1, wherein the LAESI technique is applied to determine high and low polarity compounds.

11. A method of analyzing rocks from trials of oil recovery in small or large scale, comprising the method of claim 1.

12. A method of analyzing compounds present on the surfaces of minerals from aquatic environments, comprising the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] This invention is described in greater detail below, referring to the Figures appended hereto that provide examples of the impediment thereof in a schematic manner that does not impose any constraints on the scope of this invention. The drawings show:

[0017] FIG. 1 illustrates an overview of the DESI technique for analyzing organic compounds on a reservoir rock surface: (a) tube emitting a charged particle spray; (b) charged particle spray; (c) ionization and desorption process of analytes on the rock surface; (d) reservoir rock; (e) ion transfer tube; (f) mass spectrometer;

[0018] FIG. 2 illustrates analyses of the following rocks (a) Optical Calcite, (b) Quartz, (c) Dolomite, (d) Berea Sandstone and (e) Pink by DESI technique after applying a methanolic solution of 10 ppm of the following acids: (A) cyclohexane butyric, (B) decanoic, (C) 1-naphthalene acetic, (D) 3,5-dimethyl adamantane-1-carboxylic, (E) pentadecanoic and (F) palmitic. All mass spectra were obtained in negative ionization mode;

[0019] FIG. 3 illustrates the assessment of the different solvent analysis systems on the surface 1 of the HCB3-1 rock by the DESI technique: (a) MeOH; (b) MeOH/Tol (7:3); (c) MeOH/Tol (6:4); (d) MeOH/Tol (5:5). All mass spectra were obtained in negative ionization mode;

[0020] FIG. 4 illustrates the assessment of the different solvent analysis systems on the surface 1 of the YG rock by the DESI technique: (a) MeOH; (b) MeOH/Tol (7:3); (c) MeOH/Tol (6:4); (d) MeOH/Tol (5:5). All mass spectra were obtained in positive ionization mode;

[0021] FIG. 5 illustrates chemical imaging by the DESI technique of compounds on different rock surfaces: (a) mass spectrum (negative mode) representative of all the rocks; (b) HCB3-1 (surface 1); (c) HCB3-1 (surface 2); (d) HCB3-2 (surface 1); (e) HCB3-2 (surface 2); (0 IGE (surface 1); (g) IGE (surface 2);

[0022] FIG. 6 illustrates the chemical imaging by the DESI technique of compounds on the YG rock: (a) mass spectrum (positive mode) representative of both rock surfaces; (b) surface 1; (c) surface 2;

[0023] FIG. 7 illustrates an overview of the LAESI technique for analyzing organic compounds on reservoir rock surfaces: (a) infrared resonant optical parametric oscillator with adjustable wavelengths (2900 to 3450 nm); (b) laser beam; (c) mirror 1; (d) mirror 2; (e) mirror 3; (0 laser beam focus lens; (g) reservoir rock; (h) solvent injection pump; (i) charged particle spray; (j) generation of gas-phase analyte ions (k) mass spectrometer;

[0024] FIG. 8 illustrates chemical imaging through the LAESI technique of compounds on the YG rock: (a) mass spectrum (positive mode) representative of both rock surfaces; (b) surface 1; (c) surface 2;

DETAILED DESCRIPTION OF THE INVENTION

[0025] The method for detecting and mapping the spatial distribution of organic compounds comprises a combination of two mass spectrometry ionization techniques called Desorption Electrospray Ionization (DESI) and Laser Ablation Electrospray Ionization (LAESI) for detecting, identifying, and mapping the spatial distribution of organic compounds on reservoir rock surfaces.

[0026] The DESI technique may be used to analyze polar compounds, while the LAESI technique may be used to determine low-polarity compounds. Both techniques are widely used for analyzing organic compounds on plant and animal tissue surfaces, but have never been used for studying molecular species on rock surfaces.

[0027] As shown in FIG. 1, the analysis using the DESI technique is performed by using the DESI-2D source connected to a mass spectrometer. The exact identification of the compounds in the samples is handled through high mass accuracy and high resolution. Analytes on the sample surface are extracted and ionized through a charged particle spray. in order to generate the spray, a silica capillary with an internal diameter of 50 μm in its a solvent, such as methanol, or a 1:1 methanol/toluene or methanol/water solvent mixture with a flow of 2 μL/min, while an external silica capillary with an internal diameter of 250 μm emits nitrogen gas with typical pressure of 150 psi. This spray is pneumatically directed towards the surface of the rock, which is deposited on a platform moving along the X and Y axes.

[0028] Experiments are performed under identical experimental conditions, including geometrical parameters, such as a distance of approximately 2 mm from the tip of the electrospray capillary to the sample surface, with the spray angled at 55°, at a distance of approximately 5 mm between the spray spot and the entrance to the mass spectrometer. For the chemical imaging experiments, the sample rock surfaces are swept by the spray in a single continuous horizontal movement and with a 200 μm vertical pass (spatial resolution).

[0029] The FireFly software (version 2.0) is used to convert the mass spectra files from Xcalibur 2.2 into a format compatible with the BioMap software, in order to construct spatially accurate 2D ion images. The rainbow color palette is used in the BioMap software to display signal intensity.

[0030] As shown in FIG. 7, an analysis through the LAESI technique uses an Infrared resonant optical parametric oscillator adjustable wavelengths varying from 2.9 to 3.4 μm and is used to irradiate laser beams onto the sample at a 90° angle. The laser beam wavelength may be adjusted to 2.9 μm in order to excite the O-H bonds (for polar molecule analyses), or adjusted to 3.4 μm to excite the C-H bonds (for low-polarity molecule analyses). Mirrors are used to direct the laser beam towards the sample, and a calcium fluoride plano-convex lens is used to focus the laser at a distance of 50 mm. The laser spot size is 150 to 180 μm, measured after laser beam irradiation on thermal paper. The laser beam is directed to the sample surface at a frequency of 10 Hz and with typical energy of 2.5 mJ. The rock sample is placed on a mobile platform, as described above for analyses using the DESI technique.

[0031] The material irradiated by the laser is desorbed and ionized by a charged droplet spray from an electrospray source located above the sample. The following geometrical parameters are optimized and used in the analyses: distance between the electrospray capillary and the ion transfer tube: 16 mm; distance between the electrospray capillary and the sample surface: 10 mm; distance between the focus lens and the sample surface: 50 mm.

[0032] A solvent such as methanol for example, or a 1:1 methanol/water solvent mixture with a flow of 1.5-2.0 μL/min is used as the electrospray solvent. The analyses are performed through the use of a mass spectrometer. For the chemical imaging experiments, the sample rock surfaces are irradiated by the laser beam in a continuous horizontal movement and with one 200 μm vertical pass (spatial resolution).

[0033] The FireFly software (version 2.0) is used to convert the mass spectra files from Xcalibur 2.2 into a format compatible with the BioMap software, in order to construct spatially accurate 2D ion images. The rainbow color palette is used in the BioMap software to display signal intensity.

EXAMPLES

[0034] The following examples illustrate some particular embodiments of this invention, and may not be construed as imposing constraints thereon.

Example 1: DESI Technique

[0035] As shown in FIG. 5, the DESI technique was used to perform the chemical imaging of the compounds on the surfaces of the HCB3-1, HCB3-2 and IGE rocks, collected in the Araripe Basin. Two surfaces (both sides) of each rock were analyzed.

[0036] Although thousands of compounds were detected and imaged, only nine are shown in FIG. 5. Each ion was normalized to 100% intensity separately. The nine compounds are identified in detail (exact m/z values; exact figures for masses and molecular formulas) in Table 1. Eight of these compounds were identified as carboxylic acids, and are distributed differently on each rock surface. One ion was identified as sugar (saccharose, [M+Cl].sup.−), and its distribution was specific for each rock. As the saccharose and other sugars may be produced by plants, the presence of this compound can be explained through contact between the rocks and aquatic plants in the Araripe Basin.

[0037] These findings demonstrate that the DESI-MS technique is a useful tool for investigating the spatial distribution of assorted molecular species on rock surfaces, and may provide insights into how certain compounds cluster on rock surfaces in aquatic or land environments.

TABLE-US-00001 TABLE 1 The m/z values, errors (ppm), and molecular formulas for the nine compounds as shown in FIG. 1. The ions were through using a high-resolution mass spectrometer (Thermo Scientific Q Exactive Hybrid Quadrupole-Orbitrap) Error Molecular Attempted m/z (ppm) Formula Identification 171.13913 0.449 [C.sub.10H.sub.20O.sub.2 − H].sup.− decanoic acid 199.17047 0.586 [C.sub.12H.sub.24O.sub.2 − H].sup.− dodecanoic acid 209.09334 0.834 [C.sub.10H.sub.14O.sub.3N.sub.2 − H].sup.− 3-(4-acetyl-3,5-dimethyl pyrazolyl) propanoic acid 227.20184 0.821 [C.sub.14H.sub.28O.sub.2 − H].sup.− tetradecanoic acid 241.21751 0.856 [C.sub.15H.sub.30O.sub.2 − H].sup.− pentadecanoic acid 250.14505 0.732 [C.sub.14H.sub.21O.sub.3N − H].sup.− 3-amino-3-(4-pentoxiphenyl) propanoic acid 255.23317 0.848 [C.sub.16H.sub.32O.sub.2 − H].sup.− hexadecenoic acid 269.24872 0.432 [C.sub.17H.sub.34O.sub.2 − H].sup.− heptadecanoic acid 377.08582 0.551 [C.sub.12H.sub.22O.sub.11 + Cl].sup.− Saccharose

Example 2: DESI Technique

[0038] FIG. 6 shows the chemical imaging results for the YG rock obtained by the DESI technique. The YG rock is a Berea sandstone taken from a small-scale recovery experiment using glycerin-based drilling fluids.

[0039] Both rock surfaces were analyzed and, although thousands of compounds were detected and imaged, only five are shown in FIG. 6. These compounds are identified in detail in Table 2. Few differences were found in the distributions of the different ions on the same surface, although they were distributed differently on different surfaces.

[0040] These findings suggest that chemical imaging by the DESI technique is an analytical approach with potential used for determining the exact location of compounds left over from oil recovery experiments on reservoir rocks.

TABLE-US-00002 TABLE 2 The m/z values, errors (ppm), and molecular formulas for the five compounds as shown in FIG. 2. Error Molecular m/z (ppm) Formula 239.14322 0.745 [C.sub.18H.sub.18O + H].sup.+ 253.15890 0.822 [C.sub.18H.sub.20O + H].sup.+ 267.17453 0.704 [C.sub.19H.sub.22O + H].sup.+ 281.19021 0.775 [C.sub.20H.sub.24O + H].sup.+ 295.20587 0.772 [C.sub.21H.sub.26O + H].sup.+

Example 3: LAESI Technique

[0041] The LAESI technique was used to detect and map the chemical distribution of the organic compounds on the YG rock surfaces. The laser beam wavelength was adjusted to 3.4 μm in order to excite the C—H bonds and promote the desorption of low-polarity molecules. The laser was used in the same region analyzed by the DESI-MS technique, in order to compare the chemical profiles obtained through each of these techniques.

[0042] As shown in FIG. 8, the chemical profile obtained through the LAESI technique demonstrated a gaussian with more intense ions in the 100 to 150 m/z region, in contrast to that obtained through the DESI-MS technique (more intense ions in the 250-300 m/z region). Several compounds were detected through the LAESI technique, but only nine of them are shown in FIG. 8. The detailed identification of the ions is presented in Table 3. In addition to ionization through protonation of compounds containing heteroatoms, a notable characteristic of the LAESI technique was the ability to detect radical ions, which allowed the analysis of apolar compounds (hydrocarbons). A possible explanation for this phenomenon is the use of the 3.4 μm infrared laser wavelength.

[0043] These findings pave the way for future mapping experiments analyzing apolar compounds in oil samples found on the surfaces of different types of solid materials.

TABLE-US-00003 TABLE 3 The m/z values, errors (ppm), and molecular formulas of the nine compounds as shown in FIG. 3 Error Molecular m/z (ppm) Formula 103.05430 0.710 [C.sub.8H.sub.7].sup.+− 105.06997 0.886 [C.sub.8H.sub.9].sup.+− 117.06995 0.625 [C.sub.9H.sub.9].sup.+− 130.15910 0.567 [C.sub.8H.sub.19N + H].sup.+ 131.08564 0.863 [C.sub.9H.sub.11].sup.+− 143.08562 0.650 [C.sub.11H.sub.11].sup.+− 172.11220 0.720 [C.sub.12H.sub.13N + H].sup.+ 186.12788 0.827 [C.sub.13H.sub.15N + H].sup.+ 208.11218 0.500 [C.sub.15H.sub.13N + H].sup.+

[0044] It must be noted that, although this invention has been described in terms of the drawings appended hereto, it may be subject to modification and adaptation by persons versed in the art, depending on the specific situation, and provided that this takes place within the scope of the invention defined herein.