Patent ID: 12203919

DETAILED DESCRIPTION OF THE INVENTION

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.

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.

As shown inFIG.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.

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).

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.

As shown inFIG.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.

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.

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).

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

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

Example 1: DESI Technique

As shown inFIG.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.

Although thousands of compounds were detected and imaged, only nine are shown inFIG.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]−), 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.

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 1The m/z values, errors (ppm), and molecular formulas forthe nine compounds as shown in FIG. 1. The ions werethrough using a high-resolution mass spectrometer (ThermoScientific Q Exactive Hybrid Quadrupole-Orbitrap)ErrorMolecularAttemptedm/z(ppm)FormulaIdentification171.139130.449[C10H20O2− H]−decanoic acid199.170470.586[C12H24O2− H]−dodecanoic acid209.093340.834[C10H14O3N2− H]−3-(4-acetyl-3,5-dimethylpyrazolyl) propanoic acid227.201840.821[C14H28O2− H]−tetradecanoic acid241.217510.856[C15H30O2− H]−pentadecanoic acid250.145050.732[C14H21O3N − H]−3-amino-3-(4-pentoxiphenyl)propanoic acid255.233170.848[C16H32O2− H]−hexadecenoic acid269.248720.432[C17H34O2− H]−heptadecanoic acid377.085820.551[C12H22O11+ Cl]−Saccharose

Example 2: DESI Technique

FIG.6shows 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.

Both rock surfaces were analyzed and, although thousands of compounds were detected and imaged, only five are shown inFIG.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.

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 2The m/z values, errors (ppm), and molecular formulasfor the five compounds as shown in FIG. 2.ErrorMolecularm/z(ppm)Formula239.143220.745[C18H18O + H]+253.158900.822[C18H20O + H]+267.174530.704[C19H22O + H]+281.190210.775[C20H24O + H]+295.205870.772[C21H26O + H]+

Example 3: LAESI Technique

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.

As shown inFIG.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 inFIG.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.

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 3The m/z values, errors (ppm), and molecular formulasof the nine compounds as shown in FIG. 3ErrorMolecularm/z(ppm)Formula103.054300.710[C8H7]+−105.069970.886[C8H9]+−117.069950.625[C9H9]+−130.159100.567[C8H19N + H]+131.085640.863[C9H11]+−143.085620.650[C11H11]+−172.112200.720[C12H13N + H]+186.127880.827[C13H15N + H]+208.112180.500[C15H13N + H]+

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.