Determination of physicochemical properties and API of Asmari reservoir in Ahvaz oil field using petroleum inclusions study

Fluid inclusions provide valuable evidence of the formation temperature of minerals, the pressure on their formation environment, the fluids densities that make up the minerals, and the chemical composition of the mineralizing fluids. This data can be used to interpret temperature history, maturity, determination of diagenetic environment, cementation timing, and hydrocarbon migration related to burial history.

In this study, the cores of Asmari reservoir of 7 wells from Ahvaz field (AZ) were used. After checking the appearance characteristics of the samples, 19 double-polished sections with a thickness of 200 to 300 micrometers were prepared. In order to perform microthermometric analysis, at first, all samples were placed in acetone for 24 hours. In the following, after separating the double polished samples from the slide, in order to completely remove the surface contamination, the samples were placed in an ultrasonic device for five minutes in distilled water. After the initial investigation of the occurrence of fluids inclusions in the studied samples, regardless of the size of the fluids involved, 54 intermediate loads of fluids were selected to conduct microthermometric studies. All microthermometric data were obtained using cooling and heating operations on the involved fluids using a Linkam THMSG 600 model stage placed on an Olympus microscope. In addition, in order to determine the amount of UV reflection in the Petroleum Inclusions in the study, the UV light source model U-RFL-T placed on the Olympus microscope was used. After performing microthermometric operations on the fluid’s inclusions, the selected samples were selected for Raman laser spectroscopy analysis to accurately determine the liquid and vapor phases of the Petroleum Inclusions. It should be noted that Raman laser spectroscopy analyzes were performed on microthermometric analyzed samples. All measurements were made using a LABRAM model Raman spectrometer (ISA Jobin Yvon) available in the Fluid inclusions Laboratory of Montanuniversitat University.

Petrographic studies All the samples were subjected to petrography study, which is in terms of the types of single-phase gas, single-phase liquid, two-phase liquid-rich (oil) intermediates. In these samples, hydrocarbon materials can be seen scattered and filling fractures. In terms of origin, it can be seen in different and varied types, primary and secondary false. Microthermometric studies Microthermometry was performed on 54 fluids inclusions. The homogenization temperature of fluid inclusions is between 50 and 362 degrees Celsius. The samples of the Asmari reservoir show the melting temperature of the last ice crystal between -22 and 13.9. The degree of salinity is calculated to be 0.16 to 35% by weight equivalent to table salt. API study In the samples selected from the Asmari reservoir in Ahvaz field, 54 fluid inclusions were identified. These fluid inclusions emitted the following fluorescence spectrum under UV light. The frequency of reflective color is related to green with a value of 55%, which is in the range of 30-40 API degrees, and the value of 40% belongs to blue color, which indicates the range of API degree 40. -50 and only 5% of these colors belong to the yellow color, which indicates the API degree in the range of 20-30. Therefore, in the samples of the Asmari reservoir, the green color with a frequency of 55% has a density of 0.82 to 0.74 g/cm3, which generally indicates oil with a light density. Also, in the second category of these samples, the abundance of fluorescent reflective color, blue color with an abundance of 40%, with a density of less than 0.74 g/cm3, is considered an extremely light oil. Finally, the lowest reflective color abundance of Asmari reservoir samples is yellow with 5% density of 0.9 to 0.82 g/cm3, it is considered a medium density oil. Raman spectroscopy The calculation of liquid phase salinity in petroleum inclusions cargoes using the Raman laser spectroscopy method is dependent on the geometric shape of the spectrum obtained from the liquid phase present in the petroleum inclusions. According to the Cauchy-Lorentz scattering, the Raman spectrum for pure water shows three peaks at cm-13220, cm-13433 and cm-13617. In the samples that were analyzed by Raman spectroscopy, they indicate hydrocarbon compounds in the fluid inclusions.

Based on the petrographic studies conducted on 19 samples (54 fluid inclusions) according to their diversity (primary, secondary), it indicates and confirms the different compositions of the activity of different phases of Asmari reservoir charging. Based on the data obtained from the microthermometric studies, the physicochemical properties of the reservoir, including the last ice melting temperature, homogenization temperature, and salinity of the reservoir were determined. Based on the physicochemical properties of the Asmari reservoir, it shows two temperature ranges, which can be concluded that this reservoir was charged during two phases in two different time periods. One of the reasons confirming this conclusion can be mentioned that the oil of this reservoir has two origins. Also, based on the composition of the phases in the fluid inclusions (two-phase, three-phase with oil, etc.), it is possible to predict the path of charging the reservoir.