Changes

Rock-Eval S1 or EOM yields alone have little meaning in assessing potential production because they do not account for the organic background. For example, coals might have an S1 value of 10 mg HC/g rock, but with a TOC of 50% or higher, the OSI is quite low, indicative of low oil saturation with a high expulsion or production threshold.

Rock-Eval S1 or EOM yields alone have little meaning in assessing potential production because they do not account for the organic background. For example, coals might have an S1 value of 10 mg HC/g rock, but with a TOC of 50% or higher, the OSI is quite low, indicative of low oil saturation with a high expulsion or production threshold.

An empirical value exceeding 100 mg oil/g TOC was used to identify potential reservoir intervals in a conventional reservoir in the Anadarko Basin<ref name=J&B1984 /> and similarly in vertical Monterey Formation wells.<ref name=Jrvetal1995>Jarvie, D. M., J. T. Senftle, W. Hughes, L. Dzou, J. J. Emme, and R. J. Elsinger, 1995, [http://wwgeochem.com/references/Jarvieetal1995Examplesandnewapplicationsinapplyingorganicgeochemistry.pdf Examples and new applications in applying organic geochemistry for detection and qualitative assessment of overlooked petroleum reservoirs], in J. O. Grimalt and C. Dorronsoro, eds., Organic geochemistry: Developments and applications to energy, climate, environment, and human history: 17th International Meeting on Organic Geochemistry, p. 380–382. Data from Sandvik et al.<ref name=Sndvk1992 /> and similarly by Pepper (1992) suggest organic matter retains a portion of generated petroleum cited by both authors to be about 10 g of liquids sorbed per 100 g organic matter, that is, 100 mg HC/g TOC. Thus, there is a resistance to oil flow until the sorption threshold is exceeded, that is, values of OSI greater than 100 mg hydrocarbons per g of TOC. As Rock-Eval S1 is not a live oil quantitation, but instead a variably preserved rock-oil system, there is certainly loss of light oil due to evaporation, sample handling, and preparation before analysis. Loss of S1 is often estimated to be 35% (Cooles et al., 1986), but it is highly dependent on organic richness, lithofacies, oil type (light or heavy), and sample preservation. Organic-lean rocks such as sands, silts, and carbonates as found in conventional reservoirs would have a much higher loss than organic-rich, low-permeability mudstones. Drying samples in an oven will certainly impact the free oil content in Rock-Eval S1. Oil-based mud systems preclude the use of the Rock-Eval S1 and OSI.

An empirical value exceeding 100 mg oil/g TOC was used to identify potential reservoir intervals in a conventional reservoir in the Anadarko Basin<ref name=J&B1984 /> and similarly in vertical Monterey Formation wells.<ref name=Jrvetal1995>Jarvie, D. M., J. T. Senftle, W. Hughes, L. Dzou, J. J. Emme, and R. J. Elsinger, 1995, [http://wwgeochem.com/references/Jarvieetal1995Examplesandnewapplicationsinapplyingorganicgeochemistry.pdf Examples and new applications in applying organic geochemistry for detection and qualitative assessment of overlooked petroleum reservoirs], in J. O. Grimalt and C. Dorronsoro, eds., Organic geochemistry: Developments and applications to energy, climate, environment, and human history: 17th International Meeting on Organic Geochemistry, p. 380–382.</ref> Data from Sandvik et al.<ref name=Sndvk1992 /> and similarly by Pepper (1992) suggest organic matter retains a portion of generated petroleum cited by both authors to be about 10 g of liquids sorbed per 100 g organic matter, that is, 100 mg HC/g TOC. Thus, there is a resistance to oil flow until the sorption threshold is exceeded, that is, values of OSI greater than 100 mg hydrocarbons per g of TOC. As Rock-Eval S1 is not a live oil quantitation, but instead a variably preserved rock-oil system, there is certainly loss of light oil due to evaporation, sample handling, and preparation before analysis. Loss of S1 is often estimated to be 35% (Cooles et al., 1986), but it is highly dependent on organic richness, lithofacies, oil type (light or heavy), and sample preservation. Organic-lean rocks such as sands, silts, and carbonates as found in conventional reservoirs would have a much higher loss than organic-rich, low-permeability mudstones. Drying samples in an oven will certainly impact the free oil content in Rock-Eval S1. Oil-based mud systems preclude the use of the Rock-Eval S1 and OSI.

Although an oil crossover value of less than 100 mg HC/g TOC does not rule out the possibility of having producible oil, it does represent substantially higher risk based strictly on geochemical results. It may be that samples have been dried or more volatile liquids have evaporated, particularly in conventional reservoir lithofacies.

Although an oil crossover value of less than 100 mg HC/g TOC does not rule out the possibility of having producible oil, it does represent substantially higher risk based strictly on geochemical results. It may be that samples have been dried or more volatile liquids have evaporated, particularly in conventional reservoir lithofacies.