Application to Oil Reservoirs - Goshey Energy Services

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Overview

A saturation model that is based on the difference between the compressibility of the brine and hydrocarbons occupying the reservoir rock pore spaces may encounter resolution issues as we transition from hydrocarbon gas to liquids.

The cross plot below shows how bulk modulus of various reservoir fluids changes with reservoir pressure at a temperature of 150° F. Note that while the widest difference is between gas and brine, there is still a very significant difference between hydrocarbon liquids and brine. Assuming frame moduli across a reservoir stays relatively constant, it should still be possible to estimate water saturation in conventional siliciclastic oil reservoirs. We have observed that to be the case for a number of oil reservoirs we have evaluated using our proprietary algorithm. Consider the Gulf of Mexico example below.

GOM Oil Reservoir

Our oil reservoir well log example is from offshore the Gulf of Mexico in water depths of over 6,000 ft. It is a middle Miocene-age sand reservoir in the Mississippi Canyon Block 948. Well-log data showing both the conventional saturation model (Archie’s) interpretation and Swt estimate from the new model is shown in well log below The average porosity for the pay interval is 22.7%

Description

Of significance in this example is the fact that this reservoir is a black oil reservoir. PVT testing conducted on oil samples extracted from the reservoir revealed an oil gravity of 34.2 API.

Case Study Highlights:

The average Swt calculated across the pay interval using the new model is 29%, whereas the Archie saturation model, calibrated to core-measured electrical properties and Rw determined from within the reservoir, yields an average Swt of 25%.

Well Log Plots

Well log plot of offshore GOM oil reservoir

Conclusion

New Sonic log based saturation model was successfully applied to a black oil reservoir offshore the Gulf of Mexico.

Model results was comparable to that from conventional saturation models.

*Batzle, M., & Wang, Z., 1992, Seismic properties of pore fluids. GEOPHYSICS, 57(11), 1396-1408. https://doi.org/10.1190/1.1443207

*Han, D. H.; Batzle, M. Velocity, density and modulus of hydrocarbon fluids — Empirical modeling. In SEG Technical Program Expanded Abstracts 2000, pp 1867-1870.

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