North Malay Basin - Goshey Energy Services

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Overview

This example or case study is from the NM field, it is based on the dataset published by Fadjarijanto et al. (2018)*. This is a laminated shaly sand reservoir located in the North Malay Basin. The depositional setting of the reservoir interval of interest is described as a tide-dominated coastal plain.

Description

Initially labeled as a shale interval due to high gamma-ray readings and low resistivity, the DS2-B reservoir was found to have resistivity ranging from approximately 2 to 4 ohmm, which closely resembles the 2 to 3 ohmm range observed in the overlying wet shale interval. Initial petrophysical assessments using Waxman-Smits and Indonesia saturation models suggested that the reservoir was predominantly saturated with water, with average water saturation exceeding 90% in the lower DS2-B. However, analysis of fluid samples and pressure data from a wireline formation tester revealed the interval to be gas-bearing (Fadjarijanto et al., 2018).

Case Study Highlights:

Once more, we applied the methodology outlined in Omovie (2024) to estimate Swt. The Swt estimated from the new model is the red curve labeled SwT_VpVs in the saturation track. The blue curve in the same track depicts Swt derived from Waxman-Smit’s conventional interpretation by the authors. Note that both models show comparable Swt values in the clean sandstone reservoirs both above and below the DS2-B shaly sand layer. The disparity between the models primarily arises within the DS2-B layer, attributed to its low resistivity, as previously mentioned. According to the new saturation model, the average Swt across the DS2-B shaly sand reservoir stands at 55%. This aligns closely with the 60% Swt determined by the authors through Thomas Steiber laminated shaly sand analysis.

Well Log Plots

DS2-B well log plot

Conclusion

According to the new saturation model, the average Swt across the DS2-B shaly sand reservoir is 55%. This aligns closely with the 60% Swt determined by the authors through Thomas Steiber laminated shaly sand analysis. The new model was able to identify and quantify pay across intervals that were missed by resistivity-based shaly sand saturation models.

For more information about our approach and the results achieved in the North Malay Basin, please reach out to us.

*Fadjarijanto, A.; Rachmadi, A.; Setiawan, A. S.; Praptono, A.; Suriyo, K.; Simatupang, M. H.; Pakpahan, O.; Costam, Y. R.; Zakaria, Z. U. Three Petrophysics Techniques Applied for the Thin Lamination Reservoir: The Impact towards Significant Reserve Addition. In Offshore Technology Conference Asia, 2018; D041S035R003, Vol. Day 4 Fri, March 23, 2018. DOI: 10.4043/28412-ms.

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