Passive seismic survey is a geophysical method that utilizes a spectral frequency from seismicity data to identify subsurface reservoir fluids. Rock pores that contain hydrocarbon fluids show higher low-frequency amplitude between 2-4 Hz compared with those that contain water. This paper shows the feasibility study that has been done in S Field, South Sumatra Basin. Four wells were used to validate the result of the spectral data. This method is also considered as a prospect ranking tool in the vicinity of the S field.
Eighteen measurement points were collected and grouped into 6 clusters. Four clusters are located near S-1, S-2, S-3, and S-4 wells. One cluster is located on prospect K and the other one on prospect G. Standard signal processing flows were conducted such as band-pass filter, FFT, and moving average.
The result shows that the maximum amplitude low-frequency between 2-4 Hz of K and S-1 is less than 0.017. On the other hand, S-2, S-3, S-4 and G show a relatively high amplitude of more than 0.02 which indicates a greater possibility of hydrocarbon accumulation when compared with K and S-1. This result was confirmed by gas production in S-2 and oil production in S-3. S-4 has not been tested yet, but the refined well correlation it indicates that there is a limestone reservoir of about 60 feet above OWC. S-1 shows a low amplitude which indicates low potential. The completion log confirmed that the well did not penetrate the reservoir target. Prospect G which has a high amplitude of low-frequency anomaly is more interesting than prospect K.
To conclude, low-frequency passive seismic method was successful in distinguishing between water or no hydrocarbons. It is feasible to employ this methodology as a tool for hydrocarbon detection and also as a tool to help in prospect ranking.
Authors : Andika Perbawa, Danar Yudhatama, M. Aidil Arham