Estimation of Gas Frequency Characteristics to Identify Microfault at Terra Drilling Site

We investigated the frequency characteristics of processsed GPR signals influenced by gas at a drilling site in ARTA block, Pelalawan,Riau, Indonesia. In the drilling site we found some areas with gas bubbles migrating from subsurface. This investigation was done to examine the appropriateness of this area for drilling activities. By using GPR methode we obtain radargram for 6 measurement lines. Furthermore, we calculated the frequency characteristics to find migration mechanism of the gas bubble emerging in the surface. From 9 frequency characteristics we find major differences between gas and non-gas area in subsurface enabling us to estimate gas migration mechanism. We got information of medium characteristics from two parameters, spectral bandwidth(fb) and variance σ. From aanalyzing these two frequency characteristics , we conclude that the presence of gas bubble is most likely caused by the migration of gas to the surface as the result of the existence of micro-fault. Therefore this area is classified as potential geohazard area.