Passive Hydrocarbon Search
The response of rock mass to stress depends not only on its physical properties but also on the effect of the other contributors in the medium. One of the main factors, especially at the crustal-scale, is the presence of fluid. In such cases, the rupture of rock mass may deviate from the well-known double couple (DC) model for earthquakes. The non-double couple (NDC) component of earthquakes can help to determine the possible presence of fluid. This is well observed in the correlation of the hydrocarbon fields in Uzbekistan with the clusters of NDC earthquakes. There, the smaller earthquakes show strong NDC component.
This source of information has not yet been appreciated in the hydrocarbon exploration community. SeisAnalysis AS can locate such possible reservoirs through analysis of passive seismic activity.
The coloured circles show the earthquakes and the red patches show the hydrocarbon fields. The focal mechanisms of the events show strong NDC component. The percentage of NDC component can be read from the 2nd (isotropic) and 3rd (CLVD) values in the brackets above focal mechanisms. The 1st value shows the earthquake magnitude and the 4th value shows double couple (DC) percentage. For conventional earthquakes, the isotropic and CLVD values are close to 0% and the DC component is close to 100%.