| Title | Identification Fluid Phase Based on Vp/Vs Ratio Using Seismic Tomography |
|---|---|
| Authors | Sabrianto Aswad, Akino Iskandar, Lantu ,Andri Dian Nugraha |
| Year | 2014 |
| Conference | Indonesian Geothermal Association Conference |
| Keywords | micro earthquake, seismic tomography, inversion, fluid phase, Vp/Vs ratio |
| Abstract | Permeability changes of a geotermal reservoir structure can be caused by changes of pressure, temperature and geothermal fluid phase due to the activity of the structure and the transformation of hot water phase into steam from fluid injection at the time of production. This is one of the causes of the micro-earthquake in the reservoir. The observation of micro-earthquake seismicity in physical parameters such as subsurface medium seismic velocity can be used to detect the permeability of the reservoir structure. Analysis of seismic velocity is conducted using seismic tomography modelling. Tomography modelling begins with forward modeling process in form ray tracing from the source to the receiver in 3D space to calculate the minimum travel time of wave propagation from P and S wave using 1D velocity initial model. Travel time from this calculation then becomes input in modelling velocity by iterative damped least square method in inverse modelling process which will minimalize quadrate of delay time between calculation and observation travel time. In other words, calculation time will try to calculate near from observation time (representation of subsurface condition) until sufficient minimal delay time value is obtained in iterative process. Result from this research shows velocity anomaly both P and S wave at depth between +0.5 to -1.5 km toward MSL with average value 10%-15% lower than its around relatively. Ratio data of Vp/Vs extend low value relatively at average 1.7 - 1.9. This anomaly layer on geothermal field related with gas saturated characteristic |