3:30 PM - 4:45 PM
[SCG59-P17] 4-D active monitoring of time-variant ocean bottom structure including a gas chimney type deposit methane hydrate by using seismic wave simulations
Keywords:Methane hydrate, Monitoring, Time-lapse
In this study we show the preliminary results of characteristic wave phases of reflected wave from MH reservoirs and some effective seismic source- receivers array designs through simulating the seismic wave filed by means of a finite difference method (Larsen, 2000). We calculated seismic waveform records on three types of underground seismic structure models as follows: (Model-1) a horizontal multilayered structure model, (Model-2) a horizontal multilayered structure model including a thin MH layer and (Model-3) a horizontal multilayered structure with a chimney type MH deposit in a sand stone layer. The horizontal multilayered structure model consists of four layers with a sea water, a MH or sand stone, mud stone, over an igneous basement rock.
As the results, Model-1 is the horizontal multilayer structure, so no characteristic wave phase is observed. Then the reflect wave from the MH deposit travels faster than that from sea water in the Model-2. It is because MH deposit has higher velocity. Finally, the MH deposit in Model-3 is in the sand stone layer, so the wave that is not reflected from the horizontal layer is observed. Also, we found some effective seismic phase to monitor the time-variant MH reservoir and then tried to optimize an effective source-receivers array design, the preliminary result showed that two types of receivers arrays are effective to monitor the changes of seismic velocity in a MH reservoir by using some particular seismic phases reflected at the boundary of a surface-type MH layer. One of the arrays is constructed my both a horizontal array and a vertical one with seismic active sources located at the sea bottom as we call it, ‘T-type array’. Also the other is called ‘H-type array’ which consists of a horizontal array and two vertical arrays with the seismic source at the sea bottom.