3D Seismic Modelling of Thin Intrusions
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This study presents seismic modeling of two intrusions, modeled as boreholes.The modeling was done over homogenous one-layered models in both 2D and 3D,and a two-layered model in 3D. The goal of the study was to see if seismic might bya tool to monitor the drilling of an intervening well by looking at diffracted eventscreated from the bottom of the two wells. The challenge is to locate the relativelyweak event on seismic, especially when the models becomes more complex. Byhaving a reference to how the seismic look without the intrusions the diffractedevents are easier to detect. If this method is successfully developed it might makethe monitoring of a relief well better and easier.The seismic modeling considered here was done by using a finite-differenceforward-modeling algorithm. Several different cases were considered, to see howthe amplitude of the diffracted signal changed by changing the distance between thetwo wells. To accurately check how the amplitude changed unwanted events wereremoved by muting and usage of reference models, and wiggle traces were createdfor specific receivers. The result was checked for several different receiver offsetsin order to obtain a good result to base the conclusion on.The experiments done here gave a simplified, but conclusive result. Theamplitude of the diffracted event will change when the distance between the twowells are changed. When the distance is small enough to detect interferencebetween the signals from the two wells, the signal will increase when the separationdecreases. The strongest signal will be seen when the two wells intersects, makingone big diffractor. By knowing how the amplitude of the diffracted event changes,and developing the method further, seismic might be used as a tool when drilling anintervening well.