AMBIENT SEISMIC NOISE CROSS CORRELATION FOR MONITORING RELATIVE SEISMIC VELOCITY CHANGES IN THE ZX FIELD

• Main Author: Arsyad, Mohammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87163
• Institution: Institut Teknologi Bandung

Fluid re-injection activities in the ZX Field disrupt the stability of the subsurface layer which has implications for the value of relative velocity changes. Monitoring changes in relative seismic velocity can provide information about reservoir dynamics, such as the occurrence of cracks or fluid movement. In this study, the data used are seismic recording data recorded continuously at 37 seismometer stations in the ZX Field. The duration of data recording is two months with details of 1 month before fluid injection and 1 month after fluid injection. The process of monitoring changes in relative seismic velocity utilizes ambient seismic data recorded at several pairs of stations. The method applied is the cross correlation function (CCF) for several pairs of stations that pass through the injection well and production well. Daily CCF for each pair of stations is stacked to increase the signal to noise ratio (SNR). Based on the results of the CCF stacking, the delay time and relative seismic velocity changes are calculated. This calculation is done by comparing the current CCF and the reference CCF using the Moving Window Cross Spectrum (MWCS) method. The reference used is the period before the fluid injection was carried out. After that, a plot of relative velocity changes for each pair of seismic stations was obtained, which illustrates the physical changes in the subsurface. The phase before fluid injection shows a trend of velocity changes that are not too significant, indicating the normal state of the medium. The relative seismic velocity around the injection well and production well shows a stable pattern. The fluid injection phase shows a decreasing trend around the W12 production well. When the fluid injection activity ends, Several pairs of seismic stations still show a decrease in seismic velocity which is most likely still influenced by the effects of injected fluids.