Passive seismic tomography using induced seismicity at a petroleum field in Oman

Abstract

A borehole network consisting of 5 monitoring wells was used to monitor the induced seismicity at a producing petroleum field for a period of about 11 months. Nearly 5400 microseismic events were analyzed and utilized in imaging the reservoir based on a new doubledifference (DD) seismic tomography. The DD tomography method simultaneously solves for event locations and Vp, Vs, and Vp/Vs models using absolute and differential P, S and S-P arrival times. Microseismicity in the field was primarily caused by compaction of the reservoir in and above the gas bearing formation and was distributed along the two major northeastsouthwest (NE-SW) faults in the field. The model resolution analysis based on the checkerboard test and the resolution matrix showed that the central part of the model was relatively well resolved for the depth range of 0.7 to 1.1 km. Clear velocity contrasts were imaged across most parts of the two NE-SW faults. Vp/Vs ratio estimations from the tomographic inversion were low (<1.75) in the shallow depth range, likely due to lithology and gas content, whereas they were large (>1.75) in the deeper part of the model, likely due to fluid saturated formation. In this study seismic tomography showed a great potential for reservoir imaging and property estimation using induced seismicity.2

Reservoir Structure and Wastewater‐Induced Seismicity at the Val d'Agri Oilfield (Italy) Shown by Three‐Dimensional Vp and Vp/Vs Local Earthquake Tomography

“…High-resolution local earthquake tomography (LET) has proven useful to characterize geothermal sites and hydrocarbon reservoirs especially in geologically complex areas where seismic reflection exploration is challenging (Calò & Dorbath, 2013;Julian et al, 1996;Tselentis et al, 2011;Vanorio et al, 2005;Zhang & Lin, 2014;Zhang et al, 2009). High-quality V p and V p /V s LET images help define the geometric and petrophysical properties of reservoirs, while 3-D earthquake locations allow pinpointing active faults.…”

Focal mechanism determination using high-frequency waveform matching and its application to small magnitude induced earthquakes

“…The distribution of induced events in the field is shown in Fig. 6 (Sarkar 2008;Sarkar et al 2008;Zhang et al 2009). All the events have a residual traveltime less than 30 ms, indicating they are well located.…”

“…For real application we use data from a five-station network monitoring induced seismicity at a petroleum field (Sarkar 2008;Zhang et al 2009). The method is tested with data from a synthetic seismic event and then applied to real events selected from an oil and gas field.…”

Relative location of microseismicity

“…This recognition has led to three groups of approaches that differ from each other in how the velocities are handled: first, a velocity model might be fixed a priori and the hypocenters can be computed in that model (e.g., Geiger, 1912;Asch et al, 1996;Gambino et al, 2004;Chambers et al, 2010;Ito et al, 2012); second, initially estimated velocities and possibly anisotropy coefficients might be iteratively updated based on the data supplied by events themselves and simultaneously with obtaining their hypocenters (e.g., Thurber, 1986;Iyer and Hirahara, 1993;Thurber and Rabinowitz, 2000;Zhang et al, 2009;Jansky et al, 2010;Zhou et al, 2010;Grechka and Yaskevich, 2014;Li et al, 2014); and, third, the influence of velocities on the hypocenters of events within a selected cluster might be reduced by relying on the previously located events in the same cluster and finding the hypocenters of other events relatively to them (Waldhauser and Ellsworth, 2000;Waldhauser, 2001;Waldhauser and Schaff, 2008;Li et al, 2013).…”