Velocity Calibration for Microseismic Monitoring: Applying Smooth Layered Models With and Without Perforation Timing Measurements

Abstract

Theorectically, the perforation shot origin time T 0 affects the accuracy of the inverted velocity structure, and therefore the accuracy of subsequent microseismic event locations. The origin time can be obtained from perforation timing measurements or estimated from the picked arrival times. In order to investigate the role of origin time in velocity calibration, we designed two inversion procedures. In procedure A, T 0 is calculated during the Occam's inversion while T 0 is set to its true value in procedure B. A grid search locator is applied on both inverted models to produce two locations. We constructed three synthetic P-wave velocity models and add normally distributed random noise to the synthetic arrival times of all models. The noisy synthetic data are piped through procedure A to obtain location A and through procedure B to produce location B. Graphical analysis show that location A is closer to the true shot location than location B although both are close to each other. If we remove the data noise and repeat the test, location B is closer to the true shot than location A. It was observed that the inverted location A is better in terms of the distance from the true location if using noisy data and location B is better if using noise-free data. This indicates that uncertainties due to data noise cause our inconsistent observation and implies that perforation timing measurements are not necessary and may actually result in a less accurate velocity model.

Detection and Location of Microseismic Events with Low Signal-to-Noise Ratios

“…Hence, a simple but valid approximation is a 1-D flat-layered model. This velocity model is first derived from the sonic logging data of the treatment or monitoring well, and then calibrated by locating the perforation or string shots back to their known positions Pei et al, 2008;Pei et al, 2009;Bardainne and Gaucher, 2010). Once the calibrated velocity model is gained, the travel time based source location method can be applied to estimate the microseismic source positions.…”

An Efficient Method for Velocity Calibration and Prediction of Microseismic Event Location Using very Fast Simulated Annealing

“…shale gas, tight gas and tight oil) has caused a significant interest in microseismic fracture monitoring [1,2]. Meanwhile, we are facing the enormous challenges of improving microseismic event locations and building accurate velocity model [3][4][5]. Various linear inversion techniques (e.g.…”

“…Various linear inversion techniques (e.g. least square and Singular value decomposition (SVD)) are performed to invert velocity structure and locate microseismic events by using first arrival travel times and particle motion of seismic P and/or S waves [3,4,[6][7][8][9][10][11]. However, those linear inversion methods strongly depend on the initial models that may lead to trap in local minimum [5] due to less receiver coverage (<15 geophones in the monitoring well).…”

The influence of fracturing process on microseismic propagation

“…As to the calibration shot data, the shot location, receiver location and perforation time are known, thus with the travel time known, we can calculate the best velocity value for each layer (Pei et al . ; Warpinski et al . ).…”