Improved Microseismic Fracture Mapping Using Perforation Timing Measurements for Velocity Calibration

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA method is decribed where microseismic mapping of hydraulic fractures is improved by using crosswell data to calibrate and/or verify dipole-sonic velocity data. The microseismic technique uses an array of advanced tri-axial receivers to detect microearthquakes induced by a fracture and, thus, provides a real-time image of the fracture and the way it propagates. To apply this technique, the orientation of the receivers must be determined by detecting perforations or other energetic sources in the treatment well, and the velocity structure of the intervening rock interval must be adequately known. Currently, dipole-sonic logs provide high-resolution velocity data, but significant errors may occur if the logs are old (e.g., formation has depleted), anisotropy is large (e.g., vertical velocity different from horizontal velocity), or several other conditions exist. In addition, faults or lithology changes may separate the wells and alter the velocity structure. Accurate location of the microseisms, and thus the fracture image, is strongly dependent on accurate information about the velocity structure.In the perforation-timing procedure, crosswell-velocity data are obtained by monitoring the firing pulse from the receiver-orientation perforations (or string shots) and recording the timing pulse along with the arrival data. From these results, a simple one-dimensional model of velocities can be extracted and used to validate, refine, or correct the detailed dipole-sonic data or provide a warning of discrepancies. The ultimate goal is improved accuracy in microseismic mapping, but the results are also useful for assessing the applicability of dipole-sonic logs. Perforationtiming measurements for velocity structure have now been performed in 10 separate projects that have been used to analyze approximately 120 fracture treatments.

A Comparison of Hydraulic-Fracture Modeling With Downhole and Surface Microseismic Data in a Stacked Fluvial Pay System

“…• Other recommendations such as a matched filter technique to enhance signal from induced microseismic (Hulsey et al, 2009), using perforation timing measurements for velocity calibration (Warpinski et al, 2003), and using source parameters technique to better describe the fracturing process by determining the actual failure mechanism (Mayerhofer et al, 2000) are also suggested for further review. …”

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

“…The origin time of perforation shot was assumed to be known in their study. However, the origin time of perforation shot is difficult to measure accurately [3]. To reduce the effect of the origin time of perforation shot, we develop a novel objective function for VFSA which consists of the travel time differences of P-wave first arrivals between seismic traces.…”

“…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).…”

Seismic imaging of hydraulically-stimulated fractures: A numerical study of the effect of the source mechanism

“…Two types of sources are generally present in the hydraulic stimulation process. The first is generated by the perforation of the casing of the well (Warpinski et al, 2003) and presumably radiates most of its energy as a point force monopole. Second is the induced microseismicity which generally has a dominant double couple mechanism (Song et al, 2010;Song and Toksoz, 2011).…”