Forward modeling of fracture‐induced sonic anisotropy using a combination of borehole image and sonic logs

2007 ◽  
Author(s):  
Romain Prioul ◽  
Adam Donald ◽  
Randy Koepsell ◽  
Tom Bratton ◽  
Claude Signer ◽  
...  
Keyword(s):  
Forward Modeling ◽  
Borehole Image ◽  
Sonic Logs

Forward modeling of fracture-induced sonic anisotropy using a combination of borehole image and sonic logs

Geophysics ◽  
2007 ◽  
Vol 72 (4) ◽  
pp. E135-E147 ◽  
Author(s):  
Romain Prioul ◽  
Adam Donald ◽  
Randy Koepsell ◽  
Zakariae El Marzouki ◽  
Tom Bratton
Keyword(s):  
Order Approximation ◽  
Data Interpretation ◽  
Forward Modeling ◽  
Horizontal Stress ◽  
Depth Interval ◽  
Geologic Fractures ◽  
Induced Fractures ◽  
The Individual ◽  
Borehole Image ◽  
Sonic Logs

We develop a methodology to model and interpret borehole dipole sonic anisotropy related to the effect of geologic fractures, using a forward-modeling approach. We use a classical excess-compliance fracture model that relies on the orientation of the individual fractures, the elastic properties of the host rock, and the normal and tangential fracture-compliance parameters. Orientations of individual fractures are extracted from borehole-image log analysis. The model is validated using borehole-resistivity image and sonic logs in a gas-sand reservoir over a [Formula: see text] (50 m) vertical interval of a well. Significant amounts of sonic anisotropy are observed at three zones, with a fast-shear azimuth (FSA) exhibiting 60° of variation and slowness difference between 2% and 16%. Numerous quasivertical fractures with varying dip azimuths are identified on the image log at the locations of strong sonic anisotropy. The maximum horizontal-stress direction, given by breakouts and drilling-induced fractures, is shown not to be aligned with the strike of natural fractures. We show that using just two adjustable fracture-compliance parameters, one fornatural fractures and one for drilling-induced fractures, is an excel-lent first-order approximation to explain the fracture-induced anisotropy response over a depth interval of [Formula: see text]. Given the presence of gas and the absence of clay filling within the fractures, we assumed equal normal and tangential compliances. The two inverted normal compliances are [Formula: see text] and [Formula: see text]. Predicted FSA matches measured FSA over [Formula: see text] (40 m) of the [Formula: see text] (50 m) studied interval. Predicted slowness anisotropy matches the overall variation and measured values of anisotropy for two of the three strong anisotropy zones. Analysis of the symmetries of the modeled anisotropic response shows that the medium is mostly a horizontal transverse isotropic medium, with small azimuthal variation of the symmetry axis. Analysis of each independent fracture type shows that the anisotropy is mainly driven by open or partially healed fractures, but also consistent with stress-related, drilling-induced fractures. Therefore, the measured sonic anisotropy is caused by the combination of stress and fracture effects where the predominance of one mechanism over the other is depth-dependent. This method provides a consistent approach to data interpretation by integrating borehole image and sonic logs that probe the formation at different depths of investigation around the borehole.

Fracture detection in oil-based drilling mud using a combination of borehole image and sonic logs

2017 ◽  
Vol 84 ◽  
pp. 195-214 ◽  
Author(s):  
Jin Lai ◽  
Guiwen Wang ◽  
Zhuoying Fan ◽  
Ziyuan Wang ◽  
Jing Chen ◽  
...  
Keyword(s):  
Drilling Mud ◽  
Fracture Detection ◽  
Borehole Image ◽  
Sonic Logs

Inversion-based interpretation of borehole sonic measurements using semianalytical spatial sensitivity functions

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. D111-D124 ◽  
Author(s):  
Shan Huang ◽  
Carlos Torres-Verdín
Keyword(s):  
Elastic Properties ◽  
Forward Modeling ◽  
Inversion Method ◽  
Vertical Resolution ◽  
Flexural Mode ◽  
Spatial Sensitivity ◽  
Sensitivity Functions ◽  
Synthetic Rock ◽  
Sonic Logs ◽  
Interpretation Method

One of the major challenges in the interpretation of sonic logs is the presence of bed-boundary (shoulder-bed) effects, which can decrease the accuracy of the estimated elastic properties due to spatial averaging caused by the sonic receiver array across thin beds. A reliable approach to account for shoulder-bed effects in the interpretation of sonic logs is the implementation of forward modeling and inversion techniques. We have developed an efficient inversion-based interpretation method for the estimation of in situ rock formation elastic properties from sonic logs acquired in vertical wells. The method uses semianalytical spatial sensitivity functions for fast forward modeling of sonic-slowness logs and estimates formation elastic properties by iteratively matching the available logs with numerical simulations. Due to the intrinsic vertical resolution limits of sonic logs, the inversion method requires predefined bed boundaries using other high-resolution well logs. We first developed a workflow to estimate shear slowness of thin beds from flexural mode dispersions measured at multiple discrete frequencies. Then, we extended the method to estimate layer-by-layer compressional and shear slownesses by combining the slowness logs of nondispersive P- and S-waves. The method was first successfully verified using data numerically simulated for synthetic rock formations consisting of multiple thin beds and exhibiting large elastic property contrasts. Maximum relative errors and maximum uncertainty in the estimates were less than 2% and 6%, respectively. Field data acquired in wells penetrating multiple horizontal thin beds were also used to appraise the reliability and resolution improvement of the method in the estimation of formation compressional and shear slownesses. Our results indicated that our inversion-based interpretation method improved the vertical resolution of sonic logs by 70%. The new inversion-based interpretation method opens up the possibility of integrating modern borehole acoustic measurements with nuclear and resistivity logs for improved poroelastic and petrophysical interpretations.

Carbonate Seismic Interpretation Technology Update Based On Forward Modeling And Its Application In A Oilfield

2020 ◽  
Author(s):  
Bo Peng ◽  
Xin Chen ◽  
Xiaodong Wei ◽  
Haishan Sun ◽  
Qiang Liu ◽  
...  
Keyword(s):  
Forward Modeling ◽  
Seismic Interpretation

2.5-D forward modeling and inversion of time domain IP method

2017 ◽  
Vol 70 (0) ◽  
pp. 69-79
Author(s):  
Hideki Mizunaga ◽  
Kiyotaka Ishinaga
Keyword(s):  
Time Domain ◽  
Forward Modeling ◽  
And Inversion
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