1. STATIC AND DYNAMIC RESERVOIR CHARACTERIZATION USING
HIGH RESOLUTION P-WAVE SEISMIC VELOCITY DATA IN DELHI FIELD, LA
Sidra (Shahid) Hussain and Dr. Thomas Davis
Reservoir Characterization Project, Geophysics Department, Colorado School of Mines
Abstract
Static and dynamic reservoir characterization was done on high resolution P-wave seismic data in Delhi Field, LA to study the complex stratigraphy of the Holt-Bryant sands and to delineate the CO2 flow path. The interpretation was done on bandwidth-extended seismic data. Acoustic impedance inversion done on monitor and base surveys helped in delineating CO2 flowpaths and the channel geometry in the reservoir.
Acknowledgements
I would like to thank Dr. Tom Davis and my thesis committee for helping me with this research, Denbury Resources Inc. for sponsoring the research and providing us with the data, Geotrace for doing the bandwidth extension and Colorado School of Mines, Geophysics Department’s Reservoir Characterization Project (RCP) for funding my research.
3. Dynamic Characterization
2. Static Characterization
4. Results
MCF/D
WATER INJ
WATER PROD
OIL PROD
GAS PROD 65 60 55 50 45
BPD
Primary Production RF ~14%
Secondary Production RF ~ 40%
Prior 1970
Production data not available
100,000
Time in years
2005
20,00 0
NS23A-1637
1. Introduction to Delhi Field
Areal extent is 6200 acres
15 miles long
Delhi OOIP 357 MMBbls
RCP Study Area 7 sq miles
Location of Delhi Field (Evolution Petroleum Corporation).
Location of Delhi Field in relation to the surrounding structural features (Modified after Mancini, et al. 2008a).
A generalized stratigraphic section of the Cretaceous formations in Delhi Field (Denbury Resources Inc.).
1 mile
2008
Mar 2010
RCP
June 2010
Overlap
Permanent Patch
(Jan 2010)
Location of the seismic surveys in the field. The merged survey of 2008 and March 2010 was used as the base survey for 3D interpretation and the RCP survey from June 2010 was used as the monitor survey for time-lapse interpretation in this study. (Sun Oil Co. and Denbury Resources Inc.)
20,000
Production history data of Delhi Field before the tertiary recovery started (Modified from Denbury Resources Inc.).
2.1 Bandwidth Extension
Statistical constant phase wavelets extracted from the merged ( ) survey within ms, Inline=1019 and Xline=
T= 20ms
F=1/T=50Hz
T= 12ms
F=1/T=83.3 Hz
Before Bandwidth Extension
After Bandwidth Extension
2.1.1 QC of Bandwidth Extension
QC for Phase-shift: For most peaks and troughs, there is no phase shift.
QC for Time Shift: The time difference falls within the range of -1 and +1 (see histogram) which is normal for a trace by trace computational continuous wavelet transform process.
QC of well-to-seismic ties: Synthetic seismograms (red) created using the wavelets shown below the ties; The correlation coefficient of pre-BE data is 94% while that of the post-BE data is 73% which is reasonable for a high frequency data.
Bandwidth extension was applied by Geotrace on the 3D seismic datasets using the method of continuous wavelet transform to recover the lower and the higher frequencies in the seismic bandwidth that were lost from earth’s reflectivity during transmission. The method increased the dominant frequency in the data and decreased the tuning effect.
2.2 Structural Interpretation N
-25
Injector Wells
Producer Wells
Amplitude map of the top of TUSC 7 from
the merged BE survey showing bright sandstone bodies in red. 35 -4
Amplitude map of Paluxy from the merged BE survey showing SW-NE trending meandering channel-like features in hot colors.
Authors’ s:
To monitor the flow of CO2 within Paluxy and Tuscaloosa sandstone formations, dynamic characterization was done using merged survey as the base survey and RCP (June 2010) survey as the monitor survey. The surveys were cross-equalized to increase the repeatability. Model-based acoustic impedance (AI) inversion was performed on both the surveys to quantify the changes in acoustic impedance with the addition of CO2 and water in the field. Fluid substitution modeling was done on well data to model the expected changes in AI with CO2 and water.
3.1 Cross-Equalization
Survey Re-gridding
Spectral Shaping
Static Time Shift
Time-Variant Time Shift
Cross-Normalization
NRMS maps and their respective histograms within the reservoir zone. The repeatability has improved with cross-equalization. However, some zones of low repeatability around the wells are observed where one expects to see changes with production and injection. The middle of the reservoir shows high repeatability. This could mean that the middle of the reservoir is being bypassed.
The steps taken to cross-equalize the base and the monitor surveys
Before Cross-equalization
After Cross-equalization
Positive Seismic Amplitude 2
Hierarchy of a model-based acoustic impedance inversion (Modified from Young, 2006).
An arbitrary dip line showing amplitude difference through four of the wells in the phase-1 injection pattern. The effect of CO2 can be seen around the injectors.
3.2 Model-based Acoustic
Impedance Inversion
3.3 Fluid Substitution Modeling
AI % difference map with a 2 ms window centered at with the production data from June 2010 overlain; the black dashed line is the oil-water contact; notice the negative impedance change below the OWC. The lighter yellow color shows area where Paluxy is not being swept completely.
AI % difference map at TUSC 7 top; the white triangles are TUSC 7 injectors and the white circles are TUSC 7 producers; the black polygons show the flow paths of CO2 illuminating channel-like features in the sandstone.
Percentage change in acoustic impedance with the addition of CO2 under different pressure conditions.
Percentage change in acoustic impedance with the increase in effective pressure for CO2 replacing brine.
After BE
Before BE
Post-BE data traces overlain on pre-BE data
GR log