STATIC AND DYNAMIC RESERVOIR CHARACTERIZATION USING HIGH RESOLUTION P-WAVE SEISMIC VELOCITY DATA IN DELHI FIELD, LA

Sidra (Shahid) Hussain and Dr. Thomas DavisReservoir Characterization Project, Geophysics Department, Colorado School of Mines

AbstractStatic 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.

AcknowledgementsI 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 Characterization2. Static Characterization

4. Results

MCF/DWATE

R INJ

WATER PROD

OIL PROD

GAS PROD

65605550

45

BPD

Primary Productio

n RF ~14%

Secondary Production RF ~ 40%

Prior 1970 Production data not available

100,000

0Time in years 2005

20,000

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.)

MCF/D

WATER INJ

WATER PROD

OIL PROD

GAS PROD

65605550

45

BPD

Primary Production

RF ~14%

Secondary Production RF ~ 40%

Prior 1970 Production data not available

100,000

0 Time in years 2005

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 (2008-2010) survey within 800-1100 ms, Inline=1019 and Xline=1001-1379

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 InterpretationN

0

-25

Injector WellsProducer Wells

1 mile

Amplitude map of the top of TUSC 7 from the merged BE survey showing bright sandstone bodies in red.

Injector WellsProducer Wells

1 mile

35

-4

Amplitude map of Paluxy from the merged BE survey showing SW-NE trending meandering channel-like features in hot colors.

Authors’ Emails: sidra1982@gmail.comtdavis@mines.edu

To monitor the flow of CO2 within Paluxy and Tuscaloosa sandstone formations, dynamic characterization was done using merged 2008-10 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 ShiftCross-

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-equalizationPositive Seismic Amplitude Positive Seismic Amplitude

2

0

2

0

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.

1400 1600 1800 2000 2200 2400-25

-20

-15

-10

-5

0

AI % change at different effective pressures for CO2 replacing brine

5% CO210% CO2

Pressure (psi)

AI %

cha

nge

1400

1500

1600

1700

1800

1900

2000

2100

2200

2300

2400

012345678

AI% change with effective pressure for CO2 replacing brine

5% CO210% CO2

Pressure (psi)

AI %

cha

nge

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

N