Rock Physics Estimation Of The Effect Of CO2 On Seismic Data

Goal: To show the effect on density, P-velocity, and S-velocity logs of CO2 injection into North Sea water sands, Ty tertiary formation in the xxx field.

Background purpose

Everyone wants to do CO2 injection. We need to use seismic to monitor CO2 placement and migration over time. There are many questions and information needs that can be addressed by well logs and seismic (e.g., cap Rock Capacity, Cap Rock Geometry, Cap Rock Integrity, Fault Plane Capacity, Juxtaposition Lithology Capacity and Post-Charge Reactivation).

Question: what does it look like in seismic for CO2 to be injected in formations?

https://gcep.stanford.edu/pdfs/8fZLzZEhuRbg8oR_3L_zMQ/2.3.1.zoback_04.pdf

Age

Depth range

North Sea. Off the coast of Norway.

Field

Location

Formation

Logplot

Workflow

1. Identify a candidate well

2. Determine a suitable and consistent PP and RPM formation model

3. Gather petrophysical and rock physics parameters

4. PP

5. RP

6. Compare raw and modeled logs

7. Change something to eliminate or ameliorate mismatches

8. Fluid sub

9. Compare water wet with CO2 injected cases to see can be learned

Raw well logs

GEOLINK logs

Logplot

Geologic column

No Resistivity, No NPHI, No Pe, No Caliper, No DRHO

Crossplots

RHOB vs Vp

Pimp vs Vp/Vs

Pimp vs Simp

PR vs E

Petrophysics

Shaly sand. Compute Vclay from GR. Compute PHIT from density. Compute PHIE from PHIT and Vclay. Assume Sw=100% since there is no resistivity or NPHI which might be used to indicate fluid type.

Logplot – show correspondence between the petrophysics and the geologic column.

Rock Physics

Basics

K and G equations give Vp and Vs

RHOB is used

All logs are forward-modeled using the same formation model (petrophysics). Any mismatch is due to:

1. Log problems

2. PP and/or RP model selection problems

3. PP and/or RP model parameter problems

Logplot comparison of raw and modeled logs

Why modifications to the raw well logs is the proper foundation for comparison

The CO2 injection scenario

Inject CO2 resulting in formation pressure of xxx psi at temperature xxx degF and final Sw of 15% (irreducible).

Fluid substitution

Change Sw in RP to effect a fluid sub on the well logs. 100% water to 15% water at irreducible Swirr.

The effect of CO2 injection on well logs

Look at the effects of CO2 on logs via logplot and, crossplot comparisons.

Discussion

Conclusions