SPE International Conference on CO2 Capture, Storage, and Utilization,
10-12 November 2010,
New Orleans, Louisiana, USA
Time-lapse (4-D) seismic data is often able to detect changes related to the
injection of CO2. However, to quantify these changes is problematic.
Understanding the CO2 injection process is critical to relating the seismic
response to changes within the reservoir. In most CO2 injection projects, a
pure liquid CO2 is initially injected into an oil reservoir, combining with the
oil, resulting in the oil swelling and becoming more mobile. Reservoir changes
include variations in fluid saturation, compressibility, phase and density
along with changes in reservoir temperature and pressure.
Time-lapse (4-D), multi-component (9-C) seismic data has been acquired,
processed and interpreted in three oil fields that have undergone CO2
injection. Vacuum field has been monitored with four seismic surveys during an
EOR project in the San Andres formation with CO2 being injected over a 200
meter zone. Weyburn field has been monitored with three seismic surveys during
an EOR project in the fractured Midale member of the Mission Canyon Formation
with an approximately 20 meter thick zone. West Pearl Queen field has been
monitored with two seismic surveys during a CO2 sequestration test in a 12
meter thick Queen Formation.
Combining the geologic, geophysical and petroleum engineering data allows an
integrated approach to interpreting the time-lapse anomalies associated with
CO2 injection. Integrating the multi-component seismic data allows the
separation of the fluid changes from the pressure changes, allowing a much more
definitive interpretation of the anomalies associated with the CO2 injection
process. Multi-component seismology is critical in monitoring CO2 movement in
the Vacuum, Weyburn, and West Pearl Queen fields.
The Vacuum field (Figure 1) was discovered in 1929 with the drilling of the
Socony Vacuum State 1 well in Section 13-T17S-R34E, Lea County, New Mexico.
Vacuum field produces predominately from the San Andres Formation, in a
shallow-shelf carbonate depositional setting. Structurally, it is positioned on
the shelf edge of the Permian Basin’s Northwest Shelf. The structurally high
shelf crest is located just west of the RCP study area. Porosity and
permeability within the productive zones average 11.8% and 22.0 md,
respectively. The San Andres gross pay zone can reach 200 meters in thickness.
It is divided into two main pay zones: Upper and Lower San Andres. The
Lovington Sandstone, a silty interval, segregates the two zones.
Multicomponent seismic data has revealed the presence of faults with 3 to 7
meter of vertical offset at the reservoir level. These faults cause partial
sealing conditions to occur in the immediate vicinity. This observation has
been substantiated by reservoir simulation. These faults can act to bank
hydrocarbons. This occurs mainly in the Upper San Andres because the flow units
are thin and small amounts of vertical throw are sufficient to juxtapose flow
units against flow barriers. As a result, hydraulic fracturing has been very
attractive when confined to the Upper San Andres zones. Successful horizontal
drilling efforts further support the faulting.
S-wave amplitude analysis provides a high-resolution measure of S-wave
splitting, which can be useful for resolving major flow units and deriving
reservoir parameters in areas containing secondary porosity development. The
secondary porosity and vuggy nature of the reservoir at Vacuum field allows for
S-wave characterization of the higher permeability conduits. Large S1
amplitudes correlate to high vuggy porosity in the San Andres reservoir. P-wave
seismic attributes were uncorrelated with well productivities, but
high-resolution S-wave splitting parameters derived from S-wave analysis
provided an excellent correlation to well productivity.