Case Study – Adsett Field, British Columbia
Figure 1: N-S schematic section of Devonian in NEBC
Adsett field is a gas producing field south of Fort Nelson, British Columbia. The field was discovered in 1974 but was kept behind pipe till late 90’s when larger gathering system was built in response to other discoveries in the area. The field produces gas from hydrothermal dolomites of Devonian Slave Point Formation. Devonian geology is explained by the schematic geologic section running south to north across the northern edge of Peace River Arch to North Western Territories.
Slave Point formation contains a series of carbonate build-ups which are than undergone numerous faulting episodes and subjected to chemical alteration by hydrothermal fluids. Collapse and karsting featues are visible with the help of 3D’s in other areas nearby.
Figure 2: Adsett area pools and location of seismic lines
Looking closely at Adsett area, the area is less explored compared to the Alberta part of WCSB. Although the reservoirs have been substantially bigger but the network of gas gathering system is relatively sparse. More recently there were few new discoveries made in the area with a notable constrain over the building of pipelines. One of the new well drilled to Slave Point in west Adsett came up on production at 12 MMCFD and still producing in access of 7 MMCFD. Cumulate gas to-date from this well is 12.5 Bcf. The SFD survey was acquired over the main Adsett pool as well as to the west over the new discovery. The SFD data shows significant correlation to the main pool and the new Adsett west pool.
Figure 3: SFD signature and its reference to the Adsett field
Adsett main pool has produced 130 Bcf of gas to-date and still producing at lesser rates. Previously it was considered that gas bearing dolomites have to be structurally higher to be above the regional water level. At that time SFD data have shown some promising results in the lower Slave Point bank. Late drilling have revealed that the lower bank also have significant unfound reserves and they also correlate very well with the SFD anomalies detected at that time. Figure 3 shows an excellent correlation of SFD anomaly to the reservoir.
In conclusion, the SFD acquisition in the area has shown significant anomalies, out of which some have been tested by new exploration activity. Using SFD in conjunction with other data can lead to focus areas for future exploration.