Fault Block A
Up until 1992, wells draining FBA were the A-11 (left) and A-6 (right) of Block 331, the B-2 (top), B-5 (mid) and B-7 (bottom) of Block 330, and the A-13 (left) and A-15 (right)of Block 338.
Figure 5. Demonstration of the 4D seismic changes seen in Eugene Island 330 Field FBA from 1992 to 1994. Red is increased amplitude, blue is dimmed amplitudes over time, and green are sustained, high amplitudes indicative of bypassed pay remaining in 1994.
After the 3D seismic survey of 1992 was acquired, there were only three
wells active in the fault block: new wells B-5ST, B-6ST in Block 330 and
the A-12 in Block 338. A new 3D seismic survey was acquired in 1994, and
it clearly shows drainage, or dimmed amplitudes, caused by production in
the intervening years. About 2.4 million barrels of oil equivalents were
produced from these wells, and about 600 acres were dimmed. Assuming a
100 ft thick pay sand with 30% porosity and a drop in Sw of 30%, that would
require that each ac-ft produce about 400 bbl/ac-ft, quite reasonable for
clean, Pleistocene sands in the GOM.
The bypassed oil remaining after 1994 will require the placement of yet another well into the fault block, and therein lies the power of 4D seismic monitoring. Each new well recovers an additional percentage of oil-in-place, increasing the ultimate recovery efficiency. In addition, the 4D seismic changes can be modeled within a reservoir simulator to risk the new well (Figure 6). Amplitudes drained by the new well are predicted to account for an additional 2 million barrels for a well placed horizontally from a sidetrack in the B-5 well toward the 330/338 property line to the south. In another two years, that well will water out, an additional amplitudes are predicted to remain after that. Then a well projected more east-west along the property line will be required to recover additional bypassed reserves after that.
Figure 6. Model simulation of the flow paths and drainage produced from a hypothetical well placed along the Block 330/338 property line in 1996. After two additional years of production, a new 4D survey in 1998 is predicted to observed remaining amplitudes tyhat would require another well orthogonal to this one to be drilled in 1998. Each new well is projected to produce an added 2 million barrels of oil fro the same reservoir fault block, thus increasing the ultimate recovery efficiency.