Using the Lamont 4D Software, 1988 and 1994 seismic surveys were 3D interpolated both 1) from the 100 ft bin spacing of the 1988 survey to the 42 ft bin spacing of the 1994 survey and 2) visa versa. Region growing and Semblance analyses show that the K-40 is a well-connected, lightly faulted, turbidite sand. A clear oil/water contact was observed in 1988. Approximately 2/3 of the bright (oil-filled) voxels at 1988 have been dimmed (drained) by 1994 in this water-drive reservoir.
Both the coarse/fine and fine/coarse interpolation analyses indicated
that water broke updip from west to east along fault-bounded corradores
toward the three producing wells in the K-40 sand. Resolution of the water
breakthrough was better on the fine-grid, but the coarse grid indicated
that the lower lobe of the bi-lobal sand was more affected by water than
the upper -- an observation consistent with water encroachment observed
in a subsequent downdip penetration.
There, very high oil cook-out temperatures in cuttings indicated water recently swept through the lower lobe between seismic survey 1 and 2 times.
Northern and southern producing wells were producing significant water throughout the time of the seismic acquisition in1994, but the center well only begain producing water mid-year. The 4D seismic dimming had hit the southern and center wells, but not the northern well in both the fine analysis and coarse (although only in the lower lobe.
A flow simulation module has been written for the Lamont 4D Software in which darcy's law defines fluid movement over time. Pressure drop was assumed to be radial away from perforations, and permeability is assumed to linearly scale with the CHANGE in amplitude at each voxel between the 2 seismic surveys. Correlation ofpermeability to amplitude change in the 4D case should be more realistic than correlation to amplitude alone in the 3D case.
A surprising result of the flow simulation was that the fluids did not directly move to toward the perforations. Instead, connectivity between amplitude changes among adjoining voxels first drew the fluid into a tributary network that then delivered the oil to the perforations. And even then, significant theiving toward the higher updip center well from the northern well was indicated. The complexity of the connectivity shown by the flow simulation cannot be seen from simple color bar manipulation.
