A reliable downhole sensor network will dramatically improve reservoir management practices and enable the construction of "intelligent" downhole well completion and control systems. Fiber optic technology will play a seminal role in the architecture of downhole imaging and control systems because of advantages of power, performance and reliability over conventional electronics.Results from a field test of a fiber optic seismic borehole receiver prototype demonstrate that a multi-level, fiber optic hydrophone system can improve the economics of Vertical Seismic Profiling (VSP) & cross-well surveys, and quicken the birth of permanent monitoring networks.
We studied crosswell electromagnetic and seismic images of three oil‐saturated intervals within a southern California heavy oil field undergoing steam flood. The crosswell survey is located in a portion of the field where one well is in a “cold spot,” resulting in differing steam propagation within the three units. Log analysis shows linear or second‐order polynomial relationships (with correlation coefficients greater than 0.7) between electrical conductivity and water saturation, porosity, and clay content; whereas only a weakly linear relationship can be found between velocity and temperature in the lower unit studied. Crosswell seismic data is used to produce a velocity tomogram and a reflection section, and crosswell electromagnetic data is used to produce a conductivity section and derived porosity and water saturation. The seismic velocities from the tomograms show lateral variations consistent with the lateral variations in temperature seen in observation wells on either side of the crosswell section. The continuity and disruption of seismic reflections coincide with zones of continuous and variable porosity and water saturation as produced from the crosswell electromagnetic inverted conductivity section, and the derived regression fits between conductivity and porosity/water saturation. Seismic velocities, reflections, electrical conductivity, and the derived porosity and water saturation sections all contribute to explaining the observed lateral temperature variations between the wells within the three reservoir units. The unit with high steam content has low water saturation, high porosity, and laterally continuous low‐velocity and seismic reflections, consistent with no barriers to flow. The upper unit, where steam breaks through later in the experiment, also has high porosity and laterally continuous seismic reflections. However, it shows a velocity gradient between the hot and cold wells consistent with the lack of steam in the cold well at the time of the experiment. The middle unit, in which steam never reaches the cold well during the experiment, has the highest water saturation and the largest zone of reduced porosity and disrupted seismic reflections, indicating a possible barrierto flow.
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