Chapter 17: Imaging of a Stratigraphically Complex Carbonate Reservoir with Crosswell Seismic Data
R. T. Langan, S. K. Lazaratos, J. M. Harris, A. A. Vassiliou, T. L. Jensen, J. W. Fairborn, 1997. "Imaging of a Stratigraphically Complex Carbonate Reservoir with Crosswell Seismic Data", Carbonate Seismology, Ibrahim Palaz, Kurt J. Marfurt
Download citation file:
We conducted a crosswell survey to evaluate the stratigraphy and structure in and near a stratigraphically complex limestone reservoir in the Permian Basin of West Texas. Although the reservoir was detected with surface seismic data and was successfully drilled, the surface data had insufficient resolution to image its internal structure and to determine its relationship with nearby sedimentary rocks. This is a common problem in surveys of carbonate strata, where large seismic velocities result in long characteristic wavelengths. The thickness of the reservoir in our example is ~75 m, whereas the shortest wavelength in the surface seismic data is ~60 m. The high-resolution crosswell seismic data, which contain frequencies more than 10 times greater than those of the surface data, clearly delineate the lateral and vertical extent of the reservoir unit between the wells. The data also reveal the inner stratification of the reservoir and show the stratigraphy of units adjacent to, above, and below the reservoir. Anisotropy in the compressional velocities obtained from the crosswell data is an indicator of the facies present. Our analysis of the P-wave direct arrivals suggests that the reservoir itself has little velocity anisotropy but that a thinly interbedded facies of mixed siliciclastics and carbonates has a horizontal velocity of ~5% lower than its vertical velocity. The shale units have an intermediate degree of anisotropy of ~3%.