AN APPROACH TO MAPPING OF SHALLOW PETROLEUM RESERVOIRS USING INTEGRATED CONVENTIONAL 3D AND SHALLOW P- AND SH-WAVE SEISMIC REFLECTION METHODS

Conventional 3D seismic reflection data have become a powerful tool in reservoir visualization because of their ability to define subtle subsurface structures and stratigraphy. Although conventional 3D seismic data are useful to detect and map structural patterns in the subsurface, the resolving power depends on the spatial sampling (e.g., the common mid-point (CMP) “footprint”) and frequency content of the seismic survey. These factors impose limits on the resolution and the near-surface depth of subsurface structures that can be imaged adequately. Using the famous Teapot Dome oil field as a test case, we demonstrate how high-resolution compressional (P) and horizontally polarized shear (SH) wave seismic reflection surveys can overcome these limitations using small CMP spacings (5 ft and 2.5 ft, respectively) and a higher frequency source. Teapot Dome, which is a major oil field test bed for enhanced oil recovery and carbon sequestration projects in the Wyoming foreland, provides an ideal laboratory to experiment with the integration of P- and SH- wave reflection data using a small CMP bin size and high frequencies in mapping shallow subsurface faults that affect reservoir compartmentalization. The results are integrated with 3-D seismic data, correlated drill hole logs, outcrop mapping, and trenching of shallow faults with the aim of investigating the interaction of deeper and shallow faults, as detected using the different methods. The integration of the two high-resolution seismic methods greatly enhances the detection and mapping of fine-scale deformation and stratigraphic features at shallow depth that cannot be imaged by conventional seismic methods. We show that the shallowest petroleum reservoirs at Teapot Dome (e.g., < 300-400 ft depth below ground surface) can only be imaged properly with high-resolution seismic methods. Our study therefore shows how conventional 3D seismic data exploration requires additional seismic acquisition at smaller scales in order to image deformation in shallow reservoirs. Such imaging becomes critical in cases of shallow reservoirs where it is important to define potential problems associated with compartmentalization of primary production, enhanced oil recovery, or carbon sequestration.