P. Hodgkins and D. Timko

BP Canada Energy Company, Calgary, AB

ABSTRACT: Rock Physics of Cretaceous Sands in Western Canada: Links Between Lithology, Productivity and Seismic Properties

Cretaceous reservoirs of the Western Canadian Sedimentary Basin (WCSB) present a challenging case for attempting to tie reservoir rock properties to seismic response. These reservoirs are normally thin, low porosity, gas-charged sands. The use of traditional stacked reflectivity seismic data to identify pay has been shown to be non-effective in this setting.

This paper focuses on the lower Cretaceous Bluesky Formation. Detailed core and log work show that subtle changes in Bluesky lithology have significant influence on permeability and also production. The permeability contrasts show a strong correlation with velocity variations, although there is no permeabilitydensity correlation. The key point emphasized here is that velocity measurements can be used to detect this subtle change in the reservoir although density and porosity measurements alone cannot

The velocity-permeability relationship is sufficient for acoustic impedance (AI) data (density x P-wave velocity) to be used to high-grade infill drilling locations. Acoustic impedance data can be created directly from well logs and by establishing consistent cutoffs in AI values, it is possible to discriminate reservoir quality, and therefore production capability within the Bluesky. The inversion of seismic data creates pseudo acoustic impedance logs at every trace. Thus, acoustic impedance is a natural link between reservoir quality, productivity, and seismic response.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado