The new methods address the influence of clay-bound water on results and include its quantification by nuclear magnetic resonance techniques. Traditional core analysis methods for Rw and Qv in shaly tight gas sands are limited and tend to be inaccurate or impractical due to the clay-bound water, extensive cementation, and very low permeability that characterize these formations. Representative values of the rock property Qv are necessary for Qv-based shaly sand models such as Waxman- Smits-Thomas and Dual-Water. Accurate Rw values are needed for all resistivity-based water saturation models.
According to the neutron-density porosity difference and regional geology in southwest Saskatchewan, the lithologies in this well are mostly shale, shaly sandstone and sandstone.ĪBSTRACT New core analysis methods are presented for Rw, formation water resistivity, and Qv, cation exchange capacity per unit pore volume. The porosity of the channel sand is quite high, about 30%.
Effective porosity was estimated from the average of the shalecorrected density-porosity and neutron-porosity logs. The total porosity was calculated from the average of the density-porosity and neutron-porosity logs. Clay content in the rock was estimated from the gamma-ray curve by linear scaling between its minimum and maximum values. There is about 12m of oil pay in the upper sand, while the lower sand is wet. There are two porous clean sand intervals with good permeability at 1148m-1160m and 1164m-1180m respectively, which are interpreted to be sand channels in the Cantuar formation. Well log analysis and Q estimation Figure 1 displays well log curves with formation tops from the 11-25-13-17W3 well. Density and neutron porosity, dipole sonic and resistivity logs were also available in this well. The zero-offset VSP survey used both vertical and horizontal vibrators as sources, which are favorable for estimation P- and S-wave attenuation. A multi-offset VSP survey was conducted in June 2003 (Xu and Stewart, 2003).
The producing reservoir in this well is a Cretaceous-age channel sand in the Cantuar formation of the Mannville Group. The lithologies of the studied interval are mainly shale and shaly sandstone. The borehole selected for this study is well 11-25-13-17W3 from Ross Lake, Saskatchewan. An ultimate goal of the studies is to use attenuation to provide helpful information for seismic interpretation and reservoir characterization. In this study, well log data and VSP data will be used to analyze the relationship between rock properties and attenuation. Understanding the causes of seismic attenuation and the relationship between it and rock properties is important in the acquisition, processing and interpretation of seismic data. Introduction Attenuation is one of the basic attributes of seismic waves propagating in the earth. On average, sonic log velocities are 3.4% higher than VSP velocities for the P wave, and 4.8% higher for shear waves. Velocity dispersion was observed between VSP-derived velocities and sonic velocities. Q values for S-waves also display a similar relationship. A crossplot between Qp and clay-bound water indicates more attenuation in shaly sandstone possibly caused by the interaction between mobile water and clay-bound water. Shaly sandstone shows more attenuation than pure shale and sandstone. Qp values increase with Pand S-velocities and decrease with Vp/Vs and porosity. The Q values correlate interestingly with petrophysical variables. The Q values are most reliable from 400m to 1050m for the P wave and from 225m to 1050m for the shear wave.
Interval Q values for the P wave and shear wave were estimated by applying the spectral ratio method on near-offset VSP data (which used both vertical and horizontal vibrators). Well log analysis indicates that the main lithologies in this well are shale and shaly sandstone. Summary We analyze the relationship between seismic attenuation and rock properties in well 11-25-13-17W3 from the Ross Lake heavy oilfield, Saskatchewan. drilling fluid selection and formulation (2).