Diagenesis of Marine Sands to Tight Gas Sands: Effects on Acoustic and Hydraulic Properties: ABSTRACT

Abstract

Figure The primary stages of diagenesis of marine sands usually increase total grain contact area, increase the number of contacts, decrease porosity, and increase pore network tortuosity. These microstructural factors strongly affect the continuum acoustic and hydraulic properties of the sands. To better understand diagenetic effects on these properties, compressional and shear wave velocities, Vp and Vs, and their specific attenuation, Qp-1 and Qs-1, were measured in an unconsolidated quartz sand (Ottawa sand, porosity ^approx 35%), a quartzarenite sandstone (St. Peter sandstone, porosity ^approx 22%), and a lithic-quartz arenite (Spirit River tight gas sand, porosity ^approx 5%). Measurements were made under effective press res, Pe, up to 350 bars as a continuous function of partial gas saturation, at frequencies from 10 to 15,000 Hz, and from 150 to 500 kHz. Experimental results are explained with relations derived from contact and packing theories. Results suggest that Vp/Vs and Qp-1/Qs-1 may be used to distinguish between gas and consolidation effects in reflection seismology and borehole sonic logs. Gas permeability was also measured in Spirit River tight gas sands from the Alberta Deep Basin as a function of effective pressure and partial gas saturation. These values are compared with known values for quartz sands and sandstones, and the results are examined with simple pore network models. While porosity decreases by a factor 7 from Ottawa sand to Spirit River sandstone, gas permeability drops by as much as 8 orders of magnitude. Gas permeability in all granular sedimentary materials, especially the tight sands, is a strong function of clay content, partial gas saturation, and effective pressure. End_of_Article - Last_Page 963------------