Anne Grau¹
(1) Colorado School of Mines, Littleton, CO

Abstract: Quantification of Quartz Cement and Pressure Solution Volumes, North Sea Jurassic sandstone

Quantitative studies of quartz cements are uncommon because it is difficult to differentiate authigenic quartz from detrital quartz using standard petrographic methods. The purpose of this study is to quantify quartz cements and to compare the results to estimates of silica volume loss due to chemical compaction. The study area is a North Sea petroleum reservoir, with variable distribution of quartz cement related to facies and structural position.

Photomultiplier-based cathodoluminescence detection systems combined with scanning electron microscopy (scanned CL) provide a method to distinguish quartz cements from detrital grains. The resulting high-resolution images allow for detailed quantitative analysis of quartz mineral occurrences in sandstones. Scanned CL is used to identify and quantify silica sources, such as partially dissolved feldspars and pressure solution features; as well as silica sinks, including quartz overgrowths and quartz-filled fractures or in fractured grains. A profilometer is used to measure topography and quantify minimum volumes of silica lost due to pressure solution along stylolite surfaces in core. This instrument, which is normally used to measure surface roughness, is being applied here as a new technique to evaluate chemical compaction in sandstones.

By comparing quartz cement and pressure solution volumes, the distribution of quartz cement and processes responsible for precipitation will be more clearly understood, and the quantified results will be used as part of a silica budget effort. Integration of these data with wireline log signatures will be applied to field-wide porosity modeling, quantification of reservoir pore volume, and overall reservoir characterization.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana