To supplement the engineering data and geophysical wireline logging data collected from boreholes, drill cuttings are an often overlooked but abundant source of geological data. Sometimes the cuttings are logged manually at the well site to provide qualitative information for reservoir characterization, but their full value has never been realized.

RoqSCAN is a new-generation analyzer of portable, quantitative and automated rock properties. Developed by CGG Robertson and Carl Zeiss Microscopy Ltd., the analyzer is ruggedized and fully portable, which means it can be deployed at well sites for near real-time analysis to inform on-the-fly drilling and completion decisions. RoqSCAN delivers quantitative mineralogical and textural data from drill cuttings or core pieces using nondestructive scanning electron microscopy and energy-dispersive spectroscopy techniques with a high micron resolution. Robertson has developed an extensive proprietary mineral library to translate these scans into quantitative mineral maps. The textural data include automatic detection and classification of porosity, pore size distribution, and pore aspect ratio.

This technology advancement avoids exposure to costly wireline or LWD data acquisition and lost-in-hole scenarios and requires no additional rig-time costs.

RoqSCAN has experienced success both in the field and in the laboratory, driven partly by the shale boom inthe U.S. and increasing demand from unconventional play operators for improved reservoir characterization along the lateral well to optimize completions. The analyzer is a surface-based means to generate quantitative geological datasets where cuttings samples are often the only source of data available. Only a small proportion of horizontal wells are logged, so operators often make completion decisions without any knowledge of the local subsurface heterogeneity in their shale play.

Wellsite geosteering services have used RoqSCAN mineralogical zonation schemes to identify the location of the drillbit in the formation. With a quantitative measurement of key rock texture parameters such as pore size distribution, pore aspect ratio, rock chemistry and mineralogy, a better understanding of the mechanical properties of the formation can be obtained. This has led to RoqSCAN being used to design completion programs for wells based on the actual geological and mechanical properties of the formation. For seismic reservoir characterization projects where elastic attributes from seismic inversion are used to screen plays for potential production hot spots, RoqSCAN can provide hard geological data to calibrate rock physics models and constrain the inversion to achieve a more accurate and quantitative geomodel.

Case studies published within North American shale plays demonstrate how shale well economics can be improved in terms of optimized production and cost reduction by achieving better stage and perforation cluster placement (honoring the reservoir heterogeneity), the elimination of noneffective stages, and more effective deployment of frack fluids and proppants.

CGG is in the early days of automated mineralogy supporting drilling and completion decisions, and work continues on improving the service. Two areas for development include petrophysical inversion of RoqSCAN measurements to directly generate elastic (i.e., seismic-style) rock properties and reducing the uncertainty in the depth lag associated with cuttings recovery from horizontal wells. A quality-control system using MWD gamma ray, RoqSCAN pseudo gamma ray and mineral
attributes has been developed to align cuttings samples to the correct borehole depth interval.

RoqSCAN is offered in the field through Baker Hughes.

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