QUANTIFICATION AND INTERPRETATION OF MULTIPLE GENERATIONS OF QUARTZ CEMENTS: IMPROVING RESERVOIR QUALITY PREDICTIONS IN CLASTIC RESERVOIRS

Along with core analysis and burial history, point count data obtained with conventional optical petrography have been used successfully to predict clastic reservoir quality away from well control using Touchstone ^TM.The amount of quartz cementation is a critical input to such diagenetic models. Where multiple generations of quartz overgrowth cement are present, use of conventional petrography can be challenging for distinguishing between detrital framework quartz grain and multiple generations of quartz cements. To overcome this challenge, scanning electron microscope cathodoluminescence has been employed in many diagenetic studies [e.g. 1] to improve the quantification of quartz overgrowth. Using point count methods based on color SEM-CL significantly improves interpretation and quantification of quartz cement.

We present a case study where multiple generations of quartz cements have been quantified, and their impact on reservoir quality modeling has been tested. Quartz cement was quantified in quartz arenite samples from Research Wells A and B using both traditional petrographic and SEM-CL point counting methods. Color SEM-CL revealed at least three distinct quartz cement events (inhereted from previous depositional cycle, localized pore-filling cement, and burial quartz overgrowth).

Several reservoir quality simulations were performed in Touchstone^TMto assess the impact of accurate quartz cement quantification on predictions. When only traditional petrographic point count was used, assuming all point counted quartz cement was associated with burial diagenesis, poor model calibration of porosity, permeability, and quartz cement resulted. Significant improvement of model calibration was obtained only by using quantification from color SEM-CL identified generations of quartz cement (inherited, pore filling, and burial diagenesis). This improvement leads to more robust prediction of reservoir quality away from well control.

[1] Cooper et al. (2000) Spec. Publs int. As. Sediment 29, 89-101.