Water Distribution in the Montney Tight Gas Play of the Western Canadian Sedimentary Basin: Significance for Resource Evaluation

摘要

Water distribution in unconventional gas reservoirs is a key parameter that influences many aspects of resource exploitation including selecting geographic areas for multi-well development programs, identifying target zones for horizontal wells, calculating reserves, estimating permeability, and understanding variability in gas and water production. Insights on water distribution in the Montney tight gas play of northeast British Columbia and northwest Alberta were gained by integrating reliable bulk volume water measurements from full-diameter core samples with other core, well log and geologic data. Water distribution in the studied Montney section was found to be related to stratigraphic architecture and rock fabric (defined by degree of bioturbation), and is interpreted to have been influenced by displacement efficiency of mobile formation water updip through tight Montney siltstones during hydrocarbon charging. Low gradient clinoform units with few shaly zones in the Lower Montney section enabled efficient water displacement and led to water contents close to irreducible water saturation. Higher gradient clinoform units with common shaly zones in the Upper Montney allowed less efficient water displacement, and significant volumes of mobile water were retained in parts of the section. Water saturation varies widely and directly influences effective gas permeability. A simple method for determining effective gas permeability from well logs was developed based on empirical relationships derived from the core and log data set. Effective gas permeability logs generated by this method help with the identification of target zones with superior reservoir quality for exploitation using horizontal multi-frac technology. A Pickett plot with effective gas permeability lines was found to be a useful tool for log-based comparison of Montney rock quality by stratigraphic zone or geographic area. This work shows that understanding water distribution and its influence on effective gas permeability leads to improved delineation of "sweet spots" for resource development in unconventional gas plays.