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Glauconite Sandstone Exploration: A Case Study from the Lake Newell Project, Southern Alberta
Fluvial-estuarine Glauconite channel sands of the Lower Cretaceous are arguably one of the most prolific oil and gas reservoirs in Southern Alberta. The Countess-Alderson trend extends more than 70 km and is one of several incised-valley-fill systems that trend in a northwesterly direction away from the Kevin-Sunburst Dome in Northern Montana. Cumulative production along this trend has been in excess of 100 MM bbls of oil and 200 BCF of gas.
Although exploration in the area began in the early 1950s, it was not until 1989 that the effectiveness of three-dimensional seismic programs in exploration and pool delineation became apparent. Existing well and seismic control indicated the Glauconite incised paleovalley likely extended beneath the man-made reservoir, Lake Newell. To enhance drilling success and maximize potential hydrocarbon recoveries, a shallow-water / land 3-D seismic survey was conducted over 40% of the lake.
Based on the interpretation of several amplitude anomalies (diagnostic of reservoir porosity-meters), an exploratory drilling program was undertaken. Environmental concerns and recreational development plans around Lake Newell meant further oil and gas development beneath the lake was restricted to five surface-pad locations. Some of the drilling locations required horizontal displacements of more than 2,600 metres, and rather than using conventional equipment, preference was given to slant drilling technology.
Interpretation of cores from five of the wells indicates that the portion of the Countess-Alderson Glauconite trend beneath Lake Newell is representative of facies within the bayhead-delta environment of a wave-dominated estuary. Channel deposits northwest of the lake are brackish, while those southeast of the lake are predominantly fluvial. Reservoir quality in the Glauconitic is best in the bayhead-delta sandstones; knowing this we can use the wave-dominated estuary model as a predictive tool to maximize the oil production from these reservoirs.
At the completion of the exploration and development programs, more than 15 MM bbls of recoverable oil had been discovered beneath the lake. This case study illustrates the value of integrating geology, geophysics and drilling technology in hydrocarbon exploration and development of the Glauconite incised-valley-fill play in Southern Alberta.
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