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Reservoir Architecture and Characterization of the Cenomanian Barons Light Tight Oil Sandstone Play, SW Alberta, Canada


Siliceous, organic-rich mudstones of the early Cenomanian Fish Scales Formation (Mowry eq.) are an emerging light tight oil play in southwestern Alberta. The formation is a proven conventional type oil and gas reservoir in southwest Alberta, with production from several isolated sandstone and conglomerate bodies within the organic rich mudstones. The last years numerous multistage fractured horizontal wells have been drilled into the play with varying success, highlighting the importance of a better characterization of the play. Petrophysical evaluations of this mudstone play is complicated by the abundant disseminated fish bones, general high content of pyrite, numerous bentonite beds and local presence of detrital chert grains, which all affect computations from well logs of porosity, total organic content, mudstone silica content, etc. Characteristics of the play is illustrated by the Penny Baron Pool and surrounding area – spanning Townships 7 to 9 and Ranges 21 to 24 west of 4th meridian. The conventional type light oil pool consist of a 1.5km wide, 20km long northwest-southeast trending reservoir comprised of coarsening upward shoreline sandstone reservoir with an estimated OOIP of 27827.07 MBbl and OGIP of 12.56 Bcf. Dominance of fine to coarse grained sandstone ripples, often draped by organic rich black mudstones suggest deposition on the landward side of a barrier island or spit that retrograded to the southwest. This is consistent with the general lack of hummocky cross stratification and low ichnofauna diversity, suggesting deposition in a highly bimodal shallow water depositional setting characterized by dysoxic bottom water conditions. To the southwest of the pool, landward side of the barrier island, distal barrier island/spit wash-over sandstones comprises a potential halo-type tight oil play along the southwestern margin of the Penny Pool. These 1-4cm thick thin sandstone beds consist of very-fine sand with 3.0-6.0% porosity and permeability ranging from 0.09-0.18 mD. However, these sandstone beds occur as lenticular beds within a mudstone dominated succession, and thus are likely characterized by poor connectivity, and are not capable of providing economic flow rates in vertical wells. However, hydrological fracturing increases the connectivity of these isolated sandstone beds to provide more effective drainage, and thereby increased oil flow rates and recoveries.