The results presented in this study test the efficacy of using whole-rock elemental data to characterize the stratigraphy penetrated when drilling lateral wells and use this information along with comparisons to a vertical offset well to stay in zone. This approach is tested in the Alberta Bakken Petroleum System (ABPS) in Southwestern Alberta, Canada, focusing on the Banff, Exshaw, Big Valley, and Stettler formations (Hildred et al 2013, Zaitlin 2013). Data and interpretations are presented from vertical well 11–35 and its associated lateral, which were drilled along the flank of a seismically defined anticlinal structure, making geosteering using wireline data difficult.
The target zone within the Big Valley Formation comprises a ~5m thick dolomite interval underlain by anhydrite and overlain by limestone. The dolomitic interval is geochemically identified by high MgO/CaO, Th/Al2O3 and MnO values, all of which decrease in the underlying anhydrite. It is differentiated from the overlying limestone cap by lower CaO values. Using the chemostratigraphic type section devised from the vertical offset well, it is possible to identify all of the previously defined stratigraphic units. Due to the sinuosity of the wellbore and probable faulting, some units are encountered several times along the well path; chemostratigraphic analysis has the ability to independently define the target zone when encountered.
The application of chemostratigraphy outlined in this study is relevant to many other scenarios where lateral well placement is critical. Beyond the stratigraphic use of geochemical data, it is also possible to derive the relative brittleness of the target zones in order to better identify zones for completion and the placement of frac stages, thereby making exploitation of resource plays more cost effective.
The Alberta Bakken Petroleum System (ABPS) is one of the latest play areas being evaluated in the quest to capture early entry, contingent, light tight oil (LTO) resources. The structural fabric of the Williston Basin and the foreland basin of southern Alberta and Northern Montana is dominated by the presence of large scale divergent wrench fault systems that were initiated at early Proterozoic time and continue to be active throughout the tectonic history of these basins. These structures are characterized by the presence of several pull-apart basins that acted as the focal point for the deposition of thick sections of the Bakken/Three Forks and Exshaw/Big Valley packages. These unique structural features form the prime location for the exploitation of these emerging resource plays. The main basinal difference is that the ABPS is part of a thermocline stratified ramp whereas the Williston Basin is part of low energy interior basin setting.