The objective of reservoir optimization is to produce the maximum volume of economic hydrocarbons per dollar invested. Accurately predicting results prior to drilling and completing wells is required to truly optimize development programs. Robust reservoir and completions models are necessary to confidently predict production. This work addresses the development of a comprehensive 3D earth model as a means to provide the requisite reservoir architecture and parameters as input into a reservoir simulator.
This study focuses on the Devonian Three Forks formation in the Williston Basin, North Dakota. Total thickness of Three Forks in the area of interest (AOI) ranges from 175–215 feet and is comprised of dolomitic sandstones, silty, dolo-silty and anhydritic mudstones. The dolomitic sandstone reservoir facies in the first bench of the Three Forks ranges from 5–15 feet thick across the AOI.
Eleven sediment cores encompassing all or a significant portion of the Three Forks Formation were described to understand the lithologic and depositional characteristics of the relevant core facies comprising the stratigraphic intervals of interest. Cores were selected based on their location across the AOI to represent the level of heterogeneity at the core scale.
A regional heterogeneous rock model was constructed utilizing Principle Component Analysis combined with a K-means clustering technique on quad combo wireline log suites and propagated regionally across hundreds of wells. Core Facies were subsequently upscaled to log facies resolution based on their statistical occurrence within each log facies
Log facies were upscaled to eight seismic facies based on their discretization in elastic spaces. Elastic and geomechanical properties correlate to reservoir and non-reservoir log facies which, in turn, correlate to the sandy dolomites and silty mudstones described in Three Forks core intervals. 3D Seismic data were utilized to propagate the HRA model away from well control. Simultaneous, geostatistical, prestack seismic inversion was performed exploiting available geologic, petrophysical, geophysical and geostatistical information to produce detailed seismic facies, elastic and porosity volumes.
Fully integrated results based on core to log to seismic facies and 3D seismic derived elastic, geomechanical and reservoir properties provide a well characterized representation of the stratigraphic architecture and heterogeneity of the Three Forks lithologies. These results become the high detail 3D earth model providing the inputs and constraints to a 3D reservoir model.
