Regional maturity modeling is a powerful tool to high grade areas of interest for unconventional play exploration. Unconventional plays are generally considered to be in-situ which implies that the hydrocarbons do not migrate far from where they are generated. Even when migration does occur, the migration distance is generally less than that of corresponding conventional plays.
Leigh Price of the USGS collected and analyzed an outstanding dataset for the Upper and Lower Bakken shales. These samples were analyzed for Rock-Evalt™ pyrolysis. Our Williston regional maturity model is calibrated to the Bakken using these data. Pre-Bakken maturity calibration data is sparse so maturity modeling is used to predict maturity in these potential source rock intervals.
Regional maturity modeling requires structure maps, a Tertiary erosion map and temperature gradient maps. The temperature gradient map from uncorrected well bottomhole temperatures is modified to calibrate to the Bakken vitrinite reflectance equivalence (VRE) calculated from the pyrolysis Tmax measurement. When a satisfactory calibration is made for the Bakken then other horizons can be modeled for maturity. A predicted VRE map for each horizon of interest is produced from the 3D maturity model. Where pre-Bakken maturity calibration data is available this is compared to the modeled VRE values to verify the veracity of the model. The modeled horizon which corresponds to a known or inferred source rock is a potential unconventional play target. For example, if oil is the preferred target then the oil mature area can be studied in more detail. This may save financial and human resources by focusing efforts on areas of most interest.
The Bakken is one of the most active plays in the U.S. It has long been known that there are multiple active petroleum systems in the Williston Basin (Dow, 1974, Williams, 1974, Osadetz et al., 1992 and 1994, Osadetz and Snowden, 1995). These plays exhibit differing organic facies in the source intervals which require not only an understanding of total organic carbon (TOC) but also kinetics with regard to maturation and oil quality prediction (Lillis, 2013). Maturity surfaces extrapolated from high calibration data density levels to lower calibration data density levels are powerful exploration tools.