Deciphering the Record of the Sun-Earth Dance in Well Logs: The Extra-Terrestrial Imprint and its Application to High-Resolution Stratigraphy and Well Correlation in South Furious Field, Offshore North Sabah

Abstract

South Furious is an oilfield in the Inboard Belt offshore North Sabah with oil production since 1979. The field is heavily faulted and compartmentalized, making it structurally complex and challenging for development. It is believed that the field has a low recovery factor, despite having a relatively large oil in-place volume reported. Its highly-heterogenous Stage IVA reservoir with thin sand-shale intercalations, and poor seismic imaging quality make stratigraphic interpretation and well correlations highly uncertain. Recognizing the limitations of conventional methods for well correlation in South Furious, SEA Hibiscus decided to take a quantitative approach on the existing well logs itself, particularly the gamma ray (GR) curve. This data-driven approach is a shift from the unsuccessful model-based method. Cyclostratigraphic analysis using CycloLog works on the principle that extra-terrestrial forces described by the Milankovitch Cycles have a huge influence on sedimentation processes, and its record are preserved in the well logs that we acquire while drilling, although not always obvious without the proper quantitative approach. This high-resolution stratigraphic method allows the detection of cyclic signals in facies-sensitive wireline logs (e.g., gamma ray), including subtle ones, and at resolutions that are equivalent to 4th to 6th Order stratigraphic cycles. Utilizing the Integrated Prediction Error Filter Analysis (INPEFA), geological breaks or events are quantitatively and objectively identified. Cyclostratigraphic and climate stratigraphy concepts as described by Perlmutter and Matthews (1990) and Nio (2005) form the basis of this analysis, which is an evolution of traditional sequence stratigraphic concepts. Results from the 10 pilot wells in South Furious show dramatic improvements in the stratigraphic correlation resolution, particularly in the deeper/older sections, allowing correlations to be made across different fault block segments, previously nearly impossible. With the ongoing inclusion of more wells to the cyclostratigraphic study and future plans to integrate independent chemostratigraphic data, a more robust stratigraphic framework for the field would be established. Results from the current study prove that the cyclostratigraphic method allows objective, quantitative and data-driven stratigraphic well correlations to be made from a systematic and quantitative review of existing well logs, without additional rock sampling or measurement, and in a cost-effective manner. Geoscientists should always be receptive to new ways of working, including utilizing data and techniques that have origins outside mainstream geoscience.