Improved Reservoir Mapping by Integrated Interpretation Approach Using Horizontal Wells

Abstract

Abstract Reservoir maps are essential input data for drilling operations and 3D reservoir modeling. While drilling, these maps and petrophysical data guide the horizontal geo-steering, allowing real-time reservoir structure adjustments. In 3D modelling, they are commonly used to control the reservoir properties extrapolation and lateral extension. This study proposed a best practice approach to improve reservoir maps by using seismic reference interpretation and interpreted geologic control-points linked to horizontal well data. The proposed methodology involves the interpretation of a reference horizon from a 3D seismic volume, followed by a velocity model construction and depth conversion iteratively. The first iteration of the velocity model uses the interpreted seismic horizon along with sequence stratigraphic boundaries, as interpreted from core descriptions. Next, the log signature associated to each sequence boundary in the cored wells, is applied to the log data acquired in the vertical and deviated uncored wells. Finally, the horizontal wells are added to the correlation, to define additional stratigraphic markers, that allow the calculation/interpretation of control points applied to the reference horizon, capturing the relative position of the well within the target layer. The combination of the stratigraphic markers with the interpreted control points, together with the interpreted seismic horizons, results in a structural framework for the entire reservoir including most of the available data, maintaining the velocity model updated in a short-time basis. This data integrated approach, is producing high quality reservoir maps, representing subsurface structures more accurately than conventional mapping methods. The iteration of horizontal drilling and inter-well control points in the velocity model building process reduces the uncertainty in the depth conversion (from 50 ft. to 10 ft.). Regarding that the velocity model algorithm cannot use the inter-well points directly, because they are not associated with actual well markers of the reference horizon. The study adopted a workaround that involves the adjustment of the seismic reference horizon following the spatial distribution of the control points, to iterate the velocity model workflow, updating it with real-time data in the study area. Our method improves reservoir mapping compared to the conventional workflow. It is used to build robust 3D velocity models as well as 3D geological models over stacked reservoirs by using multiple seismic reference horizons, stratigraphic boundaries, well log picks, and vertical seismic profiles (VSP) data. The inter-well points from horizontal wells use the relative position of the well, solving the lack of markers in the area between wells.