Solving Well Placement Challenges in a Multi-Fluid, Compartmented Reservoir with Proximity to a Flooded Level in a Critical Anti-Collision Area

Abstract In structurally complex reservoirs, where faults result in the dislocation of the target reservoir, well placement decisions require early identification of the position of the formation and fluid boundaries. The structural complexity can be in both the vertical plane and laterally, resulting in the potential for variability in lithology and fluids to the sides and above and below the well bore. In a well on the Norwegian Continental Shelf, an integrated geosteering approach was utilized to monitor the lateral proximity to water-flooded areas and define the 3D geolocation of the reservoir during lateral geosteering operations. It will also ensure a relevant standoff from the upper gas-oil contact (GOC) and the lower oil-water contact (OWC). From a drilling perspective, well placement decisions were constrained to maintain a safe anti-collision distance from a nearby well near total depth (TD), necessitating early decision making. Ultra-deep azimuthal resistivity (UDAR) tools can identify the strong resistivity contrast seen between sharp oil/water (OWC) contacts and even gradational resistivity profiles at distances up to 30m from the wellbore. Inversion will allow the variability of these contacts to be mapped in the vertical plane. For further insights, the near-wellbore detail, which supplements the UDAR technology, was analyzed in conjunction with additional formation evaluation logs (Gamma Ray, Density, Neutron, Resistivity, Azimuthal Resistivity Images, and related Borehole Images) in both real-time and memory. UDAR tools have been demonstrated to have sensitivity to metal such as casing; proximity to these subsurface hazards can disrupt the inversion and, therefore, has the potential to provide additional information in this critical anti-collision area. Drilling wells in a structurally compartmented reservoir with critical proximity to an active flooded level is challenging, with the narrow anti-collision window limiting placement options. Mapping of the OWC using a UDAR tool in both 1D and 3D helped to resolve this structural complexity and maintain the well at a safer stand-off from the water, both vertically and laterally. Managing the vital integration of inversions & LWD deep measurements and advanced gas analysis supported reliable fluid interpretation and helped avoid undesired intersecting boundaries. Furthermore, this approach accounted for major reservoir heterogeneities, whether stratigraphic or structural, enabling both lateral and vertical navigation to maintain the well in proximity to a major flooded fault zone. Where faults were intersected, monitoring the fault dips from density images provided a valuable QC of the inversion results and provided additional details due to the higher resolution of this tool. Considering the complex fluid profile of gas, oil, and water, the wellbore was mostly maintained within the target zone. However, some lessons learned have been obtained from insightful memory data interpretation, which will be utilized as a main input for future well placement. This approach was achieved through the integration of real-time and memory interpretation of the surrounding resistivity and geological changes whilst also allowing measuring the standoff from fluid boundaries. Early identification of any changes in the boundaries and referencing a well-planned trajectory allowed more accurate well-placement decisions to be made whilst balancing the anti-collision risk.