New technologies have been developed to achieve a higher degree of accuracy in well positioning as operators have been drilling increasingly challenging hydrocarbon pockets.The Nini East Field, Danish North Sea sector, represents a significant drilling challenge. The target is a postdepositionally remobilized sand reservoir of 2 15 meters thickness. Because of the reservoir's remobilized nature and its low resistivity, none of the standard well placement methods or the current bed-boundary mapping tools were suitable solutions for the well objectives. Previous wells drilled in this type of reservoir have been marginally economical due to sidetracks and net-pay ratios below 0.5.In view of these challenges, DONG E&P decided to collaborate to the field test of the next generation bed-boundary mapping tool to geosteer their two upcoming production wells. The technology currently in field test provides a real-time mapping of the reservoir several meters away from the wellbore. As the depth of investigation of the tool is within the same range as surface seismic measurements, the two data sources were integrated while drilling to provide look-ahead information.The two producers achieved an outstanding 0.99 and 0.96 net-pay ratio with no sidetracks or delays and were completed within budget.The inversion processing of deep directional resistivity measurements clearly shows the capability of this new generation tool to map the internal variations of the reservoir structure, enabling further understanding of its nature and depositional history and allowing optimization of the field development.
During the late life of the Siri field in the Danish North Sea, an infill water injection well was drilled to provide enhanced reservoir sweep and to help improve tail-end field production. Dynamic reservoir modeling indicated that a down-dip horizontal water injector on the southwestern flank of the field using injection inflow control devices (ICDs) could provide the necessary uplift for producers near the crest of the field. The Siri field is characterized as a high permeability, remobilized glauconitic sand package comprising multiple stacked and amalgamated sand bodies deposited from high density gravity flows in the Paleocene-Eocene Siri fairway. Seismic, well logging, and production data indicate that fluid flow is influenced by vertical and horizontal baffling. The internal flow channeling and baffle effects are likely caused by a combination of siliciclastic diagenesis, subseismic faulting, and multiple calcite-cemented paleo oil/water contacts. These baffles are capable of maintaining significant pressure differentials. They consequently have a major effect on field scale horizontal permeability and reservoir sweep efficiency. During the last decade of drilling horizontal development wells in the Siri area, Dong Energy has obtained extensive in-house experience and knowledge in the use of deep reading resistivity technology for reservoir mapping, as well as in positioning long horizontal development wells in challenging settings, such as ultra-thin reservoirs sands and thin oil columns. This paper discusses the well placement and geological evaluation of the Siri reservoir with regard to the acquired logging while drilling (LWD) data, which includes resistivity inversion, neutron porosity/bulk density imaging, and formation pressure measurements. The well trajectory was adjusted in real time to reduce footage exposure to tight facies, as well as to identify fluid boundaries related to the flow channeling present within the reservoir. Borehole resistivity inversion provides evidence that the mineralized permeability barriers are not always high-angle features. This paper also discusses insights into the Siri reservoir geology in light of the horizontal well data acquisition program and potential implications for future ICD behavior.
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