Abstract

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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