SHINE A LIGHT IN DARK PLACES:USING DEEP DIRECTIONAL RESISTIVITY TO LOCATE WATER MOVEMENT IN NORWAY’S OLDEST FIELD

摘要

The Ekofisk field,operated by ConocoPhillips Skandinavia AS,in the North Sea has been producing hydrocarbons since 1971 and receiving water injection since 1987.The field is very complex in terms of its fluid profile,which is further exacerbated because the reservoir is a fractured chalk with low matrix permeability. Major water flooding,expected to distribute the water randomly throughout the reservoir,has instead channeled water along specific paths dictated by the fractures. Successful geosteering in such an environment is very challenging;knowledge of where the water zones are becoming a fundamental element to success. A new deep directional resistivity(DDR)tool has been field tested in the North Sea.The device has a greatly enhanced depth of investigation over any other existing resistivity tool,is capable of detecting formation boundaries that often reach a distance of 100 ft true vertical depth(TVD)from the borehole,and is coupled with the ability to delineate multiple boundaries in any direction.The results from application of this tool within the Ekofisk field show that,even in very complex fluid cases such as in Ekofisk,it was possible to map the water zone,which was observed both below and above the reservoir to a distance of 90 ft TVD. The implications of the tool are multi-fold. Mapping the formation and fluid boundaries up to 100 ft TVD provided the only clear picture of fluid displacement through the reservoir away from the borehole,greatly enhancing the overall picture of formation structure and faulting within the reservoir.Prior to intersecting the reservoir in the intermediate section,a deep and early detection of top reservoir also allowed for the possibility of optimizing the landing of the horizontal well, greatly reducing the risk of drilling out through the base of the reservoir,even if the formation were structurally higher than expected.The ability to observe the resistivity profile throughout a large vertical cross-section away from the borehole also provided a multilayered petrophysical evaluation of far greater complexity than traditional borehole logging could possibly deliver. In a case study of the Ekofisk well,well 1,we describe how deep directional resistivity data were used for real-time geosteering of the well and interpretation of the reservoir.In addition,we describe how the data can be used for advanced reservoir analysis.