Goliat is an ENI Norge-operated oil field located in the Arctic Barents Sea, 85 km NW of the city Hammerfest (Fig. 1). The Goliat reservoirs have a complex structural setting characterized by a large number of faults and a relative high structural dip towards the flank of the structure. This challenging combination calls for horizontal production wells for effective drainage.
The Goliat field consists of several proven hydrocarbon reservoir units, but as of the date of this abstract, only Kobbe producers have been drilled. The Kobbe Formation is of Middle Triassic age and is divided into two main subgroups; the Upper Kobbe represents essentially a prograding deltaic system with mouth bars and tidal influenced lobes. In the Lower Kobbe, the system shifts into a more proximal, heterogeneous fluvial setting where sand bodies have limited lateral continuity.
One particular challenge is that the well design requires the 8½-in. reservoir section to be initiated in the overlaying Snadd shale. To minimize shale exposure in the landing section aggressive build-up rates are employed, decreasing the length needed in shale. However, a steep approach may lead to deeper penetration in upper Kobbe sandstone, which can result in unwanted intra-shale drilling. Therefore, the key to successful well placement is the early detection of the reservoir top and the accurate mapping of the reservoir sand architecture remote to the wellbore.
One way to successfully navigate a complex reservoir like Goliat is to use extra-deep azimuthal resistivity (EDAR) which can detect stratigraphic boundaries up 30m away from the wellbore in optimal resistivity environments (Hartmann, 2014). The development of advanced multi-component inversion modelling techniques (Sviridov, 2014) enhances the interpretations of resistivity data and can accurately provide real-time information regarding reservoir geometry.
On Goliat, the EDAR service provided the capability to detect the top of the reservoir at about 20 m true vertical depth (TVD) and nearly 100 m MD before entering the reservoir, enhancing accurate wellbore landing. Extra-deep measurements also helped reduced the uncertainty in fault detection, where related throw can be estimated based on the displacement of boundaries.
The use of a measurement with increased depth of detection (DOD), combined with advanced multi-component inversion while drilling techniques and real-time 3D visualization of data and reservoir model were vital to ensure the successful placement of the well. Real-time mapping of the reservoir geometry was key to optimize reservoir exposure.