The Nautical Petroleum appraisal well 9/02b-5Z, located in the North Sea, was recently drilled using a new deep directional resistivity tool which enabled the simultaneous real-time mapping of the upper and lower boundaries of a 100+-ft reservoir, over the length of the 2,000-ft horizontal well. This device was of great benefit in both validating the accuracy of the seismic interpretation and tying the borehole acquisition data to the seismic data. One of the greatest challenges in geosteering is that horizontal wells are planned using a seismic visualization of the reservoir but are drilled using a borehole visualization of the reservoir. There is a large disparity in the resolutions of these two systems. Often, only a vague structural outline can be trusted from the seismic data, necessitating the geosteering process, while even the deepest reading bed boundary mapping tool currently available can only visualize one boundary in anything other than a relatively thin reservoir for referencing back to the seismic data. The new generation deep directional resistivity tool, currently in field test, has a greatly enhanced depth of investigation coupled with the ability to detect multiple boundaries in any direction, allowing for the marriage in real time of the seismic and the borehole data and leading to more effective and productive drilling of horizontal wells. This paper will describe the Nautical Petroleum 9/02b-5Z case study and will detail how this data was used both in the post-well evaluation of the overall reservoir structure and in the real-time application of the data in significantly reducing the risk associated with the placement of the borehole.
Observation of basin-scale networks of sandstone intrusions are described from subsurface studies and outcrop locations. Regional scale studies are prevalent in the volume and two new regionally significant subsurface sand injection complexes are described. Higher resolution studies, both outcrop and subsurface, show the small-scale complexity but high level of connectedness of sandstone intrusions. Discordance with bedding at all scales is diagnostic of sandstone intrusions. The propensity of hydraulic fractures to develop and fill with fluidised sand in a broad range of host rocks is demonstrated by examples from metamorphic and magmatic basement, and lignite. Terminology used to describe sandstone intrusions and other elements of sand injection complexes is diverse.
Sand injectites form during shallow-crustal deformation. Short periods of elevated pore-fluid pressure, which developed regionally, triggered formation of hydrofracture networks into which sand was sometimes injected. Sand injection complexes preserve a record of this process and sandstone intrusions are significant reservoirs in many petroleum systems. Most known subsurface sand injection complexes are from offshore NW Europe and associated with Paleogene strata. Outcrop occurrence is global. Sand injection into unconventional host rocks, including granitoid and metamorphic basement and coal seams, raises awareness of the breadth of geological environments in which sand injection may occur. Discordance between sandstone intrusions and sedimentary hosts occurs on a scale from millimetres to kilometres and is a fundamental diagnostic of intrusions. Microscale textural characterization provides new opportunities to establish possible additional criteria for differentiating intrusions from depositional sandstone. The significance of sand injection complexes in shallow crustal evolution is exemplified by the wide range of lithological hosts and diverse tectonostratigraphic settings documented in this volume. Potential for original research still remains.
The Mariner field is a shallow heavy-oil field located in the UK sector of the North Sea. As part of the development of the field we are investigating which seismic technology is most appropriate for imaging and monitoring this complex field. The main challenge at Mariner is the mapping of the Heimdal sands. The new broadband acquisition solutions all open up new and unique possibilities in broadband seismic data processing, imaging, interpretation and monitoring. Broadband seismic is in its infancy. It is expected that large improvements in seismic processing, imaging/inversion and monitoring will take place in the next years, leading to huge improvements in data quality and more reliable seismic interpretation. In August 2012 a seismic survey using WesternGeco's multisensor towed-streamer technology was acquired at the Mariner field. Whilst no single interpretation strategy can be applied to all Heimdal sands on any one datatype, it is demonstrated that the multisensor streamer dataset provides a basis for Heimdal sandmapping that will reduce the reliance on stochastic Heimdal modelling in the drainage strategy. Interpretation products are expected to be associated with less uncertainty than those derived from OBC data.
Mariner is a large heavy oil discovery in block UK-9/11, located 320 km north east of Aberdeen. The execution and development of the project will be from Statoil's new Aberdeen office. The discovery contains 1-2 Billion Barrels of Oil in Place in two reservoirs (Maureen and Heimdal). 19 appraisal wells have been drilled. The oil viscosities are 67 cp (Maureen) to 508 cp (Heimdal) at reservoir conditions. Production start is in February 2017. The reservoir development is based on use of re-injected produced water. ESP pumps are used for artificial lift. In total 100 wells are planned including multilateral slanted wells and horizontal wells. Two drilling rigs and one work-over rig will be active in parallel the first 4 years. Challenges to be met are related to high oil viscosity which gives early water breakthrough and mapping of remobilized Heimdal channel sands. The available seismic only allows for a stochastic Heimdal reservoir model. A full field broadband seismic survey will be available in 2013, applying the newest advances in technology to aim at better imaging the Heimdal sands. Current development strategy for the Heimdal reservoir is pattern drilling using an inverted 9-spot pattern. The work going forward will focus on use of the new seismic data to establish a deterministic reservoir model to be used for well planning. Work is on-going to significantly optimize the Heimdal development. Active geosteering will be important to limit the use of pilot holes and improve Heimdal reservoir sand mapping. The reservoir simulation model is very computer time consuming. Coupled segment models have been constructed that replicates the full field simulation but with significant reduction in simulation time. A polymer flooding study has been initiated to realize the EOR potential.
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