The benefits of extra deep azimuthal reading logging-while-drilling (LWD) resistivity tools have been well documented previously in several papers which outlined the advantages of using these types of data to avoid the need for pilot holes and unplanned side-tracks. Typically, the focus of these tools is to land-out the well in a particular target sand and to then maximise net sand length in the well bore.
This paper will demonstrate additional benefits that these types of measurements can offer which include; reducing seismic depth uncertainty whilst increasing the confidence of the reservoir boundaries; and providing more information on the depositional architecture of the reservoir to aid integrated subsurface description. Cost savings can also be realised using these measurements, not only by mitigating pilot holes and unplanned sidetracks, but by increasing the confidence of a geological model during drilling thereby allowing an increased drilling ROP and eliminating costly delays e.g. waiting on interpretation of biostratigraphic data to enable well planning updates to occur.
Finally, this paper will look at the importance of ensuring pre-job modelling is accurate and representative of the types of formations to be drilled, provides alternative scenarios to the reference case model and how case sensitivities can be used to provide models that match the realised outcome, increasing confidence in the results and speeding up the geosteering decision making process.
This work was performed in an offshore Tertiary deepwater turbidite formation, comprising a system of stacked, confined and unconfined sands with complex fill patterns and multiple incision surfaces. The well consisted of 4 individual target sands that dipped to the north and displayed an offset stacking pattern with two sands targeted at the crest and two additional sands down dip. As the downdip target sands were previously unpenetrated, seismic depth uncertainty was large resulting in an opportunity to run extra deep azimuthal resistivity measurements to ensure that the sands could be located and drilled to maximise net sand length in the reservoir section.
High angle wells drilled in turbidite formations can be challenging to geosteer because of the unpredictability of the structure of the formations themselves and because the boundaries between net and non-net intervals are often not distinct due to anisotropic effects. The ability of extra deep directional LWD resistivity tools to remotely detect hydrocarbon bearing reservoir and image the formation boundary when approaching helps to reduce the geological risk. The data from these tools can be quickly and accurately applied to a model which leads to better and more timely decisions that can decrease rig time, reduce costs and increase the probability of drilling a successful well.
