Faults identification based on high-resolution multilayer mapping while drilling service

Background. Drilling horizontal wells into Jurassic formations in Yamal-Nenets Autonomous Okrug (YNAO) fields involves faults intersection [5]. In such cases, horizontal section geosteering strategy after crossing a fault is based on an assessment of the wellbore’s stratigraphic position and the technical capabilities available to ensure the geological objectives achievement [7]. Traditional methods for predicting faults intersection depth are rely on seismic data, while identification during drilling is based on logging data. The existing logging data depth of investigation limitations makes the task of identifying a fault and determining the wellbore’s stratigraphic position after crossing it quite complicated. As a result, decision on the subsequent steering maneuver presents significant uncertainty.

Aim. Estimate how advanced logging while drilling methods such as high-resolution multilayer mapping while drilling service complement existing fault identification techniques [2].

Materials and methods. This study based on actual drilling data from Jurassic reservoirs.  It will demonstrate examples of how using deep boundary mapping tools (resistivity-based) helps to achieve the objective of identifying faults, determining the wellbore’s stratigraphic position and detecting reservoir thin sublayers within the tool’s depth of investigation in the formations of the X field.

Results. The application of deep resistivity boundary mapping technology in Jurassic formations (enabled by the resistivity contrast between shale and reservoir layers [8]) significantly enhances, and often makes fundamentally possible, the determination of the wellbore’s position within the stratigraphic section after crossing faults. This enables more confident stratigraphic correlation and allows for trajectory optimization to achieve the pre-defined geological objectives.

Conclusion. Comparison of the resistivity inversion with other logging methods demonstrates a high degree of reliability in the data acquired while drilling and its interpretation (azimuthal imaging while drilling, borehole acoustic reflection survey). Combination of multiple approaches and different measurement types can provide even greater insight into the subject of study.

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