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The impact of biased LWD data propagated through nonbiased WL models

by Yngve Johansen, Statoil

Abstract

The petrophysical properties of a conventional oilfield are typically characterized from models based on exploration data. Datasets from explorations wells normally comprise core and wireline (WL) logged data. This forms the basis for interpretation models that later are used on the entire field or just certain parts of it. The models are naturally performing well on the exploration data itself, but how do they perform when applied to wells drilled in development phase? At the Norwegian continental shelf, data acquired in the development phase is most of the time LWD. Therefore, data from very different sensors in a very different borehole environment is propagated through older WL models before being imported to the geomodel. It is natural to reflect over how large errors or bias this approach really represents and subsequently also what the impact of this is on the geomodel and production simulations. Invasion related effects, different sensor systems/responses or a wrong set of assumptions could introduce systematic errors and this talk will demonstrate such a case. Porosity data was biased in this example case, both due to different/questionable sensor responses and invasion related assumptions/effects. The data was acquired on LWD in horizontal wells and propagated through WL models. Once the problem was understood, a new geomodel was built based on a somewhat modified interpretation model and corrected raw data. This resulted in short in more pessimistic porosity and permeability data, and somewhat higher water saturation. Production profiles will be shown for the old geomodel, the new corrected one and the new corrected one with history-matched parameterization. Also other technical changes were made to the model, but the changes seen are mainly expected to originate from the changes made to porosity and permeability.

Yngve Johansen, CV

After he graduated from NTNU with Cand.Scient degree in Physics, Yngve had a wide international experience in logging operations from field positions with Schlumberger from 2001 to 2006. Then he specialized in NMR and became Sr Physicist for the Schlumberger WL latest NMR logging technologies, during this period he became a key contributor to development of NMR technology. He joined Statoil in 2009 and has since been working as Principal Petrophysicist in different oil and gas fields.