Summary
This paper describes geological and petrophysical evaluation of a new
structure of a mature field to evaluate the reservoir potential in unproduced
reservoir zones. The well was drilled in a carbonate with variations in rock
quality and with minor subfaulting occurring. Gamma ray (GR), resistivity,
density, neutron, and image services were used in the horizontal part of the
well in addition to magnetic resonance (MR). To achieve the best possible
real-time wellbore placement, reservoir navigation and continuous follow-up on
the horizontal log interpretation were performed during drilling.
For the first time, a low-gradient-MR-while-drilling technology was deployed
in a virgin carbonate horizontal well on the Norwegian Continental Shelf. The
MR service was run to obtain porosities (including partitioning of movable and
bound fluids), hydrocarbon (HC) saturations, and permeability estimates. Fluid
saturations based on traditional methods and the MR were evaluated and compared
by core data, enhancing the understanding of the measurement and the reservoir.
For post-processing, the MR data were integrated and interpreted together with
the other measurements performed in the well, delivering an accurate and
consistent reservoir description.
The first part of the horizontal part of the well was drilled with
conductive drilling fluid and the latter part with nonconductive drilling
fluid. Laboratory measurements for the two mud filtrates were performed to
understand the influence of the two different drilling-fluid types on the MR
measurements. In the absence of water-based mud-filtrate invasion, the MR data
show good agreement with saturations from core, confirming the quality and
reliability of the MR data.
Comparison of the MR T2 distributions and volumetrics with image data
indicates that even fine variations in rock quality and lithology are reliably
resolved by the MR data. Before logging, old core data were used to refine the
constants used in the Timur-Coates MR permeability equation, which
quantitatively tracks changes in reservoir quality. The values were calibrated
when Timur-Coates constants were derived from the well's core plugs.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
11 July 2008
- Meeting paper published:
22 September 2008
- Revised manuscript received:
10 April 2009
- Manuscript approved:
29 September 2009
- Published online:
5 August 2010
- Version of record:
24 August 2010
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