Case Study: Reservoir Quality Determined from High-Resolution Images in OBM of Channel and Highly Laminated Sands

Cost-effective downlogging acquisition with Quanta Geo service obtains borehole images and dip in a 12 1/4-in wellbore, North West Shelf, Australia

Challenge: Efficiently assess reservoir quality and determine the depositional environment of the Mungaroo Formation in the North West Shelf through texture, fabric, and sedimentological analyses.

Solution: Acquire high-resolution borehole images in oil-base mud (OBM) with Quanta Geo photorealistic reservoir geology service.

Result: Conducted a cost-effective, detailed geological interpretation of key sedimentary and structural features identified along a 2,000-m interval to support formation evaluation of the targeted reservoirs and bounding beds.

Unknown reservoir quality

An operator in the North West Shelf offshore Australia needed to assess the potential economic value and reservoir quality of the Upper Mungaroo Formation (Cretaceous to Triassic), including determination of the depositional environment, reservoir presence, connectivity of nonchannel facies, and structural features. Cutting conventional core would be a lengthy and expensive operation whereas sidewall coring would provide only scattered data. Full-coverage borehole images were the most efficient approach, but the well was drilled with OBM and a large bit size. Both of these conditions would severely limit the imaging capability of conventional OBM-adapted imagers.

High-resolution imaging in oil-base mud

Quanta Geo photorealistic reservoir geology service uses completely new measurement physics enabled by a new electronic and mechanical design to deliver superb resolution and nearly complete coverage in 8-in boreholes. The resulting microresistivity images are a true visual representation of the formation geology. Image interpretation is fully powered by the Techlog wellbore software platform, making it possible for geologists to readily perform tasks such as distinguishing channels and measuring their orientation. Facies can be identified and correlated with precision and confidence that were previously possible only from core.

Unambiguous identification of geological features and their depositional environment

Coverage in the large 12 1/4-in borehole by Quanta Geo service was 64%, which is more than 3 times that of conventional OBM imagers at 21% and more than sufficient to image highly dipping events such as natural fractures and faults. The eight independently applied pads all returned highly detailed images despite the challenging hole conditions. Acquiring the images by downlogging efficiently and cost-effectively provided comprehensive information early in the logging program to save rig time and additional runs.

The continuous, high-resolution images logged over a 2,000-m interval revealed faults, cross bedding, indications of soft sediment deformation, thickly bedded shales, and highly laminated sandstones, which enabled the operator to develop an in-depth understanding of the environment of deposition and determine reservoir quality.

Download: Reservoir Quality Determined from High-Resolution Images in OBM of Channel and Highly Laminated Sands (2.21 MB PDF)

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Detail-Rich Images at 3× the Coverage in 12 1/4-in Well

Log shows clear representation of formation geology.Log shows fault zone with chaotic texture and nonplanar features.
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Downlogging High-Resolution Images and Dip in OBM

The 3D interpretation to the right of the images from a 15-ft sand interval shows the repeated, abrupt high-angle changes in dip that resulted from disruption of the sand by slumping.
Quanta Geo photorealistic reservoir geology service redefines imaging in oil-base mud environments with high resolution and full coverage to truly represent the formation geology.
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