Reservoir Geology Study of the Garn Formation

Study details a glance

Reservoir
Geology

Palaeoenvironments
& Facies

Reservoir
Quality

28
Wells

Jurassic

Key points

• Lends geological context to preserved poroperm in deeply buried sands, focusing on pore-lining chlorite

• 1,370m core from 31 wells described at a 1:50 scale, with 120 samples analysed petrographically and 50 samples for XRD and SEM analysis.

• A wide depth range of cored sections studied (between 1.7km to 4.7km depth) to assess diagenesis and geographic spread to account for variation in sediment input

This reservoir study on the Garn Formation provides an understanding of the major controls (e.g., depositional environments, diagenesis and burial depth) on reservoir quality. To test these relationships, a technically consistent, high quality database has been generated on cored sections at a range of burial depths (1660-4691m) in 31 wells across the Halten Terrace.

New facies assignments from core descriptions and mineralogical interpretation from petrography, SEM and XRD analyses (recording the occurrence of quartz, illite, chlorite and other cements) are cross-referenced against conventional core analysis (CCA) data. These datasets highlight geographic concentrations in the occurrence of pore-lining cements that are observed to protect primary porosity at great depth, and related to facies, while also indicating a variation in sediment sourcing. All observations are recorded and mapped within PetroStrat’s biostratigraphically defined Ichron Sequence (J50-70) framework.

The intention of both this Garn study, and the Sub-Garn (Tilje, Tofte and Ile) project is for operator geoscientists to use these databases as predictive tools and as a reference to understand and model reservoir properties.

Key Deliverables

• 1:50 & 1:200 scale core descriptions; ~1,370m core from 31 wells with CPI
• lithology/porosity
• Analytical Program:
  • Petrographic descriptions of 120 thin sections
  • SEM analyses on 50 samples
  • XRD analyses on 50 samples
• GIS summary maps for the J50, J60 & J70-100 time slices indicating facies & diagenetic
• relationships with depth & reservoir quality, with hyperlinked core & sample descriptions
• Core photographs illustrating sedimentological, ichnological & diagenetic features
• Facies-coded CCA database

31 Garn wells included in this study