Reservoir Geology Study of the Sub-Garn Sands Complex (Ile, Tofte and Tilje Formations)

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

• 2,650m core from 28 wells described at a 1:50 scale, with 275 samples analysed petrographically and 50 samples for XRD and SEM analysis.

• A wide depth range of cored sections studied (between 2.2km to 5.5km depth) to assess diagenesis and geographic spread to account for variation in sediment input

Introduction

Building on PetroStrat’s recently completed reservoir quality study of the Garn Formation (2021), this regional investigation on depositional and diagenetic controls affecting reservoir quality is now being extended to the early-mid Jurassic sub-Garn sands complex. PetroStrat will focus on sands coincident with the J30, J40 and J50 biostratigraphically defined sequences (i.e., beneath J50.4-J60.2 defined Garn), assigned to the Ile, Tofte and Tilje formations.

The 28 Halten Terrace wells have been identified with guidance from operators to capture a wide range of location, facies, age and depth (2.2km to 5.5km) of cored sections. This variability will help geoscientists use the database as a predictive tool and reference, as an aid to understand and model reservoir properties. Potential links between depositional facies and sediment provenance, with pore-lining chlorite formed during late diagenesis (observed to resist mechanical compaction and quartz overgrowths) will again be a focus, alongside cement phases including illite, dolomite, kaolinite.

Key Deliverables

• 1:50 & 1:200 descriptions for ~2,650m core from 28 wells alongside CPI lith/porosity
• Analytical Program:
  • Petrographic descriptions of 275 thin sections
  • SEM & XRD analyses on 50 samples
  • Chlorite polytyping on up to 20 samples
  • Isotope geochem analysis on up to 20 samples
• GIS summary maps for the J30, J40 & J50 time slices indicating facies & diagenetic relationships with depth & reservoir quality
• Core photographs illustrating sedimentological, ichnological & diagenetic features
• Facies-coded CCA database

28 Sub-Garn wells included in this study