Core & Thin Section Analysis

Core and thin section descriptions and interpretations are key components of regional to field-scale studies because depositional and diagenetic facies, stratigraphic architecture and fracture networks usually control porosity, permeability distributions and reservoir performances.

A fundamental understanding of the reservoir architecture and dynamic behaviours can only come from accurate Core & Thin Section descriptions and interpretations.

GEPlan can log and interpret cores in order to calibrate them to electric and image well logs. Main features described on cores are: depositional textures, major grain types and granulometric ditribution, sedimentary structures, sorting, lithologic composition, structural features, pore types and visual porosity. These information are used to interpret the depositional environments, water depth and to predict the distribution of sedimentary bodies.

We can place core description in the reservoir architecture by using a sequence stratigraphic approach based on the hierarchical development of sequences through base-level transit cycles of varying frequency (short-term to long-term).

Part of our core studies is devoted to an analysis of 2-D stacking patterns of facies in order to develop a rock-based sequence stratigraphic framework. We identify facies successions, important hiatal surfaces (exposure, erosional, sediment-starved, firmgrounds and hardgrounds) that bound strata units and their possible cycle organisation.

In a thin-section analysis, we focus our study on mineral constituents, allochems, texture, sorting (or crystal size range), pore types and abundance of pore-filling cements or alteration/residual products. This is the base for our diagenetic interpretation, or paragenetic history. We usually use to work with blue-dyed epoxy impregnated thin sections to highlight porosity networks. To study carbonate mineralogy, the thin sections are stained with Alizarin Red-S and potassium, whereas for siliciclastic thin sections potassium feldspar (sodium cobaltinitrite) is applied.

Reservoir quality assessment studies through integration with MICP data are also provided with associated photomicrograph atlas with pictures at different scales taken at plain or cross polarised light.