An automated and universal approach for characterising cored formation intervals: gaining more insight from comparing zonation results – according to geological facie, rock type and hydraulic units

Abstract

Formation characterisation of cored intervals presents an important challenge in defining reservoir parameters for integration of subsurface data, to gain understanding and subsequently use this information for other tasks, for example geological correlation, petrophysical calibration with open-hole logs and vertical grid definition for dynamic reservoir simulation. This paper demonstrates a fully automated and comparative analysis approach to define formation characteristics: based on geological and core description, linked to logs and pore structure – pore throat size and sorting, based on hydraulic parameters. Such comparison leads to greater understanding and more meaningful integration, taking into account all available data and ensuring consistency. Methodologies employed make use of cluster analysis and pattern recognition and use a six-parameter model space, a so-called global characteristics envelope (GCE): considering porosity, permeability, hydraulic radius, porosity group – porosity/grain volume, flow zone indicator – linked to pore-throat grain size/sorting. Comparative perspectives presented give greater insight to formation characteristics than more conventional approaches. The extended catalogue of models presented, not previously published, can be universally applied to all conventional formations, clastics and carbonates. Facie types are identified by different cluster situations exhibited in GCEs. Consistent diagenetic intervals form a base model. Very uniform intervals are those with uniform porosity or permeability, or both (a cluster). More heterogeneous intervals are highly varying diagenetic intervals; interbedded diagenetically-driven intervals, e.g. pyritisation; and alternating thinly-bedded intervals of different lithologies and fining sequences. A detailed case history is presented involving a cored formation interval exceeding 110 m plus one other example.