Pore Typing Workflow for Complex Carbonate Systems

Skalinski, Mark; Kenter, Jeroen

Determination of Petrophysical Rock Types (PRTs) in carbonates is an industry recognized best practice for reservoir characterization. However, current methods fail to capture factors such as diagenetic modification, multimodal pore throat distributions, fractures and integration of dynamic data. This paper discusses the inclusion of pore throat distributions in the pore typing step which is an integral element of the PRT workflow developed in Chevron accounting for different data scenarios depending on availability of core, MICP and logging data.

Carbonate petrophysical heterogeneity is generally the result of complex and multi-modal pore systems including fractures. Carbonate pore systems in subsurface reservoirs that have seen even mild diagenetic overprint can rarely be decomposed into contributions from end member pore types based on syndepositional texture. Conventional rock typing methods use petrographic observations including image analysis to determine pore types qualitatively or quantitatively in an attempt to relate the pore system, at least in part, to flow and textural pore types. However, such techniques more than often do not resolve the complexity and multi-modality of the pore system and result in a misrepresentation of dynamic properties as documented by examples.

Identification and prediction of pore types in the well bore from core and logs and their spatial prediction is therefore essential for a reliable rock typing in carbonate. Appropriate pore type identification comes from mercury porosimetry (MICP) interpretation. MICP is providing information on pore throat distributions controlling flow in reservoir. MICP derived pore types have to be combined with larger scale observations such as vugs and fractures. Grouping pore throat modes from capillary pressure curves and mapping those on selected and representative porosity-permeability plug data provides a reliable way to predict pore type groups in multimodal systems and include the full scale of porosity from nanopores to macropores. MICP derived pore types have to be combined with larger scale observations such as vugs and fractures using specialty logs (e.g. NMR, FM) to provide this information.

The integration of MICP data in the pore typing step in carbonate rock typing optimizes the link between the different scales of (dynamic and static) observations but at the same time challenges the geologist to capture the spatial trends an relationships between resulting PRTs.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013