Examination of Petrophysical Characteristics of Carbonate Multimodal Porosity Systems

Abstract

Carbonate petrophysical heterogeneity is generally the result of complex and multi-modal pore systems, including fractures. This complexity is due to a combination of complex depositional rock fabric textures and diagenetic modification of the rocks. Post-depositional processes can modify the original petrophysical properties (e.g. permeability and irreducible water saturation) and result in a disconnection between the original depositional rock fabric and the current reservoir properties. Pore types are a critical element of rock types since they exert a dominant control over petrophysical properties and fluid flow. Conventional pore 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 subsequently result in a misrepresentation of dynamic properties as documented by examples. Pore typing based on mercury porosimetry (MICP) draws on the modality of pore throats accessed by specific pore volumes, which is a strong factor controlling fluid flow in reservoirs. One of the primary parameters in pore typing definitions is the pore system modality. The number of modes is associated with petrophysical properties and depositional or diagenetic processes. However, a more comprehensive link to the recovery factor needs examination of the whole pore system including the pore size distribution. We've developed a method of automatic modal detection from MICP data using Gaussian decomposition. It allows an objective estimation of the modality of the pore system. We are also investigating the whole pore system defined by both: pore throats (from MICP) and pore size distributions (from NMR and image analysis). In this presentation, we will describe the integrated pore typing workflow with examples from several carbonate reservoirs. These case studies show that pore types and pore system modality are associated with petrophysical properties, depositional facies, and diagenetic modifications. Furthermore, integration of MICP, NMR measurements and 3DBSEM images on the same core plugs enable us to describe the modality of the whole pore system in a more comprehensive way, providing interesting insights on the pore system and drivers of petrophysical properties in carbonates.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016