Saturation-Height and Invasion Consistent Hydraulic Rock Typing Using Multi-Well Conventional Logs

Hydraulic rock typing is based on pore geometry, which relates to saturation-height modeling at a later stage in reservoir characterization. Additionally, pore geometry affects mud-filtrate invasion under over-balanced drilling conditions. Reliable hydraulic rock typing should simultaneously honor saturation behavior in the vertical direction and mud-filtrate invasion in the radial direction. Such a condition becomes critical when hydraulic rock typing is performed with well logs acquired in multiple wells penetrating the same or different capillary transition zones. This paper considers three conventional core-based rock typing methods, namely Leverett's k /f, Winland R35, and Amaefule's flow zone index, to appraise whether rock classifications can be extrapolated from core-data to well-log domains. A new quantitative log attribute is derived from well logs to assist hydraulic rock typing, which integrates in-situ reservoir capillary pressure (Pc) and initial water saturation (Swi). The assumption is that the reservoir under study underwent hydrocarbon migration wherein vertical fluid distribution is still well represented by the primary-drainage capillary pressure curve. Petrophysical properties that are closely linked to pore geometry are quantified by invoking both Leverett's J-function and Thomeer's G-factor. The new log attribute is based on standard well-log analysis and only requires conventional well logs for its application. Thus, it can be generally applied to both clastic and carbonate reservoirs in multi-well contexts. It overcomes the limitation of the bulk volume water method which is only applicable to reservoir zones that are at nearly irreducible water saturation. Most importantly, it provides good initial estimates to constrain in-situ dynamic rock-fluid properties such as capillary pressure and relative permeability. The method proceeds with initial estimates of dynamic properties to construct multi-layer petrophysical models with a common stratigraphic framework (CSF) for each rock type, and to simulate the process of mud-filtrate invasion.