Abstract
Transition zones in tight heterogeneous carbonate reservoirs contain a considerable amount of original oil in place. Identifying and characterizing the petrophysical flow units of the transition zone is crucial for reserve estimation and performance prediction. This paper presents a petrophysical rock typing method based on decoding pore-size distributions from mercury injection capillary pressure (MICP) data by using Thomeer hyperboles, with proven application in a tight carbonate reservoir in the Middle East region. In this study, 150 MICP data sets were used which were type curve matched using Thomeer Hyperbolas with closure correction. Multivariate clustering method has been employed to divide the samples into a number of groups for the purpose of both representing the reservoir heterogeneity and simplifying rock typing for dynamic modeling. From the MICP curves, it has been found that mainly monomodal pore systems prevail in the targeted transition zone and five different rock types are identified. It has been observed that most of the pore throat types are meso and micro types with the negligible existence of nano-pore type. The intrinsic advantage of this rock typing method is to describe the pore system quantitatively, which is different from other rock typing methods based on the apparent poro-perm relationship. The comparison of the grouped data with the petrophysical properties showed that different pore-size distributions yield similar porosity and permeability values, reinforcing the importance of grouping rocks based on pore systems instead of their resulting properties. Additionally, a study has also been conducted to improve understanding on the relative permeability in transition zone by implementing an up-to-date model for the mix-wet condition. The work in this paper provides a guide for the further understanding of rock typing and modeling of transition zones in carbonate reservoirs.
Highlights
The interval from the water–oil contact (OWC) to the height where water saturation attains its irreducible level is called transition zone of a reservoir (Bera and Belhaj 2016; Masalmeh et al 2007; Spearing et al 2014)
The transition zone contains a considerable amount of original oil in place due to high capillary pressure phenomena
Understanding the petrophysical flow units within the transition zone and correlations of capillary pressure and relative permeability study is important for performance prediction, transition zone reservoir modeling and simulation (Shi et al 2017)
Summary
The interval from the water–oil contact (OWC) to the height where water saturation attains its irreducible level is called transition zone of a reservoir (Bera and Belhaj 2016; Masalmeh et al 2007; Spearing et al 2014). Pore systems provide primary control on hydrocarbon distribution in the reservoir. They control the interaction between rock and fluid in terms of capillary pressure, relative permeability, and microscopic displacement efficiency (Clerke 2007; Clerke et al 2008). Understanding the petrophysical flow units within the transition zone and correlations of capillary pressure and relative permeability study is important for performance prediction, transition zone reservoir modeling and simulation (Shi et al 2017). Selection of a suitable mathematical model for the correlation study signifies the importance of capillary pressure and relative permeability hysteresis incorporation in the reservoir model for transition zone behavior prediction. Precise rock typing is another important issue in transition zone reservoir modeling and simulation. The purpose of rock typing is to classify the reservoir rocks into different units with respect to pore system, texture, and lithotypes
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