Pore Network Modeling of Multiphase Flow in Fissured and Vuggy Carbonates

Abstract

Carbonate reservoirs have more complex structures than silicate reservoirs because of depositional and digenetic features. Secondary porosity enhancements due to fracturing or dissolution processes result complex porosity systems and thus complex flow patterns. Carbonates may contain not only matrix and fracture but also the vugs and cavities that are irregular in shape and vary in size from millimeters to centimeters in diameter. Although many of these vugs appear to be isolated from fractures, the mechanism of oil recovery from vugs in such a system is highly dependent on the location of the vugs and connections of the vugs to the fissure/fracture system. Two phase flow in fissured and vuggy carbonates was studied by developing a novel pore network model that consists of several sub-networks including matrix, vug and fissure sub-networks. Matrix blocks were constructed by pores with triangular and pore throats with square cross-sections respectively. Fissures and vugs were represented by square cross sections. In order to obtain a spatially uncorrelated model, pore radiuses, which were obtained from previously conducted thin section analysis of a carbonate rock, and pore throat radiuses with a uniform distribution were randomly distributed. It was observed that the developed model can successfully simulate primary drainage, and secondary imbibition processes like snap-off, piston like advance and pore body filling. Comparison of pore network results and several published experimental results showed the uses and applications of the proposed pore network model. It was concluded that this novel pore network model design successfully represents two phase flow in a fissured and vuggy carbonate rock.

A Triple Pore Network Model (T-PNM) for Gas Flow Simulation in Fractured, Micro-porous and Meso-porous Media

“…Despite PNM simplifications, it is still interesting due to the low computational cost, especially with the Fig. 1 Network structure of the previous single PNMs and D-PNMs compared to the presented T-PNM, a single PNM (Blunt 2001;Fatt 1956), b D-PNM with meso-pores coupled to a lattice micro-pores (Bekri et al 2005), c dual with meso-pores and parallel micro-pores and throats (Bauer et al 2012), d a fully twoscale PNM with micro-and meso-pores (Jiang et al 2013), e dual with extra micro-throats to connect the meso-pores (Bultreys et al 2015), f dual with meso-pores and fractures with variable aperture (Hughes and Blunt 2001), g dual with meso-pores and fractures with fixed aperture (Erzeybek and Akin 2008), h D-PNM with extra bypassing fracture links (Liu et al 2017), i dual with unstructured network and variable geometry of fracture (Jiang et al 2017), j the presented T-PNM which includes meso-and micro-pores, meso-and micro-throats, fracture nodes, and fracture links have been accomplished by researchers to enhance the capability and reliability of PNMs (Baychev et al 2019) to realistically simulate and predict the properties of porous materials (Garboczi 1990;Joekar-Niasar and Hassanizadeh 2012;Xiong et al 2016), from hydraulic permeability (Dong and Blunt 2009) and mass diffusivity (Burganos and Sotirchos 1987;Erfani et al 2019) to electrical (Friedman and Seaton 1998) and thermal conductivities (Plourde and Prat 2003).…”

A forward analysis on the applicability of tracer breakthrough profiles in revealing the pore structure of tight gas sandstone and carbonate rocks

“…So far, the effects of vugs on flow properties have been experimentally investigated [Nair, 2008], and a stochastic method in which vug nodes are randomly distributed inside a regular structured lattice (with a uniform coordination number of 6) has been developed [Erzeybek and Akin, 2008]. However, to our knowledge, no deterministic pore network model that honors/quantifies the vug topology and its connection to the adjacent matrix exists in the literature.…”

Discrete Fracture-Vug Network Modeling in Naturally Fractured Vuggy Reservoirs Using Multiple-Point Geostatistics: A Micro-Scale Case

“…However, modeling such reservoirs is a challenging task due to their complexity. The main reason behind that is the co-existence of porous and free-flow domains over a broad range of scales (Erzeybek and Akin 2008;Wu et al 2006). Another reason is the abundant existence of fractures and their great impact on the displacement of fluids ), therefore, the prediction of reservoir performance.…”