Vuggy carbonate

A DOUBLE-POROSITY POROELASTIC MODEL TO RELATE P-WAVE ATTENUATION TO FLUID FLOW IN VUGGY CARBONATE ROCK... 

Okabe Hiroshi, Blunt Martin J. 2007. Pore space reconstruction of vuggy carbonates using microtomography and multiple-point statistics. Water Resources Research, 43(12). 

Figure 2.21 shows permeability versus porosity for non-vuggy carbonates. The average particle size is used as the controlling parameter. Straight lines separate data collectives with respect to particle size. The figure confirms two tendencies as learned from siliciclastic sediments ... 

Following the rock-fabric classification, Jennings and Lucia (2001) developed a systematic plot presentation for non-vuggy carbonates and subdivided limestone and dolomite into three classes with rock-fabric numbers. The generalized carbonate permeability model provides a relationship between permeability, interparticle porosity, and rock-fabric number ... 

FIGURE 2.21 Permeability (air) versus porosity for various particle-size groups in non-vuggy carbonate rocks. Lucia (1983, 1999, 2007). 

In carbonate rocks, the time-average equatimi works for most intergranular, interparticle porosities this pore distribution is somewhat similar to sandstone. In vuggy carbonates, the slowness is dominated by primary intergranular, interparticle porosity, and the resulting porosity tends, in some cases, to be underestimated by the secondary porosity (Asquith and Krygowski, 2004). 

Muller, E., 2012. A modified archie relationship for vuggy carbonates. In EAGE Extended Abstracts P373, Presented at the 74th EAGE Conference Exhibition, Copenhagen, Denmark, 4—7 June. 

Principal gangue minerals in base-metal vein-type deposits are quartz, chlorite, Mn-carbonates, calcite, siderite and sericite (Shikazono, 1985b). Barite is sometimes found. K-feldspar, Mn-silicates, interstratified mixed layer clay minerals (chlorite/smectite, sericite/smectite) are absent. Vuggy, comb, cockade, banding and brecciated textures are commonly observed in these veins. 

Class II deposits in reservoirs made up of consolidated terrigenous sediments sands not running reservoirs lying at depths from 800 to 1500 m Class III deposits in reservoirs made up of carbonate rocks with complex porosities of fracture, cavern, and and vuggy types. 

The crystal carbonate fiicies is a secondary dolomitic texture characterized by the dominance of well-developed dolomite crystals. The most cxnnmon porosity types in the dolomitized parts are i) moldic and vuggy porosity, ii) intercrystalline matrix porosity iii) iniraciystalline porosity due to the selective dissolution of crystalline dolomite iv) karst and firacture porosity. The pore structures vary fiom monomodal to trimodal with an incr e of porosity and permrability according to the development of vugs and karsts. In this fiides, the reservoir properties are mainly controlled by the crystal size. 

The complex pore system of carbonate reservoirs ranges from microcrys-talline pores to large vugs or caverns. The petrophysical characteristics are controlled by connected networks of interparticle pores (matrix), vuggy pore space, and fracmres, where ... 

Carbonates with large moldic or vuggy pores >200 w... 

But in case of more heterogeneous carbonates with moldic or isolated vuggy pore space, Archie s equation fails. Non-connected parts of the pore volume do not contribute to the conductivity and result in an extremely high resistivity and formation factor. Systematic studies of these pore types have been published, for example, by Focke and Munn (1987) and Fleury (2002) (Fig. 8.12). 

Focke and Munn (1987) found that low porosity carbonates with mostly interparticle (intercrystalline) porosity are associated with m values below 2. A higher percentage of moldic or vuggy porosity raises m values from 1.8 at low porosities to over 5 at high porosities. 

Miiller-Huber (2013) (see also MiUler-Huber and Schon, 2013a,b) analysed three sets of carbonate samples from different areas in Austria massive Dachstein limestone, fracturedAmggy Hauptdolomite, vuggy Wetterstein dolomite. 

Figure 8.13 shows the results with a separation of the three carbonate rock types. The vuggy Wetterstein dolomite is characterized by high formation factors. In a forthcoming paper (MiiUer-Huber et al., 2015), a comparison with model calculations demonstrates the effect of pore geometry, expressed by the ratio of pore-body and pore-throat radius (see Section 8.4.5). 

Iwere, F.O., Moreno, J.E., Apaydin, O.G., 2002. Vug characterization and pore volume compressibility for numerical simulation of vuggy and fractured carbonate reservoirs. SPE 74341, In SPE Intemat. Petroleum Conf. Exhib., Mexico. 

MilUer-Huber, E., 2013. New concepts for understanding the effects of complex pore structures on petrophysical properties of carbonate rocks. Dr. thesis, Montanuniversitat Leoben. MilUer-Huber, E., Schdn, J., 2013a. A modified archie relationship—a novel approach to evaluate carbonate reservoirs with regard to fracture and isolated vuggy porosity for Sw = 1. In Paper IPTC 16695 Presented at the 6th International Petroleum Technology Conference, Beijing, China, 26-28 March. http //dx.doi.org/10.2523/16695-MS. 

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