Feldspar Dissolution and Its Influence on Reservoirs: A Case Study of the Lower Triassic Baikouquan Formation in the Northwest Margin of the Junggar Basin, China

Abstract

Feldspar dissolution is a common feature in clastic rock reservoirs of petroliferous basins and has an important influence on reservoir quality. However, the effect of feldspar dissolution on reservoir quality varies under different depositional environments and diagenetic systems. The study area in this paper is located in the Baikouquan Formation in the northwestern margin of the Junggar Basin, which is significantly influenced by feldspar dissolution. Based on the analyses of core and thin section observations, QEMSEM, XRD, SEM, CL, fluorescence, and image analysis software combined with logging and physical property data, this study shows that feldspar dissolution in the subaqueous distributary channel of a fan delta plain, which has good original physical properties and low mud contents, significantly improves the properties of the reservoir. The main reasons for this are as follows: (1) the sedimentary facies with good original properties and low mud content is a relatively open system in the burial stage. The acidic fluids needed for feldspar dissolution are mostly derived from organic acids associated with the source rocks and migrate to the good-permeability area of the reservoir; (2) the by-products of feldspar dissolution, such as authigenic clay minerals and authigenic quartz, are transported by pore water in a relatively open diagenetic system and then precipitated in a relatively closed diagenetic system; and (3) the clay minerals produced by feldspar dissolution in different diagenetic environments and diagenetic stages have different effects on the reservoir. When the kaolinite content is less than 3%, the illite content is less than 4%, and the chlorite content is less than 12%, the clay minerals have a positive effect on the porosity. These clay minerals can reduce porosity and block pore throats when their contents are larger than these values.

Effect of petrography and diagenesis on the sandstone reservoir quality: a case study of the Middle Miocene Kareem Formation in the North Geisum oil field, Gulf of Suez, Egypt

“…10D) and the dissolution of feldspar and carbonates. The dissolution of feldspar grains in sandstone reservoirs has a major impact on the reservoir's primary petrophysical properties and quality (Xiao et al 2018); this phenomenon is often documented in facies II and greatly enhances the secondary porosity values (Fig. 10C, D).…”

“…The impact of the sedimentary facies and the diagenetic processes on the reservoir quality of the siliclastic reservoir rocks have been discussed by many authors, including Abouessa and Morad (2009), Ajdukiewicz and Lander (2010), Bjørlykke (2014), Khalifa and Morad (2015), Olivarius et al (2015), Nabawy and Géraud (2016), Nabawy and El Sharawy (2018), Nabawy et al (2020), Abuhagaza et al (2021), Kassem et al (2021) andZhang et al (2021). The Gulf of Suez lies between Sinai and the northern section of Egypt's Eastern Desert.…”

Formation Mechanism and Prediction Method for the Permian Fused Breccia Tuff Reservoir, Wuxia Region, Junggar Basin

“…The surface water contained a large amount of CO 2 , which forms carbonic acid when dissolved and thus plays an extremely important role in the decomposition of many minerals (especially silicate and aluminosilicate minerals). At this time, SiO 2 and CaCO 3 were decomposed [38]. The decomposition reactions are as follows:…”

Qualitative Dissolution Modeling of Etch‐Pit Formation on the K‐Feldspar Surface Through Phase‐Field Approach

“…For instance, quartz grains exhibit faceted dissolution (Prajapati et al., 2021; Snyder & Doherty, 2007), while other minerals (such as calcite, feldspar, pyroxene) exhibit the formation and growth of “etch‐pits” on the grain surface (Arvidson et al., 2003; Beig & Lüttge, 2006; Berner et al., 1980; Keith & Gilman, 1960; Lasaga & Lüttge, 2001; MacInnis & Brantley, 1992, 1993). Feldspar dissolution is an ubiquitous process occurring in sedimentary basins (Huang et al., 2003; Xiao et al., 2018), that facilitates the generation of secondary porosity, resulting in an increase of porosity and permeability, and thereby reservoir quality (Bjørlykke et al., 1988; Stoessell & Pittman, 1990; Surdam et al., 1984, 1989; Wilkinson et al., 2001; G. Yuan et al., 2015; X. Zhu et al., 2007). About one half of the volume of the earth's crust, is composed of feldspar minerals (Gout et al., 1997).…”

“…(2018); Xiao et al. (2018). However, its implications on the resulting permeability are difficult to estimate, as the generated pores may remain isolated (Pittman, 1979).…”