Origin of carbonate cements with implications for petroleum reservoir in Eocene sandstones, northern Dongying depression, Bohai Bay basin, China

Abstract

The Eocene Es4s interval is an important petroleum reservoir of sublacustrine fan dominated at the depths of 2500-4000 m in Dongying depression, Bohai Bay basin. Based on core observation, three types of carbonate-cemented beds have been identified and commonly contain ferroan calcite and ankerite predominantly and less calcite and dolomite. Precipitation temperatures range from 34.6 to 72.8 C for calcite and dolomite cements, and from 110 to 153 C for ferroan calcite and ankerite cements. The high 13 C PDB values (À0.65 to +5.59%) for calcite and dolomite suggest that dissolved inorganic carbon, derived from methanogenic fermentation of organic matter in adjacent mudstones. The low 13 C PDB values (+1.04 to +3.29%) for ferroan calcite and ankerite probably indicate a mixture of carbon derived from decarboxylation of organic acid as well as from the dissolution of early formed carbonate cements. High plug porosity is mainly developed at the central section of sandstones vertically and the porosity decreases sharply toward the top and base of the sandstones due to extensively carbonate-cemented beds. The carbonate-cemented beds varies from 0.02 to 0.5 m in thickness and might extend from tens to hundreds meters laterally. It could be served as fluid-flow barriers and seals for petroleum, and result in reservoir deterioration and significant heterogeneity.

Study on Thermal Conductivity of Thermal Insulation Cement in Geothermal Well

“…Geothermal energy is clean and sustainable and has been widely used for power generation, heating, and farming (Bildirici and Gökmenoğlu, 2017;Wang et al, 2017;Hamm and Metcalfe, 2019;Yang et al, 2021). In recent years, with the increased need for renewable energy, the exploration and utilization of medium-low temperature geothermal resources have been widely developed in China (Ma et al, 2016;Zhao and Fu, 2019). However, the temperature difference between high-temperature geothermal fluid and low-temperature formations results in the temperature in the wellhead being lower than that in the actual reservoir (Hasan and Kabir, 2002).…”

An experimental study simulating the dissolution of gypsum rock

“…Previous research indicates that over 200 mg of gypsum rock is soluble in 100 g water at room temperatures. In contrast, the solubility of limestone and dolomite, which are commonly co-deposited with gypsum rock in saline sedimentary environments and have a great influence on the accumulation of oil and gas (Liu et al, 2017;Ma et al,2016;Wu et al, 2017;Xiao et al, 2017), is an order of magnitude less, at only 12 mg per 100 g of water. Therefore, the dissolution of gypsum rock is one of the key factors to consider when evaluating its distribution and preservation, and the wider implications of its sealing properties.…”

Petrological characteristics and the impact of mineral content on reservoir quality in coal-bearing strata of Linxing area, eastern margin of Ordos Basin, China

“…Harris (2006) and Taylor et al (2010) introduced the dual role of the tectonization about the reservoir physical property, including the unfavorable tectonic compression and beneficial fractures to increase the reservoir porosity. Types and contents of minerals and rocks have a significant influence on the densification of tight sandstone reservoir (Li et al, 2016; Ma et al, 2016). However, few studies have paid sufficient attention to the influence of mineral rock composition, content, structure, and second changes on reservoir densification (Zhong et al, 2012).…”