The characteristics and genetic model of high-quality reservoir of clastic rocks in coal-bearing strata of Carboniferous Taiyuan Formation in Dawangzhuang area, Jiyang depression

Key words: 
• Carboniferous Taiyuan Formation /
• coal-bearing strata /
• high-quality reservoir /
• genetic model /
• Dawangzhuang area

Abstract: The coal-bearing strata of Carboniferous Taiyuan Formation are widely distributed in Dawangzhuang area, Jiyang depression, and the high-quality reservoir control factors in the coal strata have an important influence on oil and gas exploration. Combined with burial history, tectonic evolution history, multi-proxy analyses, including the cast thin sections, fluorescence, cathodoluminescence, scanning electron microscopy and energy spectrum, petrography of fluid inclusion and homogeneous temperature, and laser ablation inductively coupled plasma mass spectrometry, were conducted to systematically study the characteristics and genetic model of high-quality reservoir of clastic rocks in coal-bearing strata of Carboniferous Taiyuan Formation(C3t) in Dawangzhuang area, Jiyang depression. The clastic reservoir of Taiyuan Formation coal measure strata in Dawangzhuang area is mainly composed of lithic quartz sandstone. The high-quality reservoir space is dominated by secondary pores, and the dissolution is strong. It is mainly filled with interstitial materials dissolution pores and feldspar dissolution pores formed by atmospheric fresh water and organic acid dissolution. The porosity of high-quality reservoir is more than 8 %, and the permeability is more than 5 × 10-3 μm2. And two phases of quartz overgrowth and two phases of carbonate cements are developed, dominated by carbonate cements. The first phase of quartz overgrowth mainly derives from pressure dissolution of quartz particles, the second phase of quartz overgrowth is mainly sourced from the feldspar dissolution. Siderite is mainly formed by pore water precipitation in syndepositional-early diagenesis stage, and ankerite is mainly related to organic acid decarboxylation. The evolution process of the diagenesis-accumulation system of the clastic rock reservoir of coal measures strata of C3t in Dawangzhuang area of Jiyang depression is: siderite → first phase of quartz overgrowth → first-stage oil in yellow fluorescence emplacement → kaolinite → ankerite →second-stage oil emplacement in blue fluorescence → second phase of quartz overgrowth and kaolinite →pyrite. High-quality reservoirs are mainly controlled by sedimentary facies, tectonic action and diagenesis. The sedimentary facies controls the distribution of lithofacies of high-quality reservoirs. The high-quality reservoirs are mainly controlled by the late uplift of atmospheric fresh water leaching dissolution and buried organic acid dissolution. At the same time, they are controlled by tectonic activities. The distance between the high-quality reservoirs and the docking faults should be far away, so as to avoid the further precipitation of CO2 produced by decarboxylation to form ankerite to destroy the reservoir properties.