Quantification and timing of porosity evolution in tight sand gas reservoirs: an example from the Middle Jurassic Shaximiao Formation, western Sichuan, China

• DOI: 10.1007/s12182-015-0021-1
• Publication Date: 2015-04-06T07:12:09Z
• Authors: Zheng-Xiang Lü; Su-Juan Ye; Xiang Yang; Rong Li; Yuan-Hua Qing
• Keywords: Cementation (geology); Ankerite

The diagenesis and porosity evolution of the Middle Jurassic Shaximiao sandstones were analyzed based on petrographic observations, X-ray diffractometry, scanning electron microscopy carbon oxygen stable isotope geochemistry, fluid inclusion microthermometry, thermal burial history modeling results. point count data show that secondary pores (av. 5.5 %) are more abundant than primary 3.7 thus dominant pore type in sandstones. Analysis indicates alteration mainly occurred during two paragenetic stages. Mechanical compaction cementation by early chlorite, calcite, quartz typically decrease depositional (40.9 an average 37.2 %, leaving % after stage I (<85 °C, 175–145 Ma). original intergranular loss due to is calculated be 29.3 suggesting mechanical most significant diagenetic process destruction. Stage II can further divided into sub-stages (Stage IIa IIb). (85–120 145–125 Ma) characterized late dissolution, which enhanced 8.8 increased from 12.5 %. During IIb (>120 125–0 Ma), precipitation quartz, kaolinite destroyed 3.3 porosity, 9.2 rock today.