High-Resolution Sequence Stratigraphy of Terrestrial Penglaizhen Formation of Xinchang Gas Field in Western Sichuan

Key words: 
• Xinchang Gas Field /
• Penglaizhen Formation /
• base-level cycles /
• high-resolution sequence stratigraphy /
• isochronostratigraphic /
• correlation

Abstract: According to the data of rock cores, well loggings and seismic interpretations, three order base-level cycles are recognized from Penglaizhen Formation in Xinchang area, which consist of 45-47 short-term base-level cycles, 5 mid-term base-level cycles, 2 long-term bsae-level cycles and their structural types, stacking patterns and distributing models are deeply discussed by using high-resolution sequence stratigraphic theory and methods. On the basis of single-well analysis, higher-accuracy isochronostratigraphic correlation is done at the thrree order base-level cycles in Penglaizhen Formation, and the relative stratigraphic frameworks are built, meanwhile one-dimensional information about single-well is converted to three-dimensional information in gasfield. According to the analysis on characteristics of stratigraphic response course of sedimentary dynamics, favorable reservoir sands' sedimentary facies, association, occurrence, controls, and relationship with physical property in the course of mid-term and short-term base-level cycles are discussed. A table of the influence of the ratio of the accommodation and the sediment supply flux to the reservoir sands is also made in this paper. It clearly shows that the delta systems in the slowly ascent or descent process of the long-term base-level cycles are the necessary background for the favorable reservoir sands, and the main element of controlling the distribution in the time and space for the sedimentary system is the mid-term base-level cycles. The best reservoir sands are on the sides of the sequencesur face of the mid-term base-level cycles. So one of the important token of reservoir forecast is the sequence surface of the mid-term base-level cycles.