178 / 2019-06-10 08:36:43

The gravelly foreshore facies of the bottom of the Changcheng System and its petroleum geological significance

gravelly foreshore facies,,sand-gravel reservoir,Proterozoic Changcheng System,sequence stratigraphy,petroleum geological significance

The Proterozoic Changcheng System is composed of Changzhougou formation, Chuanlinggou formation, Tuanshanzi formation and Dahongyu formation from bottom to top, mainly composed of a set of shallow sea clastic rocks and carbonate rocks with a wide range of distribution. Through the observation of Changzhou Village in Jixian County of Tianjin, Shanxi Changcheng System and the Changcheng System around Beijing, combined with the thin section analysis, it is considered that the bottom of the Changcheng System is generally composed of gravelly shoreline facies, partly influenced by tidal action and paroxysmal river injection at the coastal margin, and that the sedimentary microfacies are gravel beaches and tidal channels (small tidal channels), paroxysmal braided river channel and sand-gravel foreshore deposition. They exhibit the following sedimentary characteristics: 1) two-way wedge-shaped and trough-like cross-bedding gravel-bearing coarse sandstone sedimentary sequences, 2) fish-bone-like cross-bedding and sedimentary sequences of double clay layers and tidal bundle bodies; 3) the gravelly grains have the characteristics of progressive normal grain sequence, with the wedge-like interbedded gravel-bearing sandstone sedimentary sequence, 4) the gravel grains with good roundness have the character of progressive reverse-grain sequence, and the thickness of the gravelly grains is about 1 ~ 2 m extended in a wide range of striped conglomerate depositional sequences; and 5) Massive bedding is mainly developed in gravel foreshore and low angle scouring bedding is seen in sandstone, the shoreface sedimentary sequence composed of multi-stage mudstone and sandstone parasequence in the upper part. The understanding of the gravel shoreline facies is of great petroleum significance to the exploration of deep and ultra-deep oil and gas and the study of conglomerate reservoir.