车镇凹陷陡坡带古近系湖底扇沉积规律及储层特征

Sedimentary rules and reservoir characteristics of sublacustrine fan in Paleogene in steep slope of Chezhen Sag

车镇凹陷陡坡带及洼陷带中砂砾岩体广泛发育,湖底扇是其重要成因类型之一。该区湖底扇沉积在时间上对应于低位体系域或湖侵体系域早期,在平面上受控于盆缘边界断裂的活动强度、产状及次级断层的发育。单期湖底扇沉积呈向上变细的正旋回特征,底部以杂基支撑砾岩相、块状砾质砂岩相为主,为深水重力流沉积;向上递变为块状砾质砂岩相或具变形层理的中细砂岩相,分选较好,正偏态,粒度概率曲线呈两段式,为牵引流沉积。该区湖底扇沉积的砂砾岩体具有埋藏深度大、粒度粗和分选差的特征,为超低孔超低渗透储层,以有机酸溶蚀形成的次生孔隙为主,具有孔隙和微裂缝双重孔隙介质特征。异常高压对砂砾岩储层的改善具有重要作用。

Sublacustrine fan is one of the important origin types since glu-tenites are developed widely in the steep slope and subsag zones of Chezhen Sag. Deposition of the sublacustrine fan corresponds to low stand system tract (LST)or early transgressive system tract (TST) , which was controlled by tectonic activity, attitude and secondary faults of border fracture at the edge of the basin. Single deposition of the sublacustrine fan is positive cycle with upward- fining grain size. There are matrix- supported conglomerate rocks and massive conglomerate - sandstones with an origin of deepwater gravity flow in its bottom, and massive conglomerate -sandstones and deformed bedding medium-( or fine-) sandstones with better grading, positive skewness, two - segment style of grain probability curve and an origin of tractive current. As a whole, the glutenites of the sublacustrine fan in this area is characterized by deep buried depth, coarse grain and poor grading, and belongs to super low - porosity and super low - permeability reservoirs with two-porous media of pore and micro- fractures. The secondary pore formed by organic acid chemical erosion is the main type of storage place. Surpressure has vital function for reforming reservoir quality in this area.