Research Of Sedimentary Facies And Favorable Sands Of Lower He3Member In Biyang Depression

Biyang Depression, a sub-depression covering an area of 1000km2 in Nanxiang basin locates between Tanghe and Biyang counties in southern Henan province. Based on predecessors'results, the study presents detailed analysis on provinance, single well facies, well-tie facies and in-plance facies starting with stratigraphic correlation and depositional framework; demonstrates sedimentary facies patterns, sedimentary features, sedimentary system, sand body spreading regularity with different geneses, as well as depositional history in study area,in line with various analysis measures, and combining macroscopic and microcosmic views applied. In the meanwhile, elucidates sedimentary facies and diagenesis effecting on hydrocarbon occurrence, as combined with the study of sandbody diagenesis, and predicts potential reservoir developing zones, as well as designates the future hydrocarbon exploration. The preliminary study indicates three major provinances and five minor provinances existing in lower member of H3 in the study area, in the basis of provinance distribution, rock types, sedimentary facies markers, sedimentary facies patterns, depositional evolution, sedimentary micro-facies of oil-bearing layer, sandbody genesis and distribution regularity, as well as diagenetic patterns, diagenetic facies, and potential reservoir zones related with sedimentary facies and diagenetic facies. The rocks are mainly metamorphic rock and granite at the depositional stage of lower H3, and then sedimentary rock; the rock types are divided into clastic and carbonate rocks; sedimentary structure patterns are mainly trough cross-bedding, parallel bedding, ripple bedding, convolute bedding/deformed bedding, load structure, bioturbation structure and flow structure. Four sedimentary systems, known as fan-delta, braided delta, meandering river delta and lacustrine depositional systems appear in Biyang Depression at the depositional stage. Four sandbodies distribution in vertical and lateral directions is dominated by provinance and sedimentary system spreading in the lower H3 member. In the diagenetic mechanism study, the new theory of water-rock interaction is applied to build diagenetic mechanism model suitable for study area conditions, on the basis of taking account of organic acid as key diagenetic media; make a study of main diagenetic mechanism, and then provide theoretical basis for interpretation of porous evolution and diagenetic seal mechanism. In line with the study of diagenetic patterns and its order, the diagenetic stage and diagenetic sequence study is conducted; the diagenetic stage of sandstone reservoir in the study area is divided into syngenesis, early and late stage, in which the early stage is divided into A and B stages, and the late stage is divided into A, B, and C stages; and the diagenetic environment and diagenetic assemblage at each stage are explained systematically.Based on the study of each sandbody sedimentary facies and paleo-diagenetic facies controlling on reservoir, and combining with high resolution sequence stratigraphy and achieved exploration results, the prediction on potential exploration zones of each sandbody is implemented.