松辽盆地中央坳陷南部下白垩统泉头组四段沉积相

松辽盆地中央坳陷南部下白垩统泉头组四段沉积时期，松辽盆地地形平缓，基底沉降缓慢，在湖平面整体扩张及浅水背景下河流入湖成三角洲沉积。通过岩心观察、相标志与测井相研究，该区储层主要为岩屑长石砂岩和长石岩屑砂岩，识别出三角洲平原、三角洲前缘、前角洲3种亚相，以及分支河道、天然堤、决口扇、分支河道间湾、水下分支河道、水下决口扇、河口坝、远沙坝、水下分支河道间湾9种微相三角洲平原、三角洲前缘广泛发育，前三角洲不发育。三角洲平原分支河道通过填积和频繁的分叉改道，向湖盆中心方向长距离推进，在三角前缘的浅水区域发育了大量水下分支河道，分支河道与水下分支河道砂体相互切割、叠加，形成了平均宽度200~600 m、平均厚度3~8 m的道单砂体，（水下）分支河道砂体构成了油气富集的主要储集体。该区沉积相的精细研究，为进一步调整开发井网奠定了基础。

Sedimentary facies of the Member 4 of Quantou Formation of Lower Cretaceous in southern Central Depression of Songliao Basin

The Songliao Basin is located in the Northeast China, where Daqing and Jilin oilfields were developed. At the period of the Member 4 of Quantou Formation of Lower Cretaceous in the southern Central Depression of the Songliao Basian, the basement subsided uniformly and slowly, and the topography of the basin was very flat, leading to the development of a delta at the setting of shallow water and a rapid rise in lake level. Base on studies of core, main facies markers and well-log facies, the reservoirs are mainly composed of lithic arkoses and feldspar litharenites. Three subfacies and nine microfacies were identified. The subfacies are delta plain, delta front and prodelta. The microfacies are distributary channels, levees, crevasse splays, inter-distributary bays, subaqueous distributary channels, subaqueous crevasse splays, mouth bars, distal bars and subaqueous interdistributary bays. Delta plain and delta front were well developed, and prodelta was less developed. The distributary channel advanced toward the center of the lake over a long distance through filling deposition and branching channel frequently, and developed an obvious subaqueous distributary channel at the wide shallow-water delta front. The most oil-rich reservoirs are compased of channel sand bodies which had cut and oversfacked each other. The average width of single sand body is 200 to 600 meters and its thickness is 3 to 8 meters. This study is an important foundation for further oilfield production adjustment and development.