陆相断陷盆地陡坡带早期大型斜向扇三角洲的发现及其勘探潜力

现今我国东部断陷盆地油气勘探已达到较高的程度,目的 层系逐渐向深部转移,是东部断陷盆地下一步主要勘探方向之一.断陷湖盆陡坡带早期发育短轴物源形成的垂直于边界断层的近岸水下扇、扇三角洲和湖底扇,但对于陡坡带其他方向的沉积相类型及其勘探潜力研究较少.本文依据断陷湖盆沉积学原理,采用地震地层学方法,对我国东部典型断陷湖盆陡坡...

The discovery of large- scale oblique fan delta and potential for its exploration during the early stage in the steep slope zone of the continental rift basin

At present the exploration of the rift basin in eastern China and the exploration of the target layer in the deep strata, one of the main exploration directions of the next eastern rift basin, is in focus. The current understanding generally indicates that nearshore subaqueous fans, fan deltas and sublacustrine fans, which are formed by short- axis provenance, were developed in early stage of rifting in steep slope zone. However, less attention has been paid to the types of sedimentary facies and its exploration potential in other directions of the steep slope zone. Based on sedimentological principle of rift lacustrine basin and the seismic stratigraphic method, the typical rift basins in the steep slopes in eastern China are dissected, a new viewpoint that the early intrabasinal axial provenances development is proposed, and its exploration potential is discussed in the steep slopes of the rift basins in this paper. The results of this study are as follows: (1) Based on the combination of seismic facies in the Liuzan area of the Nanpu sag, Yanjia area of the Dongying sag and Chexi area of the northern of the Chezhen sag, large- scale progradating- channel- filled (or lenticular) seismic facies are found, indicating the existence of delta deposits, and the possibility of oblique delta has been further recognized by using the seismic RMS attribute. By using the core data, it is proved that there are two kinds of flow properties, namely traction current and gravity flow. It is also proved that the gravel- rich sediments (oblique delta) with thick layers is a fan delta using the data from lithologic association, wirelines and logging data. Therefore, it is concluded that the oblique fan delta develops in early stage of rifting at the steep slope belt of the rifting lacustrine basin, which is inclined to the border fault. (2) There is a great difference between the oblique fan delta and the short- axis nearshore subaqueous fan or fan delta. The oblique fan delta is mainly controlled by the tectonic pattern and paleogeomorphic features of the basin in the early stage of rifting at the steep slope zone, and a composite sedimentary model is established spatially by the nearshore subaqueous fan or fan delta of the vertical boundary fault and the oblique fan delta, which is generally representative in the early stage of rifting. (3) The large oblique fan deltas are mostly developed in the steep slope and depression zone. It has been proven by some exploration wells that the inclined sand bodies of the oblique fan deltas have relatively high oil and gas content. In addition, the oblique fan deltas have favorable conditions for reservoir formation and great exploration potential. (4) The research results can not only be used to advance or reinforce the sedimentology of rift lacustrine basin and hydrocarbon accumulation model, but also enrich the types of reservoir facies, highlight that the deep layer has great exploration potential, and indicate that the fan delta formed by the oblique provenance is one of the important direction of next exploration in early stage of rifting at steep slope zone of rift lacustrine basin.