莺歌海盆地东方13-2重力流储层超压气田气藏性质及勘探启示

东方13-2气田是近期在莺歌海盆地发现的超压大气田，已探明天然气地质储量近700×10⁸m³。产层黄流组一段是邻近莺西斜坡的盆内坡折带所控制的重力流海底扇沉积，发育向东方1-1底辟构造翼部上超尖灭的构造-岩性圈闭，水道砂分布广、厚度大、物性优，岩心平均孔隙度17.30%，平均渗透率42.3 mD，为高温超压弹性边水大气藏，天然气组分优良。东方13-2“整装、优质、高产”大气藏的形成具有以下优越条件：①东方13-2气藏处于西物源重力流源-汇轴向区，为“甜点”储层集中发育部位；②海底扇水道多期切割，水道砂横向均质，形成阁楼式超大储集空间；③底辟侧翼较低部位盖层破坏程度低，有利于天然气动平衡保存；④大型砂体低幅超覆，有利于大面积捕获油气，实现高效疏导。基于以上诸因素高效匹配导致该区大型天然气田形成，也为中国海域高温超压盆地油气勘探提供一个典型范例。

Gas pool properties and its exploration implications of the Dongfang13-2 gravity reservoir-overpressure gas field in Yinggehai Basin

The Dongfang13-2 gas field is an overpressure super-gas pool recently found in Yinggehai Basin, Northern South China Sea. By far, the totally proved reserves have reached about 700×10⁸m³. In this gas field, the production layer of the 1st member of Huangliu Formation comprises of a set of gravity current submarine fan sediments that are controlled by secondary slope-break zones adjacent to the Yingxi slope. The huge deposition system has developed large-scale structural-lithological traps that overlap and pinch out towards the wing part of the large Dongfang 1-1 diapiric structure. Channel sand bodies are reservoirs widely distributed with great thickness and fine physical properties. The average porosity and permeability of cores analyzed reach 17.3 % and 42.3 mD, respectively. The gas pool is a high temperature and overpressure edge water-driven gas reservoir which has advanced natural gas composition. The integral, advanced and productive Dongfang 13-2 gas pool was formed mainly under the following conditions: ①Dongfang 13-2 was deposited along with the axial direction of the western gravity current source-sink system where the "dessert" reservoir was most developed; ②Multi-phase incision of submarine fan channels and horizontal homogeneity of channel sands led to the formation of super reservoir spaces in a flooring pattern; ③Lowly located cap rocks at the wing part of the diapiric structure were less destructed, conducive to the dynamic balance of natural gas preservation; and 4) Low-angle overlap of huge-type sand bodies enables broad capture and efficient migration of natural gases. An efficient matching of the above factors lead to the formation of the huge Dongfang 13-2 gas field, providing a representative example for offshore high temperature and overpressure natural gas exploration in China.