渤海海域深层低孔渗油气藏成因机制分析——以渤中1&2区块为例

渤海深层油气藏勘探潜力大,随着渤海勘探的深入,深层低孔渗油气藏已成为渤海勘探的必然选择。而深层低孔渗油气藏在成因类型和成藏机制上明显不同于先前的构造类油气藏。以渤中12区块为例,对其深层低孔渗油气藏成因机制进行深入剖析。研究表明,研究区深层低孔渗油气藏为先致密后成藏。根据深层成藏力平衡机制和浮力成藏下限理论,主要为以浮力运移动力为主的常规油气藏,以及以分子膨胀力为主的深盆致密油气藏,是两种不同成因机制的油气藏叠加在一起组成的复合油气藏。晚期原油两期充注成藏加之晚期碳酸盐胶结作用,导致古油藏的存在。先期原油的排酸作用,异常超压带虽然碳酸盐含量高,但是粒度较粗砂体碳酸盐胶结物含量较少,且颗粒溶孔也比较发育,另外超压使压实受抑制,原生孔隙得以保存,这都是深部致密带出现"甜点"的原因。研究成果对指导渤海深层勘探,拓展勘探领域有一定的借鉴意义。

Genetic mechanism analysis of deep low-porosity and permeability reservoirs in the Bohai Sea area: An example from Bozhong 1&2 block

There exists a great exploration potential of oil and gas in the deep Bohai Sea. With the further development of exploration, low- porosity and low-permeability reservoirs have become the inevitable choice for the exploration in this area. Such reservoirs are obviously different from the previous reservoirs in genetic types and accumulation mechanisms. Taking the Bozhong 1&2 block as an example, this article analyzes the formation mechanism of low- porosity and low-permeability oil and gas reservoirs at depth. Research shows that such reservoirs were generated after becoming dense. According to the force balance mechanism and the theory of the lower boundary of buoyancy-controled accumulation about the deep low-porosity and low-permeability reservoirs, the study area is of the conventional oil and gas reservoirs which are dominated by buoyancy migration dynamics and the deep basin oil and gas reservoirs controlled by the molecular expansion force. So they are composite oil and gas reservoirs with two kinds of different genetic mechanisms. Late hydrocarbon accumulation and late carbonate cementation led to the existence of the paleo oil reservoirs. Although the high content of carbonate is present in abnormal pressure zones, coarse sand bodies have less carbonate cementation, and dissolution pores developed there. In addition, overpressure inhibited the compaction, primary pores could be preserved, accounting for the existence of the "sweet spot" in deep tight bands of the area. The research results have a certain reference value for guiding the deep exploration in the Bohai Sea area and expanding the exploration field.