准噶尔盆地玛湖凹陷源上致密砾岩油富集的主控因素

Main controlling factors of tight conglomerate oil enrichment above source kitchen in Mahu sag,Junggar Basin

准噶尔盆地玛湖凹陷致密砾岩大油区是世界上储量最大的砾岩油区之一,有必要分析其油藏类型及分布特征,探讨其油气富集的主控因素,指明勘探部署方向。研究表明:玛湖凹陷源上砾岩大油区由多个扇三角洲沉积体系油藏群构成,每个油藏群由一群透镜状砂砾岩油藏构成,具有“一砂一藏、一扇一田”分布特征;玛湖凹陷油藏的岩性为扇三角洲前缘亚相水下分流河道砂砾岩,孔隙度平均为7.8%,渗透率中值为1.59 mD,属于致密油藏,具有“先致密后成藏”的特征;玛湖凹陷的油藏类型主要为砂砾岩岩性油藏,其次为断层-岩性油藏,无统一油水界面和压力系统、无明显边底水;玛湖凹陷源上砾岩大油区致密油的富集主要受控于“扇、源、断、坡”4大要素,即储-封一体扇三角洲沉积、优质烃源岩条件、广布通源断裂和弱变形缓坡背景,其中,油藏主要富集于弱变形缓坡背景之上,并有通源断裂将主力烃源岩与扇三角洲前缘亚相砂砾岩储层相沟通。

The tight conglomerate oil province in Mahu sag,Junggar Basin is known as one of the biggest with the largest reserves in the world,so it is necessary to analyze the reservoir types and distribution characteristics,explore the main controlling factors of hydrocarbon enrichment,and indicate the direction of exploration and deployment of Mahu sag.The study shows that the large conglomerate oil province above source kitchen in Mahu sag is composed of multiple oil reservoir groups in the fan delta sedimentary system,and in each oil reservoir group,there is a cluster of lenticular sandy conglomerate reservoirs,showing the distribution characteristics of“one sandbody,one reservoir;one fan,one oilfield”.The lithology of oil reservoirs in Mahu sag is conglomerate of the underwater distributary channel subfacies at the front of fan delta,with an average porosity of 7.8%and the mean permeability of 1.59 mD,which is classified as tight oil reservoir,with the characteristics of“tightening before accumulation”.The oil reservoirs in Mahu sag are mainly dominated by conglomerate oil reservoirs,followed by fault-lithologic oil reservoirs,without uniform oil-water interface,unified pressure system or obvious edge/bottom water.The enrichment of tight oil in the large conglomerate oil province above source kitchen in Mahu sag is mainly controlled by four elements including fan,source,fault,and slope,i.e.,the fan delta deposit integrated with reservoir and cap rock,the high-quality source rock,the widespread faults connected with source rocks and the gentle slope with weak deformation setting.The oil reservoirs are mainly enriched above the gentle slope,and the major hydrocarbon source rocks and subfacies conglomerate reservoirs at the front of fan delta are connected by the faults connected with source rocks.