非稳态油藏理论及其在伊朗A油田的应用

Theory of unsteady reservoir and its application in A oilfield of Iran

通过对伊朗A油田上白垩统Sarvak组油藏油水界面倾斜原因进行分析,认为水动力作用不是造成该现象的主要原因,储层非均质性能够造成该现象但也不是主要原因,而晚期的构造急剧调整是造成该现象的主要原因。在区域沉积与构造演化分析的基础上,运用地震层拉平技术对伊朗A油田不同时期古构造圈闭进行恢复,结合成藏研究认为,新近纪末扎格罗斯构造运动造成油田圈闭超晚期调整,构造调整速率远大于流体调整速率,从而造成了Sarvak组油藏油水界面大幅度倾斜,油藏目前仍处于新的运移、聚集与调整过程中,为非稳态油藏;古新世晚期Sarvak组地层形成北高南低的古背斜圈闭,新近纪扎格罗斯造山运动导致圈闭形态发生改变,南部原古构造低点大幅度抬升,快速演变为现今南高北低的构造形态;圈闭条件的改变打破了古油藏内流体的动力平衡,烃类发生二次运移,现今大幅度倾斜的油水界面为古油藏尚未调整完毕所显示的特征。油藏优势开发区域为古构造高部位,即现今Sarvak组油藏北高点的西侧,其次为古构造与现今构造高部位之间的过渡带。

The oil-water contract（OWC） of Sarvak reservoir of A oilfield in Iran is characterized by a large-amplitude one tilting from north to south. The hydrodynamic force is not the cause and the reservoir heterogeneity is not the main reason for the tilted OWC of the Sarvak reservoir. The main reason for the large-amplitude tilted OWC is the structure adjustment. Based on the analysis of sedimentary and tectonic evolution, formation flattening technique is utilized to recover the paleo-structure of different geologic stages. Combined with accumulation factor analysis, it is considered that the adjustment of traps is caused by Zagros orogeny and the structure adjustment rate is faster than the hydrocarbon adjustment rate. Now, the Sarvak reservoir is still in the new condition of migration, accumulation and adjustment,which is an unsteady reservoir. A paleo-trap which decreased from north to south formed in the Sarvak Formation in A oilfield after the late Paleocene. The Zagros orogeny during the Neogene caused the adjustment of the trap, and the former low point in the south uplifted significantly and gave birth to a new secondary trap. So, today the structure in the south of Sarvak Formation is higher than that in the north. The balance in the paleo-trap was broken, and hydrocarbon migrated to the secondary trap in the south. The large-amplitude tilted oil-water contract showed that the paleoreservoir was still adjusting and unstable. The favorable development zone is the high zone of paleostructure which is in the western Sarvak reservoir, followed by the belt of transition between paleostructure and current structure.