盆地深部形成油气藏的有利因素

本文主要阐述了形成深部油气藏的三个因素:即Ⅰ型干酪根在高成熟阶段具有一定的生烃潜力;碳酸盐岩生油岩的成熟作用慢于泥岩生油岩,晶包有机质转化及释放烃类是在高成熟阶段,碳酸盐岩生油岩生油下限的R。值在1.5％以下,液态窗的深度比泥岩大500～1000m;较高的压力是形成深部油藏的另一个重要因素。生油岩的高压生烃模拟实验揭示了高压可以使生油期滞后及提高产油率。地温梯度较低的塔里木、准噶尔盆地腹部,由于压力较高,生油的下限可达7000m。在快速沉降的新生代盆地,由于泥岩快速生油而又难以排放,形成局部异常高压带。异常高压区生油的深度可以向下延伸1000多米,封隔层之下的高压区是深部形成大规模油气藏的广阔场所。

HYDROCARBON GENERATION AND ACCUMULATION IN DEEP PART OF SEDIMENTARY BASINS

Three advantageous factors about the formation of deep hydrocarbon reservoir have been studied in this paper, i. e., type I kerogen possesses of a certain hydrocarbon-generating potential in high maturation stage; carbonate source rock maturation is slower than that of mudstone, the enclosed-organic matters transform and release hydrocarbon in high maturation stage, the lower R o limit for carbonate source rock generating oil is greater than 1.5%, their liquid window is 500-1000m deeper than that of mudstone; high pressure is another important factor for forming deep petroleum reservoir. The results of simulation experiments under high temperature and pressure indicate that higher pressure can postpone oil generation and increases oil productivity. Due to higher pressure, the lower limit of oil generation zone reaches 7000m in the hinterland of Tarim Basin and Junggar Basin possessing lower geotemperature gradients. Local abnormal high pressure zones are formed in swift burial Cenozoic basins because mudstone generates oil quickly and releases with difficulty. Oil-generating depth in the abnormal high pressure zone may extend more than 1000m. The high pressure zones under sealing layers can form large-scale oil and gas accumulation in deep.