塔里木盆地经历了多期油气充注和多期调整改造，使得已发现海相油气的确切来源层位与相对贡献量不明。虽然油－源对比研究揭示中上奥陶系烃源岩是这些油气的主要来源，但中上奥陶统内高 TOC 源岩层分布局限，不足以解释海相油气的大规模分布；并且塔中地区已发现的天然气储量已经远超3次资评结果，以上反映了叠合盆地油气成藏的复杂性与地化反演方法用来进行油源判别研究的局限性。根据叠合盆地混源油气藏的特点，基于正演研究思路，对源岩层生排运聚油气过程进行研究，从源岩总生烃量中依次扣除残留烃量、无效相态损失量、运移损失烃量、构造破坏烃量等4部分，得到最终的远景资源量，并以此计算各源岩层的相对贡献。结果表明，对于塔中地区而言，寒武系—下奥陶统源岩层相对贡献量高于中上奥陶统烃源岩，两者比率约为63％比37％；高 TOC 源岩层的相对贡献量高于低 TOC 源岩层，两者比率约为68％比32％。奥陶系已发现油气藏的规模比预期评价较大原因可能是部分油气来自下部的寒武系烃源岩或者其内部低 TOC 源岩层也对油气成藏有所贡献。%hydrocarbon accumulation namely quantity of resources can be obtained by deducting the critical saturation of residual hydrocarbon,loss of diffusion phases,loss of hydrocarbon residued in the migration and damaged by tectonic movements from the total amount of hydrocarbon expulsion,which can be used to assess the relative contributions of oil &gas of each set of source rock.Studies show that the amount of resources can be provided by the Cambrian source rocks is higher than that by Ordovician source rocks.The ratio is about 63%to 37%.The amount of resources that can be provided by source rocks with low abundance is lower than those by source rocks with high abundance.The ratio is about 32%to 68%.The reason that the scale of reserves in Ordovician is larger than the predicted may be the contribution of part oil &gas coming from the Cambrian or source rocks with low TOC (≤0.5%).
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