油气成藏门限研究及其在济阳坳陷中的应用

HYDROCARBON ACCUMULATION THRESHOLD AND ITS APPLICATION IN JIYANG DEPRESSION

成藏门限从定量角度阐述油气藏形成与分布规律。它是指确定的成藏体系内形成油气聚集所需要损耗的最低烃量 ,包括源岩残留、储层滞留、盖前排失、围岩损耗、水溶流失和扩散等 6个方面。地史过程中 ,油气生成量达到或超过成藏体系内能够损耗的最低烃量时 ,油气聚集作用才能开始进行。在源岩生油气总量一定的情况下 ,成藏体系内油气的成藏时间、运聚烃量和油气藏最大规模等都受成藏门限的制约。对济阳坳陷 2 8个成藏体系的应用研究表明 ,油大量聚集成藏前最低损耗烃量介于 0 36× 10 8～ 18 4× 10 8t,它主要随排烃强度、油气运聚范围和目的层的倾角的增大而增大 ,随砂地比、构造变动次数和剥蚀厚度的增大而减小。济阳坳陷最有利的成藏体系包括沾化凹陷的渤南 -孤岛成藏体系 ,东营凹陷的中央背斜带、北部陡坡带、滨县凸起南坡、王家港 -八面河和惠民凹陷的中央背斜带以及车镇凹陷的义和庄凸起北坡、车镇凹陷北等 ,它们均已进入成藏门限 ,远景资源量 2 18× 10 8～ 6 31× 10 8t,能够形成的最大油气藏储量规模可达 0 16× 10 8～ 4 79× 10 8t。

Hydrocarbon accumulation threshold quantitatively expounds the regularity of hydrocarbon distribution. Hydrocarbon accumulation threshold refers to the least amount of oil and gas dissipated during the process of pool formation in the accumulation system. Dissipated hydrocarbon includes those left within the source rock, detained in the reservoir bed, discharged before cap-rock being formed, adsorbed by adjacent rock, and dissolved in water, as well as oil and gas diffusion. The mechanisms of hydrocarbons dissipation within the pool-forming system mainly include being adsorbed by rocks, blocked by capillary and dissolved by subsurface water and oil. The manners for hydrocarbons dissipated out of the pool-forming system mainly involves oil and gas diffused upward, oil and gas dissolved in formation water-flow and destroyed by tectonic movement after the formation of pools. Statistics, physical modeling experiment, multiphase percolation theory and geological phenomena analyses prove that hydrocarbon accumulation threshold, like hydrocarbon generation threshold and hydrocarbon expelling threshold,exist objectively.The essential research of hydrocarbon accumulation threshold is modeling and calculating the amount of hydrocarbon disspation. On the basis of studying the regional geological condition, dividing different accumulation systems, and geological analyses of source, cap and reservoir rocks, the research is,firstly,determining the temperature and pressure conditions of pool formation and the history of oil/gas reservoir evolution,as well as measuring the amount of hydrocarbon dissipation through adsorption,dissolution and diffusion for the sake of finding out the main factors controlling the dissipation and confirming the quantitative relationship;secondly, modeling the total amount of hydrocarbon generation in the source rocks and the total amount of hydrocarbon dissipation; and lastly, discriminating the accumulation threshold and recovering the critical geological condition.In the geological history, hydrocarbon begins to accumulate when the amount of hydrocarbon generated in source rock reaches or exceeds the least amount of oil and gas dissipated. Accumulation period, amount of hydrocarbon migration and accumulation and the largest reservoir size are all constrained by hydrocarbon accumulation threshold. The research of hydrocarbon accumulation threshold of 28 accumulation systems in Jiyang depression shows that the least amount of oil and gas dissipation is from 0 036 billion tons to 1 84 billion tons, which increases with the increase intensity of hydrocarbon expulsion, range of migration and accumulation and dip angle of objective formation and decreases with the increase of sand-stratum ratio,tectonic movements and denuded thickness. Finally, on the basis of calculation and comparison the amount of hydrocarbon generation,the resources, largest oil/gas field and favorable targets can then be predicted.