下扬子中部志留系盖层封闭性动态演化评价

下扬子中部地区海相层系在印支-燕山期经历了强烈的构造改造，保存条件成为油气成藏的关键控制因素之一。志留系泥页岩盖层是下古生界的区域性盖层，对原生油气藏的保存具有决定性的作用。基于志留系样品的实测数据对志留系盖层现今的封闭性做出了评价。采用孔隙度-排替压力史法、渗透率-排替压力史法及超固结比（OCR）参数重建了志留系盖层在地质历史时期封闭性的动态演化过程。结果显示：下扬子中部志留系盖层具有低孔、低渗、高排替压力特征，总体上现今物性封闭能力较强。在埋藏阶段排替压力达到了封闭高压和超高压气藏的能力，但在早白垩世期间，句容地区志留系盖层排替压力显著降低且OCR 值超过脆性破裂门限值，下古生界保存条件破坏较为严重，在常州和泰兴地区OCR 值小于脆性破裂门限值，破坏程度相对较弱。

Dynamic estimation of seal capacity of the Silurian cap rock in central Lower Yangtze area

Marine sequences in Lower Yangtze area experienced extensive tectonic transformation in Indo-Yanshan period. Preservation condition is one of the key factors controlling accumulation of marine petroleum. The Silurian cap rock played a decisive role in the preservation or destruction of the Paleozoic primary oil and gas reservoirs. Based on the experimental data from cores of 7 wells meeting the Silurian cap rock and 3 outcrops with a total number of 33 samples, the present-day sealing capacity of the Silurian cap rock was evaluated. Based on the mathematic models of porosity-capillary pressure and permeability-capillary pressure histories and the parameter of over consolidation ratio（OCR）, the dynamic evolution of sealing capacity of the Silurian cap rock was reconstructed. The results show that the Silurian cap rock is of low porosity, low permeability and high capillary pressure and therefore with good sealing capacity in present day. At the burial stage, the capillary pressure reached as high enough as can seal high pressure or even ultrahigh pressure gas reservoirs, but in the early Cretaceous period the capillary pressure of the Silurian cap rocks in Jurong area significantly decreased and their OCR values exceed the threshold value of brittle fracture. Therefore, the preservation condition of the Lower Paleozoic experienced serious damage. Comparatively, the degree of damage of preservation condition is relatively weak in Changzhou and Taixin areas.