华北中部奥陶纪沉积特征及其天然气生储条件

ORDOVICIAN SEDIMENTARY CHARACTERISTICS AND ITS GAS GENERATING AND RESERVOIRING CONDITIONS IN CENTRAL PART OF NORTH CHINA

本文在分析奥陶纪沉积相类型与特征的基础上,提出形成天然气生、储、盖层的有利岩相带时空展布规律;并用TTI法恢复地层真厚度,建立奥陶系埋藏-热演化模式,从而探讨了有机质向油气转化的条件;最后,研究了天然气的主要储集空间类型以及成岩作用对它的影响,特别是对天然气主要聚集场所——奥陶系顶部古岩溶发育特征进行了分析。

The main sedimentary facies types in Ordovician are supratidal zone subfacies(main-ly mudstone-dolomite and gypsum-dolomite flats), intertidal and subtidal zone subfacies,lagoon-gypsum salt lake subfacies, restricted gulf and open shelf-shallow sea subfacies(in-cludes storm deposit) and shoal subfacies, of which the gypsum-dolomite flat, lagoon-gypsum salt lake and open shelf-shallow sea storm deposits are more tipical. In order to discuss the conditions of transforming organic matter into oil and gas,theauthors have set up burial-thermal evolution models of Ordovician in the east and westparts of the study area by restoring the original thickness of sedimentary stratu with TTImethod. Both of the models show that during Ordovician and after,there existed two orthree major burial periods that have been confimed by exploration in Ordos area and thewest part of the study area,and have potentially favourable conditions for natural gas.Therefore, while paying attention to self--generated gas in Ordovician,it is worth to noticecoal-formed gas from overlying Carboniferous-Permian which may migrate into Ordovi-cian erosional karst zones to accumulate again. It has been shown that karst zones with a lot of pores, vugs (or cavities) and frac-tures are widespread in top of Ordovician,and has provided the main pore spaces for gasmigration and accumulation. Besides, multiple ancient erosional haitus and karst zoneswere formed inside the Ordovician following the crustul vibration and the phreatic fluctu-ation during sedimentution,thus providing more reservoir spaces for natural gas.