Abstract: The unconventional gas resources of marine source rocks in the complex tectonic areas of southern China have great potentials. After more than 10 years of exploration and practice, PetroChina Zhejiang Oilfield Company has achieved commercial breakthroughs in exploration of multi-region, multi-stratum and multi-type hydrocarbons, including middle-deep shale gas in Huangjinba-Zijinba block of Zhaotong area, shallow shale gas in Taiyang mountain area, coalbed methane in Junlian mountain area, as well as deep shale gas and limestone source rock gas in Da’an block of western Chongqing area. Based on studying the exploration of multi-type in-source unconventional gas, the paper proposes the unconventional exploration concept of "in-source reservoir and accumulation" in three types of organic matter rich source rocks, namely argillaceous, coal-based and calcareous source rocks; moreover, further theory exploration and technology innovation have been implemented. As a large shallow monoblock shale gas field of Longmaxi Formation developed by China’s industrial sector, Taiyang gas field outside Sichuan Basin has the characteristics of "multi-field synergy, multi-factor coupling, and multi-element control on production", showing high-level enrichment and high production. On this basis, the paper establishes a three-dimensional storage system based on shale self-sealing ability and a shallow shale gas accumulation and occurrence model of "self-generating and self-preserving, supported with partial horizontal hydrocarbon supply". It also reveals the main connotation of shallow shale gas self-sealing based on "extremely low permeability of nanoscale pores, enhanced adsorbability of shallow layer, and sandwich-like pack-off capability of shale". It is proposed that the stable and contiguously distributed endogenous biogenic siliceous shale in the deep-water shelf of foreland basin is a high-quality sweet spot reservoir. Moreover, it is preliminarily speculated that the total amount of shallow shale gas in southern China can reach 10×10¹²m³. The deep shale gas in Longmaxi Formation of Da’an block is characterized with tectonic deformation of ejective folds, and has good fault sealing and shale roof and floor conditions, for which the enrichment and accumulation model of "narrow and steep anticline fault barrier, continuously distributed, wide and gentle syncline" has been established. The deep shale gas resources in southern China have great potential, and the geological resources are estimated to be about 35×10¹²m³. Junlian mountain area is the first block to achieve major breakthrough in coalbed methane exploration and a pilot test field for coalbed methane development are initially achieved in southern China. Seven years of stable production has proved that the commercial development of mountain coalbed methane is feasible, which is simultaneously influenced by several factors such as tectonics, preservation, and hydrology. Therefore, the coalbed methane accumulation model of "wide and gentle syncline rich in gas" is proposed herein. The coalbed methane resources buried at a depth shallower than 2 000 m in southern China amount to 5.46×10¹²m³. By use of the horizontal well method, major breakthroughs have been made in the exploration of unconventional natural gas in new strata and new types of source-reservoir integrated limestone source rock gas in the Member 1 of Maokou Formation of Da’an block, based on which an accumulation pattern of "source-reservoir integration supported with local tectonic migration and enrichment" was established. It is preliminarily estimated that the resources from Member 1 of Maokou Formation in Sichuan Basin can amount to 2×10¹²m³, which is expected to open up a new field of in-source unconventional hydrocarbon exploration. Various types of unconventional gas originated from in-source reservoir formation and accumulation in argillaceous, coal-based and calcareous strata are widely distributed in the complex tectonic areas of southern China, which has particularities in sedimentation, diagenesis, reservoir formation, hydrocarbon generation and accumulation, as well as strong adsorbability of micro-nano level reservoir pore space. Additionally, the regional distribution of continuous reservoirs is not controlled by tectonic traps, indicating the great potential of oil and gas resources in the study areas, and a promising prospect for unconventional gas exploration and development in new areas and new fields in the future.

Key words: complex tectonic area, in-source reservoir and accumulation, in-source unconventional exploration, geological accumulation characteristics, resource potential

摘要： 中国南方复杂构造区海相烃源岩的非常规天然气资源潜力巨大,经过10余年的探索和实践,中国石油浙江油田公司目前已成功实现了昭通黄金坝—紫金坝中—深层页岩气和太阳山地浅层页岩气、筠连山地煤层气、渝西大安深层页岩气和灰质源岩气多地区、多层系、多类型的商业性突破。基于多类型源内非常规天然气的勘探研究,提出了泥质、煤质、灰质3类富有机质烃源岩"源内成储成藏"的非常规勘探理念并进行了理论深化和技术创新。四川盆地外缘的太阳气田作为中国工业开发的大型整装龙马溪组浅层页岩气田,具有"多场协同、多元耦合、多因素控产"的富集高产特征;针对太阳气田创建了基于页岩自封闭的"三维封存体系"和"自生自储为主、部分横向补给成藏"的浅层页岩气成藏模式,揭示了基于"页岩纳米级孔隙极低渗透性、浅层吸附性增强和三明治式封隔性"的浅层页岩气自封闭的内涵,提出前陆盆地深水陆棚区稳定连片分布的内源生物硅质页岩是优质"甜点"储层,初步推测中国南方浅层页岩气的总资源量可达10×10¹²m³。大安深层页岩气藏的龙马溪组具有隔档式褶皱构造形变特点,具有良好的断层封闭和页岩顶、底板条件,对其建立了"窄陡背斜断层遮挡、宽缓向斜连续分布"的富集成藏模式;目前,中国南方深层页岩气资源潜力巨大,地质资源预计约为35×10¹²m³。筠连山地煤层气田是中国南方率先获得煤层气勘探重大突破的区块和煤层气开发先导试验区,7年的稳产证实山地煤层气可商业开发,其整体受构造、保存、水文等多因素共同制约,煤层气具有"宽缓向斜富气"的成藏模式;目前,中国南方地区埋深在2 000 m以浅的煤层气地质资源量可达5.46×10¹²m³。大安地区茅口组一段基于水平井开发方式在源-储一体型灰质源岩气中实现了新层系、新类型非常规天然气勘探的重大突破;灰质源岩气具有"源-储一体为主、兼局部构造运移富集"的成藏模式;初步估算四川盆地茅口组一段的资源量可达2×10¹²m³,有望开启一个源内非常规勘探新领域。中国南方复杂构造区具有泥质、煤质、灰质"源内成储成藏",多种类型非常规天然气广泛分布,沉积、成岩、成储、成烃、成藏的非常规"特殊性",储层中微米—纳米级孔隙空间的吸附性较强,油气藏往往具有不受构造圈闭控制的连续型区域展布的特征,油气资源潜力巨大,新区新领域的非常规天然气勘探开发前景未来可期。

关键词: 复杂构造区, 源内成储成藏, 源内非常规勘探, 地质成藏特征, 资源潜力