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

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