Abstract:

Deep and ultra-deep oil and gas resources, characterized by vast potential but low proven rates, become a key target of exploration and development in China presently. However, evaluating their resource potential still faces a series of scientific and technological challenges, such as high thermal evolution degree of source rocks, strong diagenetic modification of reservoirs, multi-stage adjustment, transformation and effective preservation of oil and gas reservoirs. Recently, new breakthroughs have been made in ultra-deep exploration in the Yuanba Area, with the discovery of natural gas reservoirs in the fourth section of the Dengying Formation at a depth of nearly 9000 meters, revealing promising exploration prospects for ultra-deep layers in the northern Sichuan Basin. Based primarily on the latest drilling data of YS1 well, combined with peripheral drilling, outcrop and analysis testing data, this study systematically investigates the key control elements of source rocks, reservoirs and oil and gas accumulation processes in the Dengying gas reservoir in the study area, aiming to provide reference for the exploration and evaluation of ultra-deep oil and gas reservoirs. The results show that: (1) The YS1 gas reservoirs of the fourth member of the Dengying Formation were derived from the Cambrian Qiongzhusi Formation source rocks. These source rocks entered a low maturity stage during the Silurian, then reached a medium high maturity stage for the main oil generation and early cracking during the Late Permian-Triassic, and reached a high over maturity stage for main cracking gas generation during the Middle Jurassic-Early Cretaceous. (2) The YS1 gas reservoirs are consist of the microbial dolomites deposited on the platform margin, which have undergone long-term compaction, pressure solution, and deep burial cementation, resulting in currently low porosity and low permeability characteristics. (3) In northern Sichuan Basin, the platform marginal mound-shoal reservoirs are adjacent to the high-quality deep-water facies source rocks of the Qiongzhusi Formation, and has favorable source and reservoir configuration conditions of “source generation in slope facies with reservoir accumulation in margin facies” and “upper source feeding lower reservoir", which provides the material basis for paleo-oil reservoir formation. (4) The gas reservoir in Member 4 of the Dengying Formation underwent multistage modifications. During the paleo-oil stage, located on the central Sichuan paleo-uplift slope, it formed large-scale lithologic paleo-oil reservoirs sealed by tight inter-shoal layers. During oil-gas conversion and gas reservoir stages, influenced by the Micang Mountain uplift, subtle structural highs developed on the Micang uplift slope, forming structure-lithology composite paleo-gas reservoirs. In the late stage, the Himalayan compression caused basin-margin uplift, adjusting the paleo-gas reservoir to form current reservoirs, with YS1 well in the favorable overlap zone. Exploration should target large paleo-oil reservoirs, identify key-period paleo-structures, and focus on areas combining effective preservation with paleo-present structural overlap as preferential enrichment zones.

Key words: ultra-deep hydrocarbon reservoirs, carbonate rocks, petroleum accumulation process, Dengying Formation, northern Sichuan Basin

摘要： 深层－超深层油气资源潜力大但探明率低，是我国油气现今勘探发展的重点领域。然而，针对深层－超深层领域的资源潜力评价仍面临烃源岩热演化程度高、储层成岩改造强、油气藏多期调整改造与有效保存等一系列科学技术难题。近期，元坝地区超深层油气勘探获得新突破，在埋深近9000 m的灯影组四段发现了天然气藏，揭示了四川盆地北部超深层良好的勘探前景。本文以最新钻井YS1井的资料为主，结合周缘钻井、露头及其分析测试等数据，对研究区灯四段气藏的烃源岩、储集层等成藏关键要素及油气成藏过程开展系统研究，以期为超深层油气藏勘探评价提供借鉴。结果表明：(1)YS1井灯四段气藏烃源岩来自寒武系筇竹寺组，烃源岩在志留纪进入低成熟阶段，至晚二叠世－三叠纪达到中－高成熟阶段，在中侏罗世－早白垩世达到高－过成熟阶段，目前处于过成熟阶段。(2)灯四段气藏储层主要为台缘丘滩相白云岩储层，其经历了长期压实、压溶和深埋胶结，现今表现为低孔、低渗的特征。(3)川北地区台缘丘滩储层紧邻筇竹寺组深水相优质烃源岩，具有“棚生缘储，上生下储”的有利源储配置条件，是古油藏形成的物质基础。(4)灯四段气藏经历了多期调整改造。古油藏期，研究区处于川中古隆斜坡区，受滩间致密层封挡形成规模岩性古油藏；油气转换期和气藏期，受北部盆缘米仓山隆升影响，研究区处于米仓隆起斜坡区的局部微幅隆起构造，形成受构造－岩性共同控制的古气藏；晚期受喜山运动影响，盆缘隆升挤压，元坝地区处于九龙山背斜南西翼，灯影组古气藏局部调整形成现今气藏，YS1井处于古气藏、现今气藏叠合有利区。四川盆地北部超深层油气藏勘探应以寻找大型规模古油藏为基础，进而落实成藏关键期的有利古构造特征；持续有效的保存条件和古、今构造高部位叠合区是油气运聚调整的有利富集区。

关键词: 超深层油气, 碳酸盐岩, 油气成藏过程, 灯影组, 四川盆地北部

CLC Number: 

• P618.13

• TP18