Li Xiangyang, Li Fengxia, Huang Zhiwen, Ji Hancheng, Wang Haibo, Chen Liang, Zhang Zhonghao, Shi Xukai
SINOPEC Key Laboratory of Shale Oil/Gas Exploration and Production Technology, Beijing, 100083, China.
SINOPEC Petroleum Exploration and Production Research Institute, Beijing, 100083, China.
Sci Rep. 2025 Aug 11;15(1):29293. doi: 10.1038/s41598-025-09954-4.
The 1 Gt oilfield discovery solidified the Mahu oilfield as the world's largest conglomerate oil region, underscoring the exploration potential of these reservoirs. However, optimizing and selecting the target interval for hydraulic fracturing remains challenging due to the significant heterogeneity of the structure and composition of conglomerate reservoirs. This study addresses key gaps in understanding conglomerate reservoir characteristics and their impact on hydrocarbon production, focusing on the Baikouquan (Tb) Formation (Fm) on the Mahu Depression's northern slope. It introduces a new classification to better manage these complexities. In contrast to other classification methods, the proposed approach incorporates key factors influencing hydraulic fracture (HF) propagation, including grain size, cementation, supporting forms, and gravel composition, the latter of which is introduced for the first time. Based on core and test results, the conglomerate reservoirs are categorized into two main groups-fan delta front and fan delta plain conglomerates-and further divided into eight lithofacies types. Fan delta front conglomerates are subdivided into four types: A-1 (tuff, metamorphic, and magmatic rocks-dominated gravel-supported cobble-to-boulder lithofacies), A-2 (tuff and magmatic rocks-dominated matrix-supported pebble-to-cobble lithofacies), A-3 (tuff-dominated matrix-supported granule-to-pebble lithofacies), and A-4 (tuff-dominated gravel-supported granule-to-pebble lithofacies). Fan delta plain conglomerates are further divided into four types: B-1 (tuff and magmatic rocks-dominated gravel-supported granule-to-pebble lithofacies), B-2 (tuff and sedimentary rocks-dominated gravel-supported pebble-to-cobble lithofacies), B-3 (tuff-dominated gravel-supported cobble-to-boulder lithofacies), and B-4 (tuff, magmatic, and sedimentary rocks-dominated matrix-supported pebble-to-cobble lithofacies). The novelty of this classification method lies in its integration of both geological and engineering perspectives, particularly in optimizing hydraulic fracturing strategies. The study evaluates lithofacies from geological factors such as bedding, composition, and poroperm characteristics, as well as engineering considerations like fracturing potential and flow capacity. The results reveal that certain lithofacies types correlate strongly with higher fracturing success, providing insights that can guide more efficient hydraulic fracturing practices. By addressing the challenge of heterogeneity of the structure and composition in conglomerate reservoirs, this study offers a comprehensive framework for selecting optimal target intervals for hydraulic fracturing, which can significantly enhance hydrocarbon exploration and production strategies. This approach is expected to be valuable for similar complex conglomerate reservoirs worldwide.
10亿吨级油田的发现巩固了玛湖油田作为全球最大砾岩油区的地位，凸显了这些油藏的勘探潜力。然而，由于砾岩油藏结构和成分的显著非均质性，优化和选择水力压裂的目标层段仍然具有挑战性。本研究聚焦于玛湖凹陷北斜坡的百口泉组（Tb）地层，解决了在理解砾岩油藏特征及其对油气产量影响方面的关键空白。研究引入了一种新的分类方法，以更好地应对这些复杂情况。与其他分类方法不同，该方法纳入了影响水力裂缝（HF）扩展的关键因素，包括粒度、胶结作用、支撑形式和砾石成分，其中砾石成分是首次引入。基于岩心和测试结果，砾岩油藏被分为两个主要类别——扇三角洲前缘砾岩和扇三角洲平原砾岩，并进一步细分为八种岩相类型。扇三角洲前缘砾岩细分为四种类型：A - 1（凝灰岩、变质岩和岩浆岩为主的砾石支撑的卵石到漂砾岩相）、A - 2（凝灰岩和岩浆岩为主的基质支撑的卵石到卵石岩相）、A - 3（凝灰岩为主的基质支撑的砂粒到卵石岩相）和A - 4（凝灰岩为主的砾石支撑的砂粒到卵石岩相）。扇三角洲平原砾岩进一步分为四种类型：B - 1（凝灰岩和岩浆岩为主的砾石支撑的砂粒到卵石岩相）、B - 2（凝灰岩和沉积岩为主的砾石支撑的卵石到卵石岩相）、B - 3（凝灰岩为主的数据支撑的卵石到漂砾岩相）和B - 4（凝灰岩、岩浆岩和沉积岩为主的基质支撑的卵石到卵石岩相）。这种分类方法的新颖之处在于它整合了地质和工程两个视角，特别是在优化水力压裂策略方面。该研究从地质因素如层理、成分和孔隙渗透率特征，以及工程因素如压裂潜力和流动能力等方面对岩相进行了评估。结果表明，某些岩相类型与更高的压裂成功率密切相关，为更高效的水力压裂实践提供了指导见解。通过应对砾岩油藏结构和成分的非均质性挑战，本研究为选择水力压裂的最佳目标层段提供了一个全面的框架，这可以显著提升油气勘探和生产策略。预计这种方法对全球类似的复杂砾岩油藏具有重要价值。
