中国海相碳酸盐岩的分布及油气地质基础问题

Distribution and fundamental science questions for petroleum geology of marine carbonate in China

中国海相碳酸盐岩在陆上与海域广泛分布,尤以陆上最具特色。中国大陆由小克拉通地块、微地块及其间的造山带镶嵌构成,发育于这些克拉通上的海相古生代盆地规模小、盆内分异明显、盆缘改造强烈,受中新生代巨厚沉积物覆盖,海相碳酸盐岩埋深大、热演化程度高,储集层非均质性强,油气成藏与分布复杂。自威远、靖边气田发现以来,尤其是近年塔河、普光、元坝、安岳等大型油气田发现以来,海相碳酸盐岩的油气勘探前景逐渐明朗。长期的勘探实践发现了海相碳酸盐岩发育礁滩体、白云岩、岩溶缝洞体、裂缝带等四类储集体,它们受沉积、成岩与构造演化的共同制约;礁/滩储层、斜坡区岩溶、风化壳岩溶、裂缝带均可大规模成藏。目前,海相碳酸盐岩的深化研究与持续勘探面临一系列重大难题。在基础科学层面,古老生物群落、古生态、古气候与古地理特征及其耦合关系,克拉通盆地的成因与构造-沉积分异机制,原始盆地面貌及其演化过程,沉积充填动力学等研究方面亟待加强;在油气勘探应用层面,在岩相古地理重建、碳酸盐岩台地边缘精细刻画与台地内部结构细化、碳酸盐岩储集层多期叠加改造机理、岩溶储集层成因分类、非均质碳酸盐岩储集层描述和评价技术等研究方面需要不断深入,在源-储配置、油气成藏过程、油气保存与调整再分配,油气富集规律方面需要深入探索。建议整体与动态研究海相碳酸盐岩层系的"成盆-成岩-成储-成藏"的全要素、全过程,厘定古裂陷槽、古台地、古隆起的分布,落实烃源岩、有利储集层(礁滩体、白云岩、顺层与层间岩溶、裂缝带等)的分布及其配置关系,构建符合实际的油气成藏模式,为油气资源潜力评价和有利区带预测奠定基础,促进中国海相碳酸盐岩油气勘探的持续发现。

The marine carbonate is widely distributed in inland and sea area around China, especially of its occurrence in mainland. The Chinese continent is composed of small-scale cratonic continental blocks, micro-continental blocks, and the intervening orogenic belts. The marine Paleozoic basins, developing upon those cratonic blocks, are characterized by small in scale, differentiated markedly in the basin interior, and modified extensively along the basin margins. The marine carbonates are deeply buried and highly thermal matured owing to the overlying Mesozoic and Cenozoic thick strata with a result of the strong heterogeneity of reservoirs and much complex for oil and gas pool-formation and occurrence. Since the discoveries of Weiyuan Gas Field in 1964 and Jingbian Gas Field in 1989, especially of such giant or super-giant oil and gas fields as Puguang, Yuanba, Tahe, and Anyue found in the recent years, the prospection for petroleum exploration in marine carbonate tends to be much more promising. The long-period exploration discovers the four types of reservoir in marine carbonate such as the reef and shoals, dolomites, karst caves, and fracture zones, which are controlled by the deposition, diagenesis, and tectonic evolution. The reef and shoals, the karst caves along slopes, the dissolution weathering crusts, and the fracture zones all have the potential to being large-scale pool-formed. At present, the on-going study and exploration on marine carbonate is faced to lots of key questions. As for the basic science, it＇s involved in the old biocoene, paleo-ecology, paloe-climate, and paleo-geography and its coupling relationships, the genesis of cratonic basin and the mechanism for its tectonic and depositional differentiation, the proto-basin and its evolution, as well as the sedimentary filling, and so on. As far as the oil and gas exploration is concerned, it＇s cared about the reconstruction of litho-facies paleo-geography, the description of carbonate platform margin, the delineation of the intra-structure of the platform, the superimposed and modified mechanism for multi-period reservoirs, the classification for karst reservoirs, and the description and evaluation of the heterogeneity carbonate reservoirs. It is needed to explore the linkage between the source rock and reservoir body, the processes for oil and gas pool-formation, the perseverance and adjustment or redistribution, and the principle for oil and gas enrichment and occurrence. The paper put forward to study the marine carbonate from a viewpoint of systematic and dynamic thought, to explore the whole factors and full processes for the ＂basin formation, diagenesis, reservoir formation, and the pool-formation＂, delineate the distribution of the paleo-rift trough, the paleo-platform, and the paleo-uplift, to make sure of the location of hydrocarbon source rocks, the distribution of the favorable reservoirs, such as the reef and shoals, dolomite, the along stratified and intervening stratified karst and fracture zones, and their coupling relationships, and to establish the oil and gas pool-formation models conserving to the real data. It will found a basis for the appraisal of oil and gas resource potential and prospection for favorable plays, and helpful for the continual oil and gas discoveries in the marine carbonate around China.