准噶尔盆地深部煤层气勘探开发进展及前景展望

Progress and prospect of exploration and development of deep coalbed methane in the Junggar Basin

  • 摘要: 新疆准噶尔盆地是中国六大陆相超级含油气盆地之一,具有构造单元类型多样,侏罗系中低煤阶煤层群发育,深部煤层气资源丰富且开发潜力大的特征。深部煤层气勘探开发历经早期油气直井过路试采初探期(1992—2019年)和近期煤层气水平井探索期(2020年至今),深部煤层气勘探开发取得突破性进展,然而与鄂尔多斯盆地中高煤阶深部煤层气勘探开发效果相比仍有差距,这与其地质资源特殊性和开发特殊性相关。地质资源特殊性主要体现在:煤储层具有中−低变质程度烟煤、低水分、低−中灰分和特低硫煤为主,孔裂隙发育,吸附性和储气能力较高,孔渗性较好但润湿性较强特征;深部煤层气成藏模式和资源类型上具有多样性,具有“古生新储”和“新生新储”共存,常规气−非常规气空间共生,有序接续的特征,推测具有全含气系统地质显现特征;深度效应下煤层气赋存态分配具有规律性变化,低中煤阶吸附气临界深度约10001500 m,总含气量临界深度约25003000 m,在2000 m后,游离气占比接近50%,且煤阶越高,游离气占比为50%对应的深度越深。开发特殊性主要体现在:煤储层压裂适配特殊性,冻胶、胍胶体系优于活性水−清洁压裂液体系,构造圈闭高部位大规模体积压裂易发生压裂液滤失,反噬压裂效果;深部煤层气水平井产出特征表现出“见气快,峰值产气量−稳定产气量中等、产水低,返排率低”的特征,产出早中期以游离气为主,产出后期以吸附气为主的“阶梯衰减”产出行为特征。针对以上特殊性,未来需开展全盆地不同资源类型地质有利区/甜点区优选;压裂及排采开发工艺适配性优化;高效低成本规模化发展模式建立。最终形成符合准噶尔盆地深部煤层气勘探开发的地质评价与开发工艺技术,推动深部煤层气的规模化效益化发展。

     

    Abstract: The Junggar Basin in Xinjiang is one of the six continental super oil and gas bearing basins in China. It is characterized by various types of tectonic units, the development of Jurassic middle and low rank coal seams, and the abundance of deep coalbed methane (CBM) resources and great development potential. The exploration and development of deep coalbed methane have gone through the early stage of oil and gas vertical well trial mining (1992−2019) and the recent stage of coalbed methane horizontal well exploration (since 2020). Breakthroughs have been made in deep coalbed methane exploration and development, but there is still a gap compared to the exploration and development effects of mid to high rank deep coalbed methane in the Ordos Basin, which is related to the special geological resources and development characteristics. The special characteristics of geological resources are mainly reflected in: Coal reservoirs are mainly composed of medium to low metamorphic bituminous coal, low moisture, low to medium ash content, and ultra-low sulfur coal, with developed pores and fractures, high adsorption and gas storage capacity, good pore permeability but strong wettability; There is diversity in the reservoir formation patterns and resource types of deep CBM, with coexistence of “ancient source-younger reservoir gas system” and “young source-young reservoir gas system”, with the characteristics of conventional unconventional gas spatial symbiosis and orderly succession, and it is speculated to have geological features of a fully gas bearing system; Under the depth effect, the distribution of CBM occurrence has regular changes. The critical depth of adsorbed gas of low middling coal rank is about 10001500 m, and the critical depth of total gas content is about 25003000 m. After 2000 m, the proportion of free gas is close to 50%, and the higher the coal rank, the deeper the corresponding depth of free gas proportion of 50%. The particularity of development is mainly reflected in: The adaptability of coal reservoir fracturing, where the gel and guar gum systems are superior to the active water clean fracturing fluid system, and large-scale volume fracturing in high structural traps is prone to fracturing fluid filtration and rebound fracturing effects. The production characteristics of deep coalbed methane horizontal wells show the characteristics of “fast gas breakthrough, peak gas production−moderate stable gas production, low water production, and low backflow rate”. The production behavior is mainly characterized by free gas in the early and middle stages, and adsorbed gas in the later stages. In response to the above particularities, it is necessary to carry out selection of geologically favorable areas/sweet spots for different resource types throughout the basin in the future. Optimization of the adaptability of fracturing and extraction development processes; Establishing an efficient, low-cost, and large-scale development model. Finally, the geological evaluation and development technology in line with the exploration and development of deep CBM in the Junggar Basin will be formed to promote the large-scale and cost-effective development of deep CBM.

     

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