准噶尔盆地滴西地区石炭系火山岩储集性能分布规律研究

火山岩储集性能分布的非均质性非常强,探索其分布规律成为火山岩油气勘探的难点和重要任务。本文以实际岩心及其分析化验等资料为基础,从滴西地区取心最佳储集性能段、最差储集性能段、风化壳储集性能分布模式、薄层熔岩储集性能分布模式、厚层熔岩储集性能分布模式等方面总结了石炭系火山岩储集性能的垂向分布规律,同时分析了储集性能的平面分布情况。火山熔岩储集性能在垂向上的分布差异,成岩阶段主要受岩相的影响,后期主要受构造作用及风化溶蚀作用等的影响。受成岩阶段岩相的影响,溢流相上部亚相和下部亚相均有可能形成较好的储集性能。与碎屑岩互层的薄层熔岩常具有较好的储集性能。与碎屑岩互层的厚层熔岩段的底部储集性能可能较好,其次是顶部,而中部常沦落为储集性能相对较差的位置。风化壳的风化粘土层、强风化带、中等风化带、弱风化带、未风化带5个垂向分带结构中,中等风化带往往具备相对最佳的储集条件。应用W风化指数新型工具对火山岩进行风化程度评估显示,准噶尔盆地火山岩具有多期风化的特征,并残留有大量未风化、轻微风化及中等风化的火山岩,这其中不乏储集性能优良的岩性段。从平面分布来看,研究区域火山岩储集性能具有强烈的各向异性特征,常表现为局部富集,快速变迁,随机分布。

Study on distribution patterns of reservoir property of Carboniferous volcanic rocks in Dixi area, Junggar basin.

The anisotropy of distribution of volcanic reservoir property is very strong, thus it's a difficult but important task to seek the distribution regularity of volcanic reservoir property in oil and gas exploration and development. Base on the bore cores, their experimental data and so on, the vertical distribution regularity of reservoir property of Carboniferous volcanic rocks in Dixi area has been summarized for the aspects such as the best section of reservoir property among cores, the worst section, the distribution patterns of reservoir property for the weathering crust of volcanic rocks, for the thin lava and for the thick lava. Meanwhile, the horizontal distribution regularity also has been analysized. The vertical diversity of reservoir property of lava is mainly controlled by lithofacies in diagenesis stage and by tectonism, weathering, dissolution and so on in later stage. Affected by lithofacies in the diagenesis stage, the upper subfacies and lower subfacies of effusive facies are likely to form good reservoir property. For example, the core box #1 from Dixi401 well is one of the sections with best reservoir property among all the volcanic cores in Dixi area, which is mainly influenced by the factors of lithofacies in diagenesis stage, partly combined with the factors of thin bed lava, and so on. The thin bed lava interbedded with clastic rocks often has good reservoir property, typically as Dixi173 well. For thick lava interbedded with clastic rocks, the bottom part is always in good reservoir property, followed by the top part, while the central part is often in poor reservoir property. A typical example is the thick bed lava composed of core box #10 and #11 from Dixi1414 well that shows good conformability to this distribution pattern of thick lava. In particularly, the central part of this thick bed lava is one of the sections with worst reservoir property among all the volcanic cores in the study area. The vertical zoning structure for a weathered crust can be divided into 5 zones composed of weathered clay layer, strongly weathered zone, moderately weathered zone, weakly weathered zone and unweathered zone. Among the 5 zones, the moderately weathered zone often has relatively fine reservoir property. Such as the moderately weathered zone situated in the core box #3 from Dixi18 well performances a relatively fine reservoir property. Evaluating the degree of weathering of volcanic rocks in Junggar basin by using a new tool named W index of weathering shows a multi-stage weathering process and a large number of unweathered, weak weathered and moderate weathered volcanic rocks remained, from which some lithology sections with excellent reservoir performance can exist. From the view of planar distribution maps, the reservoir property of volcanic rocks in study area is featured by a strong anisotropy, often enriched locally(such as drops 401, drop the west near well 172) and change rapidly at random.