柴达木盆地第四系储层特征及评价

CHARACTERISTICS AND EVALUATION OF THE QUATERNARY RESERVOIRS IN CHAIDAMU BASIN

柴达木盆地第四系储存着丰富的生物成因气,由于沉积储层埋藏浅,储层砂岩和盖层泥岩均具有较高的孔隙度,但由于毛细管压差的变化导致砂岩储层储存天然气。为了评价预测有利的沉积储层以及储盖组合,文章依据岩心、测井和SEM、储层压汞等大量的室内分析化验资料,对沉积储层的储层特征、储集物性和影响储层质量的主要控制因素进行了研究。指出砂岩储层具有粒度细、结构松散、单层厚度薄、层数多、分布稳定广泛、孔渗数值高的特点,储层质量受沉积作用和成岩作用的综合影响。存在大孔隙粗喉道、大中孔隙中粗喉道等 4 种储层结构。最后,依据第四系沉积相、砂岩沉积厚度和粒度以及储层质量与已发现气田之间的关系,预测了柴达木盆地北缘和南缘三角洲沉积区为有利的储层分布区,是进一步发现天然气资源的良好探区。

Chaidamu Basin is rich in biogenetic gas in the Quaternary reservoirs. The porosities and permeabilities of the Quaternary sandstone reservoirs and mudstone caprocks are relatively high because of their shallow burial, and the sandstone gas reservoir formation resulted from the capillary pressure difference between the sandstone and the mudstone. In order to evaluate and predict ihe favourable reservoirs and reservoir-caprock assemblaged, the sedimentary characteristics and petrophysical property of reservoir and the main control factors affecting reservoir quality were investigated in light of the data on core analysis, log, SEM and mercury injection test. It is pointed out in the paper that the sandstone reservoirs are charactrized by fine grain size, loose structure, thin single layer, multiple layer, steady and wide distribution and high porosity and permeability; the reservoir quality is comprehensively affected by sedimentation and diagensis; there exist four kinds of reservoir structures, as big pores and throats, big-medium pores and throats, and so on; and, through comparing the sedimentary facies, sandstone thickness and grain size, and reservoir quality of the Quaternary with those of the known gas fields. it is predicted that the delta sedimentary areas of the northern and southern fringes of Chaidamu Basin are the favourable reservoir distribution zones and also the potential zones of exploring for gas resources in the future.