关键词: 准噶尔盆地, 齐古断褶带, 八道湾组, 致密砂岩, 储集层, 成岩演化, 油气充注

Abstract:

To reveal the relationship between densification process and hydrocarbon charging in the tight sandstone reservoir of the Lower Jurassic Badaowan formation in the Qigu fault-fold belt of the southern margin of Junggar basin, the diagenetic history of the sandstone reservoir in Badaowan formation is studied on the basis of casting thin section observation, X-ray diffraction, field emission-SEM and fluid inclusion analysis. The paper integrates the hydrocarbon generation and expulsion history of source rocks, stratigraphic burial history and thermal history simulation to restore the densification process and pore evolution history of the sandstone reservoir, and discusses the influences of the relationship between sandstone reservoir densification and hydrocarbon charging timing on reservoir type by combining with hydrocarbon charging history. The study results show that 4 diagenetic facies of the tight sandstone in Badaowan formation can be identified such as quartz secondary enlargement-dissolution, matrix-strong compaction, carbonate mineral cementation and authigenic clay mineral cementation, among which the porosity and permeability of quartz secondary enlargement-dissolution facies are relatively good. The desification of the reservoir is caused by high content of matrix, serious carbonate mineral cementation, limited dissolution and pore plugged by authigenic clay minerals. Moreover, the tight sandstone of Badaowan formation in Qigu fault-fold belt which belongs to the reservoir of “hydrocarbon accumulation after reservoir densification” experienced 3 periods of oil and gas charging—during the period Ⅰ, most sandstone reservoir had been densified before low maturity oil charging; during the period Ⅱ and Ⅲ, low maturity oil and high maturity oil migrated along the Qigu fault, charged and finally accumulated in the tight sandstone under overpressure. At the end of Neogene, the core of the Qigu anticline began to denudate, resulting in the significant reduction of residual pressure and the loss of hydrocarbon. After structural reformation the paleo-reservoirs became small-scaled tight reservoirs. The hydrocarbon accumulation process indicates that the traps located in the high positions of Qigu anticline and in the second row and third row of structural belts have great potential for oil and gas exploration.

Key words: Junggar basin, Qigu fault-fold belt, Badaowan formation, tight sandstone, reservoir, diagenetic evolution, hydrocarbon charging