准噶尔盆地南缘吐谷鲁群盖层评价及对下组合油气成藏的意义

Sealing capacity of the Tugulu Group and its significance for hydrocarbon accumulation in the lower play in the southern Junggar Basin,northwest China

通过分析准噶尔盆地南缘下储盖组合吐谷鲁群盖层岩性、泥岩累计厚度和泥岩单层厚度等宏观评价参数以及渗透率和排替压力等微观评价参数,认为下储盖组合主力盖层为呼图壁组,岩性表现为泥岩、粉砂质泥岩及泥质粉砂岩薄互层,泥地比以80%~95%为主,平均泥岩累计厚度为337 m,泥岩最大单层厚度达138 m。吐谷鲁群泥岩渗透率为(0.000 001 84~0.000 24)×10^(-3)μm^2,排替压力为4.72~44.85 MPa,根据国内盖层封闭能力分类评价标准属Ⅰ-Ⅱ类盖层。通过恢复盖层排替压力的动态演化过程,认为泥岩封闭能力形成时期与烃源岩生、排烃时期具有较好的匹配关系,盖层能够封闭侏罗系烃源岩生成的石油及晚期生成的天然气,同时后期抬升运动及喜马拉雅构造活动产生的多条逆冲断层对盖层的封闭能力未产生较大影响。综合分析认为,吐谷鲁群盖层具有封闭大中型气田的能力。

Through the evaluation of macroscopic sealing parameters（lithology,mudstone accumulative thickness and single mudstone thickness） and microscopic sealing parameters（permeability and displacement pressure）,this paper gives a comprehensive analysis of the sealing capacity of the Tugulu Group in the southern margin of Junggar Basin. The results show that the Hutubi Formation is the main cap and comprises interbedded mudstone,silt mudstone and pelitic siltstone. The shale stratum ratio,average mudstone accumulative thickness and maximum single mudstone thickness are 80%-95%,337 m and 138 m respectively. Permeability and displacement pressure of the Tugulu Group mudstone range from0. 000 001 84 ×10^-3μm^2 to 0. 000 24 ×10^-3μm^2 and 4. 72 MPa to 44. 85 MPa respectively,suggesting type Ⅰ to Ⅱ sealing capacity based on the criteria for cap rock evaluation. By restoring the dynamic evolution of displacement pressure of cap rocks,the Tugulu Group is capable of sealing oil and late gas generated by the Jurassic source rock,because the timing of sealing capacity forming is well in tune with the timing of hydrocarbon generation and expulsion. Uplifting and thrust faults evolved during the Hemalaya Movement did not destroy the sealing capacity of the Tugulu Group. Through these comprehensive analysis,we conclude that cap rocks of the Tugulu Group maintains the capacity of sealing large to middle gas field.