摘要
塔里木盆地东北地区奥陶系为一套粉砂质泥岩和灰岩;志留系砂砾岩构成4个沉积旋回,为典型的复理石建造,含油气层位于旋回的底部,4个旋回均已倒转。成岩作用在埋深1 500 m已很显著,富含大气CO2水中沉淀亮晶方解石(Ⅰ),δ13c为 -4‰-6‰,δ180为-5‰--6‰。埋深2 400-2 600 m,硫酸盐还原带形成的碳酸盐(Ⅱ)δ13C为-7‰--10‰,δ18O为 -8‰--10‰,长石溶解形成第一次生孔隙带。埋深3 800-4 000 m,甲烷生成带脱羧作用产生的CH4形成波状消光白云石 (Ⅲ),δ13C为-1‰--16‰,而CO2直接形成的碳酸盐δ13C为20‰右右,δ18O均在-12‰--13‰,SiO2次生包体测温110- 120℃,形成第二次生孔隙带。埋深4 500-4 700 m为湿气生成带,形成的碳酸盐(Ⅳ)δ13C为-27‰--31‰,δ18O为-13‰- -14‰,包体测温130-140℃,含铁方解石大量溶解形成第三次生孔隙带。埋深达到5 000 m以上时产生大量干气(Ⅴ), δ13C为-18‰--20‰,δ18O为-1‰--14‰,与包体均一温度150-155℃相一致,形成第四次生孔隙带,孔隙度仅15％- 20％。海西运动期间褶皱地层可能倒转,抬升剥蚀可能达5 000 m左右,接着发生“退成岩作用”。
The Ordovician is composed of sihy mudstone and limestone, and the Silurian is a typical flysch formation composed of four depositional cycles of glutinite in the northeastern Tarim basin. The reservoirs occur at the bottom of each cycle. All of the 4 cycles have been inverted. Diagenesis is obvious at a depth of 1 500 m where sparry calcite （ Ⅰ ） has been precipitated from water rich in atmospheric CO2 with δ^13C in the range of -4‰ and -6‰, and δ^18O in the range of -5‰ and -6‰. At a burial depth of 2 400-2 600 m, δ^13C and δ^18O in the carbonate（ Ⅱ ） formed in the sulfate reduction zone are in the range -7‰ to -10‰ and -8‰ to -10‰, respectively, where the dissolution of feldspar constitutes the 1 st secondary pore zone. Dolomites （ Ⅲ ） with wavy extinction have been formed at a burial depth of 3 800 -4 000 m, along with the decarboxylation in the methane generating zone, the δ^13C is in the range of -11‰ and -16‰, while in the carbonate directly formed from CO2, the δ^13C is ＋ 20‰, and the δ^18O both in dolomite and carbonate range from - 12‰ to - 13‰, temperatures measured from secondary SiO2 inclusions are in the range of 110℃ and 120℃. This interval constitutes the 2nd secondary pore zone. The depth interval of 4 500 - 4 700 m is a wet gas generating zone, the δ^13C and δ^18O in carbonate （Ⅳ） formed in this interval are in the range of -27‰ to -31‰ and - 13‰ to - 14‰, respectively, and the temperature measured from inclusion thermometry is 130 - 140℃ ; and the massive dissolution of ferroan calcite has resulted in the formation of the 3rd secondary pore zone. Large amount of dry gas （ Ⅴ ） were generated at a burial depth of over 5 000 m, where the δ^13C ranges from - 18‰ to -20‰ and δ^18O ranges from - 13‰ to - 14‰, being accordant with the inclusion＇ s homogenization temperature of 150 - 155℃. This interval constitutes the 4th secondary pore zone with porosity in the range of 15% to 20%. The folded strata might have been inverted during Hereynian movement, uplifted and eroded about 5 000 m and associated with ＇ retrodiagenesis＇.
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
2006年第1期85-92,共8页
Oil & Gas Geology
关键词
包裹体均-温度
次生孔隙带
同位素
世代
碳酸盐胶结物
奥陶-志留系
塔里木盆地东北部
homogenization temperature of inclusion
secondary pore zone
isotope
generation
carbonate cement
Ordovician - Silurian
northwestern Tarim basin
