塔里木盆地塔西南坳陷柯东构造带甫沙4井原油来源及充注过程

甫沙4井位于塔里木盆地塔西南坳陷昆仑山前冲断带的柯东构造带上，北部和东部分别发育有柯克亚和柯东1井油气田。为研究甫沙4井原油来源与充注过程，对原油样品和连续抽提后的含油砂样各组分（游离态、束缚态、包裹体）进行GC、GC?MS和 GC?IRMS分析，与柯克亚凝析油气田油样进行油—油对比。结果表明：甫沙4井晚期充注原油组分具有C_29?32重排藿烷、重排甾烷和Ts相对含量高，C_27?29甾烷ααα 20R分布呈反“L”型，以及正构烷烃单体碳同位素值较低等特征，与柯克亚凝析油气田来源于二叠系普司格组（P_2?3p）烃源岩的主体原油（I类）地球化学特征一致。而早期充注的原油组分具有重排藿烷、重排甾烷和Ts相对含量较低，C_27?29甾烷ααα 20R分布呈“V”型，以及正构烷烃单体碳同位素值较高等特征，与柯克亚凝析油气田来源于中—下侏罗统湖相泥岩的II类原油地球化学特征一致。甫沙4井经历3个阶段成藏过程：①在上新世，二叠系烃源岩于生油晚期阶段生成的I类原油运移至柯克亚构造带或柯东构造带深部形成油藏；②在更新世早期，侏罗系烃源岩于生油早—中期生成的II类原油运移至甫沙4井白垩系储层；③在第四纪，强烈的构造作用使深部I类原油沿断裂调整进入甫沙4井白垩系储层。最终造成甫沙4井白垩系储层II类原油先充注，I类原油后充注的特殊现象。

Oil source and charging process of Well FS4 in the Kedong structural belt,Southwest Tarim Depression,Tarim Basin

Well FS4 is located in Kedong structural belt while Kekeya and Kedong 1 condensate gas fields are located in the north and east of the well, respectively of the Kunlun mountain thrust belt in Southwest Depression of the Tarim Basin. In order to investigate oil sources and charging process for reservoirs within Well FS4, crude oils and oil components by sequential extraction (free oils, adsorbed oils and inclusion oils) from oil-containing sandstones were analyzed using GC, GC-MS and GC-IRMS. On the basis of biomarker compositions and carbon isotopes of individual n-alkanes for oils and sequential extracted components from oil-containing sandstones, in combination with oil-oil correlation results from Kekeya condensate field, two oil groups have been identified. Group I oils were characterized by high relative concentrations of C29-32 diahopanes, diasteranes and Ts, lower relative concentration of C27 ααα 20R regular steranes and lower δ13C values of individual n-alkanes, compared with group II oils. Group I oils were derived from lacustrine source rocks within the Middle-Upper Permian Pusige Formation while group II oils were derived from the lacustrine source rocks within the Lower-Middle Jurassic strata. Oil charging process for reservoirs within the Cretaceous strata in Well FS4 can be outlined as follows: (1) In the middle-Late Pliocene, oils that formed from the Permian source rocks at the late oil-generative stage charged the paleo-reservoirs in Kekeya or Kedong structural belt; (2) In the Early Pleistocene, oils that were generated from the Jurassic source rocks at the early to bulk oil-generative stage entered the Cretaceous reservoir in Well FS4; (3) In the Quaternary, strong tectonic movements caused the Permian oil from paleo-reservoirs to re-migrate and entere the Cretaceous reservoir in Well FS4.