海拉尔盆地巴彦呼舒凹陷未熟油勘探前景

EXPLORATION POTENTIAL OF IMMATURE OIL IN THE BAYANHUSHU DEPRESSION OF HAILAR BASIN

海拉尔盆地巴彦呼舒凹陷发育南屯组和大磨拐河组下段2套未熟—低熟烃源层,以南屯组暗色泥岩最好,有效烃源岩厚度最厚可达360m;其次是大磨拐河组下段暗色泥岩,有效烃源岩厚度可达172m,其生烃能力与南屯组相当。南屯组暗色泥岩沥青“A”平均0.2798%,沉积环境以咸化—半咸化湖泊相为主,生物标志物萜烷系列中γ-蜡烷含量高,β-胡萝卜烷含量高,甾烷系列中重排甾烷含量低,这是水体咸化的标志,饱和烃色谱Pr/Ph<1,热解IH≈500mg/g,H/C原子比≈1.3,有机质类型以Ⅱ1型为主,均达到了形成未熟油的条件。烃源岩的热演化程度普遍较低,Ro多<0.55%,正处于未成熟中晚期—低成熟早期。但是,排烃能力相对较差。南屯组未熟生油强度变化一般在(1～4.5)×106t/km2,具备了形成中小型未熟油田的能力。

There are two sets of immature to low-mature source rock of the lower members of Nantun and Damoguaihe Formations developed in the Bayanhushu depression. Dark mudstone of the Nantun Formation is the best with effective thickness up to 360 m, while that of the lower member of Damoguaihe Formation is worse with effective thickness up to 172 m and its hydrocarbon-generating capacity is the same as that of the Nantun Formation. Average asphalt “A” content in dark mudstone of the Nantun Formation is 0.279 8%, and its sedimentary facies is saline to semi-saline lacustrine. In biomarker of terpane series, γ-cetane and β-cerotane is higher, and in steroid series rearranged steroid is lower, which marks water being salified. Pr/Ph of saturated hydrocarbon chromatogram is below 1,with pyrolytic IH about 500 mg/g, H/C about 1.3. Type of organic carbon is mainly type Ⅱ_1. All reaches immature oil-generating condition. Thermal evolution of source rock is commonly lower, R_o is mostly less than 0.55%, which is just under the late-stage of immature to the early stage of low-mature . Howe-ver, expulsion capacity of hydrocarbon is relatively lower. Generating capacity of immature oil in the Nantun Formation is generally (1～4.5)×106 t/km2, capable of forming middle-small size immature oil field.