牛东油气田原油中金刚烷和轻烃特征及其对油气成因的指示意义

牛东油气田是渤海湾盆地目前发现的埋藏深度最大、井底温度最高（201℃）的凝析气田。采用常规的天然气地球化学参数对天然气成因的判断存在矛盾。利用全二维气相色谱-飞行时间质谱对牛东1井和牛东101井凝析油中的轻烃和金刚烷进行了分析和绝对定量。轻烃的成熟度参数表明牛东原油的成熟度（R_O）为2.0%,原油成熟度明显高于源岩成熟度。说明原油已遭受强烈的分解；能表示原油裂解程度的3,4-二甲基双金刚烷在牛东1井和牛东101井原油中的绝对含量分别为111.743mg/kg和73.03mg/kg，金刚烷含量及原油裂解程度关系表明牛东油气田的原油裂解程度已达到60%～70%；源岩地球化学特征表明，沙河街组除了Ⅰ型、Ⅱ型有机质外，还发育不少Ⅲ型有机质。原油裂解气与Ⅲ型有机质热解气的混合造成了牛东凝析气田天然气地球化学性质的复杂和乙烷碳同位素组成偏重；牛东天然气中的二氧化碳为酸化压裂过程中酸液与白云岩储层反应形成。

Characteristics of Diamondoids and Light Hydrocarbons From Niudong Field and Implication for Oil/Gas Origin

Niudong condensate field is the one with the deepest burial depth and highest temperature (201℃) that has ever been found in Bohaiwan Basin so far.There are some contradictory results in determination of the origin of oil and gases by normal geochemical indexes.The diamondoids and light hydrocarbons in Niudong condensate field were measured using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry.The parameters of light hydrocarbons suggest that the maturity of condensate reaches to R_O of 2.0%,and this indicates that oil had suffered cracking.The concentrations of 3,4-dimethyldiamantane,an index of oil cracking degree,in oils from ND 1 and ND 101 wells are 111.743mg/kg and 73.03mg/kg,respectively.This indicates that the cracking degree of normal oil amounts to 60%-70%.The geochemistry of source rocks from ND 1 well suggests that there are some type Ⅲ organic matters in addition to type Ⅰand Ⅱ kerogen in the Shahejie Formation source rocks.The complexity and heavy carbon isotope of ethane in gases are caused by mixture of oil cracking gases and primary gases of type Ⅲ kerogen.The CO₂ in Niudong condensate field resulted from the reaction between dolomite and hydrochloric acid used in hydro-fracturing fluid during oil and gas exploitation.