济阳坳陷深层天然气成因判识

近年来，济阳坳陷深层天然气勘探工作取得了一定进展，但深层天然气成因类型判识研究才刚刚起步，成因判识的分歧之一是已发现的天然气究竟是干酪根裂解气还是原油裂解气，这两类天然气从理论上分析在济阳坳陷都有存在的可能性。为此，进行了干酪根与原油裂解的模拟实验，得出了依据ln(C₁/C₂)与ln(C₂/C₃)、甲基环己环/环己环与2,3-二甲基戊烷/甲基环己烷、δ¹³C₁与δ¹³C₂的相关关系能区分原油裂解气和干酪根裂解气的认识：原油裂解气中ln(C₂/C₃)值大，一般比干酪根裂解气中值大2以上；油裂解气中甲基环己环/环己环和2,3-二甲基戊烷/甲基环己烷值较大，分别大于1.5和1；油裂解气中δ¹³C₁与δ¹³C₂轻，初始裂解阶段仅为-55‰和-41.5‰。应用上述相关关系对济阳坳陷深层天然气进行了成因判识，结果认为：济阳坳陷深层天然气大多为干酪根裂解气，也有极少部分原油裂解气的混入。其中丰深1井天然气形成温度为120~170 ℃，原油裂解率小于15%；义115井天然气形成温度最高，原油裂解率为60%~70%。

ORIGIN OF GAS IN DEEP JIYANG DEPRESSION

Although gas exploration in deep of Jiyang depression is fruitful in recent years, the research on genetic types of the deep gas has just initiated. It is controversial about the origin of the discovered gas. Theoretically, thermal cracked gas from both kerogen and crude oil possibly occur in Jiyang depression. Simulated experiments of thermal cracking of kerogen and crude oil were performed and it was believed that the gas from thermal cracking of crude oil and kerogen can be differentiated according to the relationships of ln(C1/C2) with ln(C2/C3), MCC6/CC6 with 2,3 DMC5/MCC6, and δ13C1 with δ13C2. The ln(C2/C3) value of the thermal cracking gas from crude oil is generally over 2 larger than that of from kerogen, while the MCC6/CC6 and 2,3 DMC5/MCC6 values of the former are 1.5 and 1 larger than that of the latter, respectively. The δ13C1 and δ13C2 of the former are relatively light and are only -55‰ and -41.5‰ respectively in the initial stage of cracking. These criteria are used to identify the genetic types of the deep gas in Jiyang depression and it is believed that the deep gas in the study area is dominated by thermal cracking gas from kerogen, with small amount of thermal cracking gas from crude oil mixed. The formation temperature of gas in the well Fengshen 1 was 120~ 170 ℃, with a crude cracking ratio smaller than 15%, while that in the well Yi 115 was the highest, with an oil cracking ratio up to 60% ~ 70%.