烃源岩热解分析参数T_(max)异常的原因

Cause analysis of abnormal T_(max) values on Rock-Eval pyrolysis

归纳整理中国25 000多块烃源岩热解分析资料,发现有些岩石样品的Tmax值异常低,有些Tmax值异常高,有些Tmax在某一深度突然升高后又降低,与烃源岩所处的埋深和时代不相符。通过烃源岩、干酪根热解热模拟试验、干酪根显微组分成烃活化能分布测定、岩石热解分析称样量对Tmax影响试验等,研究Tmax异常的原因,认为可溶有机质(包括烃源岩中存在的原油和沥青)以及钻井液有机添加剂的侵入都会引起S1峰增大,还由于可溶重质组分进入S2峰而导致Tmax降低。显微组分中存在树脂体的烃源岩Tmax普遍偏低;矿物对烃类的吸附导致低有机碳含量的烃源岩Tmax偏高,受火成岩侵入的烃源岩Tmax异常高,岩石热解分析的称样量也对Tmax有影响。

The abnormal Tmax values have been observed on Rock-Eval pyrolysis in over 25 000 source rock samples in China. Some Tmax values are abnormally high, some abnormally low, and others decrease following an abrupt increase at certain depth. These phenomena are incompatible with the buried depth and ages of the samples. Source rock and kerogen simulation experiments, and activation energy distribution measurement of kerogen maceral have been carried out to find the causes of the abnormal Tmax values. The bitumen, migrated oil and contamination from organic additive and oil of drilling mud enhance S1 peaks of source rocks. Some soluble heavier fraction overlaps S2 peaks, resulting in lower Tmax values. The abundant resinite in maceral is also the cause of lower Tmax values. The mineral matrix conservation on hydrocarbons and the intrusion of igneous rock in source rocks attribute to higher Tmax values as well. The sample weight influence on Tmax value has also been discussed.