准东中下侏罗统煤地球化学特征与低熟气形成

Geochemical Characteristics of the Coal from Lower-Middle Jurassic in Eastern Junggar Basin and the Generation of Low-maturity Gas

准东地区低熟气资源丰富,其形成机制及母质来源一直是研究的重点和难点。对准东中下侏罗统八道湾组和西山窑组6块低演化煤样（长焰煤—气煤）进行了全面的地球化学分析,包括岩石热解、TOC和RO测定、可溶有机质族组成分离及饱和烃和芳烃GC—MS分析等。烃源岩评价结果表明,研究样品属于较差生油岩,但具有较大的生气潜力。RO值为0.47%～0.73%,平均值为0.63%,显示样品处于低演化阶段;有机质类型以Ⅲ型为主,原始有机质主要来自高等植物。在样品饱和烃和芳烃馏分中,检测到相对丰度较高的惹烯、咔达烯、脱氢松香烷、西蒙内利烯、降海松烷等来自树脂体的化合物,此类化合物具有较低的生烃活化能,是煤在低演化阶段形成天然气的重要物质基础;同时,较丰富的苯并藿烷、异构（2-）和反异构（3-）甲基烷烃及姥鲛烷和植烷的检出表明有机质经历过轻微—中等程度的生物降解作用。此外,样品中还检出丰度较高的重排甾烷,这是烃源岩在低演化阶段经受黏土矿物催化的重要依据。综合前人研究表明,微生物的改造作用和黏土矿物的催化均可降低有机质的生烃活化能,有利于烃源岩在低演化阶段形成低熟天然气。

The resource of low maturity gas in eastern Junggar Basin is abundant,and its formation mechanism and source material are the main difficulties and emphases in researches.With Rock-Eval,TOC,RO and GC-MS,saturated and aromatic hydrocarbons are analyzed.The geochemical characteristics of the lowmaturity coal in the Middle Jurassic Xishanyao Formation and Lower Jurassic Badaowan Formation in eastern Junggar Basin were systematically studied.The vitrinite reflectance values range from 0.47% to0.73%,with an average of 0.63%,suggesting the source rocks have entered low-mature stage.Furthermore,the coals are type III organic matter that mainly comes from vascular plants.The results of source rocks evaluation indicate that samples have a great gas-prone.As an important material basis for gas formation,a series of compounds coming from resinites have been detected in saturated and aromatic hydrocarbons.Moreover,saturated hydrocarbons contain abundant benzohopanes,iso-（2-methyl）and anteiso-（3-methyl）alkanes,pristine and phytane,and high abundance is evidence for slight-moderate biodegradation.Besides,the high abundance of diasteranes could also confirm that clay materials have catalyzed the source rocks at low-maturity.Previous research showed that the biodegradation and the catalysis can decrease the activation energy of hydrocarbon,which is beneficial to gas generation at low mature stage.