松辽盆地德惠断陷火石岭组天然气成藏机理

火石岭组是德惠断陷深层天然气有利的勘探层位。在分析研究区构造演化史的基础上,对火石岭组典型的气藏进行精细解剖,结合地震、测井、钻井等基础资料,并综合轻烃、烃源岩、流体包裹体等分析测试数据,对德惠断陷深层火石岭组的天然气成藏机理进行了研究。结果表明,火石岭组烃源岩有机碳(TOC)平均含量大于1.0%,生烃潜力(S_1+S_2)的均值范围为0.5～2.0 mg/g,有机质类型多以Ⅱ_1～Ⅱ_2型为主,Ⅲ型为辅,有机质已达到成熟,成熟度(R_o)均值为1.5%,烃源岩具有较大的生烃潜力。火石岭组下部天然气来源于火石岭组烃源岩,而火石岭组上部天然气以火石岭组烃源岩生气为主,但受上覆沙河子组烃源岩混源影响。天然气运移以垂向断裂输导为主,层内砂体横向输导为辅。基于流体包裹体分析,结合火石岭组气藏气源对比与烃源岩生排烃期,认为火石岭组天然气藏存在三期成藏:130 Ma左右,对应营城组沉积初期;115～105 Ma左右,对应泉头组沉积期;95～75 Ma左右,对应青山口组—嫩江组沉积期。

Accumulation Mechanism for Natural Gas in the Huoshiling Formation of the Dehui Fault Depression,Songliao Basin

The Huoshiling Formation is a favorable exploration layer for deep natural gas in the Dehui fault depression. Based on the analysis of the tectonic evolution in the study area, typical gas reservoirs in the Huoshiling Formation are dissected in detail. Combined with the basic seismic, well logging, and drilling data, integrated analyses of light hydrocarbon, source rock, and fluid inclusion data were used to study the gas accumulation mechanism of the deep Huoshiling Formation in the Dehui fault depression. The results show that the average total organic carbon (TOC) of the source rocks in the Huoshiling Formation is more than 1.0%, and the average value of S₁+S₂ is 0.5-2.0 mg/g. The types of the source rock are mainly Type Ⅱ₁-Ⅱ₂, and Type Ⅲ is supplemented. The organic matter has reached maturity, The R_o mean value is 1.5%, and source rocks have greater potential for hydrocarbon generation. The natural gas in the lower part of the Huoshiling Formation comes from the source rock of the Huoshiling Formation, and the natural gas in the upper part of the Huoshiling Formation is mainly derived from the source rocks of the Huoshiling Formation but is influenced by the source of the overlying Shahezi Formation. The migration of natural gas is dominated by vertical fault propagation, and the lateral transport of sand bodies in the reservoir is supplemented. Based on the analyses of fluid inclusions, gas-source correlation, and hydrocarbon generation and the expulsion of source rocks, three episodes of hydrocarbon migration can be identified, namely 130 Ma, corresponding to the deposition of the Yingcheng Formation, 115-105 Ma, corresponding to the Quantou Formation, and 95-75 Ma, corresponding to the deposition of the Qingshankou Formation-Nenjiang Formation.