CAJ | 학술논문

在川东北地区石油地质背景特征的基础上，探讨了元坝与河坝地区陆相储层天然气的成因。元坝地区侏罗系储层天然气重烃气体含量较高；多数样品甲烷δ13 C和δD值分别在-42.2‰～-34.4‰和-208‰～-168‰，乙烷δ13 C值在-31.4‰～-21.4‰，甲烷δ13 C和δD值之间相关性好；天然气主要来源于侏罗系自流井组或千佛崖组陆相烃源岩。元坝地区须家河组储层天然气重烃气体含量低；甲烷δ13 C和δD值分别为-31.7‰～-29.2‰和-170‰～-148‰，乙烷δ13 C值在-27.7‰～-26.5‰；天然气主要来源于元坝地区上三叠统须家河组高-过成熟的腐殖型烃源岩。元坝地区陆相储层天然气成因的主控因素是陆相烃源岩发育及其成熟度。河坝地区陆相储层天然气重烃气体含量变化大；甲烷δ13 C值大多重于-32‰，甲烷δD值分布范围较大，在-186‰～-122‰，乙烷δ13 C值在-33.2‰～-29.6‰；甲烷δD与δ13 C值之间相关性很差，部分样品甲烷与乙烷的δ13 C值倒转，表明河坝地区陆相储层天然气成因复杂，有来源于陆相须家河组的天然气，也有来源于海相烃源岩的天然气，以及海相与陆相来源天然气的混合气。河坝地区陆相储层天然气成因的主控因素是海相与陆相多套烃源岩与不同级别断裂。陆相储层天然气中CO2的δ13 C值多轻于-12‰，属于有机质热分解成因。稀有气体3 He/4 He比值在0.0033Ra～0.0181Ra ，分布于地壳来源或放射性成因的范围内，表明天然气中没有幔源稀有气体的贡献。
재천동북지구석유지질배경특정적기출상，탐토료원패여하패지구륙상저층천연기적성인。원패지구주라계저층천연기중경기체함량교고；다수양품갑완δ13 C화δD치분별재-42.2‰～-34.4‰화-208‰～-168‰，을완δ13 C치재-31.4‰～-21.4‰，갑완δ13 C화δD치지간상관성호；천연기주요래원우주라계자류정조혹천불애조륙상경원암。원패지구수가하조저층천연기중경기체함량저；갑완δ13 C화δD치분별위-31.7‰～-29.2‰화-170‰～-148‰，을완δ13 C치재-27.7‰～-26.5‰；천연기주요래원우원패지구상삼첩통수가하조고-과성숙적부식형경원암。원패지구륙상저층천연기성인적주공인소시륙상경원암발육급기성숙도。하패지구륙상저층천연기중경기체함량변화대；갑완δ13 C치대다중우-32‰，갑완δD치분포범위교대，재-186‰～-122‰，을완δ13 C치재-33.2‰～-29.6‰；갑완δD여δ13 C치지간상관성흔차，부분양품갑완여을완적δ13 C치도전，표명하패지구륙상저층천연기성인복잡，유래원우륙상수가하조적천연기，야유래원우해상경원암적천연기，이급해상여륙상래원천연기적혼합기。하패지구륙상저층천연기성인적주공인소시해상여륙상다투경원암여불동급별단렬。륙상저층천연기중CO2적δ13 C치다경우-12‰，속우유궤질열분해성인。희유기체3 He/4 He비치재0.0033Ra～0.0181Ra ，분포우지각래원혹방사성성인적범위내，표명천연기중몰유만원희유기체적공헌。
The origin of natural gas in terrestrial reservoirs of Yuanba and H eba regions is investigated by analyzing the geochemi-cal characteristics of natural gases and surveying the regional background of petroleum geology in the northeastern Sichuan Basin, China.Results show that:1 )In Yuanba region,natural gases from the Jurassic clastic rock reservoirs contain high levels of heavy hydrocarbon gases.Theδ13 C andδD values of methane respectively range from-42.2‰to-34.4‰and-208‰to-168‰,whereas theδ13 C values of ethane range from-31.4‰to-21.4‰in most gas samples.There is a strong correla-tion between theδ1 3 C andδD values of methane in gas samples tested,and the gases are mainly originated from terrestrial source rocks of the Jurassic Ziliujing and Qianfoya Formation.Differently,natural gases from the Xujiahe Formation contain low levels of heavy hydrocarbon gases;theδ1 3 C andδD values of methane in natural gas samples respectively range from-3 1.7‰to-29.2‰and-170‰to-148‰,whereas theδ13 C values of ethane range from-27.7‰to-26.5‰.The gases are mainly originated from high-to-over-maturity humic terrestrial source rocks of the Upper Triassic Xujiahe Formation.The origin of natural gases is mainly controlled by the development of terrestrial source rocks and their maturity.2)In Heba region,natural gases from the terrestrial reservoirs contain varying levels of heavy hydrocarbon gases.Theδ13 C values of methane are mostly greater than-3 2.0‰and the correspondingδD values widely range from-1 8 6‰to-1 2 2‰;theδ1 3 C values of ethane range from-33.2‰to-29.6‰.There is a poor correlation between theδ13 C andδD values of methane in gas samples.Theδ13 C values of methane and ethane are reversed in a few cases,suggesting the complex origin of the gases that include those from ter-restrial source rocks of the Xujiahe Formation and marine source rocks,as well as mixed gases from the above two origins.The development of marine and terrestrial source rocks as well as fractures of various levels is the main factor that controls the origin of natural gases in this region.3 )Theδ1 3 C values of carbon dioxide in natural gas samples are mostly less than-1 2‰,indica-ting that the gases are mainly generated through organic matter decomposition.Noble gas isotopic ratios of helium (3 He/4 He,0.003 3Ra~0.018 1Ra)are distributed in the range of values for deep crust or radiogenic decay,demonstrating a lack of mantle-derived noble gas in the samples tested.