用显微镜和拉曼光谱研究四川盆地高科1井、五科1井、普光5井、普光3井高密度甲烷包裹体特征与天然气成因

Study on the characteristics of high-density methane inclusions and the origin of natural gas in well Gaoke 1,well Wuke 1,well Puguang 5,and well Puguang 3 in the Sichuan Basin by microscopy and laser Raman spectroscopy

用光学显微镜和显微激光拉曼等技术手段综合研究了四川盆地4个钻孔中甲烷包裹体密度和热演化程度,以及甲烷包裹体、盐水包裹体与固体沥青的共生组合形式。结果表明,高密度甲烷包裹体主要形成于原油–沥青和干酪根高温–高压裂解的不混溶体系。研究样品中甲烷包裹体的拉曼位移为2909.76~2911.69 cm-1,计算对应的密度为0.251~0.351 g/cm3,其变化范围不仅与包裹体形成的温度、压力有关,而且还受到矿物包裹体保存条件的影响。样品的甲烷包裹体拉曼镜质体反射率(RMVRo)为3.07%~3.85%,多数>3.15%,其大小取决于地层中局域平衡体系的温度、压力和有效受热时间。各种包裹体与固体沥青的共生产出形式,反映了不同钻孔油气成因演化的重要信息:高科1井石英团块中捕获的高密度甲烷包裹体与储层焦沥青–碳沥青的产出特征,反映本区震旦系–寒武系碳酸盐岩气藏主要为储层油裂解气成因;五科1井志留系黑色页岩中的高密度甲烷包裹体产出形式和气体组成特征,反映志留系页岩气主要为残留烃和干酪根高温裂解成因,一般不含H2S并具有超压现象,据志留系黑色页岩石英脉中个别轻烃包裹体特征,推测部分奥陶系碳酸盐岩储层可能保存少量轻烃;普光5井富含H2S的高密度甲烷包裹体和焦沥青特征,提供了飞仙关组和长兴组碳酸盐岩储层中的油裂解气藏明显受硫酸盐热化学反应(TSR)影响的证据;普光3井须家河组石英脉中捕获的高密度包裹体不含H2S,甲烷包裹体中焦沥青反射率高达3.40%,而须家河组地层中固体沥青反射率为2.48%,两者热演化程度明显不匹配,提供了本区可能有深部含烃热流体沿逆冲断裂带上侵的重要信息。

The density and thermal evolution of methane inclusions in four boreholes in the Sichuan Basin as as the symbiotic combination of methane inclusions,brine inclusions,and solid bitumen were comprehensively studied using optical microscopy and laser Raman spectroscopy.Results show that high-density methane inclusions are mainly formed in the immiscible system of crude oil-bitumen and kerogen at high temperatures and pressures.The Raman shifts of methane inclusions in the studied samples are 2909.76 cm-1 to 2911.69 cm-1,and the corresponding calculated densities are 0.251 g/cm3 to 0.351 g/cm3.The variation range is not only related to the formation temperature and pressure of methane inclusions,but is also affected by the preservation conditions of the mineral inclusions.The thermal evolution degree of methane inclusions in samples was RMVRo=3.07%–3.85%,mostly>3.15%,and their size depended on the temperature-pressure and effective heating time of the local equilibrium system in the formation.The co-production of inclusions and solid bitumen in the sample provides important information on the genetic evolution of oil and gas.The high-density methane inclusions captured in the quartz blocks of well Gaoke 1 and the production characteristics of the reservoir pyropitch-anthraxolite indicate that the Sinian-Cambrian carbonatite gas reservoirs in this area originated from high temperature-high pressure oil cracking gas.The density and gas composition characteristics of the methane inclusions produced in the Silurian black shale in well Wuke 1 indicate that the Silurian shale gas is mainly caused by residual hydrocarbons and kerogen pyrolysis,and the shale gas in this area generally does not contain sulfide hydrogen and exhibits an overpressure phenomenon.Based on the individual light hydrocarbon inclusions found in the Silurian black shale,it is speculated that some Ordovician carbonate reservoirs may contain a small amount of light hydrocarbons.The production characteristics of the H2S-rich,high-density methane inclusions and pyrobitumen in well Puguang 5 reflect the oil-cracking gas reservoirs produced in the carbonatite reservoirs of the Feixianguan and Changxing Formations,which are affected by the sulfate thermochemical reaction(TSR).The high-density inclusions captured in the quartz veins of the Xujiahe Formation in well Puguang 3 do not contain hydrogen sulfide,and the reflectance of pyro-asphalt in methane inclusions is as high as 3.40%,whereas the reflectance of solid asphalt in the Xujiahe Formation is 2.48%,which obviously does not match the thermal evolution degree of high-density methane inclusions,providing important information that there may be deep hydrocarbon-containing thermal fluids intruding along the thrust fault zone in this area.