岩浆侵入对围岩储层的成岩及其变质特征的影响及意义——以松辽盆地南部辉绿岩侵入带露头研究为例

Diagenetic and metamorphic characteristics and implications for hydrocarbon reservoirs in the country rocks influenced by magmatic emplacement： A case study from an outcrop of diabase intrusion in the southern Songliao Basin

以松辽盆地南部团山子采石场辉绿岩侵入露头为例，采用连续密集取样、常规分析和碳氧稳定同位素测试等方法，对围岩储层的成岩及其变质特征进行分析，进而探讨岩浆侵入对围岩的影响及其储层意义。岩浆侵入对角岩围岩的影响包括：1）自生绢云母距离侵人体越远，其含量越少；2）粘土矿物主要为成岩晚期的伊利石和绿泥石；3）角岩中发育特殊“气孔-杏仁”构造。岩浆侵入对上覆砂岩的影响表现为：1）造成自生石英的特征分布；2）造成粘土矿物的不均匀分布；3）形成反映应力挤压特征的颗粒结构。角岩中浊沸石发育和高岭石不发育对应碱性环境，不利于热液微裂缝中碳酸盐矿物的溶蚀。因此，尽管角岩发育微孔、微缝等少量储集空间（平均孔隙度为1．70％），但其渗透能力很低（平均渗透率小于0．1mD）。侵入活动对研究露头砂岩储层物性造成的不利影响，主要是由于挤压作用和热液流动作用使自生矿物不均匀分布，从而导致或加剧了砂岩储层的非均质性。

Magmatism is encountered widely in hydrocarbon-bearing basins worldwide. However, its influences on country rocks as hydrocarbon reservoirs have been controversial. The current study takes an outcrop of diabase intrusion in the Tuanshanzi area, southern Songliao Basin, as a case study, aiming to investigate diagenetic and metamorphic characteristics of country rocks, on the basis of continuous sampling, thin-section observations, scanning electronic images （SEM）, electron probe microanalysis （EPMA）, fluid-inclusion microthermometry, X-ray diffraction analysis （XRD）, and oxygen and carbon stable isotopes. The intrusive outcrop is diabase, and upward country rocks are hornfels and metasandstones. Authigenic sericite is an indicator of metamorphism in hornfels. The sericite content is decreasing with increasing distances from diabase intrusion. Due to heat influence caused by diabase intrusion, the clay matrices are characterized by illite and chlorite, which commonly represent later-stage diagenesis. Vesicle-amygdule structures, which are filled with laumontite, develop exclusively in hornfels. In addition, augite grains are detected in country hornfels. These aspects indicate that the country rocks were weak consolidated when intruding occurred. Diagenetic and metamorphic features of overlying metasandstones influenced by diabase intrusion include： 1） characteristic distribution of authigenic quartz. In locations adjacent to diabase intrusion,authigenic quartz is mainly microcrystalline quartz grains, while in places distal from diabase, authigenic quartz is mainly quartz overgrowth; 2） uneven distribution of clay minerals. The content of mineral contents increases with increasing distances from intrusion body; 3） forming characteristic structure reflecting mechanical pressure, such as cracking and wavy extinction of quartz grains. The mechanical pressure gradually weakens with increasing distances from diabase intrusion. Although minor reservoir pore spaces are developed in hornfels （average porosity of 1.70% ）, barely no seepage potential in them （average permeability of 〈 0.1 roD）, mainly because that microfissures formed due to hydrothermal fluids breaking are filled completely with calcites. The occurrence of laumontite and depleted kaolinite reflect alkaline diagenetic environment, which prevents the dissolution of calcites in the microfissures. Metamorphism is fundamental for hornfels turning into hydrocarbon reservoirs, while later-stage dissolution is crucial for them to be effective reservoirs. In sandstones, mechanical pressure and hydrothermal fluids flow result in heterogeneous distribution of authigenic minerals, thereby causing or intensifying reservoir heterogeneity.