准噶尔盆地吉木萨尔凹陷及周缘二叠系芦草沟组异重流沉积

Hyperpycnal flow deposits of the Permian Lucaogou Formation in the Jimusaer Sag and its peripheries， Junggar Basin

陈轩 陶鑫 覃建华 许长福 李映艳 邓远 高阳 尹太举

Xuan CHEN Xin TAO Jianhua QIN Changfu XU Yingyan LI Yuan DENG Yang GAO Taiju YIN

准噶尔盆地吉木萨尔凹陷二叠系芦草沟组储层的沉积成因一直存在争议。基于芦草沟组露头、岩心、测井、地震及分析化验资料，开展沉积学分析。研究表明：①准噶尔盆地吉木萨尔凹陷二叠系芦草沟组储层岩性为粉-细砂岩及泥质粉砂岩，发育对偶粒序及内部侵蚀面、块状层理及陆源植物碎片，为湖泊异重流成因。②异重流水道亚相主要由块状及交错层理粉-细砂岩组成，单层厚度0.8 ~ 2.8 m，平均1.6 m，核磁孔隙度值6.0 % ~ 12.0 %，平均9.5 %；朵叶体亚相主要由粒序层理、爬升波纹层理粉砂岩组成，单层厚度0.5 ~ 1.4 m，平均0.9 m，核磁孔隙度3.5 % ~ 7.8 %、平均5.2 %。③水道亚相具有透镜状充填地震反射特征，砂体厚层状加积充填，平面上为条带状或舌状，横向宽度1 ~ 3 km；朵叶体亚相具有披覆状地震反射特征，砂体薄层状侧积、前积发育，平面为扇形，长度及宽度均超过10 km。④芦草沟组沉积时期，南部山区频繁发生的洪水异重流携带陆源碎屑及有机质在吉木萨尔凹陷快速沉积，形成了砂岩储层与优质烃源岩，造成了水道-朵叶体砂体与异重流侧缘-深湖烃源岩大面积接触、频繁互层。湖泊异重流沉积模式为吉木萨尔凹陷“粗-细共存、源-储共生”高品质页岩油的成因提供了新的沉积学解释机制。

The sedimentary origin of the Permian Lucaogou Formation reservoirs in the Jimusaer Sag， Junggar Basin has long been a controversial topic. Based on data from outcrop and core observations， logging， and seismic surveys， as well as lab tests of the Lucaogou Formation， we conduct sedimentary analysis， obtaining the following results： （1） The reservoirs of the Permian Lucaogou Formation in the study area are of siltstone/fine-grained sandstone and argillaceous siltstone. They feature well-developed paired graded bedding sequences with internal erosion surfaces， massive bedding， and terrestrial plant fragments， which can be an interpretation of a sedimentary origin of lacustrine hyperpycnal flows； （2） The channel subfacies of hyperpycnal flow deposits consists primarily of massive- and cross-bedding siltstone/fine-grained sandstone， with a single-layer thickness of 0.8～2.8 m， averaging 1.6 m and NMR-derived porosity of 6 %～12 %， averaging 9.5 %. In contrast， the lobe subfacies of hyperpycnal flow deposits predominantly comprises siltstones showing graded bedding and climbing-ripple bedding， with a single-layer thickness of 0.5～1.4 m， averaging 0.9 m and NMR-derived porosity of 3.5 %～7.8 %， averaging 5.2 %； （3） The channel subfacies showing seismic reflections featuring lensoid filling presents a stacking pattern of aggradation with thick laminated accretionary fillings that are in the shape of bands or tongues on the plane， with a lateral width of 1～3 km. In contrast， the lobe subfacies displays draping seismic reflections， the sand bodies of which are of thinly laminated lateral-accretion and progradational bedding in the shape of fan on the plane， with both length and width exceeding 10 km； （4） During the deposition of the Lucaogou Formation， terrigenous clastics and organic matter， carried by frequent flood-induced hyperpycnal flows in the mountainous area of the southern Jimusaer Sag， were rapidly deposited in the sag， forming sandstone reservoirs and high-quality source rocks， and leading to the extensive contact and frequent alternation between the sand bodies of channel and lobe subfacies and the source rocks of hyperpycnal flow deposits of marginal and deep lacustrine facies. Such a sedimentary pattern of lacustrine hyperpycnal flows characterized by the coexistence of coarse- and fine-grained sandstones and paragenetic source rock-reservoir sequences， provides a novel sedimentary interpretation on the origin of high-quality shale oil reservoirs in the Jimusaer Sag.

10.11743/ogg20230615