Zhong Gaorun, Li Yajun
School of Petroleum Engineering and Environmental Engineering, Yan'an University, Yan'an, Shaan'xi 716000, China.
State Key Laboratory for Continental Dynamics/Department of Geology, Northwest University, Xi'an 710069, China.
ACS Omega. 2023 Jul 21;8(30):27206-27215. doi: 10.1021/acsomega.3c02433. eCollection 2023 Aug 1.
The study of the geochemical characteristics of source rocks is an important part of tight oil evaluation. The Zhahaquan area of the Qaidam Basin is a new area for tight oil exploration in China. During the sedimentary period of the Neogene Upper Ganchaigou Formation (N1) in the Zhahaquan area, a set of source rocks of semideep lake and deep lacustrine facies as well as a set of thin, interbedded fine sandstone and argillaceous limestone was deposited, providing favorable conditions for the formation of tight oil. However, the study on the geochemical characteristics of source rocks in this area is relatively weak. The geochemical characteristics of the source rocks in the Zhahaquan area were determined via the experimental analysis of parameters such as vitrinite reflectance (Ro), chloroform bitumen "A", total organic carbon (TOC), group components, kerogen types, rock pyrolysis, and aromatic compounds of crude oil. The following results were obtained: the Zhahaquan area had II-type hydrocarbon source rock organic matter, and the TOC was 0.32%-1.32%. The type index (TI) was 48.70-72.23, the chloroform bitumen "A" content was 0.0034%-0.1133%, Ro was 0.810%-1.265%, and the cracking hydrocarbon peak temperature () was distributed in the temperature range of 362-444 °C. The hydrocarbon generation conversion rate was 0.89%-10.0%. The reservoir mainly had intergranular pores, dissolution pores, and microfractures. The average porosity was 8.0%, and the average permeability was 0.861 × 10 μm. The average oil saturation was 30.0%, and the average water saturation was 21.6%. From a comprehensive analysis of the results, the following inferences were derived. The parent material of the source rocks in the Zhahaquan area mainly originated from algae and other phytoplankton in the lake basin, which was a good source rock for oil exploration. The source rocks of this area have entered the threshold of hydrocarbon generation and are in the peak oil-generation stage. They have potential as industrial oil and gas resources. The oil test results of YD103 and seven other wells showed that the daily oil index per meter ranges from 0.38 to 6.5 m/d·m, indicating that the source rocks have the ability to form industrial oil. Analysis of the geochemical characteristics of source rocks and study of reservoir geological characteristics will provide theoretical support and reference for tight oil exploration and development in Zhahaquan.
烃源岩地球化学特征研究是致密油评价的重要组成部分。柴达木盆地扎哈泉地区是我国致密油勘探的新区。扎哈泉地区新近系上干柴沟组（N1）沉积时期，沉积了一套半深湖—深湖相烃源岩以及一套薄互层状细砂岩和泥灰岩，为致密油形成提供了有利条件。然而，该地区烃源岩地球化学特征研究相对薄弱。通过对镜质体反射率（Ro）、氯仿沥青“A”、总有机碳（TOC）、族组分、干酪根类型、岩石热解、原油芳烃化合物等参数进行实验分析，确定了扎哈泉地区烃源岩的地球化学特征。取得如下结果：扎哈泉地区烃源岩有机质为Ⅱ型，TOC为0.32% - 1.32%，类型指数（TI）为48.70 - 72.23，氯仿沥青“A”含量为0.0034% - 0.1133%，Ro为0.810% - 1.265%，裂解烃峰值温度（）分布在362 - 444℃温度范围内，生烃转化率为0.89% - 10.0%。储层主要发育粒间孔、溶蚀孔和微裂缝，平均孔隙度为8.0%，平均渗透率为0.861×10μm，平均含油饱和度为30.0%，平均含水饱和度为21.6%。综合分析结果得出如下推论：扎哈泉地区烃源岩母质主要来源于湖盆藻类等浮游植物，是良好的勘探烃源岩。该地区烃源岩已进入生烃门限，处于生油高峰期，具有成为工业油气资源的潜力。YD103等8口井试油结果表明，单米日产油指数为0.38 - 6.5m/d·m，说明烃源岩具有形成工业油流的能力。烃源岩地球化学特征分析和储层地质特征研究将为扎哈泉致密油勘探开发提供理论支撑和参考。
