我国陆相中高熟页岩油富集条件与分布特征

我国相继在多个盆地陆相页岩油勘探中获得突破，展示了良好的发展前景。基于现阶段勘探认识，本文认为陆相页岩油富集主要条件是：(1)稳定且有规模和适宜热成熟度的富有机质页岩是重要物质基础，以TOC含量>2%,最佳为3%～4%、母质类型Ⅰ和Ⅱ₁型为主，R_o>0.9%或更高(咸化环境0.8%);(2)有一定容积规模的微纳米孔隙且具脆性的多类储层是重要条件，页岩储层有效孔隙度宜>3%～6%;成岩阶段偏低时，纯页岩段不是中高熟页岩油富集段，致密砂岩和混积岩黏土含量宜<20%;成岩阶段高时，页岩黏土含量可高至40%左右；(3)滞留烃数量大且品质好是重要保证，以S₁>2 mg/g为门限，最佳>4～6 mg/g;气油比>80 m³/m³,最佳150～300 m³/m³;(4)顶底板具封闭性保持超压且滞留足够多轻-中组分烃类。陆相页岩油分布特征是：(1)有外物质注入的深-半深湖相是页岩油主要富集区；(2)具备“四高...

Lacustrine medium-high maturity shale oil in onshore China: Enrichment conditions and occurrence features

A series of breakthroughs in shale oil exploration have been made in several onshore non-marine basins in China showing good exploration and production potentials. Here we summarize our current understandings on the lacustrine shale oil enrichment and distribution characteristics as well as recent research achievements. The main enrichment conditions are the following: (1) Stable and widely distributed shales with high organic content and appropriate thermal maturity act as the material base for shale oil retention. The critical shale parameters are organic carbon (TOC) greater than 2% (optimal 3%-4%); kerogen Ⅰ and Ⅱ₁ as the dominant organic matter type; and vitrinite reflectance (R_o) greater than 0.9% (0.8% for brackish water environment). (2) Diverse reservoir types with brittle accumulation zones and certain volume of micro-nano-scale porous space are critical for shale oil accumulation. The preferred reservoir features are porosity greater than 3%-6%; non-dominating pure shale interval while including tight sandstones and hybrid rocks with clay content less than 20% in the early diagenetic stage; and higher clay content (up to ~40%) in the pure shale interval in the mid-to-late diagenetic stage. (3) High-abundance and good-quality retention hydrocarbons are important for ensuring high-mobility shale oil accumulation. Generally, a S₁ threshold higher than 2 mg/g is needed (optimal 4-6 mg/g), and a GOR threshold greater than 80 m³/m³ (optimal 50-300 m³/m³) is desired. (4) Excellent roof/floor sealing conditions in the shale oil enrichment interval is essential for maintaining overpressure and retaining sufficient amount of good-quality hydrocarbons. The distribution characteristics of lacustrine shale oil can be summarized as the following: (1) Major shale oil enrichment zones are concentrated in the semi-deep to deep lacustrine deposition areas that have external material inputs such as falling volcanic ashes, hydrothermal solutions, radioactive substances, etc. (2) Intervals with the aforementioned enrichment conditions, or the so called “four highs, one retention” condition, control the vertical distribution of the enrichment intervals. (3) Favorable lithofacies and lithologic assemblages also determine the distribution of enrichment areas. According to the preliminary estimates China has a total of (131-163)×10⁸ t medium-high thermal maturity shale oil reserves, among which (67-84)×10⁸ t are economically viable resources, which are distributed mainly in the Chang 7¹⁺² interval of the Ordos Basin, the Qing-1, 2 members of the Gulong sag, Songliao basin, the Cangdong sag, Qikou sag and Kongdian-Shahejie formations of the Jiyang depression, Bohai Bay basin, and the Lucaogou formation, Junggar basin.