Lithofacies Characteristics and Sweet Spot Distribution of Lacustrine Shale Oil Reservoirs: A Case Study of the Second Member of the Kongdian Formation in the Cangdong Sag, Bohai Bay Basin
Author:
Zhan Yuan12, Lin Chengyan12, Ma Cunfei1, Han Wenzhong3, Ma Pengjie4ORCID, Li Guiang12
Affiliation:
1. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China 2. National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China 3. Research Institute of Exploration and Development, Dagang Oilfield Company, PetroChina, Tianjin 300280, China 4. Sanya Offshore Oil & Gas Research Institute, Northeast Petroleum University, Sanya 572025, China
Abstract
In contrast to marine shale oil reservoirs, lacustrine shale exhibits rapid lithofacies changes and strong mineral compositional heterogeneity, posing new challenges for the evaluation and distribution prediction of shale oil sweet spots. The oiliness, reservoir properties, oil fluidity, and fracability of different lithofacies were analyzed using emission-scanning electron microscopy (FE-SEM) observation, low-pressure nitrogen physisorption (LNP) analysis, mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and triaxial compression testing. Based on the mineral composition obtained from X-ray diffraction (XRD) analysis, total organic carbon (TOC) content, and sedimentary structure, four lithofacies were classified, which are organic-rich laminated calcareous shale (LC), organic-rich laminated siliceous shale (LS), organic-rich laminated mixed shale (LM), and organic-poor massive calcareous shale (MC). Considering the factors of oiliness, reservoir properties, oil fluidity, and fracability, the LC and LS lithofacies were determined as being high-quality sweet spots (type I). Within the stratigraphic sequence divided by GR-INPEFA curves, multi-resolution graph-based clustering (MRGC) analysis of sensitive well logs was used to classify the lithofacies, after which the distribution of sweet spots was predicted. The results reveal that the sweet spots exhibit regular changes in their vertical distribution and a ring-like pattern in their planar distribution, influenced by variations in the sedimentary environment. This finding can offer valuable guidance for the future exploitation of shale oil in the Guandong region.
Funder
National Natural Science Foundation of China
Subject
Geology,Geotechnical Engineering and Engineering Geology
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