关键词: 孔二段, 沙三段, 沙一段, 纹层型页岩, 储集性, 含油性, 压裂效果, 黄骅坳陷, 渤海湾盆地

Abstract: The development of laminae is one of the typical characteristics of continental shale in faulted lake basins in eastern China. Three sets of shale layers were developed in the second member of the Paleogene Kongdian Formation (Kong 2 member), the third member of Shahejie Formation (Sha 3 member) and the first member of Shahejie Formation (Sha 1 member) in Huanghua Depression, Bohai Bay Basin, which were deposited in different sedimentary environments, thus forming different laminae units. The oil-bearing property, reservoir storage capacity and fracability vary, which restricts the exploration and development achievements of shale oil. Based on core samples, wireline logging and mud logging data of three sets of shale layers in Huanghua Depression, basic geochemical and rock mineral analysis has been conducted, and multi-scale fine characterization on various types of shale laminae has been implemented by comprehensively using technical measures such as AMICSCAN mineral scanning, high resolution scanning electron microscopy, energy spectrum elements, micro-CT scanning, and true triaxial hydraulic fracturing simulation, clarifying the depositional environment, reservoir storage capacity, flow capacity and fracability of different types of laminated shale. The study results show that Kong 2 member shale is mainly composed of felsic shale, as well as mixed shale and a small amount of limy-dolomitic shale; Sha 3 member shale is dominated by mixed shale, with felsic shale; Sha 1 member shale is mainly mixed shale, with a small amount of limy-dolomitic shale and felsic shale. The felsic laminae are mainly observed in Kong 2 member shale, with a small amount of limy-dolomitic laminae and clay laminae. The limy-dolomitic laminae and clay laminae are dominant in Sha 3 member shale, with a small amount of felsic laminae. While the dolomitic laminae are dominant in Sha 1 member shale, with a small amount of felsic laminae and clay laminae. The clay laminae generally have high organic matter content, and are responsible for hydrocarbon generation in the microscopic source rock–reservoir system, which lays a foundation for shale oil enrichment. The felsic laminae and limy-dolomitic laminae usually have high storage capacity, serving as the reservoir part in the microscopic source rock–reservoir system, providing reservoir and storage space for shale oil. Compared with layered and massive shale, shale reservoirs with high-frequency lamination have larger specific surface area, larger area for hydrocarbon charging, better pore connectivity, and an overpressure state due to the constant hydrocarbon generation and pressurization. In addition, the micron-scale dissolution pores of feldspar and dolomitic minerals were formed by organic acids in the process of hydrocarbon generation, which improved physical properties of shale reservoirs. The physical fracturing simulation experiments show that the laminated felsic shale has the best fracturing effect, followed by the laminated mixed shale, while the massive limy-dolomitic shale has the poorest fracturing results.

Key words: the second member of Kongdian Formation, the third member of Shahejie Formation, the first member of Shahejie Formation, laminated shale, reservoir storage capacity, oil-bearing property, fracturing effect, Huanghua Depression, Bohai Bay Basin