# High-Resolution Mapping of Subsurface Sedimentary Facies and Reservoirs Using Seismic Sedimentology
## 1 Introduction  
In the early days of subsurface seismic technology in 1977, [PERSON] et al. introduced seismic stratigraphy [1]. It was developed for the low-resolution (50-500 m thick) analysis of basin-scale depositional systems. So-called \"seismic facies\" are analyzed as a group of seismic events. Because most hydrocarbon reservoirs of sedimentary origin are typically at the seismic resolvable limit or even thinner (a couple of meters to low tens of meters, often within the width of a single seismic event), seismic facies defined by multiple seismic events are unable to describe seismically thin beds. The popular RMS amplitude attribute [2] cannot catch thickness information beyond the dominant frequency, frequently misleading interpreters in a horizontal map view. Consequently, seismic stratigraphy cannot satisfy the increasing demand for high-resolution reservoir prediction for hydrocarbon exploration and development. After decades of extensive exploration and development, most of the more accessible hydrocarbon plays in thick reservoir sequences have been discovered. The remaining hydrocarbon potential primarily lies in thin beds, such as those less than 5 m thick, particularly in non-marine basins in China and elsewhere [3]. In response to the growing need for high-resolution thin-bed mapping in sedimentary basins, seismic sedimentology emerged in the 1990s. [PERSON] [4, 5, 6] pioneered seismic geomorphology in the early 2000s. It aimed to interpret paleo-landforms of depositional systems using horizontal and 3D seismic displays, with a high clarity and resolution unthinkable with seismic stratigraphy. This technology is popular in the industry and has enormous potential for reducing cycle time. However, it still has room for improvement. Without emphasizing the alignment of lithology logs (e.g., gamma ray) to seismic traces, predicting lithology (e.g., sandstone, shale, and carbonates) directly from data beyond geologic models has limited utility. Also, seismic resolution is less optimal in a typical zero-phase seismic data set (an industry standard), hindering the interpretation of very thin reservoirs. Seismic sedimentology could stretch our thin-bed mapping capability further. What is seismic sedimentology? Since [PERSON] et al. [7] used the word for the first time, consensus has evolved. In reservoir geophysics [8], seismic lithology uses seismic attributes to predict lithology types, such as sandstone, shale, carbonates, and evaporates. Together with seismic geomorphology, it can better describe depositional systems and related reservoir distribution patterns in a plane or 3D view. [PERSON] [9] suggests seismic sedimentology as a tool for sedimentary research, aiming to image, interpret, and model the seismic response of layered sedimentary rocks. [PERSON] and [PERSON] [10], [PERSON] et al. [11], and [PERSON] et al. [3] define seismic sedimentology as the seismic investigation of sedimentary rocks and depositional processes by the combined study of seismic lithology and seismic geomorphology, emphasizing the complementary nature of the two. By using the workflow of seismic sedimentology, nowadays, we can routinely predict sedimentary facies and reservoirs at around a 1-5 m resolution [10,12]. The industry is paying significant attention to thin-bedded conventional reservoirs and shale oil formations. In the effort to push for new reserves, high-resolution is the keyword for new tool development. The ongoing discussion about improving seismic resolution is timely, as it focuses on enhancing the prediction of these thin beds. Improving seismic resolution is a broad topic that has to consider various aspects of seismology and geology [13]. These aspects address designing and acquiring 3D surveys, processing them, and interpretation issues. Given the limited scope of this paper, it is impractical to cover all these areas thoroughly. In this study, I will focus on the third aspect: interpretation.