Xinghe Yu

Reservoir Characterization and Modeling: A Look Back to See the Way Forward

As the demand for fossil fuels continues to grow and fields mature, reservoir characterization has become increasingly important. At the same time, the maturation of many of the worlds fields presents new challenges for reservoir characterization. The history of various phases of petroleum geology and reservoir characterization illustrates how these challenges were met in the past, and what new tools and techniques will be emerging in the future. Important past developments include the transition from general petroleum geology to reservoir geology, from disciplinary-focused reservoir description to integrated reservoir characterization, from two-dimensional conceptual mapping of geology to three-dimensional numerical modeling of reservoirs, and from reservoir deterministic analysis to uncertainty analysis. The challenges and perspectives for the future developments in reservoir characterization are also discussed in this chapter.

Sedimentology of a topset-dominated, braided river delta of Huangqihai Lake, North China: implications for formation mechanisms

AbstractnSedimentary characteristics and genesis of a sandy, topset-dominated braided river delta from Huangqihai Lake were investigated using trenching and a ground penetrating radar survey. Ten lithofacies types were identified with assistance of grain size distribution to record a broad range of depositional processes within an overall coarsening upward sequence. Four distinct architectural elements, including channel fill, compound bar, sand sheet, and river mouth bar, built up this delta. No obvious foreset can be identified in this braided river delta. A gentle slope (0.2°) and shallow basin (<10xa0m deep), young age (~25xa0years), and low sediment supply caused by human disturbance and semi-arid climate, are believed to allow this type of topset-dominated delta to form.

Role of sea-level change in deep water deposition along a carbonate shelf margin, Early and Middle Permian, Delaware Basin: Implications for reservoir characterization

Abstract The architecture and sedimentary characteristics of deep water deposition can reflect influences of sea-level change on depositional processes on the shelf edge, slope, and basin floor. Outcrops of the northern slope and basin floor of the Delaware Basin in west Texas are progressively exposed due to canyon incision and road cutting. The outcrops in the Delaware Basin were measured to characterize gravity flow deposits in deep water of the basin. Subsurface data from the East Ford and Red Tank fields in the central and northeastern Delaware Basin were used to study reservoir architectures and properties. Depositional models of deep water gravity flows at different stages of sea-level change were constructed on the basis of outcrop and subsurface data. In the falling-stage system tracts, sandy debris with collapses of reef carbonates are deposited on the slope, and high-density turbidites on the slope toe and basin floor. In the low-stand system tracts, deep water fans that consist of mixed sand/mud facies on the basin floor are comprised of high- to low-density turbidites. In the transgression and high-stand system tracts, channel-levee systems and elongate lobes of mud-rich calciturbidite deposits formed as a result of sea level rise and scarcity of sandy sediment supply. For the reservoir architecture, the fan-like debris and high-density turbidites show high net-to-gross ratio of 62 %, which indicates the sandiest reservoirs for hydrocarbon accumulation. Lobe-like deep water fans with net-to-gross ratio of 57 % facilitate the formation of high quality sandy reservoirs. The channel-levee systems with muddy calciturbidites have low net-to-gross ratio of 30 %.

Research Methods of Sedimentary Facies and Sedimentation

The identification of sedimentary environments and sedimentary facies is based mainly on various facies markers that are determined and obtained from geology, logging, and seismic data. However, data analysis and research cannot be separated from discussions on the formation mechanism of these markers or sedimentation.

Theory and Methods for Studying Clastic Sequence Stratigraphy

Sequence stratigraphy is the scientific study of rock relationships using a repetitive and genetically geochronologic sequence stratigraphic framework, which is demarcated by an erosion surface, a non-sedimentation surface, or a correlative conformity surface. It is a new approach for dividing, contrasting, and analyzing sedimentary strata. When combined with biostratigraphy and tectonic subsidence analysis, it enhances the feasibility of chronostratigraphic correlation, paleogeographic reconstruction, and prediction of petroleum reservoirs, source rock, and seal bed before drilling. The application of sequence stratigraphy to sedimentary strata can potentially provide a complete and unified stratigraphic concept, similar to the complete and unified structure concept for plate tectonics. Moreover, sequence stratigraphy has changed the fundamental principle for stratigraphic record analysis and started a new stage in understanding the history of the Earth. As a result, it triggered a revolution in geology in the 1980s.

Fluvial Depositional System

Rivers are not only the main geological agent for corroding and transforming continental topography and carrying weathered materials to lakes or seas but are also important sedimentary agents in continental areas. Given an appropriate structural environment and sedimentary background, sometimes a fluvial sedimentary stratum with thickness of thousands of meters can develop.

Basic Features of Clastic Reservoirs

Oil and gas reservoirs worldwide are dominated by sedimentogenic clastic rock and carbonate rock strata. Therefore, it is necessary to study the relationships among the various sedimentary environments of petroleum reservoirs, paleogeographic conditions, spatial distribution features of sedimentary systems, and various sedimentary facies belts to build a reservoir depositional model and geological model.

Lacustrine Depositional System

Lakes are low-lying areas that collect running water on land. Currently, the total area of lakes all over the world is approximately 250 × 104 km2, which accounts for 1.8% of the global land area. In China, only 1% of the land area is covered by lake water. Lakes were scattered like stars in China during the Meso-Cenozoic era. More than 10 large oilfields, such as Daqing, Shengli, Liaohe, and Dagang, were found in these lacustrine strata. They constitute a feature of Chinese petroleum geology and occupy a unique place in the global petroleum industry.

Sandy Coast (Shore) and Neritic Depositional System

As we know, the marine environment is quite different from the continent. In addition to physical and chemical conditions, there are great disparities between coastal and submarine deposition conditions and processes. Because submarine environment characteristics are related to seawater depth, the sea area can be divided by seawater depth into four zones, shore (coast), shallow sea, semi-deep sea, and deep sea. The continental shelf (also called shelf), continental slope, continental rise (also called continental apron), and ocean floor (also called abyssal plain) can be divided by the geomorphic features of the continental margin. Shelf break is the turning point (or zone) of the continental shelf and continental slope.

Deep-Water Depositional System

As global petroleum exploration constantly goes deeper underground, exploration based on architecture has matured, and all architectures that can be found have been explored in petroliferous basins with relatively high degrees of exploration. Thus, in the future, exploration should focus on looking for lithostratigraphic reservoirs. The presence of a bathymetric or lowstand fan is the main condition for the formation of stratigraphic traps. As a result, studying deep-water depositional systems, particularly deep-water gravity flow depositional systems, is very important. One of the main scientific challenges in the 21st century is understanding resource formation and exploration mechanisms in deep water (sea).