Diagenetic Evolution and Formation Mechanisms of High-Quality Reservoirs under Multiple Diagenetic Environmental Constraints: An Example from the Paleogene Beach-Bar Sandstone Reservoirs in the Dongying Depression, Bohai Bay Basin

Abstract

The diagenetic environment, diagenetic responses, diagenetic transformation model and formation mechanisms of high‐quality reservoirs (beach‐bar sandstones of the Paleogene fourth member) in the Dongying depression were studied through the analysis of fluid inclusions, thin section and burial evolution history. The diagenetic fluids of the beach‐bar sandstone reservoirs evolved from early high salinity and weak alkalinity to low salinity and strong acidity, late high salinity and strong alkalinity and late low salinity and acidity, which were accompanied by two stages of oil and gas filling. The fluids at the margins of the sandbodies were continuously highly saline and strongly alkaline. The western (eastern) reservoirs experienced early open (closed), middle open, and late closed diagenetic environments during their burial history. The flow pattern was characterized by upwelling during the majority of the diagenesis (in the east, a non‐circulating pattern transitioned into an upwelling current). Due to the evolution of the diagenetic fluids, the diagenetic sequence of the beach‐bar reservoirs was as follows: early weak carbonate cementation; feldspar and carbonate cement dissolution and authigenic quartz cementation; late carbonate and anhydrite cementation, authigenic feldspar cementation, and late quartz dissolution; and late carbonate cementation, feldspar dissolution, and authigenic quartz cementation. The diagenetic strength during these stages varied or was absent altogether in different parts of the reservoirs. Due to the closeness of the diagenetic environment and the flow pattern of the diagenetic fluids, the diagenetic products are variably distributed in the sandstones interbedded with mudstones and in the fault blocks. The evolution of multiple alternating alkaline and acidic diagenetic environments controlled the distribution patterns of the reservoir diagenesis and reservoir space, and the reservoir quality index, RQI, increased gradually from the margins to the centers of the sandstones. The closeness of the diagenetic environment and the flow patterns of the diagenetic fluids controlled the differences in the reservoir properties among the fault blocks. With increasing distance from the oil‐source faults, the RQI values in the west gradually decreased and in the east initially increased and then decreased.

Tight Carbonate Microstructure and its Controls: A Case Study of Lower Jurassic Da'anzhai Member, Central Sichuan Basin

“…Sedimentary environment has a great impact on reservoir properties Feng et al, 2015;Guo et al, 2015;Rupprecht et al et al, 2017;Wang et al, 2017). Most high-yield wells targeting the Lower Jurassic Da'anzhai Member in central Sichuan Basin were drilled at high-energy shell beaches (Fig.…”

Study on the Mathematical Model and Propagation Characteristics of AE Waveform Signals during Rock Fracture

“…As a typical multiphase composite geological body, rocks are nonuniform, anisotropic, and viscous under the comprehensive action of materials (particles), structure (coupling between particles, diagenetic environment, and transformation), and boundary conditions (stress, temperature, water, and the free boundary) [1][2][3]. As the fracture of engineering rock mass becomes increasingly complex, the problem of the inaccurate prediction of failure precursors has become increasingly prominent.…”

“…Assuming that the incident SH-wave propagates from the fracture source A(x A , y A ) to the rock boundary 2 , and the velocity the of incident SH-wave and the reflected SH-wave is v SH .…”

“…Suppose that the incident SH-wave propagates from the fracture source/AE source point A (x A , y A ) to the mineral boundary 2 , and the refracted SH-wave propagates from point O to point C(x C , y C ) over distance 2 . en, the total loss of energy is…”

Porosity evolution of high-quality reservoirs in deep Palaeogene lacustrine carbonate rocks in the central Bohai Sea

“…Carbonate rock reservoirs are important targets for petroleum exploration and development. Since the late 1990s, breakthroughs have been made in the field of deep carbonate rock reservoirs in China (Ma et al, 2005; Wang et al, 2013a; Wu et al, 2007; Zhang, 1999; Zhang and Yan, 2007; Zhao et al, 2014), mainly in marine carbonate rock reservoirs. However, in the field of lacustrine carbonate rock reservoirs, few breakthroughs have been made, though relevant research work began in the mid-1980s in China (Yan et al, 2014).…”