Review of diagenetic facies in tight sandstones: Diagenesis, diagenetic minerals, and prediction via well logs

An integrated analysis of the petrographic characteristics and types and distribution of diagenetic alteration in the upper Paleozoic Benxi–Taiyuan, Shanxi, and Xiashihezi Formations provides insights into the controlling factors on variations in porosity and permeability in tight sandstones (85% of the sandstone samples display porosity values <10% and 90% of the samples exhibit permeability <1 md). Diagenetic alteration includes mesogenetic compaction, cementation by dolomite, ankerite, and quartz, dissolution of feldspar, and illitization of smectite. Eodiagenesis includes compaction, development of smectite, cementation by pore-filling quartz and disordered kaolinite, and precipitation of calcite and Fe-calcite. Chlorite and quartz preserve primary pores against damage, whereas kaolinite, illite–smectite (I/S) mixed layer, and illite significantly diminish reservoir quality via permeability reduction. Chlorite and I/S content decrease abruptly as depth increases, whereas the kaolinite content remains elevated at depth because of the complete destruction of K-feldspar. The transformation from smectite to illite provides silica ions for the widely distributed quartz overgrowths. As the depositional environment transformed from fluvial (Xiashihezi) to deltaic (Shanxi) and to epicontinental (Taiyuan and Benxi), the dissolution effect increased monotonically. Feldspar dissolution is dominant in the Shanxi Formation, whereas the Benxi and Taiyuan Formations commonly contain quartz dissolution pores. The Taiyuan Formation has markedly higher porosities than in the overlying and underlying formations, caused by strong dissolution and high silica content. The decrease in porosity in the Benxi Formation results from the extensive formation of clay minerals caused by high frequency transgressions in a transitional environment.

Diagenetic sequences of continuously deposited tight sandstones in various environments: A case study from upper Paleozoic sandstones in the Linxing area, eastern Ordos basin, China

Analyzing the effects of multi-scale pore systems on reservoir Properties—A case study on Xihu Depression, East China Sea Shelf Basin, China

Process-based and dynamic 2D modeling of shale samples: Considering the geology and pore-system evolution

Sedimentological and diagenetic control on the reservoir quality of deep-lacustrine sedimentary gravity flow sand reservoirs of the Upper Triassic Yanchang Formation in Southern Ordos Basin, China

Diagenetic history and reservoir quality of tight sandstones: A case study from Shiqianfeng sandstones in upper Permian of Dongpu Depression, Bohai Bay Basin, eastern China

The Es1 sandstone is a fruitful hydrocarbon zone of Eocene Shahejie Formation. Therefore, the present study comprises the subsurface facies analysis established on the description of seven wells. Methods include core observation, thin section petrography, scanning electron microscope (SEM), cathodoluminescence (CL), and X-ray diffraction to evaluate the microfacies, lithofacies, and rock characteristics. Two microfacies of lithofacies have been established as sandstone microfacies and mudstone microfacies on the basis of grain size. Among them, sandstone is further divided into four sub-microfacies on the basis of microscopic studies, rock fragments and mineral composition, which are arkose sandstone, lithic arkose, feldspathic litharenite, and litharenite. These microfacies consisting quartz, feldspar as abundant detrital grains followed by rock fragments and micas, whereas calcite, ferro-calcite, quartz overgrowth, and clay are the main cement. The Es1 sandstone consists of good primary porosity and permeability as well as good secondary porosity caused by fracturing and dissolution of unstable minerals that enhance the reservoir quality. Whereas cementation and compaction reduce the reservoir characteristics. Studied formation divided into five lithofacies including conglomerate sandstone lithofacies, medium to coarse-grain sandstone lithofacies, fine sandstone lithofacies, siltstone lithofacies, and mudstone lithofacies. Core observation, sedimentary structures, facies sequences of the well log, and sedimentary composition reveal that Es1 deposited into the lacustrine delta fan depositional environment. Rock grain size indicates that Es1 contains mixtures of grains including pebbles, sand-size as well as minor silt and clay size. Grain size varies from conglomerate to clay size. The Es1 sandstone was deposited in braided river (conglomerates sandstone), channel bar, lacustrine, fluvial channel (massive bedding, cross-bedding, and graded bedding sandstone), deltaic, and flood-plain (siltstone and mudstone) sedimentary environment. It is concluded that higher transport energies in channels deposited coarse-grain sediments in shallowest part of the lake setting. However, the energy decreases towards greater depth which deposited mudstone in central part of the lake.

Kamran Shehzad

Papers

Diagenetic history and reservoir quality of tight sandstones: A case study from Shiqianfeng sandstones in upper Permian of Dongpu Depression, Bohai Bay Basin, eastern China

Sedimentology of Shahejie Formation, Bohai Bay Basin: a case study of E s 1 member in Nanpu Sag