Clay mineral content, type, and their effects on pore throat structure and reservoir properties: Insight from the Permian tight sandstones in the Hangjinqi area, north Ordos Basin, China

2020 ◽  
Vol 115 ◽  
pp. 104281 ◽  
Author(s):  
Ren Wang ◽  
Wanzhong Shi ◽  
Xiangyang Xie ◽  
Wei Zhang ◽  
Shuo Qin ◽  
...  
Keyword(s):  
Clay Mineral ◽  
Mineral Content ◽  
Ordos Basin ◽  
Pore Throat ◽  
Reservoir Properties ◽  
Content Type ◽  
Area North

Pore types, pore-network analysis, and pore quantification of the lacustrine shale-hydrocarbon system in the Late Triassic Yanchang Formation in the southeastern Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF63-SF79 ◽  
Author(s):  
Robert G. Loucks ◽  
Stephen C. Ruppel ◽  
Xiangzeng Wang ◽  
Lucy Ko ◽  
Sheng Peng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Mineral Content ◽  
Ordos Basin ◽  
Pore Network ◽  
Black Shales ◽  
Late Triassic ◽  
Ductile Material ◽  
Crushed Rock ◽  
Porosity And Permeability

Continental Upper Triassic Yanchang “black shales” in the southeastern Ordos Basin have been proven to be unconventional gas reservoirs. Organic-matter-lean and organic-matter-rich argillaceous mudstones form reservoirs that were deposited in a deeper water lacustrine setting during lake highstands. In the stratified lake, the bottom waters were dysaerobic to anoxic. This low-energy and low-oxygen lake-bottom setting allowed types II and III organic matter to accumulate. Interbedded with the argillaceous mudstones are argillaceous arkosic siltstones deposited by gravity-flow processes. Rock samples from the Yanchang Chang 7–9 members are very immature mineralogically. Mineral grains are predominantly composed of relatively equal portions of quartz and feldspar. The high clay-mineral content, generally greater than 40%, has promoted extensive compaction of the sediments, permitting the ductile material to deform and occlude interparticle pores. Furthermore, this high clay-mineral content does not favor hydraulic fracturing of the mudstone reservoir. The pore network within the mudstones is dominated by intraparticle pores and a lesser abundance of organic-matter pores. Interparticle pores are rare. The mean Gas Research Institute (GRI) crushed-rock porosity is 4.2%. Because the pore network is dominated by poorly connected intraparticle pores, permeability is very low (the GRI-calculated geometric mean permeability = 9.9 nd). The dominance of intraparticle pores creates a very poor correlation between GRI porosity and GRI permeability. Several methods of porosity analysis (GRI crushed rock, nitrogen adsorption, and point count) were conducted on each samples, and the results were compared. There is no significant correlation between the three methods, implying that each method measures different pore sizes or types. There is also no relationship between the porosity and permeability and total organic carbon. Much of the mature (peak oil window) organic matter is nonporous, suggesting that it is of type III. Most of the organic-matter pores are in migrated solid bitumen. Overall, the samples analyzed have low porosity and permeability for mudrocks.

Characteristics of Chang 7 shale gas in the Triassic Yanchang Formation, Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF31-SF39 ◽  
Author(s):  
Xiangzeng Wang
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Shale Gas ◽  
Mineral Content ◽  
Ordos Basin ◽  
Central China ◽  
Late Triassic ◽  
Yanchang Formation ◽  
Geochemical Parameters ◽  
Porosity And Permeability

The Yanchang Formation in the Ordos Basin in North Central China represents a large, long-lived lacustrine system of the late Triassic Period. The extensive shales within this system provide hydrocarbons (HCs) for conventional and unconventional oil and gas reservoirs. In the formation, the Chang 7 shale is the thickest shale with the best geochemical parameters, and it is the main source rock in this area. In recent years, the discovery of shale gas in the Chang 7 shale has promoted the exploration and development of lacustrine shale gas in China. We have estimated the shale gas resource potential based on the analysis of the geologic conditions of the Chang 7 shale. The average thickness of the Chang 7 shale reaches 42.6 m, and the main organic matter types are types [Formula: see text] and [Formula: see text]. The average content of organic carbon is more than 3%, and the average HC potential is [Formula: see text]. However, the thermal maturity of the Chang 7 shale is low with a vitrinite reflectance [Formula: see text] ranging from 0.83% to 1.10%. The Chang 7 shale lithology consists of shale and sandy laminations or thin sandstones. The shale is characterized by high clay mineral content and poor porosity and permeability, with an average porosity of 1.8% and an average permeability of [Formula: see text]. The sandy laminations or thin sandstones are characterized by relatively higher brittle mineral content, relatively lower clay mineral content, and higher porosity and permeability. The pores of the Chang 7 shale include primary intergranular and intragranular pores, secondary intragranular and intragranular dissolved pores, fracture pores, and organic-matter-hosted pores. The proportion of adsorbed gas, free gas, and dissolved gas is approximately 52%, 37%, and 11%, respectively, and the shale gas resources of the Chang 7 shale are [Formula: see text].

Depositional Environment Drive as Overpressure Generation: Study Case in “Gap” Field, North West Java Basin

2020 ◽  
Author(s):  
A., C. Prasetyo
Keyword(s):  
Clay Mineral ◽  
Depositional Environment ◽  
Mineral Content ◽  
Hydrocarbon Generation ◽  
Well Test ◽  
Burial History ◽  
The South ◽  
North West ◽  
The North ◽  
Geological Processes

Overpressure existence represents a geological hazard; therefore, an accurate pore pressure prediction is critical for well planning and drilling procedures, etc. Overpressure is a geological phenomenon usually generated by two mechanisms, loading (disequilibrium compaction) and unloading mechanisms (diagenesis and hydrocarbon generation) and they are all geological processes. This research was conducted based on analytical and descriptive methods integrated with well data including wireline log, laboratory test and well test data. This research was conducted based on quantitative estimate of pore pressures using the Eaton Method. The stages are determining shale intervals with GR logs, calculating vertical stress/overburden stress values, determining normal compaction trends, making cross plots of sonic logs against density logs, calculating geothermal gradients, analyzing hydrocarbon maturity, and calculating sedimentation rates with burial history. The research conducted an analysis method on the distribution of clay mineral composition to determine depositional environment and its relationship to overpressure. The wells include GAP-01, GAP-02, GAP-03, and GAP-04 which has an overpressure zone range at depth 8501-10988 ft. The pressure value within the 4 wells has a range between 4358-7451 Psi. Overpressure mechanism in the GAP field is caused by non-loading mechanism (clay mineral diagenesis and hydrocarbon maturation). Overpressure distribution is controlled by its stratigraphy. Therefore, it is possible overpressure is spread quite broadly, especially in the low morphology of the “GAP” Field. This relates to the delta depositional environment with thick shale. Based on clay minerals distribution, the northern part (GAP 02 & 03) has more clay mineral content compared to the south and this can be interpreted increasingly towards sea (low energy regime) and facies turned into pro-delta. Overpressure might be found shallower in the north than the south due to higher clay mineral content present to the north.

scholarly journals A reservoir quality evaluation approach for tight sandstone reservoirs based on the gray correlation algorithm: A case study of the Chang 6 layer in the W area of the as oilfield, Ordos Basin

2021 ◽  
pp. 014459872199851
Author(s):  
Yuyang Liu ◽  
Xiaowei Zhang ◽  
Junfeng Shi ◽  
Wei Guo ◽  
Lixia Kang ◽  
...  
Keyword(s):  
Quality Evaluation ◽  
Comprehensive Evaluation ◽  
Ordos Basin ◽  
Reservoir Quality ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Evaluation Approach ◽  
Correlation Algorithm ◽  
Gray Correlation ◽  
Sandstone Reservoir

As an important type of unconventional hydrocarbon, tight sandstone oil has great present and future resource potential. Reservoir quality evaluation is the basis of tight sandstone oil development. A comprehensive evaluation approach based on the gray correlation algorithm is established to effectively assess tight sandstone reservoir quality. Seven tight sandstone samples from the Chang 6 reservoir in the W area of the AS oilfield in the Ordos Basin are employed. First, the petrological and physical characteristics of the study area reservoir are briefly discussed through thin section observations, electron microscopy analysis, core physical property tests, and whole-rock and clay mineral content experiments. Second, the pore type, throat type and pore and throat combination characteristics are described from casting thin sections and scanning electron microscopy. Third, high-pressure mercury injection and nitrogen adsorption experiments are optimized to evaluate the characteristic parameters of pore throat distribution, micro- and nanopore throat frequency, permeability contribution and volume continuous distribution characteristics to quantitatively characterize the reservoir micro- and nanopores and throats. Then, the effective pore throat frequency specific gravity parameter of movable oil and the irreducible oil pore throat volume specific gravity parameter are introduced and combined with the reservoir physical properties, multipoint Brunauer-Emmett-Teller (BET) specific surface area, displacement pressure, maximum mercury saturation and mercury withdrawal efficiency parameters as the basic parameters for evaluation of tight sandstone reservoir quality. Finally, the weight coefficient of each parameter is calculated by the gray correlation method, and a reservoir comprehensive evaluation indicator (RCEI) is designed. The results show that the study area is dominated by types II and III tight sandstone reservoirs. In addition, the research method in this paper can be further extended to the evaluation of shale gas and other unconventional reservoirs after appropriate modification.

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