Study on identification method of gas-bearing carbonate reservoirs based on joint acoustic-resistivity experiments – an example from the Sichuan Basin of China

2020 ◽  
pp. 1-9
Author(s):  
Haitao Li ◽  
Shaogui Deng ◽  
Yuexiang Wang ◽  
Xuquan He
Keyword(s):  
Sichuan Basin ◽  
Carbonate Reservoirs ◽  
Identification Method ◽  
The Sichuan Basin ◽  
Gas Bearing

scholarly journals Classification of Void Space Types in Fractured-Vuggy Carbonate Reservoir Using Geophysical Logging: A Case Study on the Sinian Dengying Formation of the Sichuan Basin, Southwest China

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5087
Author(s):  
Kunyu Wang ◽  
Juan Teng ◽  
Hucheng Deng ◽  
Meiyan Fu ◽  
Hongjiang Lu
Keyword(s):  
Sichuan Basin ◽  
Southwest China ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Void Space ◽  
Identification Method ◽  
Geophysical Logging ◽  
Dengying Formation ◽  
Porosity And Permeability ◽  
Core Description

The fractured-vuggy carbonate reservoirs display strong heterogeneity and need to be classified into different types for specific characterization. In this study, a total of 134 cores from six drilled wells and six outcrops of the Deng #2 and Deng #4 members of the Dengying Formation (Sichuan Basin, Southwest China) were selected to investigate the petrographic characteristics of void spaces in the fractured-vuggy carbonate reservoirs. Four void space types (VSTs) were observed, namely the solution-filling type (SFT), cement-reducing type (CRT), solution-filling breccia type (SFBT) and solution-enlarging fractures and vugs type (SEFVT). The CRT void spaces presented the largest porosity and permeability, followed by the SEFVT, SFBT and SFT. The VSTs presented various logging responses and values, and based on these, an identification method of VSTs using Bayes discriminant analysis (BDA) was proposed. Two test wells were employed for the validation of the identification method, and the results show that there is good agreement between the identification results and core description. The vertical distribution of VSTs indicates that the SFT and SEFVT are well distributed in both the Deng #2 and Deng #4 members. The CRT is mainly found in the Deng #2 member, and the SFBT occurs in the top and middle of the Deng #4 member.

scholarly journals Logging identification method of depositional facies in Sinian Dengying Formation of the Sichuan Basin

2021 ◽  
Author(s):  
Qingfu Feng ◽  
Yuxiang Xiao ◽  
Xiulin Hous ◽  
Hongkui Chen ◽  
Zecheng Wang ◽  
...  
Keyword(s):  
Sichuan Basin ◽  
Depositional Facies ◽  
Identification Method ◽  
Dengying Formation ◽  
The Sichuan Basin

Fluid Identification Derived from Non-Electric Measurements and Reservoir Characterization of Tight Carbonate in Sichuan Basin, China

2021 ◽  
Author(s):  
Zuo AN Zhao ◽  
Yue Wang ◽  
Qiang Lai ◽  
Kai Xuan Li ◽  
Xian Ran Zhao ◽  
...  
Keyword(s):  
Sichuan Basin ◽  
Reservoir Characterization ◽  
Water Saturation ◽  
Carbonate Reservoirs ◽  
Free Fluid ◽  
Formation Water ◽  
Fluid Identification ◽  
Fluid Saturation ◽  
Tight Carbonate ◽  
The Sichuan Basin

Abstract Natural gas production in the Sichuan Basin reached 30 billion m3 in 2020, but the gap between this and the production goal of 50 billion m3 in 2025 requires further exploration. The complex mineralogy and low porosity in tight carbonate reservoirs lower the accuracy of formation water saturation calculation from Archie's equation, which brings uncertainties to the reservoir characterization. It is, therefore, necessary to incorporate other methods as supplements to methods based on resistivities. This paper outlines a method that incorporates wireline induced gamma spectroscopy, nuclear magnetic resonance (NMR), array dielectric, and borehole images. Spectroscopy is not only utilized to estimate the mineralogy of the reservoir, but it also provides non-electric measurements, such as chlorine concentration and thermal neutron capture cross-section (sigma). The amount of chlorine in the formation is proportional to the water volume in the reservoir, thus formation water saturation. Sigma is also an indicator of the formation water saturation. It enables formation water saturation calculation without resistivities. Case studies are presented from carbonate reservoirs in the Sichuan Basin, China. A robust and comprehensive petrophysical description of mineralogy, porosity, pore geometry, free fluid volume, rock type, and formation water saturation is presented. Calculation of formation water saturation from chlorine and sigma proves to be successful in both water-based mud and oil-based mud environments. The depth of investigation (DOI) of chlorine from spectroscopy is about 8 to 10 in. for 90% of the signal. The various DOI of different measurements must be considered when performing the fluid identification. Bound fluid saturation could reach more than 50% in tight carbonate reservoirs. Formation water saturation is not the only factor that determines the fluid type. Free fluid saturation from NMR must be incorporated. Finally, a robust methodology integrating formation water saturation derived from dielectric and spectroscopy, and free fluid saturation derived from NMR shows great advantage in fluid identification in tight carbonate reservoirs. This paper discusses a novel combination of wireline logging tools for the fluid identification of tight carbonate reservoir in Sichuan Basin. It lowers the uncertainty in the estimation of formation water saturation when application of resistivities is limited in oil-based mud environments. The gas zones identified by the new method have promising gas productions. The workflow can also be applied to other tight carbonate plays in China.

scholarly journals Pore Preservation and Failure Mechanism of Sinian Dengying Formation Carbonate Reservoirs: A Case Study of Two Ultradeep Wells in the Sichuan Basin, Western China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Zeqi Li ◽  
Wei Sun ◽  
Shugen Liu ◽  
Zhiwu Li ◽  
Bin Deng ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Sichuan Basin ◽  
Pressure Coefficient ◽  
Carbonate Reservoirs ◽  
Western China ◽  
Dengying Formation ◽  
Contraction Joints ◽  
Average Porosity ◽  
The Sichuan Basin ◽  
Gas Fields

Despite being one of the most important factors in deep oil and gas exploration, the preservation mechanisms of ultradeep carbonate reservoirs remain poorly understood. This study performed thin-section, geochemistry, field emission scanning electron microscopy, fluid inclusion, and basin model analysis of samples from two boreholes over 8,000 m deep in the Sichuan Basin to determine the pore features and preservation mechanism of the Sinian (Ediacaran) Dengying Formation carbonate reservoirs. The reservoir of CS well #1 is characterised by pore diameters larger than a centimetre (average porosity 7.48%; permeability 0.8562 mD), and the pores are mainly filled with dolomite or bitumen. In contrast, the reservoir of MS well #1 is predominantly composed of micron-scale residual pores (average porosity 1.74%; permeability 0.0072 mD), and the pores are typically filled with dolomite, bitumen, and multistage quartz. The burial thermal histories suggest that both reservoirs were subjected to high pressure (i.e., pressure   coefficient > 1.5 ) before the Late Cretaceous. However, the pressure coefficient of the reservoir of MS well #1 has decreased to less than 1.0 owing to strong structural adjustment this well since the Late Cretaceous, which allowed other ore-forming fluids to enter and fill the pores, resulting in further compaction of the pores. In contrast, the pressure coefficient of CS well #1 is 1.1–1.2, which effectively prevented other ore-forming fluids from entering and filling the pores. The findings show that the dynamic adjustment of the Dengying Formation palaeo-gas reservoir indirectly affects the preservation or failure of the reservoir. The occurrence and geometry of bitumen in the Dengying reservoir exhibit good consistency with the pressure changes in both boreholes. In particular, bitumen with an annular shape and contraction joints in reservoir pores is widespread in CS well #1, which is attributed to the continuous preservation of palaeo-gas fields. Conversely, bitumen with a broken particle shape is located among the epigenetic minerals widespread in MS well #1, which is attributed to failure and depletion of the palaeo-gas fields.

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