Effect of Acid Fluid on Deep Eocene Sweet Spot Reservoir of Steep Slope Zone in Lufeng Sag, Pearl River Mouth Basin, South China Sea
Abstract
:1. Introduction
2. Geological Setting
3. Data and Methods
3.1. Data and Samples
3.2. Methods
4. Results
4.1. Characteristics of Eocene Reservoir in Steep Slope Zone of Lufeng Sag
4.2. The Influence of Diagenesis on Reservoir Petrophysical Properties
4.3. Development Mechanism and Distribution Characteristics of Sweet Spot Reservoir
4.3.1. Controlling Factors of Reservoir’s Petrophysical Property
4.3.2. Prediction of High-Quality Dissolved Reservoir in Steep Slope Zone
5. Discussion
5.1. Effect of Organic-Inorganic Acid Fluid on Sweet Spot Reservoir
5.2. Prediction of Eocene Favorable Area of Steep Slope Zone in Lufeng Sag
6. Conclusions
- (1)
- Parent rock type and transport distance, parent rock properties, tuffaceous content, sand body connectivity, diagenetic fluid retention, and single-sand body thickness jointly control reservoir-development characteristics in the steep slope zone of the Lufeng Sag in the Pearl River Mouth Basin. Although the compaction background is generally developed in the Paleogene of Lufeng Sag, continuous transformation and effective discharge of acidic fluid is an important controlling factor for developing secondary dissolution pore zones in high-quality reservoir segments.
- (2)
- Through the analysis of 1140 thin sections from 57 depth points, five types of diagenesis are identified in the Lufeng Sag. Combined with the control factors of the secondary dissolution pore-development zone and the vertical and plane distribution characteristics of diagenetic facies in the steep slope zone of Lufeng Sag, it is finally determined that the front edge of the fan delta, the front of the thin layer, and the near margin of the thick layer of the braided river delta are favourable zones for the development of the high-quality sweet-spot reservoir.
- (3)
- The oil and gas charging time of the Wenchang–Enping Formation in the steep slope zone of the Lufeng Depression is relatively late, and only the first phase of 5-0 ma oil and gas charging has been found. However, the CO2 charging time in the steep slope zone is earlier, mainly between 35–40 MA. As a result, the reservoir has been modified by an inorganic-organic acidic fluid before oil and gas charging. According to the analysis of the critical moments of hydrocarbon accumulation and the dominant sedimentary facies zones, it is concluded that the fan delta front of well LF X-D and the deep layer of LF Y may have better conditions for hydrocarbon accumulation and preservation, which is a favourable area for the development of the steep slope zone in the Lufeng Depression.
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Stratum | Areal Porosity (%) | |||||||
---|---|---|---|---|---|---|---|---|
Interparticle Pore | Intergranular Dissolved Pore | Intragranular Dissolved Pore | Intercrystal Pore | Moldic Pore | Fracture | Total Dissolved Pore | Total Pore | |
Wen-5 and 6 Member | 2.21 | 0 | 1.14 | 2.14 | 1.36 | 0.07 | 4.64 | 6.92 |
Wen-4 Member | 4.78 | 0 | 0.75 | 1.7 | 0.9 | 0 | 3.35 | 8.13 |
Wen-3 Member | 7.5 | 0 | 0.25 | 0.5 | 1 | 0 | 1.75 | 9.25 |
Wen-1 and 2 Member | 0 | 0 | 4 | 0 | 3 | 0 | 7 | 7 |
En-4 Member | 1.96 | 0.27 | 1.19 | 2.42 | 1.27 | 0 | 5.15 | 7.11 |
En-3 Member | 2.56 | 1.08 | 1.33 | 2.34 | 0.13 | 0 | 4.88 | 7.44 |
En-1 and 2 Member | 3.82 | 0.31 | 0.93 | 2.06 | 0.25 | 0 | 3.55 | 7.37 |
Enping Formation and Wenchang Formation | Average Porosity/% | Mean Permeability/mD |
---|---|---|
Braided river delta (n = 5) | 16 | 31.3 |
Fan delta (n = 15) | 6.9 | 0.33 |
Braided river delta plain | / | / |
Braided river delta front (n = 5) | 16 | 31.3 |
Fan delta plain (n = 14) | 6.5 | 0.2 |
Fan delta front (n = 1) | 13.1 | 2.23 |
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Zhong, K.; Bian, L.; Zhao, S.; Feng, K. Effect of Acid Fluid on Deep Eocene Sweet Spot Reservoir of Steep Slope Zone in Lufeng Sag, Pearl River Mouth Basin, South China Sea. Processes 2024, 12, 895. https://doi.org/10.3390/pr12050895
Zhong K, Bian L, Zhao S, Feng K. Effect of Acid Fluid on Deep Eocene Sweet Spot Reservoir of Steep Slope Zone in Lufeng Sag, Pearl River Mouth Basin, South China Sea. Processes. 2024; 12(5):895. https://doi.org/10.3390/pr12050895
Chicago/Turabian StyleZhong, Kai, Lihao Bian, Shijie Zhao, and Kailong Feng. 2024. "Effect of Acid Fluid on Deep Eocene Sweet Spot Reservoir of Steep Slope Zone in Lufeng Sag, Pearl River Mouth Basin, South China Sea" Processes 12, no. 5: 895. https://doi.org/10.3390/pr12050895