A study of petrophysical properties based on digital core technology: A case study of a porous carbonate reservoir in the overseas J Oilfield
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摘要:
走向海外是解决我国能源安全问题的必由之路。但海外油气藏评价往往缺乏第一手岩心资料, 使得储层孔隙结构和渗流规律认识不清, 影响评价效果。以海外J油田孔隙型碳酸盐岩油藏为例, 应用数字岩心技术开展油气藏孔渗特征研究。①以不同流动单元的铸体薄片图像作为输入数据, 经过中值滤波和阈值分割预处理后, 基于马尔科夫链蒙特卡洛数值重构算法构建数字岩心; ②分析孔喉分布、孔喉连通性、孔隙度特征; ③基于格子玻尔兹曼模拟方法开展单相和油水两相流动模拟, 计算数字岩心的绝对渗透率和相对渗透率曲线。结果表明, 构建的三维数字岩心能够刻画不同流动单元孔隙型碳酸盐岩的孔喉半径分布及孔喉连通程度的差异化特征。数字岩心孔隙度与铸体薄片孔隙度吻合度高, 数字岩心渗透率与真实岩心渗透率存在较好的正相关关系, 且符合真实岩心所属的流动单元。油水两相稳态流动模拟计算的相对渗透率曲线体现了不同流动单元的两相渗流能力差异, 可作为数值模拟输入条件, 以及估算油藏采收率。数字岩心分析与物理实验结果吻合良好, 证明了该方法的可靠性。为岩心资料稀缺条件下油气藏表征和渗流特征分析提供新的思路, 对油气藏精细描述具有重要的参考价值。
Abstract:Developing overseas petroleum exploration and production businesses is a necessary way to guarantee the energy security in China. However, in evaluating overseas reservoirs or designing development plans, due to lack of the first-hand data, the pore structures and seepage mechanisms cannot be well understood and the evaluation effects are influenced. In this study, with the porous carbonate reservoir of the overseas J Oilfield as a case study, the digital core technology is proposed to analyze the pore structure and seepage mechanism. ①With the thin section images of different flow units as the input data, after preprocessing of the medium filtering and threshold segmentation, the digital cores are reconstructed based on the Markov Chain Monte Carlo numerical reconstruction algorithm. ②The bore throat distribution, pore throat connectivity and porosity of the digital cores are analyzed. ③The lattice Boltzmann method is adopted to perform a single phase and two phase oil-water flow simulation in the digital cores, and the absolute permeability and relative permeability curves are calculated based on the simulation results. The reconstructed three-dimensional digital core can describe the differential characteristics of the pore throat radius distribution and pore throat connectivity of porous carbonate rocks in different flow units. The digital core porosity is highly consistent with the porosity of thin section images, and the digital core permeability shows a good positive correlation with the core permeability, thus conforming to the flow unit of the real core. The relative permeability curves of oil-water two-phase flow simulation show differences in the two-phase seepage capacity of different flow units, which can be used as the input of numerical simulation and the estimation of reservoir recovery. The results of digital core analysis are consistent with the results of physical experiments, thus verifying the reliability of the digital core analysis technique. This study provides a new strategy for reservoir evaluation and seepage study in case of data insufficiency and is valuable for reservoir description and effective development.
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Key words:
- porous carbonate reservoir /
- digital core /
- pore structure /
- rock physics
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图 1 研究区典型样品铸体薄片图像(蓝色表示孔隙)
Figure 1. Typical thin section images of target rock samples
图 2 薄片分析孔隙度与岩心实测孔隙度交会图
Figure 2. Crossplot of thin section porosity and actual core porosity
图 3 铸体薄片图像二值化分割处理
Figure 3. Binarized segmentation processing procedure of the thin section images
图 4 MCMC算法邻域系统分解示意图(i, j, k表示x, y, z方向的网格坐标)
Figure 4. Schematic diagram of neighborhood segmentation in the MCMC algorithm
图 5 重构的数字岩心三维结构和切片图
Figure 5. Three-dimensional structure and slices chart of the reconstructed digital core
图 10 不同流动单元的油水两相相对渗透率曲线
Figure 10. Oil-water two-phase relative permeability curves of different flow units
表 1 铸体薄片的基本参数
Table 1. Fundamental parameters of selected thin section images
序号 深度/m 流动单元 孔隙度/% 渗透率/10-3 μm2 水平像素数 垂直像素数 图像分辨率/mm 1 5 126 Ⅰ 16.7 432 868 650 0.025 2 5 230 Ⅰ 17.7 830 994 745 0.011 3 5 310 Ⅰ 25.1 3 620 870 652 0.025 4 5 311 Ⅰ 10.9 2 440 1 123 838 0.019 5 5 409 Ⅰ 21.5 3 330 850 636 0.025 6 5 132 Ⅱ 19.1 85.5 868 650 0.013 7 5 162 Ⅱ 14.1 19.0 868 650 0.025 8 5 164 Ⅱ 14.8 32.9 868 650 0.013 9 5 309 Ⅱ 23.4 852 870 652 0.025 10 5 322 Ⅱ 21.3 572 990 739 0.006 11 5 351 Ⅱ 21.8 917 870 652 0.025 12 5 360 Ⅱ 26.4 260 870 652 0.025 13 5 363 Ⅱ 20.2 360 870 652 0.025 14 5 285 Ⅲ 13.3 4.53 850 636 0.025 15 5 306 Ⅲ 14.1 5.35 870 652 0.013 16 5 316 Ⅲ 14.8 2.09 941 702 0.006 
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