Earth Science Frontiers ›› 2025, Vol. 32 ›› Issue (2): 311-331.DOI: 10.13745/j.esf.sf.2024.5.31

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Structure analysis and intelligent prediction of carbonate fractured-vuggy reservoirs in ultra-deep fracture zone

LI Fenglei1,2,3,4(), LIN Chengyan1,2,3,*(), WANG Jiao4, REN Lihua1,2,3, ZHANG Guoyin1,2,3, ZHU Yongfeng5, LI Shiyin5, ZHANG Yintao5, GUAN Baozhu5   

  1. 1. State Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China
    2. Shandong Key Laboratory of Oil Reservoir Geology, Qingdao 266580, China
    3. School of Geosciences, China University of Petroleum (East China), Qingdao 266580, China
    4. Shandong Institute of Petroleum and Chemical Technology, Dongying 257061, China
    5. Research Institute of Petroleum Exploration and Development,Tarim Oilfield Company, PetroChina, Korla 841000, China
  • Received:2024-01-05 Revised:2024-04-10 Online:2025-03-25 Published:2025-03-25

Abstract:

Ultra-deep carbonate fractured-vuggy reservoirs, typically located near fault zones, are characterized by significant burial depth, large vertical extent, and narrow horizontal distribution, making seismic identification highly challenging. Conventional fracture-vuggy identification techniques primarily rely on amplitude response characteristics, which only provide the general orientation and approximate extent of the reservoir. To address these limitations, a refined interpretation method for fractured-vuggy reservoirs was proposed based on a two-dimensional Res-UNet residual network and optimized label data. This method enhances the update frequency and optimization efficiency of 2-D training samples by modifying the Res-UNet residual network structure, thereby improving the accuracy of reservoir prediction. Geological models of faults, fractures, and karst caves were constructed using a combination of satellite imagery, UAV scanning, field reconnaissance, geological radar, and seismic interpretation results. Wavelet analysis of 3-D seismic data in the depth domain, along with imaging and acoustic logging, was performed to extract formation and reservoir velocities. Wavelets at frequencies of 20 Hz, 25 Hz, and 35 Hz were selected to create forward models for different reservoir widths. An empirical formula was derived to establish the relationship between reservoir characteristics and seismic response based on frequency and formation velocity. Verification of the empirical formula was conducted using horizontal well trajectories, vertical well remote detection data, and logging data to extract the relationship between actual reservoir characteristics and seismic responses. This formula was then applied to amplitude attributes of the target layer in the study area to estimate the reservoir width range. The reservoir combination characteristics of the study area were identified, and a comprehensive detection workflow—incorporating analysis, design, verification, and redesign—was established through the analysis of 3-D seismic profiles. Optimal parameters, including wavelet frequency, migration aperture, and sampling interval, were designed for the forward model of the study area. A 2-D training sample database capable of real-time updates was developed, and the fracture-vuggy labels were iteratively optimized by integrating synthetic fracture-vuggy data with actual data. Using this database, the Res-UNet residual network was trained and applied to address the degradation problem commonly encountered in deep networks. This approach enabled the fine-scale prediction of fracture-vuggy structures, significantly improving the resolution and accuracy of reservoir interpretation.

Key words: Tarim Basin, fault-controlled fracture-vuggy reservoirs, deep learning, Res-UNet residual network, sample library optimization

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