A New Method of Digital Core Construction and Analysis for Unconsolidated Sandstone

Abstract

A new method of digital core construction and analysis for unconsolidated sandstone is presented in this paper to solve the problem for friable cores. Results are compared with conventional experimental techniques and routine digital core construction methods. The new method procedures: Firstly, rocks are full-closure cored from unconsolidated formation and frozen; multi-scale (meter/millimeter/micron) CT scanning for core samples with original formation fluids, and the core heterogeneity has been analyzed. Then, skeleton and pore space of samples are segmented with the watershed algorithm. Finally, pore network model is extracted with maximum sphere method. After building the digital core, petrophysical parameters and fluid flowing characteristic are simulated. Compared with conventional experimental method, samples preparation is convenient under lower requirements of the size and shape. Without cleaning, the distortion of experimental parameters are avoided due to damages to the original pore structure of friable core samples, especially for unconsolidated samples. Compared with conventional digital core construction, the focused scanning mode is used for micron scanning, without catching the smaller samples. The new method not only simplifies the preparation of conventional core analysis that reduces the difficulty of sample preparation of unconsolidated sandstone natural core, but also guarantees the quality of core analysis data. The new method is successfully applied and results are compared in field of South China Sea. The results from different methods with consolidated samples analysis, such as porosity, permeability and parameters of relative permeability, show the relative errors are less than 10%. The results from unconsolidated samples analysis with conventional experimental method show obvious errors: permeability of some samples are more than 15 Darcy, the relative permeability curve is obviously not consistent with the actual field performance. While results from unconsolidated samples analysis with the new method show good agreement with actual field performance. This method can accurately test the petrophysical parameters of unconsolidated sandstone, reduce the experimental errors caused by conventional methods and shorten the experimental schedule. It could be applied to core analysis of similar formation.