Experimental study on the effectiveness of using 3D scanning and 3D engraving technology to accurately assess shale fracture conductivity

Abstract

Accurately evaluating fracture conductivity is key to optimizing the shale fracturing process. However, the influence of fracture morphology on conductivity remains unknown due to the non-replicability of rough samples in most laboratory-based studies. Thus, accurately duplicating rock samples with identical surface morphology and mechanical properties in the laboratory is a major concern for future fracture conductivity studies. Herein, a new method of reproducing rock samples for conductivity testing was proposed. Essentially, a laser scanner was used to obtain split rough fracture surface three-dimensional point cloud data for reverse reconstruction, which were subsequently combined with 3D engraving technology. This method successfully produced a significant number of conductivity test samples with uniform surface morphology and similar mechanical properties that can be used in experimental research on shale fracture conductivity. Comparison of the split shale sample with that created using the proposed method showed an area tortuosity error of only ±0.35%, a comparable elevation distribution frequency, and a high degree of similarity between the surfaces. Furthermore, due to the influence of the fracture surface roughness, rock samples with a proppant concentration below a certain “critical proppant concentration” may exhibit higher conductivity than samples with higher proppant concentrations under low closure pressure. Moreover, the “critical proppant concentration” was positively correlated with large-scale waviness, but did not show obvious correlation with small-scale unevenness. • A new method was proposed to reproduce shale samples with uniform surface morphology by integrating 3D scanning and 3D engraving techniques. • Under low closure stress, higher conductivity may be produced at a proppant concentration below a certain critical value, namely “critical proppant concentration". • The “critical proppant concentration” was positively correlated with large-scale waviness, which determines the proppant distribution and thus affects conductivity.