Experimental study on surface morphology and relevant plugging behavior within acid-etched and unetched fractures

Abstract

Plugging and diverting acid fracturing is an indispensable and promising technology that aims to enhance productivity for complex carbonate reservoirs. The key to success for this technology is the formation of effective plugged zones within preexisting fractures. However, because fracture pattern before and after acid-etching is quite different, the plugging behavior of fibers and particulates within acid-etched fractures is correspondingly distinct with respect to within smooth and hydraulic fractures. Till now, a number of researches have been studied on plugging experiments with various apparatuses. However, the plugging laws within acid-etched fracture are still unclear, and the experimental results are insufficient in revealing specific plugging laws, particularly with respect to fracture morphology. In this paper, we propose new parameters to analyze fracture morphology and introduce an integrated experimental method as well to study plugging behavior within fractures with different morphologies. Firstly, we obtain acid-etched fracture profiles with a 3D scanner and reproduce the rough physical-model fracture using 3D printing technology. Then, we perform a series of experiments to grasp plugging laws. Finally, in terms of fracture features analysis and experimental results, we further analyze the correlation between plugging behavior and surface morphology. The calculation results of digital parameters show that after acid-etching the roughness of the whole fracture increases due to acid-rock interaction, and channels are formed along the flow direction. Meanwhile experimental results show that flat fractures are relatively difficult to be plugged with respect to rough fractures because it has corresponding lower abilities to capture fibers and particulates. Pure fibers can independently plug 2 mm-wide fractures, as fracture width increased, the addition of particulates will improve the plugging efficiency. Additionally, fracture surface morphology has a huge influence on plugging behavior and dominate the possibility of plugging formation. Plugged zones generally are formed in the roughest areas of the fracture.