Surface Etching Pattern and its Effect on Fracture Conductivity in Acid Fracturing

摘要

Conductivity in acid fracturing after fracture closure depends on the contact of the non-uniformly etched fracture surfaces created by the acid.The surface topography of the fracture faces after acid injection is rarely investigated and,therefore,poorly described.The concept of average fracture width has been used in the fracture conductivity models to predict fracture conductivity in acid fracturing.Previous study showed that the characterization of fracture faces after acid etching plays an important role in fracture conductivity.If channels and wormholes are created,fracture conductivity cannot be described by the conventional model.For more evenly distributed etching,surface topography characteristic strongly influences the resulting conductivity.With a surface profilometer,a laser device that accurately measures the height of the asperities on the rock surface,we obtain a digital image that can be used to quantitatively characterize the etched surface topography after acidizing.Using this data we are able to define the channel geometry and etching patterns as numerical values.The distribution of these numerical values is later converted and analyzed as surface texture parameters and standard statistical variables for rough surface characterization.When two roughness parameters of each corresponding fracture surface are superposed,the fracture conductivity can be related to the statistical parameters of etching.In this paper we present experimental results for a wide range of acid fracturing conditions that provide the variables and controlling parameters relating roughness of the fractures surface to fracture conductivity measurements.The findings of this study is important to understanding the effect of etcing pattern of fracture face on fracture conductivity behavior,and it also helps to develop lab scale fracture conductivity correlations in acid fracturing.