Study On Acid-fracture Conductivity Considering The Acid Etched Surface Topography

Acid fracturing technology is one of the most effective stimulation measures for carbonate reservoir,which aims to non-uniformly etch on fracture surface after the formation is fractured.Under the closure stress,some rock samples support each other to form a cross flow channel and improve the production capacity of oil and gas reservoirs.The topography of fracture surface is one of the key factors affecting the acid fracture conductivity,which is an important index to evaluate the effect of acid fracturing.Therefore,the topography of the acidized fracture surface needs to be described accurately.It is of great significance to reveal the relationship between the microscopic topography and the macroscopic flow for predicting the conductivity correctly and designing the acid fracturing treatment rationally.Based on previous studies,this paper has quantitatively analyzed the acidized fracture surface topography and studied the variation trend of rock mechanical parameters before and after acidizing.The modified parameters were put into the calculation model of the fracture width,and finally the model of conductivity was integrated to meet the needs of the field production.The main research contents and results were as follows:(1)Obtaining the rock mechanics parameters before and after acidizing.The compressional and shear wave velocities of rock samples were measured,and the rock samples with similar velocities were selected as comparable rock samples.Dynamic rock mechanical parameters were calculated based on the two wave velocities.The static mechanical parameters of rock samples were measured by triaxial compression experiment.(2)Analyzing the characteristics of fracture surface before and after acidizing.The optical profilometer was used to scan the crack surface before and after acidizing,and 3D imaging was performed on the scanned digital signals.At the same time,a surface topography analysis program was developed to quantitatively analyze the topography of the surface before and after acidizing.The results showed that the overall height,the roughness and randomness of the fracture surface were enhanced after acidizing decreased.(3)Modifying the change of fracture width under closure stress.Contact type between fracture was judged.Based on the classical Hertz contact theory,the rock mechanics parameters before and after acidizing were used to calculate the deformation quantity of the fracture surface under the closure stress.The results showed that the deformation quantity with modified mechanical parameters were more than 111%larger than those leave out of consideration.Finally,the fracture width distribution was obtained by using the developed fracture width calculation program.(4)Studying the model for calculating the acid fracture conductivity considering the acid etched surface topography.The calculation model of the acid fracture conductivity was worked out with MATLAB,and the fracture width distribution data was put into it.The acid fracture conductivity under various experimental conditions was simulated,and the results of laboratory experiments were compared to analyze the causes of errors.The results of this paper have important guiding significance for the prediction of the topography of the acidized fracture surface and the acid fracture conductivity,revealing the relationship between rock mechanical parameters and fracture deformation quantity after acidizing,and obtaining the corrected distribution of fracture width and conductivity,which is of certain value for exploring the acid fracture conductivity.