New insights about acid fracture conductivity at laboratory scale
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abstract
Copyright 2014 by the Society of Petroleum Engineers. Recent studies suggested that the fracture face texture affects the acid etching patterns and fracture conductivity of acid fracturing at laboratory scale. This paper presents a systematic study to clarify the effect of fracture topographic features on acid fracture conductivity; as its importance lies on that most of the industry correlations to predict acid fracture conductivity are based on acid conductivity experimental studies at lab-scales. We conducted acid injection tests in fractured cores from two different carbonate formations: the Austin Chalk, a soft calcite formation, and San Andres Dolomite, a hard rock with high levels of dolomitization. We investigate the effect of injection temperature, pumping time and acid type on fracture conductivity. We also studied the influence of the core fracture surfaces texture before the acid injection. Two types of fracture surface textures were used; rough surface and smooth surface; to quantify the effect of surface texture. After the acid injection, we analyzed how conductivity was created by examining the computer generated profiles of the fracture surfaces. For the smooth fractures, the uneven etching of the rock which creates roughness on the surfaces was responsible for the resulting conductivity. For rough surfaces, acid conductivity was more related to the deepening of the initial features on the sample surface than by creating more roughness. These results suggest that acid conductivity is possibly created by a combination of both mechanisms, from which deepening may be dominant in homogenous formations. Therefore, it is not correct to disregard the contribution of uneven etching to acid conductivity. Additionally, we found that it is acceptable to perform conductivity tests with either rough or smooth surfaces for soft formations such as the Austin Chalk. The props that kept the fracture open deformed the same for both textures and therefore the conductivity results did not differ significantly at formation closure stress. For San Andres Dolomite, the conductivity results for rough surfaces were one order of magnitude larger than for smooth surfaces due to the high rock embedment strength of this formation. These results serve as guidelines for performing acid conductivity tests.
Society of Petroleum Engineers - International Petroleum Technology Conference 2014, IPTC 2014 - Innovation and Collaboration: Keys to Affordable Energy
author list (cited authors)
Nino-Penaloza, A., Al-Momin, A., Zhu, D., & Hill, A. D.
