| The acid fracturing is a key stimulation techniques of carbonate reservoir. The effective distance of acid is a important factor evaluating the result of acid fracturing. The leak-off of wormhole and matrix seriously constraints the length of etched fracture, affecting the result of stimulation. Accurate understanding of acid’s leak-off mechanism is very important for optimization of acid fracturing technology. However, the corresponding research is not mature, mainly because the present models of acid’s leak-off don’t take the comprehensive effect of leak-off of multi-wormhole and matrix into consideration.This Thesis study acid’s leak-off mechanism from the standpoint of multi-factor. We study matrix leak-off regularity and establishes matrix leak-off model via coupling of Darcy scale and pore scale; study the regularity of wormhole’s dynamic extension and leak-off mechanism, and establish leak-off model of single wormhole by coupling the flow and reaction of wormhole and reservoir’s flow; establish model for predicting population of wormhole based on the law of wormholes contend; establish model of acid’s flow and reaction based on the feature of acid’s flow and reaction in the fracture.It’s illustrated in the paper as following:the acid leak-off in the acid fracturing treatment falls into three parts:the leak-off in matrix, the leak-off on the wormhole wall and the leak-off from increase of wormhole volume. Among the three, the leak-off on the wormhole wall and the leak-off from increase of wormhole volume are the main parts. The leak-off of acid has close connection with the factors of the treatment(acid’s rate, acid’s viscosity, acid’s concentration, acid’s volume) and physical property of reservoir. We can decrease the acid’s leak-off and increase the length of etched fractures by optimizing treatment factor.The article analyses the fundamental theory of acid fracturing in deeper level, makes the calculation of leak-off more accurate, and can direct the treatment better. |
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