Acid fracturing is an indispensable technology in the efficient development of carbonate oil and gas reservoirs. As for deep and ultra-deep marine carbonate oil and gas reservoirs, however, existing acid fracturing technologies can hardly create complex fracture networks because of their particular engineering and geological characteristics. In order to realize the efficient three-dimensional development of deep and ultra-deep marine carbonate oil and gas reservoirs, this paper revealed the acid fracturing difficulties of this kind of reservoirs based on the engineering and geological characteristics of deep marine carbonate oil and gas reservoirs in China. Then, by taking the efficient three-dimensional development of deep and ultra-deep marine carbonate oil and gas reservoirs as the target, the technical concept of three-dimensional acid fracturing (3D-AF) was put forward based on the techniques of volume acid fracturing and deep acid fracturing. In addition, its technical connotation was illustrated, and its key technologies were described in detail. Finally, its development direction in the next step was pointed out. And the following research results were obtained. First, the 3D-AF technology contains three basic connotations: (1) selecting the corresponding acid penetration technology according to reservoir types so as to realize sufficient reservoir stimulation on the plane; (2) creating complex acid-fracture volume with higher flow conductivity under high closed pressure; (3) deploying acid-fracture volume rationally along the long hole section so as to realize sufficient reservoir stimulation in the wellbore direction. Second, there are three key technologies of 3D-AF, i.e., the technology for predicting the effective acid-penetrate distance under the coupling action of multi-field, multi-scale and multi-fluid, the technology for optimizing the flow conductivity of complex acid-fracture volume, and the technology for precisely deploying acid in the long section of horizontal well or highly deviated well. Third, in order to promote the further development of 3D-AF technology, it is necessary to carry out researches on three technologies, i.e., the technology for predicting and reducing the fracturing pressure of ultra-deep reservoir, the technology for predicting the geometry of acid-fracture body in a strongly heterogeneous reservoir, and the staged reservoir production technology and new fluid technology with high temperature resistance, low reaction rate and low friction resistance coefficient for long hole sections (over 7000 m).
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