Closed-fracture acidizing

C-2. Generic acid fracturing treatment for a tight limestone (viscous fingering procedure closed-fracture acidizing [CFA] method).262... 

Strong acid leaching produces the most acid experimental ZPC s. As evidenced by agreement between experimental and calculated ZPC s, the surface produced is a close approximation of an unaltered fracture surface. Cleavage planes probably do partly control the Al/Si ratio (cf. kyanite data), and it is important to recognize the correct site distribution of Al(III) (cf. andalusite data). 

Foamed Acid Fracturing. The goal of add fracturing is to create a fracture within the reservoir and to etch the sides of the fradure face. Etching of the fracture face with add dissolves a portion of the fradure face and allows a conductive path to be created after the fradure has closed. The further the live add can reach into the fracture, the longer the conductive channel will increase well productivity. 

Figure 4.4 SEM photographs of the compact tension fracture surface of 4 phr VTBN-modified VE resin showing a) transition from fast fracture to crack-initiation region and b) close-up of one particle. Propagation was from left to right. The specimen was stained with osmic acid. Reprinted with permission from J.S. Ullett, and R.P.Chartoff, Polymer Engineering and Science, 1995, 35, 13, 1086 1995, John Wiley and Sons Publishers...

The formation is readily soluble in the acid system used, but the fracture face dissolves uniformly so that differential etching does not take place. When the fracture closes, conductivity is lost. 

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