Experimental study on influencing factors of acid-fracturing effect for carbonate reservoirs

Acid fracturing treatment is the key technique for stimulation and stable production in carbonate reservoirs. In order to improve the carbonate reservoirs acid fracturing effect, in this paper, with a large number of experiments as the main research methods, study on influencing factors of acid-fracturing effect for carbonate reservoirs from increase the effective distance of living acid, increase acid corrosion eched fracture conductivity, reduce the acid fluid loss, etc. The effective distances of live acid calculated with reacted acid limitations measured in different acid systems are quite different from those calculated according to previous standard. Fracture conductivity is one of the key parameters that affects acid fracturing effects, but it's difficult to be predicted accurately due to the strong randomness of acid-rock reaction as well as various influence factors. Analyses of the impacts on fracture conductivity resulted from the rock embedment intensity, closure stress, acid dosage, rock-acid contact time, acid fluid loss, acid pumping rate through self-developed small-core fracture capacity test instrument. Fluid loss during acid fracture can be well controlled by thickened liquid as well as solid particles, but formation damage occurs inevitably. Foamed acid is a specific fluid with high viscosity, low fluid loss, small friction resistance, good retarding property, strong fracture making ability, easy flowback and low damage, which is an ideal acid system for low pressure and low permeability carbonate reservoirs. In this paper, the theoretical study on percolation mechanism and fluid-loss control mechanism of foam (acid) in porous medium are presented with the help of visual microscopic model fluid drive unit.