EFFECTS OF HYDRAULIC FRACTURING IN SHALLOW BEDROCK FORMATIONS

This paper presents a method of predicting the bedrock and hydraulic effects of hydraulic fracturing in shallow, low permeability fractured bedrock formations. A theoretical method is proposed to estimate post-fracturing fracture size and transmissivity. As a test of the methodology, data collected from two wells were used for verification. These two wells had borehole geophysical and hydraulic measurements made before and after hydraulic fracturing. Five different pumping test analysis methods were used to evaluate the well hydraulic data. The most effective methods were the Papadopulos-Cooper model (1967), which includes wellbore storage effects, and the Gringarten-Ramey model (1974), known as the single horizontal fracture model. The hydraulic parameters resulting from fitting these models to the field data revealed that as a result of hydraulic fracturing, the transmissivity of one well was increased more than 46 times and increased 285 times in the other well. The developed model considers horizontal radial fracture propagation from the hydraulically fractured well, and the geometry of such a fracture is then used to estimate fracture hydraulics after hydrofracturing. For the two studied wells, their fractures could have propagated to distances of almost 175m or more and developed maximum apertures of about 2.20 mm and hydraulic apertures close to 0.50 mm. Hydraulic apertures calculated from pumping test analyses closely matched the results obtained from the hydraulic fracturing model. As a result of this model, post-fracturing geometry and resulting post-fracturing well yield can be estimated prior to the actual hydrofracturing.