New Techniques for Fracture Height Determination in Exploration Wells Drilled in the Xihu Sag, East China Sea

Anisotropy analyses of conventional array acoustic cross dipole data failed to determine the vertical heights of fractures formed in reservoir formations in exploration wells drilled in the Xihu Sag, East China Sea. To eliminate such technical challenges, innovative techniques have been developed to determine the fracture heights in reservoir formations after fracturing in such exploration wells. To determine the features in radial directions after fracturing operations, 2D velocity profiles for formations in vicinity of sidewalls before and after fracturing were created by using the longitudinal wave travel time tomography technique. It was found that such fracturing operations might make a huge difference such velocity profiles if the formation were fractured successfully. Meanwhile, the hydraulic fracturing operations might also create a series of micro-fractures around the major fractures. Capable of detecting those micro-fractures, the dipole acoustic far-field images could be used to determine heights and widths of the resulting fractures. Research results showed that the acoustic speed reduced by 20% after the fracture were created near the wellbore, whereas the strong acoustic reflection and scattering confirm the presence of volumetric fractures were created within 20 m around the well. The dipole acoustic far-field images could identify the fracture heights with high resolution up to 0.152 4 m. Combination of the longitudinal wave travel time tomography technique and the dipole acoustic far-field images could effectively enhance accuracy in the determination of fracture heights in exploration wells. Eventually, the comprehensive performances of fracturing operations can be assessed more accurately.