Numerical Study of Pore Structure Effects on Acoustic Logging Data in the Borehole Environment

Abstract

Existing methods of well-logging interpretation often contain errors in the exploration and evaluation of carbonate reservoirs due to the complex pore structures. The differences in frequency ranges and measurement methods deviated between the acoustic well logs and indoor ultrasonic tests cause inconsistent results. Based on the elastic wave equation and the principle of the control variable method, a 2D axisymmetric borehole model with complex pore structures was developed, and the numerical simulation method for acoustic log was constructed. The modeling results show that the power function can well describe the effects of pore structure on the acoustic waves, while the velocity of the Stoneley wave is not sensitive to the pore structure. Crack-like pores with pore aspect ratio (AR) less than 0.1 significantly affect the velocities of P- and S-waves, whereas “spherical” pores have fewer effects. The models with larger pore sizes have high velocities of P- and S-waves. The velocities calculated by the equivalent medium theory are always higher than the numerical simulation results. The velocity deviation caused by the difference in frequency is much smaller than the pore structure. A fractal approach to quantify the effects of pore structures is applied in the acoustic logging data. The fractal dimension increases with the pore AR or size when the porosity is constant, which can be described by a simple power function. This gives us new ideas and methods for pore structure evaluation in the lower frequency range than the conventional petrophysical model.

Using a Synthetic Borehole Model to Determine the Pore Aspect Ratio Dependence of Velocities from Acoustic Well-Logging Data

“…Currently, techniques such as acoustic emission experiments, acoustic logging, and seismic monitoring, which are based on elastic wave theory, have become important methods for detecting underground structures, oil and gas minerals, and geothermal resources. However, the changes in pore structure can significantly impact the elastic frame moduli of naturally occurring rocks, resulting in changes in their elastic wave velocities [4][5][6][7][8][9].…”

Effects of microstructure on compressive strength of silica sand-enhanced oil well cement at a wide temperature range

“…The fractal theory has drawn lots of attention to characterize the complexity of porous media in the past decades [ 23 – 30 ]. Gao et al .…”

“…The fractal theory has drawn lots of attention to characterize the complexity of porous media in the past decades [23][24][25][26][27][28][29][30]. Gao et al [31] examined the multifractal property of microstructure in cement paste by using X-ray computed tomography to acquire the realistic three-dimensional microstructure.…”

Numerical Simulation of Polymer Dispersion Systems for Polymer Injection on Offshore Platforms

“…As an alternative approach, the nonlinear dynamic finite element method has become a useful complementary method for flow field simulation. 30 − 33 This method has the advantages of (i) conveniently achieving single-factor control and (ii) minimizing uncertainties caused by human errors. 34 Thus, a large amount of research studies have been carried out for numerical simulating the polymer dispersion and dissolution system.…”

“…Although the ejector performance of the two premixing methods is well recognized, the systematic study on the polymer dispersion and dissolution is still insufficient. As an alternative approach, the nonlinear dynamic finite element method has become a useful complementary method for flow field simulation. − This method has the advantages of (i) conveniently achieving single-factor control and (ii) minimizing uncertainties caused by human errors . Thus, a large amount of research studies have been carried out for numerical simulating the polymer dispersion and dissolution system. ,− At present, simulation research studies are concentrated to determine the hydrodynamics of bubbly flow of a gas–liquid ejector within Venturi tubes − and scrubbers .…”