Digital core construction of fractured carbonate rocks and pore-scale analysis of acoustic properties

Tan, Maojin; Su, Mengning; Liu, Weihua; Song, Xiaodong; Wang, Siyu

doi:10.1016/j.petrol.2020.107771

“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Xiao

¹

,

Li

²

,

Du

³

et al. 2023

Geofluids

0

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Revealing the elastic wave properties of carbonate rocks with complex pore structures and improving the reliability of carbonate reservoir descriptions have always been a global challenge in the field of carbonate geophysical exploration. In this study, we established a synthetic borehole model by selecting different particle sizes of cement, carbonate cuttings, and micro-silicon as the matrix, and silicon disks as the pores in carbonate rocks. We conducted four sets of low-porosity (0-3%) borehole models with different pore aspect ratios (ARs) and measured the P- and S-wave velocities ( V P and V S ) at the well-logging scale obtained from an acoustic logging system with one source and two receivers. The results indicate that the relationship between velocities and porosities in these borehole models follows a linear relation, with the pore AR significantly influencing the velocities at any given porosity. The velocity variation caused by pore AR reaches 560 m/s and 410 m/s at 3% porosity for the P-wave and S-wave within the AR range of 0.017-0.13. The theoretical DEM models provide a high and broad estimation of V P and V S at the well-logging scale in our measurement. They could perform better in fractured formation than in dissolved porous formation in carbonate reservoirs. The linear relation of V P and V S is independent of the pore AR and is effective for both fractured and dissolved porous formations. The change of V P / V S in different pore AR is more responsive to porosity and nonlinear dependent on the pore AR. The relationship between the defined normalized V P and V S indicates the pore AR has a more significant effect on V S than V P in our model. The constructed borehole models provide a unique opportunity for evaluating the availability of rock physics models at an acoustic logging scale. The study’s findings have significant implications for improving the reliability of carbonate reservoir descriptions and enhancing the accuracy of geophysical exploration in carbonate rocks with complex pore structures.

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“…Accurate modeling of core 3D pore structure is of fundamental significance to the study of physical and transport properties [7,8,9,10,11]. The digital core [12,13,14,15,16,17,18,19] is a popular technique for modeling 3D core pore structure, which can be obtained by imaging equipment, such as X-ray Computed Tomography (micro-CT). Generally, imaging equipment captures only a single length-scale core feature in a single imaging session.…”

Section: Introductionmentioning

confidence: 99%

Multiscale reconstruction of porous media based on multiple dictionaries learning

Yan¹,

Teng²,

He³

et al. 2022

Preprint

0

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Digital modeling of the microstructure is important for studying the physical and transport properties of porous media.Multiscale modeling for porous media can accurately characterize macro-pores and micro-pores in a large-FoV (field of view) high-resolution three-dimensional pore structure model. This paper proposes a multiscale reconstruction algorithm based on multiple dictionaries learning, in which edge patterns and micro-pore patterns from homology high-resolution pore structure are introduced into low-resolution pore structure to build a fine multiscale pore structure model. The qualitative and quantitative comparisons of the experimental results show that the results of multiscale reconstruction are similar to the real high-resolution pore structure in terms of complex pore geometry and pore surface morphology. The geometric, topological and permeability properties of multiscale reconstruction results are almost identical to those of the real high-resolution pore structures. The experiments also demonstrate the proposal algorithm is capable of multiscale reconstruction without regard to the size of the input. This work provides an effective method for fine multiscale modeling of porous media.

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“…The influence of a fracture orientation on borehole collapse pressure was quantitatively analyzed, and a variation law of borehole collapse pressure with weak plane occurrence characteristics under different borehole trajectories was studied, which provided a basis for wellbore stability during drilling operations. To study the elastic properties of fractured carbonate rocks, Tan et al 9 used media filtering and threshold segmentation technology to establish carbonate digital cores by X-ray CT scanning. Then digital carbonate cores of different fracture types were constructed by inserting fractures into scanned slices.…”

Section: Introductionmentioning

confidence: 99%

Study on Rock Mechanical Properties and Wellbore Stability of Fractured Carbonate Formation Based on Fractal Geometry

Liu

¹

,

Cui

²

,

Meng

³

et al. 2022

ACS Omega

8

0

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To mitigate borehole wall instability in fractured carbonate formations in an oilfield, the main factors affecting borehole wall instability were determined by combining the characteristics of underground cores, logging data, and a series of laboratory mechanics experiments. The geometric morphology characteristics of a carbonate rock fracture surface were studied together with an artificial rock fracture surface formed by triaxial mechanics experiments. A relationship between the geometric morphology characteristics of a fracture surface and rock mechanical properties was established based on fractal geometry. Using the Mohr–Coulomb failure and weak plane failure criteria, a rock strength criterion based on the fractal characteristics of a rock fracture surface was established. Finally, the mechanical rock properties characterized by fractal geometry were imported into the established borehole stability evaluation model. The results show that a collapse formation is mainly limestone with relatively developed microfractures, and some fractures are filled with expansive clay. The anisotropy of mechanical properties of bedrocks and microfractured rocks is obvious, whereas drilling-fluid immersion has little effect on the mechanical properties of a rock. 3D scanning experiments of artificial fracture surfaces formed after a triaxial mechanical test of a bedrock and fracture surfaces of a rock with microfractures show that the geometric characteristics of fracture surfaces after bedrock failure were more complex than those of fractured rocks. The geometric characteristics of rock fracture surfaces were numerically expressed through astatistical analysis and fractal geometry. Function relationships among cohesion, an internal friction angle, and fractal dimensions of bedrocks and microfracture rocks were fitted. A numerical simulation of borehole stability based on the fractal model of a carbonate fracture surface shows that different fracture inclinations and borehole trajectories significantly influence the collapse pressure equivalent density of a borehole wall. On drilling a horizontal well along the inclination of a fracture, the collapse pressure equivalent density of the borehole wall is relatively low when the fracture inclination is along the direction of the minimum horizontal principal stress. Unlike that from a conventional borehole stability model, the collapse pressure equivalent density calculated from the fractal model will increase by 0.1–0.2 g/cm3. The study results provide a theoretical basis for safe and efficient drilling in fractured carbonate formations.

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Digital core construction of fractured carbonate rocks and pore-scale analysis of acoustic properties

Cited by 30 publications

References 20 publications

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

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

Multiscale reconstruction of porous media based on multiple dictionaries learning

Study on Rock Mechanical Properties and Wellbore Stability of Fractured Carbonate Formation Based on Fractal Geometry

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