Estimation of directional crack density and fluid properties from well logs in vertical wells

Author:

Xu Song1ORCID,Tang Xiao Ming1ORCID,Chen Ming2,Su Yuan Da1ORCID,Qian Yu Ping3,Sun Dianqiang2ORCID,Torres-Verdín Carlos4ORCID

Affiliation:

1. China University of Petroleum (East China), Key Laboratory of Deep Oil and Gas, Qingdao, Shandong 266580, China and China University of Petroleum (East China), School of Geosciences, Qingdao, Shandong 266580, China.(corresponding author); .

2. CNOOC China Limited Hainan Branch, Haikou, Hainan, 570300, China..

3. China Oil Field Services Ltd., Oil Field Technology Department, Sanhe, Hebei 065201, China..

4. University of Texas at Austin, Hildebrand Department of Petroleum and Geosystems Engineering, Austin, Texas 78712, USA..

Abstract

The study of elastic properties of fractured/cracked rocks has been an important subject of interest in seismology and geophysical exploration. Downhole logging provides a direct measurement of fractured rock properties in terms of elastic wave velocities and anisotropy. Most existing studies only provide qualitative descriptions of fracture properties as evidenced from the acquired measurements. To better use downhole measurements, we have derived a comprehensive theoretical analysis and developed an inversion technique to characterize fracture properties. Theoretical results for cracked rocks show that crack density, crack alignment direction, and crack filling materials are the three main fracture parameters that strongly affect the elastic wave properties of fractured rocks. Furthermore, a detailed analysis of the crack effects on elastic properties shows that the measured elastic moduli can be used to evaluate the crack parameters of cracked rocks. We assume that cracks with any orientational distribution can be divided into two parts: horizontal and vertical. Based on the theoretical analysis, we develop an inversion method to estimate fracture parameters from well logs acquired in a vertical borehole. We assume a rock-physics model for rocks that adds effective horizontal and vertical cracks that are filled with liquid in an isotropic background, the elastic and fluid properties of which are inverted from the measured logs. The inversion method enables the quantification of the directional crack density and crack-filling material when applied to field logging measurements acquired in fractured formations. Theoretically predicted fracture properties are validated with formation microresistivity scan logging data and are consistent with the interpretation results.

Funder

the Fundamental Research Funds for the Central Universities

the National Natural Science Foundation of China

China Postdoctoral Science Foundation

Qingdao Postdoctoral Applied Research Project

the Natural Science Foundation of Shandong Province

Publisher

Society of Exploration Geophysicists

Subject

Geochemistry and Petrology,Geophysics

Reference62 articles.

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3. Bandyopadhyay, K., 2009, Seismic anisotropy: Geological causes and its implications to reservoir geophysics: Ph.D. thesis, Stanford University.

4. Long‐wavelength propagation in composite elastic media II. Ellipsoidal inclusions

5. Effective stress for transport properties of inhomogeneous porous rock

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