## Effective Pressure Law for the Intrinsic Formation Factor in Low Permeability Sandstones: EPL law for the formation factor

## Abstract

The effective pressure law for the intrinsic formation factor of low permeability sandstones from the Ordos Basin (northwest of China) was studied experimentally by measuring the electrical resistivity of brine saturated rock samples while cycling the pore and confining pressures, p _{p} and p _{c}. We used a 100,000 ppm NaCl solution so that the results could be directly interpreted in terms of the intrinsic formation factor F. The Response Surface method was used to construct a quadratic function of pp and pc fitting the experimental data, from which the coefficient α of the effective pressure law, p _{eff} = p _{c} – αp _{p}, was determined. We found that the coefficient α generally had low values, mainly from 0.2 to 0.4, thus contradicting the theoretical prediction that α should be equal to 1 for scale-invariant properties, such as F, in linear elastic materials having a homogeneous solid matrix. Since the two underlying assumptions, linear elasticity and homogeneity of the solid matrix, are likely violated in reservoir rocks, we tried to assess their effects on α using simple analytical models, based on idealized geometries of the pore and solid phases. Analysis of these models suggests that non-linear elasticity associated withmore »

- Authors:

- Southwest Petroleum Univ., Chengdu (China)
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

- Publication Date:

- Research Org.:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

- Sponsoring Org.:
- USDOE Office of Science (SC)

- OSTI Identifier:
- 1537222

- Grant/Contract Number:
- FG02-97ER14760

- Resource Type:
- Accepted Manuscript

- Journal Name:
- Journal of Geophysical Research. Solid Earth

- Additional Journal Information:
- Journal Volume: 122; Journal Issue: 11; Journal ID: ISSN 2169-9313

- Publisher:
- American Geophysical Union

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 58 GEOSCIENCES; Geochemistry & Geophysics

### Citation Formats

```
Chen, M., Li, M., Bernabé, Y., Zhao, J. Z., Zhang, L. H., Zhang, Z. Y., Tang, Y. B., and Xiao, W. L. Effective Pressure Law for the Intrinsic Formation Factor in Low Permeability Sandstones: EPL law for the formation factor. United States: N. p., 2017.
Web. doi:10.1002/2017jb014628.
```

```
Chen, M., Li, M., Bernabé, Y., Zhao, J. Z., Zhang, L. H., Zhang, Z. Y., Tang, Y. B., & Xiao, W. L. Effective Pressure Law for the Intrinsic Formation Factor in Low Permeability Sandstones: EPL law for the formation factor. United States. doi:10.1002/2017jb014628.
```

```
Chen, M., Li, M., Bernabé, Y., Zhao, J. Z., Zhang, L. H., Zhang, Z. Y., Tang, Y. B., and Xiao, W. L. Fri .
"Effective Pressure Law for the Intrinsic Formation Factor in Low Permeability Sandstones: EPL law for the formation factor". United States. doi:10.1002/2017jb014628. https://www.osti.gov/servlets/purl/1537222.
```

```
@article{osti_1537222,
```

title = {Effective Pressure Law for the Intrinsic Formation Factor in Low Permeability Sandstones: EPL law for the formation factor},

author = {Chen, M. and Li, M. and Bernabé, Y. and Zhao, J. Z. and Zhang, L. H. and Zhang, Z. Y. and Tang, Y. B. and Xiao, W. L.},

abstractNote = {The effective pressure law for the intrinsic formation factor of low permeability sandstones from the Ordos Basin (northwest of China) was studied experimentally by measuring the electrical resistivity of brine saturated rock samples while cycling the pore and confining pressures, pp and pc. We used a 100,000 ppm NaCl solution so that the results could be directly interpreted in terms of the intrinsic formation factor F. The Response Surface method was used to construct a quadratic function of pp and pc fitting the experimental data, from which the coefficient α of the effective pressure law, peff = pc – αpp, was determined. We found that the coefficient α generally had low values, mainly from 0.2 to 0.4, thus contradicting the theoretical prediction that α should be equal to 1 for scale-invariant properties, such as F, in linear elastic materials having a homogeneous solid matrix. Since the two underlying assumptions, linear elasticity and homogeneity of the solid matrix, are likely violated in reservoir rocks, we tried to assess their effects on α using simple analytical models, based on idealized geometries of the pore and solid phases. Analysis of these models suggests that non-linear elasticity associated with the formation of solid–solid contacts in the compressed rocks (e.g., during closure of rough cracks or crack-like pores along the grain boundaries), may be more effective in producing the low α values observed than inhomogeneity of the solid matrix.},

doi = {10.1002/2017jb014628},

journal = {Journal of Geophysical Research. Solid Earth},

number = 11,

volume = 122,

place = {United States},

year = {2017},

month = {10}

}

Works referenced in this record:

##
Nature of surface electrical conductivity in natural sands, sandstones, and clays

journal, March 1998

- Revil, A.; Glover, P. W. J.
- Geophysical Research Letters, Vol. 25, Issue 5, p. 691-694