Methods and systems for determining bulk density, porosity, and pore size distribution of subsurface formations

• US 10,422,916 B2
• Filed: 08/10/2017
• Issued: 09/24/2019
• Est. Priority Date: 08/10/2017
• Status: Active Grant

• Current Assignee: Saudi Arabian Oil Company (Government of Saudi Arabia)
• Original Assignee: Saudi Arabian Oil Company (Government of Saudi Arabia)
• Inventors: Zhang, Jilin, Althaus, Stacey Marie, Chen, Jin-Hong
• Primary Examiner(s): Ha, Nguyen Q.
• Application Number:
  US15/673,996
• Publication Number:
  US 20190049616A1
• Time in Patent Office: 775 Days
• CPC Class Codes: G01N 15/088 Investigating volume, surface area, size or distribution of pores; Porosimetry
• CPC Class Codes: G01N 24/081 Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
• CPC Class Codes: G01N 24/082 Measurement of solid, liquid or gas content
• CPC Class Codes: G01R 33/448 Relaxometry, i.e. quantification of relaxation times or spin density G01R33/50 takes precedence
• CPC Class Codes: G01V 3/32 operating with electron or nuclear magnetic resonance

Abstract

Herein methods and systems for determining matrix or grain density of a subsurface formation are described. This includes measuring in-air mass of a fluid-saturated sample of the subsurface formation, wherein the in-air mass comprises mass of matrix or grains of the sample, mass of a fluid surrounding the sample, and mass of the fluid inside the sample. The volume of the fluid inside the sample, V_ϕ, and volume of the fluid surrounding the sample, V_sur, are determined using nuclear magnetic resonance (NMR). The fluid-saturated sample can then be submerged in a predetermined volume of a weighing fluid and mass of the fluid-saturated sample without the surrounding fluid in the weighing fluid, m_f is measured. Using the measured and determined values one can determine the volume of the sample without the surrounding fluid, V_c, the bulk density of the fluid-saturated sample without the surrounding fluid, ρ_b, the volume of the matrix, V_m, and the matrix or grain density of the subsurface formation, ρ_m.

Claims

1. A method for characterization of a subsurface formation, the method comprising:

measuring in-air mass of a fluid-saturated sample of the subsurface formation, wherein the in-air mass comprises mass of matrix or grains of the sample, mass of a fluid surrounding the sample, and mass of the fluid inside the sample, the in-air mass of the fluid-saturated sample, m_s, given by the formula;

m_s=V_mρ

_m+(V_ϕ

+V_sur)ρ

_l

where ρ

_m is a density of the matrix of the subsurface formation, ρ

_l is a density of the fluid inside and surrounding the sample, V_m is a volume of the matrix, V_ϕ

is a volume of the fluid inside the sample, and V_sur is a volume of the fluid surrounding the sample;

determining volume of the fluid inside the sample, V_ϕ

, and volume of the fluid surrounding the sample, V_sur, using nuclear magnetic resonance (NMR);

placing the fluid-saturated sample in a predetermined volume of a weighing fluid;

measuring mass of the fluid-saturated sample in the weighing fluid;

determining mass of the fluid-saturated sample without the surrounding fluid in the weighing fluid, m_f, given by the formula;

m_f=V_mρ

_m+V_ϕ

ρ

_l−

V_cρ

_f

where ρ

_f is the density of the weighing fluid; and

determining a volume of the fluid-saturated sample without the surrounding fluid, V_c, using the formula;

V_c=(m_s−

m_f−

V_surρ

_l)/ρ

_f.

2. The method of claim 1, further comprising:

determining a bulk density of the fluid-saturated sample without the surrounding fluid, p, using the formula;

3. The method of claim 2, further comprising:

determining volume of the matrix, V_m, using the formula;

V_m=(m_s−

m_f−

V_surρ

_f)/ρ

_f−

V_ϕ

.

4. The method of claim 3, further comprising:

determining matrix or grain density of the subsurface formation, ρ

_m, using the formula;

5. The method of claim 1, further comprising:

washing the sample using a washing fluid prior to measuring, wherein the washing fluid is same as a drilling fluid.

6. The method of claim 1, wherein at least one dimension of the fluid-saturated sample is about 0.5 mm to 3 mm.

7. The method of claim 1, wherein the weighing fluid is a drilling fluid, or a fluid with gravimetric properties similar to the drilling fluid.

8. The method of claim 1, wherein the weighing fluid is diesel.

9. The method of claim 1, wherein the fluid-saturated sample does not require physical removal of the surrounding fluid.