Shale Gas Evaluation and Producing

4. ?

5. ?

7. Mudrocks are sedimentary rocks with grain size distribution less than 62 μm. Pore
body and pore throat size distributions are typically smaller ranging, well below the
microporosity classification(<0.1μm) into the nanometer territory.
Measurement of physical properties at these small scales becomes challenging and
requires an understanding of the molecular size of the working fluids used in test
protocols.
Kinetic diameter of
various molecules and
compounds
as estimated from van
derWaals equation and
various
sources.

8.  Van derWaal spherical molecular diameter:
Modified ideal gas law：
Molecules, compounds model as sphere:
Discussion :
Does the size disparity of molecular induce error in the
measurement of mudrock properties?

10.  Knudsen flow parameters to extend the applicability of the Darcy
equation beyond slippage, into transition and diffusion flow at ultra-low
permeability (<1 μD).
 Karniadakis and Beskok (2002) developed a flow rate model for gas flow
in microtubes over the entire Knudsen regime. The Karniadakis - Beskok
"microflow" model is given as:

11.  Cui et al (2009) suggest that the larger
effective adsorption porosity, the greater
the underestimate of the permeability.
 Clearly, if lab tests apply incomplete flow
models or do not account for diffusion or
adsorption effects, then a broad of errors
may be incurred.

13.  Errors or differences can be associated with a number of contrasting protocols including
differences in: crushing and sieving which result in test particle size differences, extraction
methods, permeameter design, and test conditions (STP vs. reservoir). So who is correct?
 In the subsequent sections, we will expand on the measurement of rock composition,
porosity, saturation, permeability, and mechanical properties.

15. Figure 10 - XRD versus FTIR mineralogical volume percent for quartz (circles) and total clays
(triangles). Log display at right illustrates how with such separation on the Neutron-Density and Sonic-
Density logs (Track 4) the FTIR Total Clay volumes (blue circles) best match the Clay Volume (VCL) curve
derived for this interval (Track 2)

16. This table presents the characteristics responses in mature gas shale for
common logging tools

17. There are multiple techniques and protocols to measure porosity in gas
shales. Among the factors affecting the validity of gas shale porosity
measurements are:
1. Removal of water and liquid hydrocarbon from the pore system
2. Pore access problems to gas and liquid due to low permeability
3. Absorption effects
4. Sample size, crushing methods, and crushed sample weight
5. Effect of pore pressure and net overburden stress on microfractures.

18.  Soeder(1988)
 Sample: using tap water to cut horizontal
plugs with the samples then being dried until
weight were stable.
 Workflow: placing sample cylinders in a
Boyles Law apparatus with 1000 psi pore
pressure under a confining stress (1750-6000
psi). He used methane to measure grain
volume (considering the effect of adsorption).

19.  Luffel and Guidry(1992)
 Sample: introduced a crushing technique to increase the surface area of
the available pore networks.
 Workflow: cleaning and drying techniques are similar to Soeder’s
method. Samples are crushed into chips around 0.5 in, while the same
samples crushed and passed through 12 mesh sieve.
 Grain volumes and weight were measured on the chips/crushed samples.
Porosity were calculated using a combination of the dry density(ρ) and
weight(m).

20. All measurements show
exceptional agreement
and are considered well
within experimental error.

21.  Karastathis (2007): crushed rock method, adding mass
conservation.
 Sondhi and Solano(2009) ： developed a simple
porosity measurement process which used thermal
gravimetric analysis (TGA) to define heat treatment
(before porosity measurements ).
 Improper (high) heat treatment drives off bound water
and can decompose organics.
 They coupled TGA with FTIR(Fourier Transform Infrared
Spectroscope) to identify evolved gases.

24.  Adsorption and the effect of gas molecule size
are specifically addressed by Cui et al.(2009):
1. Molecule with smaller diameter will yield
higher porosities than when larger diameter
elements such as N2.
2. Providing a Langmuir type of adsorption
correction.
 Other measuring methods: MICP and NMR.

25.  Porosity estimation use a combination of nuclear,
resistivity and sonic logs within an expert-based or
statistical system to compute mineralogy, TOC and
fluid volumes.

27.  Darcy’s formula for perm:
kA
Q P
L
  
•Is it applicable to measure gas permeability?
•Why?
•Klinkenberg (1941) found that the perm
is not constant when using gas as fluid
during measurement. It depends on gas
using and the average pressure existing in
core ?

28.  Popular techniques:
1. Pressure pulse decay
2. Pressure decay
3. Steady state
Ultra low
permeability
rocks
 Can be applied to:
1. Crushed samples
2. Whole plug samples

29. Why perm. and poros. in crushed samples is lower?
Why we need to measure it?
?

30. Two obvious conclusions can be drawn from Fig. 27:
a)Young’s modulus displays very little pressure dependence
b) the range inYoung’s modulus and Poisson’s ratio is quite large, factors of 6 and
9, respectively, suggesting mineralogy strongly controls mechanical properties in
shales.

31. Fig. 28 suggests that the magnitude of Poisson’s ratio increases with confining
pressure.Where Poisson’s ratios of horizontal and 45° plugs are measured, they are
greater than those measured on vertical plugs.

32.  1. Using toluene via the Dean Stark method
 2. Retort method

34.  Mineralogy varies considerably in a particular shale
 TOC estimation by Passey et al. (1990) method works well with a
multiplier
 Logs require independent mineralogy calibration , FTIR fast and
sufficient
 Core handling and preparation needs to be standardized
 Permeability on crushed samples reflect grain size more than matrix
perms
 Permeability measurements on cores display a strong crack component
 Variable salinities render Archie saturation calculations questionable
 Anisotropy is strong (30-50%) and influences closure stress estimates
and fracture containment
 Recommend a committee to create standards and protocols for shale
measurements revisit the GRI recommendations

35. Thanks!
Presentation done using paper SPE131768, data from related presentation, logos from Open Learning Campus of
World Bank and China University of Petroleum, Beijing. Presentation was held during Unconventional Oil and
Gas Resources course by students in China University of Petroleum, Beijing