The Pore Structural Evolution of Mudrocks: A Case Study of Marcellus Shale

Size: px

Start display at page:

Download "The Pore Structural Evolution of Mudrocks: A Case Study of Marcellus Shale"

James Edwards
6 years ago
Views:

1 2014 Eastern Unconventional Oil and Gas Symposium - November 5-7, 2014 in Lexington, Kentucky, USA The Pore Structural Evolution of Mudrocks: A Case Study of Marcellus Shale Liaosha Song Timothy R. Carr Department of Geology and Geography West Virginia University November 6th, 2014 Lexington KY, USA

2 Motivation The pore structure of mudrocks has a strong impact on the storage capacity, the produced fluid type and rate, and the porosity and permeability of shale reservoirs. Gas-molecule locations in a kerogen grain pore system of a mudrock From Javadpour, 2009 From Sondergeld et al., /20

3 Geological Background Location of Cored Wells Stratigraphic Column A B C 2/20

4 Geological Background Mahantango A B C Medium dark gray silty claystone with a low organic content, a low carbonate content, and high clay abundance. Very sparse mineralized fractures. 3/20

$fractures are concentrated$

5 Geological Background Marcellus A B C Upper part: dark gray silty shale with a moderate organic content, low to moderate carbonate content, and moderate to high clay abundance. Lower part: dark gray to black silty shale with a high organic content, low to moderate carbonate content, high pyrite content, low to moderate clay abundance, vertical fractures are concentrated in the lowermost part. 4/20

6 Mineral Composition A B C 5/20

7 Bulk Porosity/% Gas Saturation/% Bulk Porosity/% Gas Saturation/% Porosity and Permeability Well B Well C y = x R² = Permeability/nanoDarcy y = x R² = Permeability/nanoDarcy Permeability is in nano-darcy scale y = x R² = Permeability/nanoDarcy y = x R² = Permeability/nanoDarcy 6/20

8 Organic-Matter Pore Types SEM Images Processing Workflow Isolating each part by grey scale setting Well A, ft, SE-SEM Original Pores Organic Matter High Density Particles 7/20

9 Organic-Matter Pore Types Spongy, ambiguous bitumenite or kerogen The most common organic matter pore type Well B ft Well C ft 500nm 500nm 8/20

10 Organic-Matter Pore Types Complex, organic matter pore involved with inorganic matrix forming a complex network Well B ft Well C ft 500nm 500nm 9/20

11 Organic-Matter Pore Types Discrete porosity, single organic matter pore developed in kerogen 500nm 500nm 500nm 500nm Well C ft Bubble porosity, featured high viscosity fluid Well C ft 500nm 500nm 500nm 500nm Well C ft Well A ft 10/20

12 Organic-Matter Pore Types Crack-like porosity, affected by post-depositional processes or stress release 1000nm 1000nm Well B ft 1000nm 1000nm Well C ft 11/20

13 An Interesting Observation There is no correlation between abundance of Organic matter and SEM-visible porosity in it. Averaged SEM porosity of all 32 samples 12/20

14 TOC/wt% Organic matter /% Bulk Porosity/% An Interesting Observation Digitalized SEM vs. Core analysis(gri Method) Well B y = x R² = Porosity/ % No correlation between OM and visible porosity in SEM, But positive correlation in GRI measured result Gas-filled Porosity/% y = x R² = Bulk Porosity/% 13/20

15 TOC/ wt% Organic Matter % Bulk Porosity/% An Interesting Observation Well C Digitalized SEM vs. Core analysis(gri Method) y = x R² = Gas-filled Porosity/% y = x R² = Porosity % Also, SEM porosity is lower than bulk porosity. Pores smaller than 10 nm cannot be identified Bulk Porosity/% 14/20

16 Gas-filled Porosity/% Gas-filled Porosity/% An Interesting Observation 9.00 Well B 6.00 Well C y = 0.621x R² = y = x R² = TOC/wt% TOC/wt% GRI method actually measures the interconnected pore space, which is mostly developed in OM. So, usually samples with higher TOC will show a higher porosity. 15/20

17 An Interesting Observation A significant portion of the effective porosity is less than 10 nm, which resulted in this deviation between the porosity from crushed-core-analysis and digitalized SEM. 16/20

18 Thermal Maturity and SEM Porosity 2D SEM Porosity Well A Ro: 2.59~2.89% Average Porosity: 2.52% Well B Ro: 1.37~1.46% Average Porosity: 2.0% Well C Ro: 1.36~1.39% Average Porosity: 1.0% Highest thermal maturity correlates with the highest SEM porosity 17/20

19 Count Thermal Maturity and SEM Porosity <Ro< <Ro< <Ro< Pore Size (feret diameter)/nm As thermal maturity increases, pores become smaller, and have a wider spectrum of size. 18/20

20 Conclusions Organic matter pores can be classified into five types according to their shape and relative location with the inorganic matrix: spongy, bubble, complex, discrete, and crack-like; SEM-visible porosity doesn t correlate with percentage of organic matter present. It does have a positive correlation with the thermal maturity and clay content; Pore size varies significantly in mudrock reservoirs, a finer pore size was noticed as thermal maturity went higher; In the Marcellus Organic-rich Shale, a significant portion of the effective porosity is less than 10 nm. 19/20

21 Acknowledgements 20/20

Application of NMR for Evaluation of Tight Oil Reservoirs

Application of NMR for Evaluation of Tight Oil Reservoirs Rick Lewis & Erik Rylander Iain Pirie Stacy Reeder, Paul Craddock, Ravi Kausik, Bob Kleinberg & Drew Pomerantz Lots of oil in place what is pay?