Access the full text.
Sign up today, get DeepDyve free for 14 days.
E. Sloan, C. Koh (1990)
Clathrate hydrates of natural gases
(2010)
A instrument for measuring the physical properties of hydrate-bearing reservoirs
A. Masui, H. Haneda, Y. Ogata, K. Aoki (2007)
Mechanical Properties of Sandy Sediment Containing Marine Gas Hydrates In Deep Sea Offshore Japan
R. Z. Huang (1999)
104
T. Yun (2005)
Mechanical and Thermal Study of Hydrate Bearing Sediments
U. Tinivella (1999)
A method for estimating gas hydrate and free gas concentrations in marine sedimentsBollettino Di Geofisica Teorica Ed Applicata, 40
Sun Zhi (2002)
Determination of Dissociation Heat of Natural Gas HydratesJournal of Instrumental Analysis
(1998)
Research on triaxial shear strength principle of typical artificially frozen soil
C. Tan, R. Freij-Ayoub, M. Clennell, B. Tohidi, Jinhai Yang (2005)
Managing wellbore instability risk in gas hydrate-bearing sediments
B. Wu, C. Tan, T. Aoki (1997)
Specially designed techniques for conducting consolidated undrained triaxial tests on low permeability shalesInternational Journal of Rock Mechanics and Mining Sciences, 34
H. Niandou, J. Shao, J. Henry, D. Fourmaintraux (1997)
Laboratory investigation of the mechanical behaviour of Tournemire shaleInternational Journal of Rock Mechanics and Mining Sciences, 34
A new type of hydrates shear strength apparatus. Chinese Patent: ZL
X. S. Chen (1998)
2Mine Construction Technology, 19
(1999)
Calculation model of borehole collapse and fracturing pressure
C. Clayton, J. Priest, A. Best (2005)
The effects of disseminated methane hydrate on the dynamic stiffness and damping of a sandGeotechnique, 55
(1994)
Confi ned shear test on sea ice
W. Winters, I. Pecher, W. Waite, D. Mason (2004)
Physical properties and rock physics models of sediment containing natural and laboratory-formed methane gas hydrateAmerican Mineralogist, 89
E. Hoek (1980)
989Journal of the Geotechnical Engineering Division, 106
E. Hoek, E. Brown (1980)
EMPIRICAL STRENGTH CRITERION FOR ROCK MASSESJournal of Geotechnical and Geoenvironmental Engineering, 106
E. Hoek, E. Brown (1980)
Empirical strength criterion for rock massesJournal of the Geotechnical Engineering Division, 106
Pet.Sci.(2011)8:177-182 177 DOI 10.1007/s12182-011-0132-2 An experimental study of shear strength of gas-hydrate-bearing core samples Zhang Weidong , Ma Qingtao, Wang Ruihe and Ren Shaoran School of Petroleum Engineering, China University of Petroleum, Dongying, Shandong 257061, China © China University of Petroleum (Beijing) and Springer-Verlag Berlin Heidelberg 2011 Abstract: The shear strength of gas-hydrate-bearing reservoirs is one of the most important parameters used to study mechanical properties of gas-hydrate-bearing reservoirs. The shear strength of gas-hydrate- bearing reservoirs changes with fi lling and cementation of gas hydrates, which will affect the wellbore and reservoir stability. Traditional shear tests could not be conducted on gas-hydrate-bearing core samples because the gas hydrates exist under a limited range of temperature and pressure conditions. This paper describes a novel shear apparatus for studying shear strength of gas-hydrate-bearing core samples under original reservoir conditions. The preparation of gas-hydrate-bearing core samples and subsequent shear tests are done in the same cell. Cohesion and internal friction angle of the core samples with different saturations of gas hydrates were measured with the apparatus. The effect of gas hydrates on the shear strength of reservoirs was quantitatively analyzed. This provides a foundation for studying wellbore and reservoir stability of gas-hydrate-bearing reservoirs. Key words: Natural gas hydrate, reservoir, experimental apparatus, shear test, internal cohesion, internal friction angle and quartz powders containing gas hydrates in the laboratory. 1 Introduction Moreover they studied the cohesion and friction angle of Shear strength is one of the most important mechanical quartz powders when the saturations of gas hydrates were parameters of reservoir rocks in analyzing wellbore stability. 50% and 0. However, it is diffi cult to measure the shear strength of gas- In this study, we developed a new experimental setup to hydrate-bearing core samples with commonly-used shear investigate the properties of gas-hydrate-bearing core samples apparatus due to the presence of gas hydrates, which form under high pressure and low temperature. when natural gas molecules and water come into contact at low temperature and high pressure (Tan et al, 2005). 2 Experimental To solve this problem, Wu et al (1997) developed a Hoek triaxial cell for gas hydrate-bearing deposits. This device 2.1 Experimental apparatus could be used to measure mechanical properties and failure The shea r apparatus shown in Fig. 1 was used for gas mechanisms of sediments containing gas hydrates under hydrate formation followed by shear testing. In the same cell, confi ning pressures. However, its core cell is so small that the the core samples containing gas hydrates were formed and gas hydrates are not evenly distributed in the artificial core then shear tests were conducted, avoiding inconveniences samples, leading to large errors in shear strength. Clayton and involved in core preparation and installation in shear tests. Priest (2005) built a resonant column apparatus to synthesize The main component of this device was the shear unit methane hydrate-bearing sediments and to measure their installed in the pressure cell and the shear unit consisted shear strength based the original triaxial shear apparatus. of the shear cell and piston mechanisms. The shear cell After conducting triaxial shear tests on original hydrate had two chambers, and the connection was sealed with an deposits from the Malik 2L-38 well, Mackenzie Delta, annular piston. The upper cell was equipped with a piston for Northwest Territories, Winters et al (2004) proposed that the compacting and a water inlet, a transverse piston mechanism shear strength of sediments containing gas hydrates increased was installed on the middle of the upper cell. Piston with an increase in gas hydrate saturation. Researchers at the mechanisms were installed on both side of the lower cell. Georgia Institute of Technology tested the Poisson ratio, shear The lower cell had a gas inlet and a water outlet. All piston strength, and other mechanical parameters of sands, clays, mechanisms were connected to the high pressure pump by hydraulic lines. The lower shear cell was fi xed on the bottom of *Corresponding author. email: wdzhang@upc.edu.cn the high pressure cell, and the upper one was connected to the Received October 9, 2010 top of the high pressure cell. A circulating water bath with an 178 Pet.Sci.(2011)8:177-182 Pet.Sci.(2011)8:177-182 179 Table 1 Data acquired in the shearing process water from the bottom of the shear cell until the pressure reaches 7 MPa. 13) The pressure in the high pressure cell Pressure in Confi ning Shear pump Time Temperature will decline as the reaction goes on. It is necessary to refill the shear cell pressure pressure s ºC the distilled water at frequent intervals to maintain pressure MPa MPa MPa at 7 MPa. 14) Repeat Step 13 until the pressure is constant. 0 10.7 11.0 6.00 3.9 The methane injected into the cell will completely react with 5 10.7 11.0 6.13 3.9 water to form hydrates. Shear test 1) Apply the confi ning pressure of 7 MPa to 10 10.8 11.1 6.22 3.9 the shear cell, which equals the pressure in the high-pressure 15 10.8 11.2 6.28 3.9 cell. 2) Push the annular piston down to shear the core 20 10.8 11.1 6.32 3.9 sample. 3) Record the pressure changes. The pressure will rise slowly at the beginning and then decline sharply when 25 10.8 11.1 6.32 3.9 the core sample is sheared. 4) Record the pressure P when 30 10.8 11.1 6.32 3.9 the shear failure happens in the shear cell. The lateral pushing force F is equal to the product of the pressure P times the area 35 10.7 11.2 6.32 3.9 of the lateral piston A. The ratio of F to A is the shear strength 40 10.8 11.1 6.32 4.0 of the hydrate-bearing core sample. 45 10.9 11.2 6.32 4.0 2.3 Determination of gas hydrate saturation 50 10.9 11.2 6.32 4.0 The hydration reaction of methane is given by (Sloan, 52 10.9 11.2 6.32 4.0 1998): 54 11.0 11.1 6.40 4.0 CH (g)+nn H O (l) o CH H O (s) 4 hyd 2 4 hyd 2 56 11.0 11.1 6.45 3.9 58 11.0 11.1 6.58 3.7 where n is the hydration number, the molar ratio of water hyd reacting with methane, n = 5.75 in this case. hyd 60 11.0 11.0 6.78 3.5 After the temperature and pressure of the core cell are 62 11.0 11.0 6.90 3.4 stabilized, all methane injected into the cell is assumed to react completely with water. There are only gas hydrates and 64 11.0 11.0 6.44 3.4 water remaining in the artifi cial core samples. Then the gas 66 11.0 11.0 6.32 3.4 hydrate saturation can be calculated as follows (Ren et al, 68 11.0 11.0 6.32 3.4 2010): 70 11.0 11 6.32 3.4 P VM CH CH h ZRTV U pore h during 0-20 s, and the shear piston began to move when the pressure reached 6.32 MPa, i.e. starting pressure under where S is the gas hydrate saturation; V and P are the h CH CH 4 4 experimental conditions. The shear piston began to move injection volume and pressure of methane, L; M is the molar upwards to push the upper shear cell at the time of 54 s, and mass of methane hydrates, g/mol; R is the gas constant, the shear failure occurred during 54-62 s for gas-hydrate- R = 8.31 J/(mol·K); V is the pore volume, L; Z is the pore bearing core samples. The maximum shear pressure was gas compressibility factor; ρ is the gas hydrates density, 3 6.9 MPa. It was at the pressure release stage after 62 s, and ρ = 0.91 g/cm . the pressure was back to 6.32 MPa at the end. So the shear strength was 0.58 MPa (6.90−6.32) under the test conditions. 2.4 Analysis of shearing process In the process of gas hydrate formation, the injection 7.0 pressure of methane was kept at 3.7 MPa and the methane injection volume was 2 L. The gas hydrate saturation was 6.7 calculated to be 55% from Eq. (2). In the shearing process, the back pressure was kept at 11 MPa to insure the confi ning 6.4 pressure higher than 11 MPa. At the early stage, the shear piston did not contact with the shear cell and the data were 6.1 recorded every 5 seconds. At the later stage, the piston pushed down into the shear cell and the data were recorded every 2 seconds as the pressure changed quickly. The experimental 5.8 0 20 40 60 80 results are shown in Table 1. Time, s 2.4.1 Shear pump pressure As shown in Fig. 3, the shear pump was pressurized Curve of pump pressure vs. time in the shearing process Fig. 3 Pressure, MPa m 180 Pet.Sci.(2011)8:177-182 4.2 2.4.2 Shear cell temperature As Fig. 4 shows, the temperature of the high-pressure 4.0 cell increased slightly due to the interference of external temperature in the piston compression process. The 3.8 temperature declined significantly at 58 s, eventually to 3.4 3.6 ºC. This is because the lower and upper shear cells were disconnected and the gas hydrates absorbed heat and then 3.4 partially dissociated into gas and water (Sun et al, 2002). 3.2 0 20 40 60 80 3 Result analyses Time, s Shear test data on gas-hydrate-bearing core samples Fig. 4 Curve of temperature vs. time in the shearing process are shown in Table 2. The shear strength is the cohesion of hydrate-bearing samples when the axial pressure is 0. The 3.1 Cohesion internal friction angle of hydrate-bearing core samples was Fig. 5 shows that the cohesion of artifi cial hydrate-bearing calculated according to the Mohr-Coulomb criterion and core samples increased quickly with increasing hydrate shear forces at different axial pressures (Huang et al, 1999). Table 2 Shear test data on core samples containing different contents of gas hydrates Gas hydrate Gas hydrate Gas hydrate formation Temperature Axial pressure Shear force No. saturation formation time pressure ºC MPa MPa % h MPa 1 0 158 11.1 3.7 1.0 0.29 2.0 0.56 0 0.05 2 5 162 11.0 3.7 1.0 0.32 2.0 0.60 0 0.14 3 15 160 11.3 3.7 1.0 0.45 2.0 0.78 0 0.20 4 25 160 11.2 3.5 1.0 0.55 2.0 0.9 0 0.28 5 35 159 11.0 3.5 1.0 0.72 2.0 1.13 0 0.41 6 45 160 11.0 3.5 1.0 0.95 2.0 1.47 0 0.52 7 50 161 11.2 3.3 1.0 1.06 2.0 1.62 0 0.55 8 55 161 11.1 3.3 1.0 1.22 2.0 1.85 Temperature, °C Pet.Sci.(2011)8:177-182 181 182 Pet.Sci.(2011)8:177-182 Slo an Jr. E D. Clathrate hydrates of natural gases. Marcel Dekker Inc. Acknowledgements New York. 1998. 15-18 Sun Z G, Fan S S, Guo K H, et al. Determination of dissociation heat of The authors are grateful for financial support from natural gas hydrates. Journal of Instrumental Analysis. 2002. 21(3): “Preliminary Research on natural gas hydrates production” 7-9 (in Chinese) from SINOPEC (No. P06070). Tan C P, Freij-Ayoub F, Clennell M B, et al. Managing wellbore instability risk in gas-hydrate-bearing sediments. Paper SPE 92960 References presented at Asia Pacifi c Oil & Gas Conference and Exhibition, 5-7 Che n X S, Wang C X and Wu C Y. Research on triaxial shear strength April 2005, Jakarta, Indonesia principle of typical artificially frozen soil. Mine Construction Tin ivella U. A method for estimating gas hydrate and free gas Technology. 1998. 19(4): 2-4 (in Chinese) concentrations in marine sediments. Bollettino di Geofisca Teorica Cla yton C R I and Priest A I. The effects of disseminated methane Applicata. 1999. 40. 19-30 hydrate on the dynamic stiffness and damping of a sand. Win ters W J, Pecher I A, Waite1 W F, et al. Physical properties and Geotechnique. 2005. 55(6): 423-434 rock physics models of sediment containing natural and laboratory- Hoe k E and Brown E. Empirical strength criterion for rock masses. formed methane gas hydrate. American Mineralogist. 2004. 89: Journal of the Geotechnical Engineering Division. 1980. 106(GT9): 1221-1227 989-1013 Wu B, Tan C P and Aoki T. Specially designed techniques for conducting Hua ng R Z, Deng J G and Chen M. Calculation model of borehole consolidated undrained triaxial tests on low permeability shales. collapse and fracturing pressure. Beijing: Petroleum Industry Press. International Journal of Rock Mechanics and Mining Science. 1997. 1999. 104-112 (in Chinese) 34: 3-4 Mas ui A, Haneda H, Ogata Y, et al. Mechanical properties of sandy Yin Y W, Zhang W D, Wang R H, et al. A new type of hydrates shear sediment containing marine gas hydrates in deep sea offshore strength apparatus. Chinese Patent: ZL 200820027803. 6 (in Chinese) Japan. In: Proceedings of the 17th International Offshore and Polar Yue Q J, Zhou X A and Shen W. Confi ned shear test on sea ice. Journal Engineering, Ocean Mining Symposium, Lisbon, Portugal. July 1-6, of Glaciology and Geocryology. 1994. 16(1): 77-78 (in Chinese) 2007. 53-56 Yun T S. Mechanical and thermal study of hydrate bearing sediments. In: Ren S R, Shang X S and Zhang W D. A instrument for measuring the Partial Fulfi llment of the Requirements for the Degree of Doctor of physical properties of hydrate-bearing reservoirs. Chinese Patent: Philosophy in Civil and Environmental Engineering. May 24, 2005 201020127827.6 (in Chinese) (Edited by Sun Yanhua)
Petroleum Science – Springer Journals
Published: May 28, 2011
You can share this free article with as many people as you like with the url below! We hope you enjoy this feature!
Read and print from thousands of top scholarly journals.
Already have an account? Log in
Bookmark this article. You can see your Bookmarks on your DeepDyve Library.
To save an article, log in first, or sign up for a DeepDyve account if you don’t already have one.
Copy and paste the desired citation format or use the link below to download a file formatted for EndNote
Access the full text.
Sign up today, get DeepDyve free for 14 days.
All DeepDyve websites use cookies to improve your online experience. They were placed on your computer when you launched this website. You can change your cookie settings through your browser.