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Limitation of fault-sealing and its control on hydrocarbon accumulation—An example from the Laoyemiao Oilfield of the Nanpu Sag

Limitation of fault-sealing and its control on hydrocarbon accumulation—An example from the... Pet.Sci.(2008)5:295-301 295 DOI 10.1007/s12182-008-0049-6 296 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 297 SDT, μs/m 3 Compensated density, g/cm 200 240 280 320 1.8 2 2.2 2.4 2.6 2720 2720 2740 2740 Upper induced fracture zone 2760 2760 Crushed zone Lower induced fracture zone Fig. 3 Log response characteristics of fault belt in M28-1 well in the Laoyemiao Oilfi eld or only change gradually, which would result in a consistent where H is the highest oil column sealed by the fault, m; g is oil-water boundary on one side of the fault like a “brush”. the acceleration of gravity, m/s ; is the water density in the 3 3 The following sections present the analysis about the reservoir, g/cm ; is the oil density in the reservoir, g/cm , relationship between oil column height at present and oil which is 0.8g/cm in this area. column boundary height sealed by the fault. The critical height of an oil column sealed by the fault can The fault sealing capability could be evaluated by the be calculated according to the above empirical equations and displacement pressure of the fault belt. Acoustic travel the statistical data are showed in Table 1. The measured data time is dependent on lithology, and its response to the rock of nine reservoirs in two wells in the study area are compared pore configuration is sensitive. Thus there is normally a with the calculated values sealed by the corresponding faults. good correspondence between acoustic travel time and It indicates that the deviations between oil columns in the sealing capability of faults. The displacement pressure lower reservoirs and the calculated values are small, below can be calculated directly from acoustic travel time. Some 7%. The good agreement of measured oil column values and researchers have made studies on this subject in the Songliao calculated critical height values indicates that the reservoir Basin, Tarim Basin and Qiongdongnan Basin. Taking the is in critical saturation condition. However, the differences data of the Songliao Basin for example, the corresponding between the oil column heights in the upper reservoirs and relationships between the displacement pressure and porosity, the calculated values are above 8%. It indicates that they are acoustic travel time and porosity of mudstone, silty mudstone not in the critical saturation condition. Generally speaking, as well as argillaceous siltstone have been established. An the hydrocarbon sealing capability of the fault is limited. empirical equation between the displacement pressure and Hydrocarbons would spill over along the fault and migrate to acoustic travel time for mudstone, silty mudstone as well as the upper reservoirs if the oil column height in the reservoir argillaceous siltstone has been presented (Qu et al, 2005). reaches the critical value which could be sealed by the fault. According to the lithological characteristics of fault belts in The limited sealing capability of the faults can be inferred the Nanpu Sag area, the empirical equation for silty mudstone from the above discussion. The fault does not have complete is chosen to calculate the displacement pressure of the fault sealing capability and is only effective within a limited belt. oil column height. Smith (1966) demonstrated a theory by Pc=108/(0.0745∆t 13.5745) 4 .0 (1) displacement pressure. He believed that hydrocarbon would where Pc is the displacement pressure of the fault, MPa; ∆t is migrate along the fault and accumulate in the lower wall the acoustic travel time of the fault belt, μs/m. of the fault if there was a difference between displacement Based on the sealing principle of capillary pressure, the pressures of fault belts and that of the reservoir beds (the highest oil column that the fault could seal is: displacement pressure of the fault belt is larger than that of the reservoir bed) until the buoyancy force caused by oil H=Pc/g( ) (2) column height balanced the displacement pressure difference. w 0 Depth, m Depth, m 298 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 299 300 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 301 and implications for hydraulic structure of fault zones. Journal of capability of the lower induced fracture zone with fewer Structural Geology. 1997. 19(11): 1393-1404 fractures and some permeability is found to be between that Fau lkner D R, Lewis A C and Rutter E H. On the internal structure of mudstone and sandstone; the middle crushed zone has the and mechanics of large strike-slip fault zones: fi eld observations of best sealing and confi ning capability, which can prevent fl uids the Carboneras fault in southeastern Spain. Tectonophysics. 2003. from leaking. 367(3): 235-251 2) The physical simulation, geological statistics and Fu X F , Fang D Q, Lv Y F, et al. Method of evaluating vertical sealing theoretically calculated data indicate that the fault-sealing of faults in terms of the internal structure of fault zones. Earth for hydrocarbons in the Nanpu Sag is limited. Hydrocarbons Science—Journal of China University of Geosciences. 2005. 30(3): will spill over along the lower induced fracture zone when 328-336 (in Chinese) the buoyancy force caused by oil column is greater than the Gér aud Y, Diraison M and Orellana N. Fault zone geometry of a mature difference between displacement pressures of the reservoir active normal fault: a potential high permeability channel (Pirgaki Fault, Corinth Rift, Greece). Tectonophysics. 2006. 426(1-2): 61-76 and the lower induced fracture zone. In this situation, Mic arelli L, Benedicto A and Wibberley C A J. Structural evolution and the reservoir is in its critical saturation state, and its size permeability of normal fault zones in highly porous carbonate rocks. reaches a maximum. The charging sequence of the fault- Journal of Structural Geology. 2006. 28(7): 1214-1227 sealed reservoirs in the lower wall of the fault is from lower Qu J H, Peng J L and Lei Z J. The appraisal of cap formation enclosing formation to upper formation. The size and saturation of the capability in the Kela2 gas fi eld by acoustic logging method. Natural upper reservoirs depends on hydrocarbons supplied. Gas Geoscience. 2005. 16(6): 758-760 (in Chinese) 3) Fault-sealed hydrocarbon reservoirs in the Nanpu Sag Smi th D A. Theoretical considerations of sealing and non-sealing faults. can be divided into consequent fault-sealed trap and reverse AAPG Bulletin. 1966. 50(2): 363-374 fault-sealed traps according to the dips of the fault and the Son g S H. Analysis of hydrocarbon migration based on the interior formation. The former trap is sealed by the upper induced structure of fault zone. Journal of Daqing Petroleum Institute. 2005. fracture zone, whereas the latter is sealed by the lower 30(3): 17-20 (in Chinese) Tsu tsumi A, Nishino S, Mizoguchi K, et al. Principal fault zone width induced fracture zone. The difference in sealing capability and permeability of the active Neodani Fault, Nobi fault system, between upper and lower induced fracture zones results in southwest Japan. Tectonophysics. 2004. 379(1-4): 93-108 a huge difference of oil-bearing properties between these Wib berley C A J and Shimamoto T. Internal structure and permeability two kinds of fault-sealed traps. The consequent fault-sealed of major strike-slip fault zones: the Media Tectonic Line in Mie trap has a poor reservoir sealing capability and should be prefecture, southwest Japan. Journal of Structural Geology. 2003. avoided in future selection of drilling targets. It is suggested 25(1): 59-78 that the reverse fault-sealed traps should be the favorable and Xin R C, Jiang Z X and Li S T. Physical modeling of secondary oil preferred exploration targets in the Nanpu Sag. migration and accumulation in deltaic sandstone reservoir and its result analysis. Earth Science—Journal of China University of Acknowledgements Geosciences. 2002. 27(6): 780-782 (in Chinese) Zh ou H M, Cong L Z, Dong Y X, et al. Description of petroleum This work is supported by the Key Project of Chinese accumulation dynamics and petroleum systems in rift basins— National Programs for Fundamental Research and using the Nanpu Sag in the Bohai Bay Basin as an example. Beijing: Development (973 Program, No. 2006CB202308) and the Petroleum Industry Press. 2005a. 10-16 (in Chinese) National Natural Science Foundation of China (Grant No. Zho u H M, Dong Y X, Xie Z A, et al. Theoretics and practice of 40472078). petroleum exploration in rift basins—using the Nanpu Sag in the Bohai Bay Basin as an example. Beijing: Petroleum Industry Press. References 2005b. 72-93 (in Chinese) Zho u Q H. Study on fault closure based on interior structure of fracture Eng land W A, Mackenzie A S, Mann D M, et al. The movement and belt. Petroleum Geology & Oilfi eld Development in Daqing. 2005. entrapment of petroleum fluids in the subsurface. Journal of the 24(6): 1-3 (in Chinese) Geological Society. 1987. 144(2): 327-347 Eva ns J, Forster C and Goddard J. Permeability of fault-related rocks, (Edited by Hao Jie) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Petroleum Science Springer Journals

Limitation of fault-sealing and its control on hydrocarbon accumulation—An example from the Laoyemiao Oilfield of the Nanpu Sag

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Publisher
Springer Journals
Copyright
Copyright © 2008 by China University of Petroleum (Beijing) and Springer-Verlag GmbH
Subject
Earth Sciences; Mineral Resources; Industrial Chemistry/Chemical Engineering; Industrial and Production Engineering; Energy Economics
ISSN
1672-5107
eISSN
1995-8226
DOI
10.1007/s12182-008-0049-6
Publisher site
See Article on Publisher Site

Abstract

Pet.Sci.(2008)5:295-301 295 DOI 10.1007/s12182-008-0049-6 296 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 297 SDT, μs/m 3 Compensated density, g/cm 200 240 280 320 1.8 2 2.2 2.4 2.6 2720 2720 2740 2740 Upper induced fracture zone 2760 2760 Crushed zone Lower induced fracture zone Fig. 3 Log response characteristics of fault belt in M28-1 well in the Laoyemiao Oilfi eld or only change gradually, which would result in a consistent where H is the highest oil column sealed by the fault, m; g is oil-water boundary on one side of the fault like a “brush”. the acceleration of gravity, m/s ; is the water density in the 3 3 The following sections present the analysis about the reservoir, g/cm ; is the oil density in the reservoir, g/cm , relationship between oil column height at present and oil which is 0.8g/cm in this area. column boundary height sealed by the fault. The critical height of an oil column sealed by the fault can The fault sealing capability could be evaluated by the be calculated according to the above empirical equations and displacement pressure of the fault belt. Acoustic travel the statistical data are showed in Table 1. The measured data time is dependent on lithology, and its response to the rock of nine reservoirs in two wells in the study area are compared pore configuration is sensitive. Thus there is normally a with the calculated values sealed by the corresponding faults. good correspondence between acoustic travel time and It indicates that the deviations between oil columns in the sealing capability of faults. The displacement pressure lower reservoirs and the calculated values are small, below can be calculated directly from acoustic travel time. Some 7%. The good agreement of measured oil column values and researchers have made studies on this subject in the Songliao calculated critical height values indicates that the reservoir Basin, Tarim Basin and Qiongdongnan Basin. Taking the is in critical saturation condition. However, the differences data of the Songliao Basin for example, the corresponding between the oil column heights in the upper reservoirs and relationships between the displacement pressure and porosity, the calculated values are above 8%. It indicates that they are acoustic travel time and porosity of mudstone, silty mudstone not in the critical saturation condition. Generally speaking, as well as argillaceous siltstone have been established. An the hydrocarbon sealing capability of the fault is limited. empirical equation between the displacement pressure and Hydrocarbons would spill over along the fault and migrate to acoustic travel time for mudstone, silty mudstone as well as the upper reservoirs if the oil column height in the reservoir argillaceous siltstone has been presented (Qu et al, 2005). reaches the critical value which could be sealed by the fault. According to the lithological characteristics of fault belts in The limited sealing capability of the faults can be inferred the Nanpu Sag area, the empirical equation for silty mudstone from the above discussion. The fault does not have complete is chosen to calculate the displacement pressure of the fault sealing capability and is only effective within a limited belt. oil column height. Smith (1966) demonstrated a theory by Pc=108/(0.0745∆t 13.5745) 4 .0 (1) displacement pressure. He believed that hydrocarbon would where Pc is the displacement pressure of the fault, MPa; ∆t is migrate along the fault and accumulate in the lower wall the acoustic travel time of the fault belt, μs/m. of the fault if there was a difference between displacement Based on the sealing principle of capillary pressure, the pressures of fault belts and that of the reservoir beds (the highest oil column that the fault could seal is: displacement pressure of the fault belt is larger than that of the reservoir bed) until the buoyancy force caused by oil H=Pc/g( ) (2) column height balanced the displacement pressure difference. w 0 Depth, m Depth, m 298 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 299 300 Pet.Sci.(2008)5:295-301 Pet.Sci.(2008)5:295-301 301 and implications for hydraulic structure of fault zones. Journal of capability of the lower induced fracture zone with fewer Structural Geology. 1997. 19(11): 1393-1404 fractures and some permeability is found to be between that Fau lkner D R, Lewis A C and Rutter E H. On the internal structure of mudstone and sandstone; the middle crushed zone has the and mechanics of large strike-slip fault zones: fi eld observations of best sealing and confi ning capability, which can prevent fl uids the Carboneras fault in southeastern Spain. Tectonophysics. 2003. from leaking. 367(3): 235-251 2) The physical simulation, geological statistics and Fu X F , Fang D Q, Lv Y F, et al. Method of evaluating vertical sealing theoretically calculated data indicate that the fault-sealing of faults in terms of the internal structure of fault zones. Earth for hydrocarbons in the Nanpu Sag is limited. Hydrocarbons Science—Journal of China University of Geosciences. 2005. 30(3): will spill over along the lower induced fracture zone when 328-336 (in Chinese) the buoyancy force caused by oil column is greater than the Gér aud Y, Diraison M and Orellana N. Fault zone geometry of a mature difference between displacement pressures of the reservoir active normal fault: a potential high permeability channel (Pirgaki Fault, Corinth Rift, Greece). Tectonophysics. 2006. 426(1-2): 61-76 and the lower induced fracture zone. In this situation, Mic arelli L, Benedicto A and Wibberley C A J. Structural evolution and the reservoir is in its critical saturation state, and its size permeability of normal fault zones in highly porous carbonate rocks. reaches a maximum. The charging sequence of the fault- Journal of Structural Geology. 2006. 28(7): 1214-1227 sealed reservoirs in the lower wall of the fault is from lower Qu J H, Peng J L and Lei Z J. The appraisal of cap formation enclosing formation to upper formation. The size and saturation of the capability in the Kela2 gas fi eld by acoustic logging method. Natural upper reservoirs depends on hydrocarbons supplied. Gas Geoscience. 2005. 16(6): 758-760 (in Chinese) 3) Fault-sealed hydrocarbon reservoirs in the Nanpu Sag Smi th D A. Theoretical considerations of sealing and non-sealing faults. can be divided into consequent fault-sealed trap and reverse AAPG Bulletin. 1966. 50(2): 363-374 fault-sealed traps according to the dips of the fault and the Son g S H. Analysis of hydrocarbon migration based on the interior formation. The former trap is sealed by the upper induced structure of fault zone. Journal of Daqing Petroleum Institute. 2005. fracture zone, whereas the latter is sealed by the lower 30(3): 17-20 (in Chinese) Tsu tsumi A, Nishino S, Mizoguchi K, et al. Principal fault zone width induced fracture zone. The difference in sealing capability and permeability of the active Neodani Fault, Nobi fault system, between upper and lower induced fracture zones results in southwest Japan. Tectonophysics. 2004. 379(1-4): 93-108 a huge difference of oil-bearing properties between these Wib berley C A J and Shimamoto T. Internal structure and permeability two kinds of fault-sealed traps. The consequent fault-sealed of major strike-slip fault zones: the Media Tectonic Line in Mie trap has a poor reservoir sealing capability and should be prefecture, southwest Japan. Journal of Structural Geology. 2003. avoided in future selection of drilling targets. It is suggested 25(1): 59-78 that the reverse fault-sealed traps should be the favorable and Xin R C, Jiang Z X and Li S T. Physical modeling of secondary oil preferred exploration targets in the Nanpu Sag. migration and accumulation in deltaic sandstone reservoir and its result analysis. Earth Science—Journal of China University of Acknowledgements Geosciences. 2002. 27(6): 780-782 (in Chinese) Zh ou H M, Cong L Z, Dong Y X, et al. Description of petroleum This work is supported by the Key Project of Chinese accumulation dynamics and petroleum systems in rift basins— National Programs for Fundamental Research and using the Nanpu Sag in the Bohai Bay Basin as an example. Beijing: Development (973 Program, No. 2006CB202308) and the Petroleum Industry Press. 2005a. 10-16 (in Chinese) National Natural Science Foundation of China (Grant No. Zho u H M, Dong Y X, Xie Z A, et al. Theoretics and practice of 40472078). petroleum exploration in rift basins—using the Nanpu Sag in the Bohai Bay Basin as an example. Beijing: Petroleum Industry Press. References 2005b. 72-93 (in Chinese) Zho u Q H. Study on fault closure based on interior structure of fracture Eng land W A, Mackenzie A S, Mann D M, et al. The movement and belt. Petroleum Geology & Oilfi eld Development in Daqing. 2005. entrapment of petroleum fluids in the subsurface. Journal of the 24(6): 1-3 (in Chinese) Geological Society. 1987. 144(2): 327-347 Eva ns J, Forster C and Goddard J. Permeability of fault-related rocks, (Edited by Hao Jie)

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Petroleum ScienceSpringer Journals

Published: Nov 21, 2008

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