Modelling of the Normal Fault Pattern above a Basement Horst in the Lufeng Sag, China

96 Pages·2016·10.26 MB·English

Examensarbete vid Institutionen för geovetenskaper
Degree Project at the Department of Earth Sciences
ISSN 1650-6553 Nr 385
Modelling of the Normal Fault
Pattern above a Basement Horst
in the Lufeng Sag, China
Modellering av förkastningsmönster ovanför en
berggrundshorst i Lufen-sänkan, Kina
Yu Niu
INSTITUTIONEN FÖR
GEOVETENSKAPER
DEPARTMENT OF EARTH SCIENCES

Examensarbete vid Institutionen för geovetenskaper
Degree Project at the Department of Earth Sciences
ISSN 1650-6553 Nr 385

Modelling of the Normal Fault
Pattern above a Basement Horst
in the Lufeng Sag, China
Modellering av förkastningsmönster ovanför en
berggrundshorst i Lufen-sänkan, Kina

Yu Niu
ISSN 1650-6553

Copyright © Yu Niu
Published at Department of Earth Sciences, Uppsala University (www.geo.uu.se), Uppsala, 2016
Abstract

Modelling of the Normal Fault Pattern above a Basement Horst in the Lufeng Sag, China
Yu Niu

The analogue models and the kinematic models based on the seismic data results were used to simulate
the fault pattern which develops above a basement horst. The two major normal faults intersect with
each other along the strike in the sedimentary covers. The fault pattern developed in the sedimentary
cover is controlled by the dip of the basement fault and the width of the basement horst. The single horst
structure was only developed in the sedimentary covers above the wider end of the basement horst. The
hourglass structure was developed in the sedimentary covers above the narrower end of the basement
horst. The precursor faults developed ahead of the major second-order normal faults when the dip angle
of the basement fault is larger than 60°. The antithetic faults developed ahead of the major second-order
normal faults when the dip angle of the basement fault is less than 50°. The analogue models were
designed in a way that the two hanging wall blocks glide down along the basement horst simultaneously
to simulate the activity of the basement faults. The kinematic models were designed based on the
alternative sequential slip method to study the kinematic behaviors of the conjugate normal faults. The
Lufeng Sag was characterized by the basement horst in the center and the deep half-grabens developed
beside the horst. The width of the basement horst decreases along its strike. The models indicates that
the second-order normal faults developed above the basement horst, observed in the Lufeng Sag seismic
profiles, were reproducible and much more detailed structures were revealed.

Keywords: Conjugate normal fault, analogue modelling, kinematic modelling, Lufeng Sag, MOVETM

Degree Project E1 in Earth Science, 1GV025, 30 credits
Supervisors: Hemin Koyi and Fusheng Yu
Department of Earth Sciences, Uppsala University, Villavägen 16, SE-75236 Uppsala (www.geo.uu.se)

ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, No. 385, 2016

The whole documents is available at www.diva-portal.org
Sammanfattning

Modellering av förkastningsmönster ovanför en berggrundshorst i Lufen-sänkan, Kina
Yu Niu

I detta projekt har analog modellering och kinematiska modeller baserade på seismiska data använts för
att simulera förkastningsmönster ovanför en berggrundshorst. Två stora normal förkastningar möts i
strykningsriktningen hos de ovanliggande sedimentlagren. Förkastningsmönstret som utvecklats i
ovanliggande sedimentlager styrs av stupningen hos underliggande urberg samt bredden hos den
underliggande horsten. Den enda horststrukturen som utvecklades i sedimentlagren skedde i fallet med
en bredare underliggande horststruktur. En timglasstruktur bildades i den sedimentära successionen vid
den smalare ändan av berggrundshorsten. De initiala förkastningarna bildades tidigt för att sedan övergå
i andra ordningens normalförkastningar i de fall då stupningen hos underliggande berggrund överstiger
60°. Mindre antitetiska förkastningar bildades före andra ordningens förkastningar där berggrunds-
stupningen understiger 50°. Den analoga modell som nyttjades experimentellt var konstruerad så att de
två hängväggskomponenterna kunde röra sig fritt samtidigt längs med berggrundshorsten för att
simulera aktivering av befintliga förkastningar i berggrunden. De kinematiska modeller som nyttjades
var konstruerade enligt metoden för sekventiella rörelser (eng - sequential slip method) för att studera
kinematiska beteenden hos konjugerande förkastningspar. Lufeng-sänkans utseende har kontrollerats av
berggrundshorsten i mitten samt av de djupa halv-grabens på båda sidorna av horsten. Bredden på
berggrundshorsten minskar längs dess stupning. Modellerna påvisar att andra ordningens normal-
förkastningar bildades ovanför berggrundshorsten, likt i de seismiska profilerna över området, samt att
strukturerna var reproducerbara och väldigt detaljrika.

Nyckelord: Konjugerande förkastningspar, analog modellering, kinematisk modellering, Lufeng-
sänkan, MOVETM

Examensarbete E1 i geovetenskap, 1GV025, 30 hp
Handledare: Hemin Koyi och Fusheng Yu
Institutionen för geovetenskaper, Uppsala universitet, Villavägen 16, 752 36 Uppsala (www.geo.uu.se)

ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, Nr 385, 2016

Hela publikationen finns tillgänglig på www.diva-portal.org
Table of Contents

1. Introduction ..................................................................................................... 1
2. Background ...................................................................................................... 4
2.1 Geological setting ................................................................................................................... 4
2.2 Structural evolution of the Pearl River Mouth Basin .............................................................. 7
2.3 Lufeng Sag .............................................................................................................................. 8
2.4 History and the principle of the analogue modelling ............................................................ 11
3. Methodology ................................................................................................... 12
3.1 Materials and preparations .................................................................................................... 12
3.2 Extension ............................................................................................................................... 14
3.3 Scanning ................................................................................................................................ 16
3.4 Cutting ................................................................................................................................... 16
3.5 Modelling in 3D-MOVETM ................................................................................................... 17
4. Results ............................................................................................................. 20
4.1. Analogue models .................................................................................................................. 20
4.1.1 Model-1 .................................................................................................................... 21
4.1.2 Model 2 .................................................................................................................... 24
4.1.3 Model 3 .................................................................................................................... 34
4.2 2D kinematic models ............................................................................................................ 45
4.2.1 Faults 5 and 6 case ................................................................................................... 45
4.2.2 Faults 1 and 2 and Faults 5 and 6 case ..................................................................... 49
4.2.3 Faults 3 and 4 and Faults 5 and 6 case ..................................................................... 52
4.2.4 Quantitative description for the kinematic models .................................................. 59
5. Discussion ....................................................................................................... 62
5.1 Comparison between the kinematic models and the analogue models ................................. 62
5.1.1 Faults 1 and 2 ........................................................................................................... 62
5.1.2 Faults 3 and 4 ........................................................................................................... 64
5.1.3 Faults 5 and 6 ........................................................................................................... 66
5.1.4 Relationship between the Faults 1 and 2, Faults 3 and 4, Faults 5 and 6 and Faults A
and B ................................................................................................................................. 67
5.1.5 Graben-horst structure ............................................................................................. 69
5.2 Comparison between the three analogue models .................................................................. 72
5.3 Comparison between the analogue models and the seismic sections .................................... 73
5.4 Improvement for the methods ............................................................................................... 74
Table of Contents (Continued)

6. Conclusions .................................................................................................... 77
7. Acknowledgements ........................................................................................ 78
8. References ...................................................................................................... 79
Appendix: Section position with respect to the D-side .................................. 84
1. Introduction

The Lufeng Sag is located in the northeastern part of the Pearl River Mouth Basin (Luo et al., 2011).
The Pearl River Mouth Basin is a large Cenozoic hydrocarbon-bearing sedimentary basin within the
South China Sea. The modern hydrocarbon exploration in the South China Sea started from the 1950s
(Fu et al., 2008). But the hydrocarbon indicator in this area was found over 100 years ago. The Pearl
River Mouth Basin was revealed by the geophysical exploration with the regional gravity anomaly and
the 2D seismic study during 1971-1980. The first 7 drillings were done from 1977 to 1980 with the total
drilling depth of 17275m. The Pearl River Mouth Basin was confirmed to be a hydrocarbon-bearing
sedimentary basin with the discovery of the oil flow from the Zhuhai Formation (Fu et al., 2008).
Since 1982, the cooperation with the international oil companies has greatly improved the
exploration and the commercial producing of the Pearl River Mouth Basin. 29 hydrocarbon fields were
identified with 5×108 𝑡 oil, 6.2×109 𝑚3 dissolved gas, 6.03×1010 𝑚3 natural gas and 6.67×
106 𝑡 condensate oil. (Fu et al., 2008).
The first commercial oil field was discovered with the drilling of the Huizhou-21-1-1 in 1985 and
gave a producing ability of 2311.5 𝑚3 oil and 4.3×105 𝑚3 gas per day during the testing stage. The
well Huizhou-26-1-1 drilled in 1988 gave a producing ability of 4228 𝑚3 𝑡 oil per day during the testing
stage and refreshed the oil producing record in China. The drilling of the Liuhua-11-1-1A revealed the
first and the largest offshore coral reef oil field in China. The Xijiang oil field was discovered in 1985
with the drilling of the Xijiang-24-1-1. The major producing formation of the Xijiang oil field is the
Zhuhai Formation with the evaluated total volume of 3.137×107 𝑚3 oil. The Panyu oil field was
discovered with the drilling of the Panyu-4-2-1 in 1997. The major producing formation is the Hanjing
Formation and the Zhujiang Formation with 1606 t oil per day during the testing stage. The Lufeng oil
field was discovered with the drilling of the Lufeng-13-1-1 in 1986. The major producing formation is
the Zhujiang Formation and the Zhuhai Formation with a daily producing ability of 733 𝑚3 oil. The
total evaluated oil volume is 2.568×107 𝑚3 (Fu et al., 2008).
The reservoir type found in the Pearl River Mouth Basin can be classified into the Fault-Block trap,
the rollover anticline trap, the stratigraphy trap and the coralreef trap (Shi et al., 2014).
For the Lufeng oil field. All the current producing wells are located within the Hui-Lu uplift area,
which is situated in the western part of the Lufeng Sag. After 20 years producing, the decrease of the
hydrocarbon output requires a new discovery in this area. Horizontally, the center area of the Lufeng
Sag is poor studied during the early exploration stage. Vertically, the formations beneath the Zhuhai
Formation may also be a potential reservoir for hydrocarbons. The development of the Lufeng Sag was
controlled by the major boundary faults. The fault system presented at the sag center plays an important
role on the hydrocarbon migration from the deep source rock to the upper reservoirs. So the study of the
fault evolution and the properties is always a key issue.
1
The seismic interpretation reveals that an E-W trending basement horst was located at the center of
the Lufeng Sag. The different strike of the boundary faults cause the varying width of the basement horst
along the strike. A series of second-order normal faults developed in the sedimentary covers above the
basement horst. Some of the second-order normal faults intersect with each other, defined as the
conjugate normal fault, and forming a hourglass structure.
The conjugate normal faults are characterized by the similar shear sense but the different dip direction
(Anderson, 1951; Ciftci et al., 2012). The hourglass structure was reported in arrange of tectonic settings
and scales from the crustal scale to the outcrop scale (Horsfield, 1980; Woods, 1988, 1992; Ciftci, 2012).
Horsfield (1980) and Woods (1988) used the simple extension sandbox models to explore the kinematic
behaviors of the conjugate normal faults (Ferrill et al., 2000). The strata correlation and the restoration
across the hourglass structure area is always a problem for the seismic interpreters in the petroleum
industry. So it is essential to get a deep understanding about the origin and the development mechanism
of the conjugate normal faults (Ferrill, 2000).
The simultaneous running of the intersected conjugate normal faults introduces a compatibility
problem around the intersection zone (Fig. 1.1) where the fault block deformation and volume losing or
a redistribution are required (Ramsey & Huber, 1987; Odonne & Massonnat, 1992). The systematic
reducing of the displacement and a corresponding increase in the ductile strain toward the intersection
zones was suggested by Nicol (1995) to accommodate the compatibility problem (Ciftci, 2012). The
intergrain slip, volume decreasing or multiple smaller scale faults were suggested by Watterson (1998)
to explain the vertical displacement gradients and the increasing in the ductile strain toward the
intersection zone (Ciftci, 2012). Ciftci (2012) suggested that the upper graben structure developed
independently from the bottom horst structure in the Timor Sea hourglass case. Morley (2014) recorded
a unique conjugate faults that pinch out in a thinned basal sandstone before reaching the intersection
zone (Morley, 2014).

a) b) c)

Figure 1.1 a) The strata was divided into four parts by the conjugate normal faults (in red color). b) The
simultaneous extension introduces an extra space for the compensation. c) The simple vertical compensation
causes the overlapping around the intersection zone.

2