ty le ca cuoc 188bet Predicting hydrocarbon migration and accumulation in Block 09-3/12, Cuu Long basin by 3D petroleum system modelling

Summary

Block 09-3/12 is located to ty le ca cuoc 188bet southeastern margin of ty le ca cuoc 188bet Cuu Long basin. Up until now five wells have been drilled in ty le ca cuoc 188bet block, resulting in discoveries at two fields, Soi Main and Central A. In this study, 3D petroleum system modelling has been used for determining ty le ca cuoc 188bet kitchen areas as well as evaluating hydrocarbon migration and accumulation for ty le ca cuoc 188bet remaining prospects in Block 09-3/12. ty le ca cuoc 188bet petroleum system modelling indicates that ty le ca cuoc 188bet Oligocene source rock is ty le ca cuoc 188bet major source for ty le ca cuoc 188bet prospects in Block 09-3/12. ty le ca cuoc 188bet kitchen area for ty le ca cuoc 188bet Central and Western A structures is ty le ca cuoc 188bet East Bach Ho trough, while ty le ca cuoc 188bet kitchen in ty le ca cuoc 188bet Southeast Soi area is ty le ca cuoc 188bet main source for ty le ca cuoc 188bet Southeast A structure. ty le ca cuoc 188bet simulation results predict ty le ca cuoc 188bet presence of oil accumulations in Lower Miocene and Oligocene reservoirs for ty le ca cuoc 188bet A structure.

Key words: Petroleum system modelling, A prospect, drainage area, hydrocarbon migration and accumulation, Block 09-3/12.

1. Introduction

Block 09-3/12 covers an area of 5,559km2 and lies in ty le ca cuoc 188bet southeast portion of ty le ca cuoc 188bet Cuu Long basin (Figure 1). ty le ca cuoc 188bet water depth is about 10 - 50m. ty le ca cuoc 188bet study area has several oil discoveries in Lower Miocene and Oligocene sandstones. ty le ca cuoc 188bet success of Soi-1X in ty le ca cuoc 188bet Soi Main prospect and especially ty le ca cuoc 188bet A-2X, 3X and 4X wells in ty le ca cuoc 188bet Central A prospect proves that there is an active petroleum system in ty le ca cuoc 188bet area.

Detailed 3D basin modelling of Block 09- 3/12 focuses on ty le ca cuoc 188bet A structure and covers all of ty le ca cuoc 188bet potential fetch area of ty le ca cuoc 188bet source kitchen. ty le ca cuoc 188bet aim of 3D basin modelling is to investigate ty le ca cuoc 188bet migration and charge history of ty le ca cuoc 188bet recent discoveries and help predict where other accumulations in Lower Miocene and Oligocene plays lie on ty le ca cuoc 188bet remaining prospects in ty le ca cuoc 188bet Western A and Southeast A area (Figure 1).

2. Geological setting

ty le ca cuoc 188bet tectono-structural characteristics of Block 09-3/12 and adjacent areas are influenced by ty le ca cuoc 188bet tectonics of ty le ca cuoc 188bet Cuu Long basin. ty le ca cuoc 188bet Cuu Long basin is an oval-shaped, early Tertiary rift basin, located on ty le ca cuoc 188bet southern continental shelf of Vietnam. It is separated from ty le ca cuoc 188bet Gulf of Thailand basins to ty le ca cuoc 188bet west by ty le ca cuoc 188bet Khorat High and from ty le ca cuoc 188bet Nam Con Son basin to ty le ca cuoc 188bet southeast by ty le ca cuoc 188bet Con Son swell. Block 09- 3/12 encompasses ty le ca cuoc 188bet East Bach Ho trough and ty le ca cuoc 188bet Southeast slope (Figure 2).

Figure 1. Location of Block 09-3/12.

Figure 2. ty le ca cuoc 188bet structural map with major structural components (a) and ty le ca cuoc 188bet general stratigraphic column (b) of Block 09-3/12 [1]. ty le ca cuoc 188bet study area is highlighted.

Figure 3. A seismic cross-section through ty le ca cuoc 188bet study area [1].

Figure 4. Workflow for 3D basin modelling.

ty le ca cuoc 188bet geological evolution of ty le ca cuoc 188bet Cuu Long basin can be divided into 3 episodes: pre-rift (Pre-Tertiary), syn-rift (Eocene to Oligocene), and post-rift (Miocene - Present) (Figure 3). ty le ca cuoc 188bet pre-rift period saw widespread magmatic activities in both ty le ca cuoc 188bet present day onshore and offshore, which formed ty le ca cuoc 188bet crystalline basement for ty le ca cuoc 188bet basin. During ty le ca cuoc 188bet Oligocene, syn-rift basins were initially filled with coarse-grained alluvial to fluvial sand-dominant sediments, represented by ty le ca cuoc 188bet F and lower E sequences. During ty le ca cuoc 188bet Late Oligocene, lacustrine environment dominated, resulting in forming ty le ca cuoc 188bet E and D shale sequences, which are ty le ca cuoc 188bet main source rocks in ty le ca cuoc 188bet basin, as well as in Block 09-3/12. A compressional phase in ty le ca cuoc 188bet Late Oligocene took place which fractured ty le ca cuoc 188bet basement and created folding and reverse faulting, which is observed in much of ty le ca cuoc 188bet basin. ty le ca cuoc 188bet post rift starts from ty le ca cuoc 188bet Early Miocene, from which point ty le ca cuoc 188bet whole basin enters ty le ca cuoc 188bet thermal sag phase, dominated by fluvio-marine to shallow marine environments [1].

3. Methodology and model input

- Methodology

ty le ca cuoc 188bet method of modelling used combines geological, geophysical, geochemical and petroleum system data [2]. ty le ca cuoc 188bet modelling process using ty le ca cuoc 188bet PetroMod software aims to determine ty le ca cuoc 188bet maturity of source rocks, and model migration and accumulation processes of hydrocarbon through geological time based on ty le ca cuoc 188bet 3D petroleum systems modelling workflow (Figure 4).

- Construction of 3D structural model

ty le ca cuoc 188bet 3D structural model includes ty le ca cuoc 188bet main horizons and fault surfaces. There are 08 horizons interpreted from seismic data: Top Basement (SH-B), Top Lower Oligocene (SH-11), Top Intra Upper Oligocene (SH-10), SH-8b, SH-8, Top Upper Oligocene (SH-7), Top Intra Lower Miocene (SH- 5), and Top Lower Miocene (SH-3) (Figure 5). ty le ca cuoc 188bet fault systems in ty le ca cuoc 188bet study area are mostly normal faults trending NE-SW, and a number of small faults trending NW-SE or E-W. In total, there are about 50 main faults chosen to be included in ty le ca cuoc 188bet 3D petroleum system model to simulate ty le ca cuoc 188bet entrapment and migration of hydrocarbon along fault surfaces (Figure 6). ty le ca cuoc 188bet structural model is constructed by PetroMod 3D in ty le ca cuoc 188bet depth domain.

Figure 5. ty le ca cuoc 188bet 3D view of grids of 8 main horizons derived from seismic interpretations.

 Figure 6. ty le ca cuoc 188bet 3D view of fault plane used for modelling.

- Source rock properties

ty le ca cuoc 188bet geochemistry analysis results of samples from wells in Block 09-3/12 and ty le ca cuoc 188bet surrounding area show that mature Oligocene sediment is ty le ca cuoc 188bet main source rock with good to very good generation potential [3]. ty le ca cuoc 188bet average TOC values of Oligocene source rock vary from 3 - 5%wt, and HI values higher than 400mgHC/gTOC. Oligocene source rock, which is shale deposited in fluvial-deltatic and lacustrine environments, contains mainly kerogen type I and mixture of type I and III. In contrast, Lower Miocene sediment is not good enough to become source rock because it is immature and has low organic matter richness (Figures 7 and 8) [4].

- 1D well modelling and Heat Flow

ty le ca cuoc 188bet 1D petroleum system model and heat flow are ty le ca cuoc 188bet controlling factor of ty le ca cuoc 188bet maturation modelling in ty le ca cuoc 188bet 3D petroleum system model. ty le ca cuoc 188bet 1D petroleum system model is built for wells A-2X and A-3X, in which ty le ca cuoc 188bet vitrinite reflectance (%Ro) and well temperature (oC) are used to calibrate ty le ca cuoc 188bet heat flow as well as model output.

In this study, ty le ca cuoc 188bet heat flow profile depends on ty le ca cuoc 188bet onset of rifting phase and subsidence phase. Because Cuu Long basin is a Cenozoic rift basin, ty le ca cuoc 188bet heat flow profile is based on ty le ca cuoc 188bet McKenzie model. Heat flow was low during ty le ca cuoc 188bet Pre-rift phase (about 40Ma) and then increased in rifting phase and peaked at 28Ma. In Lower Miocene (subsidence phase), heat flow has decreased until ty le ca cuoc 188bet present time at 40 - 50mW/ m2 (Figure 9).

 Figure 7. TOC vs (S1+S2) diagram of T20 in Block 09-3/12 and adjacent area, Cuu Long basin.

Figure 8. HI vs Tmax diagram of T20 in Block 09-3/12 and adjacent area, Cuu Long basin.
 

Figure 9. Heat flow curve of study area based on ty le ca cuoc 188bet McKenzie model.

Figure 10. 1D basin modelling at A-3X and A-2X.

 Figure 11. Maturity maps of top basement, SH10, SH8b and SH8.

Figure 12. Generation timing of hydrocarbon.

 In general, ty le ca cuoc 188bet 1D model results show good agreement between ty le ca cuoc 188bet output and ty le ca cuoc 188bet measured Ro and temperature in ty le ca cuoc 188bet wells (Figure 10). Evaluation of ty le ca cuoc 188bet source rock at ty le ca cuoc 188bet well shows most of ty le ca cuoc 188bet Oligocene source rocks are in ty le ca cuoc 188bet early maturation window.

4. Model results

4.1 Source rock maturity

ty le ca cuoc 188bet start of ty le ca cuoc 188bet maturation depth (0.55 - 0.72%Ro) is about 2,700 - 3,900m; ty le ca cuoc 188bet oil window depth (0.72 - 1.3%Ro) is about 3,520 - 6,500m; and ty le ca cuoc 188bet condensate/wet gas window depth is from 6,500m. In ty le ca cuoc 188bet study area, there exist 2 main kitchens for ty le ca cuoc 188bet A prospect group, which are ty le ca cuoc 188bet Southeast Soi and East Bach Ho troughs.

ty le ca cuoc 188bet East Bach Ho trough is ty le ca cuoc 188bet main kitchen area, which is currently in ty le ca cuoc 188bet condensate/wet gas stage (1.3 - 2.0%Ro) in ty le ca cuoc 188bet deepest part, while ty le ca cuoc 188bet Southeast Soi trough is just in ty le ca cuoc 188bet oil window with Oligocene source rock (Figure 11).

Figure 13. Hydrocarbon migration pathway for Upper Oligocene reservoirs (upper) and 2D cross-section through ty le ca cuoc 188bet A Centre structure (lower).
 

Figure 14. Hydrocarbon accumulation for Upper Oligocene reservoirs.

Figure 15. Hydrocarbon migration pathway for Lower Miocene reservoirs (upper) and 2D cross-section through ty le ca cuoc 188bet Soi structure (lower).

In general, most of ty le ca cuoc 188bet hydrocarbon accumulations are from ty le ca cuoc 188bet products of ty le ca cuoc 188bet Oligocene source rock. Meanwhile, ty le ca cuoc 188bet Lower Miocene shale does not meet ty le ca cuoc 188bet requirements for an effective source rock in ty le ca cuoc 188bet study area due to low organic matter concentration and low maturity level. Through ty le ca cuoc 188bet source rock maturity and transformation ratio results from ty le ca cuoc 188bet 3D petroleum system modelling, it can be predicted that ty le ca cuoc 188bet source rock in ty le ca cuoc 188bet East Bach Ho trough (area I and II) has gone through different maturity levels and is ty le ca cuoc 188bet main source rock for ty le ca cuoc 188bet study area. ty le ca cuoc 188bet oil and gas generation history from ty le ca cuoc 188bet Upper Oligocene source rock (SHB-SH10) in area I and II (Figure 12) started from about 28Ma; hydrocarbon migration was strong at about 20Ma, until Middle Miocene. For ty le ca cuoc 188bet SH10- SH8 layer, ty le ca cuoc 188bet hydrocarbon generation took place later and peak oil generation varies from Upper Miocene to Pliocene. While in ty le ca cuoc 188bet Southeast Soi trough (area III), only ty le ca cuoc 188bet SHB-SH10 sequence source rock is in ty le ca cuoc 188bet hydrocarbon generation stage.

4.2. Hydrocarbon migration and accumulation

ty le ca cuoc 188bet most important output for ty le ca cuoc 188bet 3D petroleum system model is ty le ca cuoc 188bet restoration of ty le ca cuoc 188bet migration and accumulation process of hydrocarbon from ty le ca cuoc 188bet past to ty le ca cuoc 188bet present [5]. Based on ty le ca cuoc 188bet newest geological interpretation, 3 prospects in ty le ca cuoc 188bet A prospect group are identified, including: Western area, Central area (Blocks Ia, Ib, and II) and Southeast area (Blocks I and II). In ty le ca cuoc 188bet Central area (Blocks Ia and Ib), there are two exploration wells: A-2X and A-3X.

 Figure 16. Hydrocarbon accumulation for Lower Miocene reservoirs.

 4.2.1.Upper Oligocene reservoir (SH10-SH8b layer)

ty le ca cuoc 188bet results from two wells A-2X and A-3X show that this is an important reservoir in ty le ca cuoc 188bet study area, especially ty le ca cuoc 188bet Central A area. ty le ca cuoc 188bet result of ty le ca cuoc 188bet migration simulation in this region indicates that for ty le ca cuoc 188bet Upper Oligocene reservoir, there are two main kitchen areas: ty le ca cuoc 188bet East Bach Ho trough (Kitchen I) and ty le ca cuoc 188bet Southeast Soi trough (Kitchen II). Kitchen I charges Blocks Ia and Ib, while Kitchen II charges Block II of ty le ca cuoc 188bet Central A cluster as well as ty le ca cuoc 188bet Southeast A cluster (Figures 13 and 14).

Because Kitchen I has a larger extent compared to Kitchen II, and has gone through most of ty le ca cuoc 188bet maturation stages, it has better charge potential than Kitchen II. As a result, Blocks Ia and Ib have better conditions for receiving oil (migration direction denoted by ty le ca cuoc 188bet green arrows) than Block II of ty le ca cuoc 188bet Central A cluster and also ty le ca cuoc 188bet Southeast structure.

ty le ca cuoc 188bet predictions indicate that ty le ca cuoc 188bet migration and accumulation of hydrocarbon for ty le ca cuoc 188bet Central A-I and II are very favourable and consistent with ty le ca cuoc 188bet results of ty le ca cuoc 188bet A-2X and A-3X. Meanwhile, ty le ca cuoc 188bet Southeast A prospect is predicted by ty le ca cuoc 188bet petroleum system model to contain no hydrocarbon, due to source rock quality risks (Figure 13).

4.2.2 Lower Miocene reservoir

ty le ca cuoc 188bet results of drilling and well tests from A-2X/3X wells have proven ty le ca cuoc 188bet existence of oil bodies in ty le ca cuoc 188bet Upper Oligocene and Lower Miocene interval. ty le ca cuoc 188bet main kitchen area for ty le ca cuoc 188bet prospects in ty le ca cuoc 188bet Lower Miocene section is ty le ca cuoc 188bet Oligocene source rock in ty le ca cuoc 188bet East Bach Ho trough (Kitchen I) (Figure 15). ty le ca cuoc 188bet migration and accumulation model at ty le ca cuoc 188bet Lower Miocene reservoir shows ty le ca cuoc 188bet presence of hydrocarbon in Central & Western A prospect and Soi structure which are mainly provided by ty le ca cuoc 188bet Oligocene source rock from Kitchen I (Figures 16 and 17) while for ty le ca cuoc 188bet accumulation in Southeast A prospect charged by Kitchen II.

Figure 17. 2D hydrocarbon migration cross-section through ty le ca cuoc 188bet Soi structure (upper) and A Centre structure (lower).

In general, based on ty le ca cuoc 188bet results of ty le ca cuoc 188bet 3D Petroleum System Model, for ty le ca cuoc 188bet undrilled structures ty le ca cuoc 188bet Western A and Block II of ty le ca cuoc 188bet Central A prospects are ty le ca cuoc 188bet most favourable for receiving hydrocarbon, with ty le ca cuoc 188bet main kitchen being ty le ca cuoc 188bet East Bach Ho trough. ty le ca cuoc 188bet Southeastern prospect group has lower potential due to limited hydrocarbon pathways and charge volume. This study was carried out before ty le ca cuoc 188bet drilling of well A-3X and its conclusions contributed to ty le ca cuoc 188bet decision of ty le ca cuoc 188bet well location. A-3X was a discovery, which is consistent with ty le ca cuoc 188bet study’s results.

5. Conclusions and recommendations

In particular, ty le ca cuoc 188bet Oligocene source rock in ty le ca cuoc 188bet East Bach Ho trough is ty le ca cuoc 188bet main hydrocarbon source for ty le ca cuoc 188bet Central and Western A prospect group. Meanwhile ty le ca cuoc 188bet source rock in ty le ca cuoc 188bet Southeast Soi trough provides hydrocarbon for ty le ca cuoc 188bet Southeastern prospect group.

ty le ca cuoc 188bet early maturation threshold of ty le ca cuoc 188bet source rock is at about 2,700 - 3,900m, ty le ca cuoc 188bet oil window is at about 3,500- 6,500m, and ty le ca cuoc 188bet condensate/wet gas window is below 6,500m. ty le ca cuoc 188bet oil and gas generation history from ty le ca cuoc 188bet Upper Oligocene source rock in ty le ca cuoc 188bet East Bach Ho trough started from about 28Ma. Hydrocarbon migration was strong at about 25Ma, until Middle Miocene. For ty le ca cuoc 188bet SH10-SH8 layer, ty le ca cuoc 188bet hydrocarbon generation took place later, from Lower Miocene to ty le ca cuoc 188bet present. In ty le ca cuoc 188bet Southeast Soi trough, only ty le ca cuoc 188bet SHB-SH10 sequence source rock is in ty le ca cuoc 188bet hydrocarbon generation stage.

ty le ca cuoc 188bet simulation result shows ty le ca cuoc 188bet presence of hydrocarbon (oil) accumulations in Lower Miocene and Oligocene reservoirs for ty le ca cuoc 188bet Central and Western A structure, and in Lower Miocene for ty le ca cuoc 188bet Southeastern structure. Among those, Western A and Block II of ty le ca cuoc 188bet Central A structure have ty le ca cuoc 188bet most favourable conditions for hydrocarbon migration and charge. 

References

1. VSP. Cơ sở địa chất lựa chọn vị trí giếng khoan A-4X Lô 09-3/12. 2016.

2. Armin I.Kauerauf,Thomas Hantschel. Fundamentals of basin and petroleum systems modeling. Springer. 2009.

3. VPI. Báo cáo địa hóa mẫu vụn và mẫu dầu - Giếng khoan A-3X. 2016.

4. Kenneth E.Peters, Clifford C.Walters, J.Michael Moldowan. ty le ca cuoc 188bet Biomarker Guide, Volume 2: Biomarkers and isotopes in petroleum systems and earth history. Cambridge University Press. 2005.

5. Lê Hải An. Tổng hợp tài liệu Địa chất - Địa vật lý và chính xác hóa tiềm năng dầu khí sau khi khoan giếng khoan A-2X. VSP. 2015.