link 188bet cho dien thoai 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 link 188bet cho dien thoai southeastern margin of link 188bet cho dien thoai Cuu Long basin. Up until now five wells have been drilled in link 188bet cho dien thoai block, resulting in discoveries at two fields, Soi Main and Central A. In this study, 3D petroleum system modelling has been used for determining link 188bet cho dien thoai kitchen areas as well as evaluating hydrocarbon migration and accumulation for link 188bet cho dien thoai remaining prospects in Block 09-3/12. link 188bet cho dien thoai petroleum system modelling indicates that link 188bet cho dien thoai Oligocene source rock is link 188bet cho dien thoai major source for link 188bet cho dien thoai prospects in Block 09-3/12. link 188bet cho dien thoai kitchen area for link 188bet cho dien thoai Central and Western A structures is link 188bet cho dien thoai East Bach Ho trough, while link 188bet cho dien thoai kitchen in link 188bet cho dien thoai Southeast Soi area is link 188bet cho dien thoai main source for link 188bet cho dien thoai Southeast A structure. link 188bet cho dien thoai simulation results predict link 188bet cho dien thoai presence of oil accumulations in Lower Miocene and Oligocene reservoirs for link 188bet cho dien thoai 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 link 188bet cho dien thoai southeast portion of link 188bet cho dien thoai Cuu Long basin (Figure 1). link 188bet cho dien thoai water depth is about 10 - 50m. link 188bet cho dien thoai study area has several oil discoveries in Lower Miocene and Oligocene sandstones. link 188bet cho dien thoai success of Soi-1X in link 188bet cho dien thoai Soi Main prospect and especially link 188bet cho dien thoai A-2X, 3X and 4X wells in link 188bet cho dien thoai Central A prospect proves that there is an active petroleum system in link 188bet cho dien thoai area.

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

2. Geological setting

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

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

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

Figure 3. A seismic cross-section through link 188bet cho dien thoai study area [1].

Figure 4. Workflow for 3D basin modelling.

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

3. Methodology and model input

- Methodology

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

- Construction of 3D structural model

link 188bet cho dien thoai 3D structural model includes link 188bet cho dien thoai 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). link 188bet cho dien thoai fault systems in link 188bet cho dien thoai 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 link 188bet cho dien thoai 3D petroleum system model to simulate link 188bet cho dien thoai entrapment and migration of hydrocarbon along fault surfaces (Figure 6). link 188bet cho dien thoai structural model is constructed by PetroMod 3D in link 188bet cho dien thoai depth domain.

Figure 5. link 188bet cho dien thoai 3D view of grids of 8 main horizons derived from seismic interpretations.

 Figure 6. link 188bet cho dien thoai 3D view of fault plane used for modelling.

- Source rock properties

link 188bet cho dien thoai geochemistry analysis results of samples from wells in Block 09-3/12 and link 188bet cho dien thoai surrounding area show that mature Oligocene sediment is link 188bet cho dien thoai main source rock with good to very good generation potential [3]. link 188bet cho dien thoai 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

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

In this study, link 188bet cho dien thoai heat flow profile depends on link 188bet cho dien thoai onset of rifting phase and subsidence phase. Because Cuu Long basin is a Cenozoic rift basin, link 188bet cho dien thoai heat flow profile is based on link 188bet cho dien thoai McKenzie model. Heat flow was low during link 188bet cho dien thoai 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 link 188bet cho dien thoai 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 link 188bet cho dien thoai 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, link 188bet cho dien thoai 1D model results show good agreement between link 188bet cho dien thoai output and link 188bet cho dien thoai measured Ro and temperature in link 188bet cho dien thoai wells (Figure 10). Evaluation of link 188bet cho dien thoai source rock at link 188bet cho dien thoai well shows most of link 188bet cho dien thoai Oligocene source rocks are in link 188bet cho dien thoai early maturation window.

4. Model results

4.1 Source rock maturity

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

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

Figure 13. Hydrocarbon migration pathway for Upper Oligocene reservoirs (upper) and 2D cross-section through link 188bet cho dien thoai 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 link 188bet cho dien thoai Soi structure (lower).

In general, most of link 188bet cho dien thoai hydrocarbon accumulations are from link 188bet cho dien thoai products of link 188bet cho dien thoai Oligocene source rock. Meanwhile, link 188bet cho dien thoai Lower Miocene shale does not meet link 188bet cho dien thoai requirements for an effective source rock in link 188bet cho dien thoai study area due to low organic matter concentration and low maturity level. Through link 188bet cho dien thoai source rock maturity and transformation ratio results from link 188bet cho dien thoai 3D petroleum system modelling, it can be predicted that link 188bet cho dien thoai source rock in link 188bet cho dien thoai East Bach Ho trough (area I and II) has gone through different maturity levels and is link 188bet cho dien thoai main source rock for link 188bet cho dien thoai study area. link 188bet cho dien thoai oil and gas generation history from link 188bet cho dien thoai 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 link 188bet cho dien thoai SH10- SH8 layer, link 188bet cho dien thoai hydrocarbon generation took place later and peak oil generation varies from Upper Miocene to Pliocene. While in link 188bet cho dien thoai Southeast Soi trough (area III), only link 188bet cho dien thoai SHB-SH10 sequence source rock is in link 188bet cho dien thoai hydrocarbon generation stage.

4.2. Hydrocarbon migration and accumulation

link 188bet cho dien thoai most important output for link 188bet cho dien thoai 3D petroleum system model is link 188bet cho dien thoai restoration of link 188bet cho dien thoai migration and accumulation process of hydrocarbon from link 188bet cho dien thoai past to link 188bet cho dien thoai present [5]. Based on link 188bet cho dien thoai newest geological interpretation, 3 prospects in link 188bet cho dien thoai A prospect group are identified, including: Western area, Central area (Blocks Ia, Ib, and II) and Southeast area (Blocks I and II). In link 188bet cho dien thoai 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)

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

Because Kitchen I has a larger extent compared to Kitchen II, and has gone through most of link 188bet cho dien thoai 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 link 188bet cho dien thoai green arrows) than Block II of link 188bet cho dien thoai Central A cluster and also link 188bet cho dien thoai Southeast structure.

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

4.2.2 Lower Miocene reservoir

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

Figure 17. 2D hydrocarbon migration cross-section through link 188bet cho dien thoai Soi structure (upper) and A Centre structure (lower).

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

5. Conclusions and recommendations

In particular, link 188bet cho dien thoai Oligocene source rock in link 188bet cho dien thoai East Bach Ho trough is link 188bet cho dien thoai main hydrocarbon source for link 188bet cho dien thoai Central and Western A prospect group. Meanwhile link 188bet cho dien thoai source rock in link 188bet cho dien thoai Southeast Soi trough provides hydrocarbon for link 188bet cho dien thoai Southeastern prospect group.

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

link 188bet cho dien thoai simulation result shows link 188bet cho dien thoai presence of hydrocarbon (oil) accumulations in Lower Miocene and Oligocene reservoirs for link 188bet cho dien thoai Central and Western A structure, and in Lower Miocene for link 188bet cho dien thoai Southeastern structure. Among those, Western A and Block II of link 188bet cho dien thoai Central A structure have link 188bet cho dien thoai 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. link 188bet cho dien thoai 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.