Study team

Attendants at the meeting were representatives from Exploration Division (PVN), board of management of VPI, study team and clients namely as Vietsovpetro JV, Premier Oil, Chevron Vietnam, Talisman Vietnam, ExxonMobil, JOC “Vietgazprom”.

The study has been jointly undertaken by VPI and Core Laboratories Sales NV (UK), presenting a geological evaluation of the hydrocarbon reservoirs and candidate seal horizons developed within the Tertiary successions of the Cuu Long, Nam Con Son and Malay - Tho Chu basins.

Objectives of the study

1. Construction of a stratigraphic framework for the study wells, unifying data from several different biostratigraphic disciplines, cyclostratigraphic analysis and seismic interpretation.

2. Sedimentological description and interpretation of depositional facies and environments for the study sections, both in the cored and uncored intervals, integrating lithological descriptions and interpretation of electric logs.

3. Assessment of controls on reservoir quality through determination of petrographic and petrophysical properties, utilizing core analysis data, Rock-Typing in uncored sections, and log interpretation.

4. Evaluation of seal effectiveness.

Study database

The study database is largely well-based, consisting of an extensive legacy dataset enhanced with results from new analysis. A total of 40 wells have been evaluated from the 3 study basins: 8 from Cuu Long, 24 from Nam Con Son and 8 from Malay - Tho Chu, detailed in:

No.

Well

Operator

 

Cuu Long basin

 

1

Agate-1X (01-E-1X)

Petronas

2

Emerald-1X

Petronas

3

15.1-SD-1X

Cuu Long

4

15.2-VD-1XR

JVPC

5

15.2-RD-5X

Petronas

6

Rong-1X

Vietsovpetro

7

17-VT-1XR

Enterprise

8

09.2-COD-1X

HVJOC

 

Nam Con Son basin

 

1

04.2-NB-1X

Lasmo

2

04.1-SDN-1XR

British Gas

3

05-DH-2X

BHP

4

05-DH-6X

BHP

5

05.1b-TL-1X

MJC

6

05.2-HT-1X

BP

7

05.3-CTT-1X

Bien Dong

8

05.2-NT-1XR

BP

9

06-A-1X

ONGC

10

06-HDB-1X

BP

11

10-BM-1X

Shell

12

10-PM-1X

Shell

13

11.1-CC-1X

Total

14

11.1-CH-1X

Total

15

11.2-RVD-1X

Pedco

16

12-B-1X

Agip

17

12-A-1X

Agip

18

20-PH-1X

PetroCanada

19

21-S-1X

Enterprise

20

28-A-1X

Bow Valley

21

29-A-1X

Bow Valley

22

PV94-2X

PVEP

23

12W-HA-1X

Can Pet

24

03-BOS-1X

PetroCanada (Viet) Inc.

 

Malay - Tho Chu basin

 

1

48/95-TDD-1X

Unocal

2

B-KQ-1X

Unocal

3

52/97-AQ-3X

Unocal

4

51-UM-1X

Fina

5

46-DD-1X

Fina

6

B-KL-1X (49-KL-1X)

Unocal

7

46-KM-1X

Fina

8

52/97-AQ-8X

Unocal

In addition, over 4000 km of seismic provide an understanding of basin fill away from well control.


Study areas

Analytical methods

The stratigraphic framework has been constructed using cyclostratigraphic analysis of gamma ray logs, age-calibrated using biostratigraphic control from a combination of micropalaeontological, nannopalaeontological and palynological data. StrataBugs software has been used to bring the various data together as a digital database. The resulting stratpac scheme has been tied to a broad seismic grid to provide an understanding of stratigraphic development away from well locations.

Core logs were generated using WellCad/CoreCad software. Core photographs of whole core and close-ups were also taken of each core and integrated with the core logs, together with core porosity and permeability measurements (legacy data only). Moving beyond the cored intervals, detailed sedimentological logs (SEDLogs) have been constructed for the whole succession studied. These incorporate wireline logs, lithology of uncored intervals (based on both actual cuttings descriptions and interpreted lithologies from final well logs), close-up core and thin section photographs and poroperm data.

Thin section analysis was performed on representative facies from all cored wells. The petrographic data provide reliable information on mineralogy, grain-size distribution, sorting, matrix distribution, cement phases and pore types. In addition to the thin section data available from cores, cuttings samples were selected for thin section analysis of uncored reservoir intervals.

Petrophysical characterization of the uncored intervals was achieved by “Rock Typing” cuttings samples from reservoir intervals.

Data from both core analysis and rock-typing have been utilized in petrophysical interpretation of wireline log suites over the study sections.

To investigate the potential of candidate seal horizons, a total of 20 samples from 14 wells have been subjected to a series of analyses, including petrography and high-pressure mercury injection.

Integration and display of the various stratigraphic and reservoir geological data was undertaken using ODM (Oilfield Data Manager). New maps produced in the study were generated using ArcGIS software.

 

The main results of the study may be summarized as follows:

Stratigraphy

1. Biostratigraphic interpretation utilizes a combination of microfossil, nannofossil and palynomorph data integrated with the results of cyclostratigraphic analysis of gamma ray logs.

2. These data provide age and paleoenvironmental control for all study wells and enable time-calibration of the cyclostratigraphic stratpac framework.

3. Sixteen strapacs are recognized through the Oligocene (4), Miocene (9) and Pliocene (3) interval studied and these form the basis of well correlations and time-slices for palaeogeographic mapping.

Reservoir Geology

1. Systematic integration of all available geological datasets has facilitated the reconstruction of basin evolution through time and elucidation of the relationship between the major structural elements and the lateral and vertical distribution of sands, shales and carbonates observed within the three study basins.

2. A total of 436.2m of core, in 12 wells, has been described in the study; detailed core descriptions, at 1:20 scale, comprising facies characteristics and addtional data (e.g. high-resolution close-up photos, porosity-permeability measurements, etc.) were constructed.

3. For elucidation of petrographic/reservoir quality features of the cored reservoir successions a number of 152 samples were studied in thin sections, SEM and XRD.

4. A further 315 cuttings samples were selected for petrographic analyses of the uncored sections, from 28 wells. All manufactured thin sections were subjected to “petrographic screening”, involving a summary description of the observed lithotypes (in approximate percentage terms). Of these samples, 167 were selected for detailed petrographic analysis. Analog petrophysical properties were determined through rock-typing on a number of 49 samples from various reservoir sections.

Geo-seismic sections

Seals

1. High pressure mercury injection analyses and seal capacity calculation (hydrocarbon column height), supported by XRD, SEM, TOC analyses, were performed on selected samples to assess seal quality.

2. A total of thirty samples fron 19 wells were analysed from the 3 study basins. All samples were cuttings. An attempt has been made to distinguish samples regarded as having regional seal potential from those having more local or intraformational seal potential.

3. The seal lithologies observed are mainly varieties of claystones, siltstones or “shales” in which seal quality is mainly a function of interdependent rock properties: lithology composition, microtextures and microstructures, which in turn have a bearing on porosity and permeability.

4. In the regional data set, seal quality clearly increases with decreasing permeability; good or better seal quality is expected where permeability is <0.01mD. The interdependence of rock properties as the control on seal quality is highlighted by the lack of any correlation between seal quality and certain sepcific properties such as total clay or total organic carbon content.

5. An arbitrary scale based on increments of incresing hydrocarbon column height has been used to classify of each sample. Seal quality is highly variable on both a local and a regional scale, ranging from very poor to excellent.

6. Good or better seal quality tends to occur more frequently in the regional Oligocene and Ealy Miocene Stratpacs, and locally in the Late Miocene and Early Pliocene Stratpacs (which may also have regional seal potential). Otherwise, seal quality in the Middle to Late Pliocene tends to be poorer.

 

 

Report references include 2 volumes: Volume I - Text, Volume II - Figures & Tables. Large format charts together with a range of supporting data are included on 3 accompanying Digital Data Disk.

All are kept at VPI’s Library.

The report, in both paper and digital forms, is the non-exclusive property of VPI and Core Laboratories Sales NV.

 
Website for the non-exclusive study

Reported by: NTMX - Planning & Finance Division

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