XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela

1988198819881988----2008200820082008 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO

UNDERSTANDING THE PETROLEUM SYSTEM OF CARUPANO BASIN:

A 2D/3D BASIN MODELING APPROACH.

Noya José1, Vargas Adrian2, Perez Adriana2. 1.- PDVSA – Exploración – Costa Afuera, Puerto La Cruz, Estado Anzoátegui, Venezuela. noyaj@pdvsa.com

2.- PDVSA – INTEVEP, Los Teques, Estado Miranda, Venezuela.

ABSTRACT Carupano basin is located in the northeastern offshore of Venezuela. This area characterized by the interaction between the Caribbean and the South American Plate (figure 1), is composed by two structural highs, the first one “LosTestigos” is the northern limit of the basin and the second one named “Patao” high positioned between Caracolito sub-basin and Paria sub-basin. Main production fields are located in the last one but there is one productive gas well in the Testigos high.

Figure 1. Geological framework of Carupano basin

This study integrates all available data up to date trying to generate a consistent model with the regional geological interpretation of the Carupano basin managed by PDVSA. A 3D-block has been constructed and a pair of 2D section was extracted from the block, which was modeled and calibrated in term of thermal maturity and hydrocarbon generation attempting to reproduce known fields and to establish new possible accumulation. The main result of this study was the confirmation of an active petroleum system in the Carupano basin. Moreover, the possibility of many petroleum systems associated to different source rocks and secondary alteration processes affecting them. Additionally, this study shows very prospective zones linked to the southern flank of Los Testigos high. However, additional studies are necessary in order to reduce the uncertainties. Key words: Petroleum system, Offshore, Carupano basin and Caribbean plate. GEOLOGICAL FRAMEWORK Many companies and consortiums have studied the Carupano basin from the late 70’s till now establishing great petroleum potential in the basin but many uncertainties regarding the petroleum system still remain and require more research. Two possible source rock levels have been identified by well drilling. A Lower Miocene type II/III source interval where the paleontological studies suggest that this rock sequence was deposited in a slope position (outer neritic-upper bathyal) with significant quantities of amorphous algal and vitrinitic macerals as principal components. The Middle Miocene

Grenada Basin

Tobago Basin

Columbus

Basin

À REA DE INTERES

Oca Fault System

Columbus Fault System

El Pilar Fault System

Grenada Basin

Tobago Basin

Columbus

Basin

Carupano Basin

Oca Fault System

Columbus Fault System

El Pilar Fault System

XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela

1988198819881988----2008200820082008 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO

source rock is from moderate to good in quality (TOC going from <1 to 4%) and is immature in all of the well penetrations (Shell, 2004). Measured hydrogen indices from cuttings are in the range from 200-350. A not proved deeper Eocene source rock was penetrated by the Caracolito-1 well. This source interval consists of dominantly terrestrial (vitrinite) material and has measured hydrogen/carbon, oxygen/carbon ratios that are consistent with a type III/gas-prone source. Although the source rock contains poor-moderate TOC ranges (<0.5-1.0), the presence of wet gas during the drilling and gas and condensate tested in the Los Testigos high, which have a probable source in the Caracolito sub-basin, suggests that there is an active pod in this basin (Shell, 2004). METHODOLOGY The workflow used for this study is described as follow:

• Review and compilation of the well data of the basin (BHT, TOC, Tmax, type of kerogen and Fluids)

• Input data of structural depth maps in Temis® application.

• Revision and correction of depth maps in map editor module.

• Construction of different kind of maps (Surface temperature, Heat flow, TOC, type of kerogen, lithologies, etc)

• Building of 3D block

• Extraction of 2D section and geometry checking

• Run the 2D and 3D model and calibrate trying to reproduce the observed data in the

wells. RESULTS AND DISCUSSIONS Once the block was constructed, the next step was the thermal calibration. In order to obtain the best calibration possible 2D sections were extracted across de block. Those 2D sections E-W (red) and NW-SE (blue) extracted from Location Map (Temis 3D) and exported to Temis 2D®, (figure 2 a,b,c). a) b) c)

Figure 2: a) Location of 2D section, E-W in red NW-SE in blue, b) Thermal calibration of Caracolito 1X well, red points measured data and red line modeled values, c) overburden Caracolito 1X well diagram showing maturity levels.

As it is noticed, in the previous figures, it has obtained a good matching between measured data and modeled line, and its evident that the lower section in Caracolito 1X well is in the oil window at present. Thermal maturity of the NW-SE section is shown in the figure 3a, it can be seen, how the lower part of the section (Eocene-Oligocene) is overmature in Caracolito sub basin. By the other hand, in Paria sub basin this section (Eocene-Oligocene) is not present and is only the middle Miocene that is in oil window at recent time. The upper left part of the figure 3, shows the hydrocarbon expulsion vs time curves for Eocene (blue), Oligocene (Red) and middle Miocene (green) in Caracolito sub basin.

XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela

1988198819881988----2008200820082008 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO

As it becomes evident in this curves, the Eocene and Oligocene sections began their expulsion processes in Caracolito sub basin (left depression) 16my and 10my ago respectively, moreover, middle Miocene section in this sub basin has not reached enough maturity level to start the hydrocarbon expulsion. However, middle Miocene is in the oil window in Paria sub basin (right depression) and it began the hydrocarbon expulsion 5my ago. a) b)

Figure 3: Maturity, generation and expulsion model for the a) NW-SE section, b) E-W section. As it becomes evident in this curves, the Eocene and Oligocene sections began their expulsion processes in Caracolito sub basin (left depression) 16my and 10my ago respectively, moreover, middle Miocene section in this sub basin has not reached enough maturity level to start the hydrocarbon expulsion. However, middle Miocene is in the oil window in Paria sub basin (right depression) and it began the hydrocarbon expulsion 5my ago. The E-W section shows (figure 3b) a large pot area along Caracolito sub basin with maturity level more than 1 (blue to red), including large part in over maturity level (>2). It is important to notice that the expulsion times for Eocene (red line) and Oligocene (green line) sequences began earlier in the deeper part of Caracolito sub basin (figure 3b), moreover, in this section it can be seen the initial generation of the early Miocene source rock (white line). In term of migration, the section NW-SE shows some areas with relatively high saturation (hot colors, figure 4a) these high saturation areas are mainly associated with stratigraphic pinch out against the flanks of Patao and Testigos highs, (figure 4). a) b)

Figure 4: Migration pathways and hydrocarbon saturation model for a) NW-SE section, b) E-W section.

XI CONGRESO LATINOAMERICANO DE GEOQUÍMICA ORGÁNICA 2-6 de Noviembre de 2008 Isla de Margarita, Venezuela

1988198819881988----2008200820082008 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO 20 AÑOS DE ALAGO

Additionally, the section E-W confirm this kind of possible accumulations against the Testigos high (figure 4b), this possible accumulation are very interesting due to the fact that Testigos 1 well, located up dip in the same high, had a gas test of 17MCF. However, there are many uncertainties to be resolved as distribution and quality of reservoir, quality of deeper (?) Eocene Source rock, timing and total hydrocarbon generated (mass balance). The geometry of the basin can be seen in the figures 5a and 5b, they represent a 3D views from different angles, lateral and under view respectively, showing large pot area in caracolito sub basin.

a) b)

Figure 5: 3D views of Carupano basin highlighting structural features.

CONCLUSION

• Based on available data the Carupano basin present all the elements of petroleum system. However, the quality of a possible Eocene source rock is still unknown.

• 2D sections shows very prospective zones associated to pinch out against the Testigos high.

• A detailed sedimentary model is necessary in order to obtain a facies maps that allow establish migration pathways and good quality reservoir distribution.

• Once generated facies maps, load it and run full 3d model trying to reproduce possible accumulations.

• This study confirms that Carupano basin has very interesting structural and stratigraphic features from oil exploration point of view and supports the acquisition of new 3D seismic survey covering the southern flank of the Testigos high.

REFERENCES CITED

• EFAI, 2008. MSE Informe final.

• INTEVEP, 2007. Cuenca de Carupano, Costa Afuera.(in press)

• SHELL, 2004. Extract from MSLNG final report.

Patao high

Testigos high

Caracolito sub-basin

Paria sub-basin

Patao high

Testigos high

Caracolito sub-basin Paria sub-basin