Basin evolution and thermal modeling on the Arabian Peninsula

Establishing a source rock maturity model for the Rub’ Al-Khali

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BackgroundThe Arabian Peninsula is known for its

supergiant hydrocarbon resources. In the

eastern part, source rocks of Paleozoic and

Jurassic age show exceptional quality and

have a wide distribution.

The Paleozoic petroleum system is sourced

by the Early Silurian “hot shale” The

reservoir layers are Devonian and Permian

sandstones and, most importantly, the

carbonates of the Late Permian Khuff

Formation. Anhydrites and shales of younger

Permian age seal off the Paleozoic petroleum

system.

The Jurassic petroleum system is sourced by

organic-rich, marine carbonates of Middle

Jurassic age. Upper Jurassic carbonates serve

as reservoirs which are sealed by overlying

anhydrites.

In the eastern part of the Arabian Peninsula,

these petroleum systems were widely

explored and several large oil and gas fields,

including the world’s larges conventional oil

field Ghawar, were found.

Further to the south, in the Rub’ Al-Khali

Basin, the exploration has been relatively

limited, which is to a certain degree owed to

the difficult desert conditions. Based on the

predicted extent of the source rocks and the

geological history of the area, further

important oil and gas reserves could be

found in this region.

The Arabian Peninsula is the richest petroleum prov-ince of the world. However, the Rub’ Al-Khali Basin in Southern Saudi Arabia remains still underexplored due to its remoteness. One of the reported exploration issues is the source rock maturity and the occurrence of anoma-lous heat flows. TNO has developed new technologies to estimate the heat flow evolution through time based on tectonic events that can help developing a valid model for the source rock maturity. In order to explore and understand these anomalies, ETS and TNO are propos-ing a basin modeling study to investigate source rock maturity along with a detailed analysis of paleo tempera-tures and heat flow evolution.

Figure 1 Overview map of the major structural elements of the Arabian Peninsula with the

position of the studied well and 2D section (modified after Pollastro, 2003)

Challenge

• Duetothelesslimitedexploration,the

maturity of the source rocks in the Rub’

Al-Khali Basin is not well known.

Especially, the maturity and the geological

evolution of the area play an important

role in predicting hydrocarbon reservoirs.

Important influence on the maturity of

the Paleozoic source rock has its present-

day burial depth in relation to its burial

depth before the erosion phase during the

Herzynian Orogeny. Another important

factor is lateral migration. In parts of

Central Saudi Arabia oil fields charged

with Paleozoic-sourced oil were found

about 60 km away from possible source

rocks with matching maturity levels

(McGillivray and Husseini, 1992;

McGillivray, 1994; Cole et al., 1994).

• Thegeologicevolutionofthestudyarea

has an important influence on the

maturity of the Jurassic source rock as

well. According to Cole et al. (1994) the

main phase of oil generation from the

Jurassic source rock in the area of Ghawar

began in the Cretaceous but different

burial depths cause the source rock to be

immature in the area of Khurais even at

present-day. Depending on the

overburden, the source rock can be

immature or even overmature.

• Anothercrucialfactorintheestimationof

source rock maturity is the paleo heat

flow. Especially in tectonic active areas

such as the Arabian Peninsula the paleo

heat flow can vary significantly.

Estimation of paleo heat flow values is in

most basin modeling studies considered

to be a user defined input. In this project

we aim to utilize a tool for paleo heat

flow prediction based on the tectonic

evolution of the area.

Figure 2 Burial history and hydrocarbon generation for the Jurassic

petroleum system in a well near the Safaniya field (from Pollastro, 2003)

Figure 3 Geologic section through Central Saudi Arabia crossing the

Gwahar oil field (modified after Pollastro, 2003)

Project aim

To understand the temperature and maturity

evolution of the area a 2D basin simulation

will be performed. Using state of the art

petroleum systems modeling software and

heat flow estimation based on tectonic

modeling, we propose to build an in depth

geologic model of the temperature and

maturity evolution of the Rub’ Al-Khali area.

With the help of this model it will be possible

to achieve a better understanding of the

petroleum generation and migration, leading

to better prediction of hydrocarbon

accumulations.

In order to build this model input data of the

study area is needed. An interpreted seismic

section through the study area as well as well

data with logs and vitrinite reflection (or

other maturity calibration data), present day

temperature measurements and lithology

information is needed. For the estimation of

generation and possible migration, Rock-Eval

and TOC measurements are advantageous.

Experience

TNO applies basin modeling to integrate the

wealth of data and information gathered and

mapped to evaluate the interdependencies of

the different processes that affect rocks and

fluids during their geological history. Special

attention is paid to processes and conditions

affecting hydrocarbon potential.

In the recent years TNO has developed a

probabilistic heat flow prediction tool called

Petroprob. The tool has been used in various

research projects and consultancy work for

predicting tectonic heat flow for basin

modeling in PetroMod (of IES). A coupling

with TEMIS (IFP) is being developed. The

benefits of using tectonic heat flows instead

of user input heat flow are improved

temporal and spatial constraints on heat flow

evolution. In particular spatial and temporal

extrapolation which is based on a physical

tectonic model instead of geostatistical

techniques aids considerably in exploration

basin modeling for frontier areas where data

abundance is scarce and spatial (and

temporal variability) is high. The strength of

Petroprob is that it is capable of efficiently

calculating tectonically modelled heat flows,

which inverts for burial history and is

calibrated to maturation and temperature

data in wells.

Knowledge Transfer

We consider transfer of our knowledge about

the project to your staff an important part of

our job. This will enable you to build on our

studies in the future.

Further InformationFor more information on TNO Petroleum

Consultancy and the many services we offer

please contact us.

ReferencesMcGillivray, J.G. (1994). CSPG Memoir 17,

383-396.

McGillivray, J.G., Husseini, M.I. (1992). American

Association of Petroleum Geologists Bulletin 76,

1473-1490.

Cole, G.A., Carrigan, H.H., Colling E.L., Halpern,

H.I., Al-Khadhrawi, M.R., Jones P.J. (1994). CSPG

Memoir 17, 413-438.

Pollastro, R.M. (2003). USGS Bulletin 2202-H,

pp. 80

Tectonic modelTectonic Subsidence Heat Flow

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Figure 4 Tectonic subsidence curve and calculated paleo heat flow based on the tectonic evolution of the well near the Safaniya field.

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