EKSPLORASI MIGAS & PANAS BUMI

Chapter 1EKSPLORASI MIGAS

BASICS OF GEOLOGY

Earth Profile

Rock Types

Geologic Time• Geologic time >>>>>>>>>>>>>>>>>>>>> our time• Penentuan age dating dengan :– Fossils– Radioactivity --> radiochronology of sedimentary :• The Carbon-14 technique for organic materials.• The Potassium-Argon and Rubidium-Strontium techniques for

glauconites, hornblende, microclines, muscovites, biotites, etc.• The Thorium-230 technique for deep ocean sediments and

aragonite corals.• The Protactinium-231 technique for ocean sediments and

aragonite corals.• The Uranium-238 technique for apatite, volcanic glass, zircon,

etc.

Geologic Time

Stratigraphy• Stratigraphy is the study of the origin, composition,

distribution, and sequence of layers of sedimentary rock, or strata.

Geologic Time Scale

Oil & Gas Field due to Geologic Age

PETROLEUM SYSTEM

Oil Cycle

Akumulasi Hidrokarbon• Batuan terakumulasi didalam cekungan sedimen• Diantaranya ada yang kaya akan organik material yang akan

menjadi source rock• Tekanan dan suhu menjadikan source rock mengalami

maturration, kondisi dimana hidrokarbon keluar dari source rock

• Migrasi adalah proses perpindahan hidrokarbon ke batuan porous, yang disebut batuan reservoir

• Batuan reservoir akan mengalami deformasi atau ditumpangi dengan batuan impermeabel akan mengakibatkan hidrokarbon mengalami trap

Akumulasi Hidrokarbon

Cekungan Sedimen• Cekungan sedimen merupakan hasil pergerakan tektonik

lempeng

Cekungan Sedimen• Beberapa tipe cekungan sedimen

Source rock• Contohnya adalah shales, about 90% organic matter• Proses terbentuk hidrokarbon adalah organic materialnya

abundant dan lack of oksigen sehingga proses dekomposisi berlangsung lambat. Proses sedimentation burial juga berpengaruh terhadap masaknya hidrokarbon

• Salah satu organic matter adalah phytoplankton, adalah alga laut yang hidup di bagian atas lautan.

• Contohnya : Kimmeridge clay yang menjadi source dari lapangan Northen North Sea sedangkan batubara dari jaman Karbon nya menjadi source Gas disana

Types of Hydrocarbon1) Kerogen & Bitumen– Kerogen is that part of the organic matter in a rock that is

insoluble in common organic solvents.– The organic content of a rock that is extractable with organic

solvents is known as bitumen.

Types of Hydrocarbon2) Crude oil– Crude oil is a mixture of many hydrocarbons that are liquid at

surface temperatures and pressures, and are soluble in normal petroleum solvents.

– Specific gravity is the ratio of the density of a substance to the density of water.

– The lower the specific gravity, the higher the API gravity, for example, a fluid with a specific gravity of 1.0 g cm-3 has an API value of 10 degrees.

Types of Hydrocarbon2) Crude oil

No Rank API Value Specific Gravity

1 Heavy Oils < 20 > 0.93

2 Normal Oils 20 - 40 0.83 – 0.93

3 Light Oils > 40 < 0.83

Types of Hydrocarbon3) Asphalt– Asphalt is a dark colored solid to semi-solid form of

petroleum (at surface temperatures and pressures) that consists of heavy hydrocarbons and bitumens.

– It can occur naturally or as a residue in the refining of some petroleum.

– It generally contains appreciable amounts of sulphur, oxygen, and nitrogen and unlike kerogen, asphalt is soluble in normal petroleum solvents.

– It is produced by the partial maturation of kerogen or by the degradation of mature crude oil.

– Asphalt is particularly suitable for making high-quality gasoline and roofing and paving materials.

Types of Hydrocarbon4) Natural Gas• There are two basic types of natural gas, biogenic

gas and thermogenic gas.– Biogenic gas is a natural gas formed solely as a result of

bacterial activity in the early stages of diagenesis, meaning it forms at low temperatures, at overburden depths of less than 3000 feet, and under anaerobic conditions often associated with high rates of marine sediment accumulation

– Thermogenic gas is a natural gas resulting from the thermal alteration of kerogen due to an increase in overburden pressure and temperature

Types of Hydrocarbon4) Natural Gas• There are two basic types of natural gas, biogenic gas

and thermogenic gas.– Biogenic gas is a natural gas formed solely as a result of

bacterial activity in the early stages of diagenesis, meaning it forms at low temperatures, at overburden depths of less than 3000 feet, and under anaerobic conditions often associated with high rates of marine sediment accumulation

– Thermogenic gas is a natural gas resulting from the thermal alteration of kerogen due to an increase in overburden pressure and temperature

– The major hydocarbon gases are: methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10)

Types of Hydrocarbon4) Natural Gas

Maturation• Adalah perubahan material sedimen organik menjadi

petroleum / hidrokarbon• Tipe hidrokarbonnya bergantung dari jenis organik matter• Organik matter disebut juga kerogen• Kerogen yang melimpah didalam shale jika tidak dimasuk

pada suhu yang tepat akan menjadi oil shale deposit• Batas pembentukan oil ke gas adalah suhu 130⁰ C

Maturation

• Temperature depend on geothermal gradient, 3⁰ C/100 md

Migration• Migrasi dimulai dari tempat yang lebih panas di suatu basin• Hidrokarbon lebih ringan dari pada air, akan terus bergerak

keatas didalam reservoir• Migrasi ada 2 tahap – Primary migration, migrasi HC pada source rock melewati mikro

fracture atau pori2– Second stage migration, migrasi HC pada reservoir secara bebas

melalui bidang perlapisan atau fault

Reservoir• Reservoir rocks are either of clastic or carbonate

composition. The former are composed of silicates, usually sandstone, the latter of biogenetically derived detritus, such as coral or shell fragments.

• Pori2 di dalam reservoir biasanya terisi oleh pore water, yang kemudian digantikan dengan HC saat terjadi migrasi

• Pori2 disebut porosity sedangkan permeability adalah kemampuan batuan untuk mengalirkan fluida did alam porosity.

Traps• Main trapping mechanism

• Need timing of geologic time to know this traps has no leak and there is not any bacteria degrade the HC.

• Every third exploration well is substantial amounts of HC and every tenth well is successful in wildcat area

Metode Eksplorasi• Low cost and waktu singkat• Tahapan eksplorasi :– Reconnaissance, mencakup studi pustaka & desk study– Geophysical methods; gravity surveys, magnetic surveys, CSEM

seabed logging, – Seismic acquisition dan precessing– Seismic interpretation– Seismic atributes– AVO– Time-lapse seismic surveys (4D seismic)– Costs and planning

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