1-basic Geology_lw.pdf

Log Evaluation and QA/QC Seminar Basic Geological Concepts

Lukas Wihardjo April - 2014

HYDROCARBON FORMATION

Hydrocarbon Formation

Hydrocarbon Movement Hydrocarbon are less dense than the formation water. It will then migrate up through the rock until it is trapped or seeps out onto the surface. Geologists look for these traps to find commercial amounts of petroleum.

GEOLOGICAL CONCEPTS

What is a Mineral? • There are many definitions of the word "mineral." -- "a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties."

What is a Rock? • Rocks are naturally occurring solids composed of one or more minerals. Rocks are identified by the minerals they contain and are grouped according to their origin into three major classes: sedimentary, igneous, and metamorphic. Each group is subdivided on the basis of texture and mineral composition (lithology).

What is lithology?

The gross physical character of a rock or rock formation. The microscopic study, description, and classification of rock.

ROCKS

Three Types of Rocks

• Metamorphic

• Igneous

• Sedimentary

Metamorphic Rocks • Pressure, heat, directed pressure, and catalytic action act to change parent rock into new rock with different texture and compositions

• This type of rock has no source potential but if fractured and or weathered can be a source for reservoir rock

Igneous Rocks • Rocks that resulted from the cooling and crystallization of magma.

• Igneous Rocks have no source potential. They can provide reservoir potential in porous and permeable weathered igneous rock.

Sedimentary Rocks • Formed from the cementation of individual sediments • Good source potential • Good reservoir potential

Two Main Classes of Sedimentary Rocks • Clastic – Sediments consisting of broken fragments derived from preexisting rocks and transported elsewhere and redeposited. • Non-Clastic – Sedimentary rocks that are created either from chemical precipitation, crystallization, lithification of once living organic matter.

Clastic Rocks

• Sandstone – usually made up of quartz and feldspar. Grain size is 2-1/16 mm.

• Shale – made up of clay and silt. Grain size is < 1/256 mm

Non-Clastic / Clastic Rocks

• Limestone – Made from the mineral calcite which comes from the beds of evaporated seas and lakes and from animal shells. CaCo3 • Depending how the limestone is formed, it could also be classified as either a clastic or non-clastic rock

Non-Clastic Rock • Dolomite – Forms when calcite, CaCO3 interacts with Magnesium rich ground waters. CaMg(CO3)2

Non-Clastic Rock

• Anhydrite – Formed by the dewatering of Gypsum (CaSO42H2O). CaSO4

SHALES

Why Study Shales? • The most important rock type to the Oil and Gas industry is sedimentary rock • Shales form some 60% of the sedimentary rocks found in the world • Some shales form hydrocarbon reservoirs (shale gas and shale oil) • Shales are not only abundant but they also affect : – Petrophysical Analysis – Reservoir Modeling – Geology – Drilling/Completion

Shale Definition • A general class of fine grained, detrital sedimentary rocks with a grain size < 0.031 mm that consists dominantly of a mixture of clay minerals (>35%) and silt grains.

Silt • Silt refers to soil or rock particles of a certain very small size range (see grain size). On the Wentworth scale, silt particles fall between 0.004 and 0.063 mm (4 - 62.5 μm), larger than clay but smaller than a sand.

Clay • Clay minerals (Grimm, 1962): a group of fine grained hydrous alumino-silicate minerals with the general formula X(Al2O3) Y(SiO2) Z(OH) which contain minor but important amounts of other elements such as Mg, Fe, Na, Ca, K.

Kaolinite – Al2O3 2SiO2 2H20 Illite – KAl2(OH)2[AlSi(O,OH)]10 Smectite – (MgCa) Al2O3 5 SIO2 nH20 Chlorite – (MgFe)5 Al(AlSiO3) O10 (OH)5

FORMATION OF SEDIMENTARY ROCKS

The Rock Cycle

Weathering – Breakdown of Rock • Mechanical Weathering – rocks are physically reduced to fragments. • Chemical Weathering – rock alterations and breakdown caused by exposure with chemical agents.

Erosion – Removal of Rock Material • Downslope Movement – Gravity forces all weathered rock material downhill with or without the aid of flowing water • Stream Erosion – Running water moves weathered rock. Depends on stream patterns, slope gradient, velocity, bed load, base level

Deposition – Depositing of rock material

• Stream Deposits

• Delta Deposits

Life Cycle • At the same time as the rock cycle happens so is the life cycle. Plants and animals are born, live and die • The dead organic matter is washed away just like the weathered rock • It is deposited on the sea floor and cemented into the rock matrix

Cementation • The individual sediments are cemented together as precipitates form between the grains from the pore fluids. • Calcite and Quartz are common cement forming minerals

Decomposition Most of organic debris is destroyed and digested by bacteria, some is deposited in oceans, lagoons, lakes and river beds protected from bacterial action.

Sedimentation Organic debris mix with sediments (sand, salt, etc..) and accumulates in beds for million of years, oldest beds been buried by newest beds.

Sediments are Sorted

• Marine Currents • Depth

• Waves • Marine Life

Grain Sorting

• The deposition of the grains may be : – Well sorted with similar grain sizes – Poorly sorted with differing grain sizes

• These can affect both the permeability and porosity

Porosity Porosity is defined as the void space in the rock matrix

Porosity Types • Porosity can be classified in two main types according to their origin • Primary

• Secondary

What is in the Void Space? • Oil

• Gas • Water

Permeability • Is defined as the interconnectivity of the pores. • Represented by Darcy’s Law K = Permeability Q = Flow Rate

A = Cross Sectional Area L = Length of Sample u = Viscosity

P1 = Exit Pressure P2 = Entrance Pressure

Q L K  A P2  P1

THE RESERVOIR

The Reservoir

The Reservoir •To form a reservoir you need – Organic material source (terrestrial or marine)

– Appropriate combination of heat, pressure and time. – Oxygen free environment

– A suitable basin

The Reservoir

The main elements of a reservoir are: • Permeable Rock (stores hydrocarbon) • Source Rock (produces hydrocarbon) • Impermeable Rock (retains hydrocarbon) • Trap (captures fluids)

Tectonics

41

Maturation

42

Migration

43

Trapping

44

HISTORIC FRAME

First Oil Well • The history of the oil business as we know it began in 1859 in Pennsylvania, thanks to Edwin L. Drake, a career railroad conductor who devised a way to drill a practical oil well. • On august 27, 1859 a well drilled by Drake in Oil Creek, Titusville, found oil at 69 ft.

Oil Exploration in Iraq • First successful well in Iraq found oil on October 14, 1927 • The well at Baba Gurgur was located by geologist J.M. Muir just north of Kirkuk.

• It was drilled by TPC (Turkish Petroleum Corporation).

First Electric Log Recorded by Schlumberger in 1927

ADDITIONAL SLIDES FOR BACKUP

Hydrocarbon Formation • Diagenesis – Immature stage and is associated with no new hydrocarbon generation. The only hydrocarbons were present when the organisms died

• Catagenesis – Second stage of kerogen degradation and the start of thermal degradation. Brought on by the increase of temperature and pressure as burial depth increases. Main stage of oil generation

• Metagenesis – Thermal Cracking of previously generated hydrocarbons and additional generation of methane directly from kerogen. Oil is thermally cracked into dry gas.

Compositional States of Petroleum • Natural Gas – Gases that do not condense at 20 C and at atmospheric pressure (methane, ethane, propane, nbutane) • Liquid States – “Crude Oil” a mixture of hydrocarbons that occur as a liquid in underground reservoirs and remains liquid on surface • Plastic States – Very high molecular weights ( asphalts, bitumen, resins)

What is a Mineral? • There are many definitions of the word "mineral." The Glossary of Geology (Bates and Jackson, 1980, p. 401) defines a mineral as "a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties." Minerals differ from rocks, which are naturally occurring solids composed of one or more minerals. Rocks do not have a distinctive chemical composition or crystal structure. The earth science definition, however, is not always used to define minerals.

What is a Rock? • Rocks are naturally occurring solids composed of one or more minerals. Rocks are identified by the minerals they contain and are grouped according to their origin into three major classes: sedimentary, igneous, and metamorphic. Each group is subdivided on the basis of texture and mineral composition (lithology).

What is lithology?

The gross physical character of a rock or rock formation. The microscopic study, description, and classification of rock.