INTRODUCTION TO EXPLORATION & PRODUCTION

By: Vinay Varghese

HOW DO WE KNOW WHERE TO EXPLORE ?• Exploration is a tricky business, it is a guessing game. • Since there is a lot of investment once you fix a location to

explore, we do not leave everything to chance.• We look for a petroleum system.• So, what is a petroleum system ?

•A Petroleum System is a dynamic hydrocarbon system that functions in a restricted geologic space and time scale.

•A Petroleum System requires timely convergence of geologic events essential to the formation of petroleum deposits.

WHAT ARE THE GEOLOGICAL EVENTS WE LOOK FOR ?

•Mature source rock•Hydrocarbon expulsion•Hydrocarbon migration•Hydrocarbon accumulation•Hydrocarbon retention

Cross Section Of A Petroleum System

Overburden Rock

Seal Rock

Reservoir Rock

Source Rock

Underburden Rock

Basement RockTop Oil WindowTop Gas Window

Geographic Extent of Petroleum System

Petroleum Reservoir (O)

Fold-and-Thrust Belt(arrows indicate relative fault motion)

EssentialElements

ofPetroleum

System

(Foreland Basin Example)

(modified from Magoon and Dow, 1994)

O O

Sedi

men

tary

Bas

in F

ill

O

Stratigraphic Extent of

PetroleumSystem

Pod of ActiveSource Rock

Extent of Prospect/FieldExtent of Play

• The following are basic principles or laws are used to evaluate the relative ages and the relations among rock layers.

• Uniformitarianism - “The present is the key to the past.” By studying modern geologic processes, we can interpret past geologic events and rock-forming processes.

• Original Horizonality - “Sedimentary layers are deposited in a horizontal or nearly horizontal position.” If sedimentary layers are tilted or folded, they have been subjected to deforming stresses.

• Superposition - “Younger sedimentary beds occur on top of older beds, unless they have been overturned or faulted.”

• Cross-Cutting Relations - “Any geologic feature that cuts another geologic feature is younger than the feature that it cuts.”

Basic Geologic Principles

FORMATION OF PETROLEUM

ROCKS• Before we proceed to understand where oil is formed we must familiarize

ourselves with a few terminologies of rocks.• The three major rock types are sedimentary, igneous, and metamorphic rocks.

Their classification is based on their origins.• Sedimentary rocks are formed from particles derived from igneous,

metamorphic or other sedimentary rocks by weathering and erosion. Sedimentary rocks provide the hydrocarbon source rocks and most of the oil and gas reservoir rocks.

• Igneous rocks are formed from molten material which is either ejected from the earth during volcanic activity (e.g., lava flows, and ash falls), or which crystallizes from a magma that is injected into existing rock and cools slowly.

• Metamorphic rocks are formed by subjecting any of the three rock types to high temperatures and pressures, that alter the character of the existing rock. Common examples of metamorphic rocks are marble derived from limestone.

The Rock Cycle

Magma

MetamorphicRock

SedimentaryRock

IgneousRock

Sediment

Heat and Pressure

Weathering,Transportationand Deposition

Weathering, Transportation,

and Deposition

Cooling and

SolidificationMelt

ing (Crystalization)

Hea

t And

Pres

sure

(Met

amor

phis

m)

Weathering,

TransportationA

nd Deposition

Cementation andCompaction(Lithification)

• Petroleum is not found in a large pool or a whole accumulation of liquid like an underground storage tank.

• It id found in the pore spaces of the rock.• What is porosity ?

RESERVOIR TRAPS• When we look for a water reservoir on land, we look for

depressions because water will move downhill naturally and accumulate in a bowl shaped formation.

• For oil, it is not the same. We all know one thing that oil floats on top of water, because it has a density lighter than that of water.

• So naturally it will not settle in depressions but will accumulate on troughs or under dome like structures.

• For this to occur we need an impermeable or low permeability layer of rock over the rock in which the petroleum has accumulated.

GEOLOGICAL STRUCTURE BECOME THE TRAPS

• As we saw earlier, that petroleum is formed mainly in sedimentary rocks. Sedimentation occurs layer over layer, mostly in a horizontal manner or near to horizontal manner.

• This horizontal sedimentary rock is disturbed by continuous tectonic activity, which causes the rocks to fold, break, slide along the path of least resistance, crack. Basically it damages the structure which took millions of years to form.

• This damage when leads to an impermeable layer against a reservoir, trapping the petroleum, when it forms fold for accumulation of petroleum is a boon to us.

SURVEY• We can conduct a survey of the chosen field, by various

methods.1. Gravity: The density of basement rocks is always higher to that of

sedimentary rocks and so the gravitational pull due to the high density basement is more. So from this we get a profile of the basement rocks.

2. Magnetic: The magnetic field of the basement rock creates anomalies in the earths gravitational field, so if the basement rock is closer the distortion will be higher and vice versa.

3. Seismic: Every rock has an intrinsic property of allowing a certain amount of sound waves to pass through and it reflects the rest. Using this property of the different rocks, we can determine which rock is at what depth depending on the reflectivity of that layer. Giving us a picture of the sub surface.

DRILLING•Drilling an oil well is in many ways similar to drilling a hole into the wall, only the desired level of safety and precaution is much higher because we do not know what we are going to face in the subsurface.•We do go in with a fair idea, but it is never full proof. We are dealing with high pressure fluids, at high temperatures, which if left unmonitored will surely lead to a disaster.

WHAT DO WE NEED TO DRILL ?• Drill bit: This is the most useful equipment on the rig, because

this is what will crush the rock and allow us to move deeper into the earth.

• Drilling mud: As the drill bit faces higher temperatures and harder rocks, its temperature will keep on increasing, which is not good for the life of the bit, so we introduce drilling mud which lubricates, cools and helps bringing the cut/grinded material back to surface.

BLOWOUT PREVENTOR• From the discussion above we know that drilling a well is not

such an easy task because of the pressure and flammable fluids that we may encounter in the sub surface.

• To avoid the sub surface fluids to reach the surface in case of entering an unexpected interval of hydrocarbon fluid, we use an equipment what is known as a Blowout Preventor (BOP).

• BOP is a stack of RAMS that cut the annulus region from the surface in case of a blowout.

• There are three type of RAMS:1. Annular RAM2. Pipe RAM3. Blind RAM

ENHANCED OIL RECOVERY• Enhanced oil recovery deals with maintaining the pressure of

the pressure of the reservoir by injecting water or gas, polymers to push the liquid further towards the well.

• In situ combustion and steam injection for highly viscous petroleum to heat it and allow the fluid to flow towards the wellbore.

THANK YOU FOR YOUR PATIENCE