Intro to Petroleum Engineering

Name the 3 Exploration Well Evaluation Techniques

• Physical Samples of Underground Rocks

  • Core samples

  • Cutting samples

• Well Log

  • Drillers log, the driller keeps a record of rock and fluid types, encountered & the time it took to drill through a particular layer

  • Wireline log, a sonde is lowered into wellbore at end of wireline. Sonde measures electrical, radioactive or acoustic properties of formations

  • Logging while drilling

• Well Testing

  • Drill Stem Test

  • Wireline formation tester

  • Helps detect mobile hydrocarbons

  • Expensive due to cost of tech and rig time

What are the 5 phases of field development and their objectives

• Exploration, Identifying potential reservoir

• Evaluation, Identifying prospect reservoir

• Development, Design and set-up facilities

• Production, Maximising efficiency

• Abandonment, Safety and security

What are the three types of stratigraphy and what data do they analyse?

• Lithostratigraphy, Rock types

• Biostratigraphy, Fossil content

• Sequence stratigraphy, Arrangement or grouping of layers

What are the different types of survey’s and what do they measure

Magnetic Survey

• Anomalies (slight variations) in the earth’s magnetic field due to magnetic properties of subsurface rocks

Gravity Survey

• Measure anomalies in the earth’s gravitational field, due to variation in the density of sub-surface rocks

Seismic Surveys

• Measure the time taken for sound waves to travel through sub-surface rocks due to variation in the density, depth and mineralogy of rocks

What are the three main parts of the drilling operation and their descriptions

• Drilling top hole, High rate of penetration

• Middle hole, Lower rate of penetration

• Reservoir sections, Minimise formation damage

What are the criteria for starting coring

• Special depth given by geologist

• Increase in penetration rate, indicating porous zone

• Hydrocarbon indications (visual signs of oil/gas)

• Cutting showing transition from capstone to reservoir rock

What technique is used for induction Log and what information do you get from it

Tool has one source and two detectors held on callipers against the formation and a counter picks up gamma ray diffused by the formation towards the borehole. Number counted is related to number of electrons, which is related to formation density, which is used to get porosity.

What are the different types of recovery and what methods do they contain

Primary

• Gas-cap

• Solution-gas

• Water

• Gravity

• Compaction

• Combination

Secondary

• Water injection

• Gas injection

Tertiary

• Near miscible gas injection

• Steam-injection

What are the pressure, production and gas-oil-ratio behaviours for the solution gas mechanism

Production will result in a rapid decline in pressure; hence, low recovery is expected, 5-30% STOIIP. Gas-oil ratio starts low then rises to a maximum

What phrases refer to the phase behaviour of a gas reservoir

• Wet gas

• Gas-condensate

Is this statement true “Because of small thermal capacity and surface area of porous reservoir, flow processes in a reservoir occur at variable temperature”

No

What does a typical volume factor (Bo) vs pressure profile

Trends

• Above the bubble point oil expands as pressure is reduced hence Bo increases

• Below the bubble point oil shrinks as gas comes out of solution therefore Bo. decreases

What assumptions can be made for Darcy’s law for single-phase flow

• Laminar flow

• Homogenous rock

What are parts of the phase behaviour for a single-component pure system

• Vapour-Pressure line

• Critical point

• Tripple point

What are flow regimes that can occur in a reservoir and a key characteristic pressure behaviour for it

• Semi-steady-state flow:pressure gradient is constant but abs pressure declines

• Transient flow regime: When the flow starts in the well, there is an immediate reduction in pressure. This pressure perturbation moves through fluid at a rate dictated by rock permeability and fluid properties. Producing a pressure variation along the model.

What is the conceptual separation process taking place in gravity separators

Driven by density difference between the gas, oil and water phases. Gas flashes from the well-head fluid as the pressure is reduced.

Why would water separated from the field production be injected back into the oil reservoir

• Reservoir pressure support

• Oil sweep from injectors to producers

What does the cemented and perforated bottom-hole completion look like

Why would cemented and perforated bottom-hole production be preferred in a heterogeneous, multi-phase saturated

Cemented & Perforated production liner/casing would be preferred in a heterogenous, multi-phase saturated reservoir because of its ability to control the zonal inflow of unwanted fluids

if the well productivity index increases what would you expect to happen to the wellbore pressure

It will increase (more pressure is required to pump fluid up well)

What are the 5 Exploration Techniques

• Previous geological/geophysical data

  • Large collections of data

  • General depositional trends

• Aerial and Satelite Images

• Geophysical Methods

  • Applies physics to study subsurface geology

    • Measurements of earth’s magnetism, gravity and seismic vibrations to determine thickness of sediments and shape of geophysical structures

• Oil and Gas Seeps

  • Most obvious sign

    • slow difficult to read

    • most have already been exploited

• Exploration Drilling

  • Based on previous methods a location is selected

  • Data on lithology, porosity, permeability, fluid distribution and saturation evaluated to predict if resv has enough oil or gas to justify completion of exploratory well

What are the main objectives and required information for evaluation

Objectives

• Determination of fluids in place

• Estimation of amount of hydrocarbon and recovery factor

Information

• Identification of depositional sequences, thickness and mineralogy of layers

• Info relating to porosity, permeability, fluid distribution and saturation

• Data on reserve and production capacity of resv

What are the objectives for an appraisal well

To delineate reservoir boundaries if exploration successful

• Appraisal wells drilled in succession

• Ideally intersect contacts between oil and water and oil and gas

How are the different types of rock formed and what is their porosity

Igneous

• By crystallisation of molten material

• They have very low or no porosity, no permeability

Metamorphic

• Recrystallisation of older rocks, either by direct heating or by heating accompanied by pressure and deformation

• Very low or no porosity

Sedimentary Rocks

• Formed by accumulation of particles as sediment

• Depends on rock texture

What is stratigraphy and the different types

The study of the history of deposition of layers deposited in a basin is called stratigraphy

Types

• Rock types: Lithostratigraphy

• Fossil Content: Biostratigraphy

• Chemical Composition: Chemostratigraphy

• Magnetic Signatures: Magnetostratigraphy

• Arrangement or grouping of layers into sequences: Sequence stratigraphy

What are the types of petroleum migration and what are their definitions

Primary Migration

• Expansion of sufficient amount of generated petroleum causes the source rock to fracture and allow fluid to escape

Secondary Migration

• Petroleum then migrates away from source rock and through pore spaces of surrounding rocks upwards and sometimes along the beds

What is Petroleum Entrapment

Petroleum which is prevented from reaching the surface due to a ‘trap’ (Impermeable seal rock unit)

The resv seal and trap must be in place before hydrocarbon formation

What are the types of hydrocarbon traps

Stratigraphic

• Formed during deposition of reservoir beds

• Unconformity or Lenticular (Pinch out)

Structural

• Created by tectonic processes after deposition of the resv beds

• Anticline/dome, fault and salt dome plug

Combination

• Formed by a combination of those during deposition and by tectonic activities

• Resv could occur in an anticline that is faulted and associated with unconformity

What is the definition for reserves

Quantities of petroleum that are anticipated to be commercially recovered from accumulations from a given date forward

What are the degrees of uncertainty in reserves

Proved

• Commercially recoverable from known resvs and current economic conditions and regulations (at least 90% probability)

Unproved

• Probable

  • more likely to be recovered than not (50% probability)

• Possible

  • Less likely to be recovered than recovered (10% probability)

What are the causes of abnormal pressure

Thermal effects

• Expansion or contraction of sealed fluids in rock

Rapid burial of sediments

• consisting of layers of sand and clay. Speed of burial does not allow fluids to escape from the pore space

Clay diagenesis

• Montmorillonite diagenesis to illite produces water from the clay particles as they compact

Osmotic effects

• via salinity differences. Clay acts as a semipermeable membrane across which water may glow if there are different salt solutions on either side of the barrier

Depletion

• Production from the reservoir, natural or man-made

Geological changes

What are the pressure gradients for hydrocarbon pressure regimes

Gas: 0.08

Oil: 0.36

Water: 0.45

What are the types of electric logs

Spontaneous potential log

• Record of weak electric potential that is developed naturally in the rock

Resistivity log

• Sonde sends an electrical signal through the formation and relays it back to a receiver at the surface

Induction log

• measures. conductivity created by a electromagnetic field

Electric log

• measured is measured in uncases sections of the borehole

What are the types of non-electric log

Nuclear logs

• Record natural and induced radioactivity

  • Gamma ray log

  • Neutron log

Sonic Log

• Acoustic sonde transmits and receives sound waves

What factors affect porosity

• Particle shape

• Particle packing

• Particle size distribution and arrangement

• Cementing material, bugs and fractures

What is the permeability of a rock

The ease at which fluid flows through the pore structure

What assumptions are made for Darcy’s law

• Steady state flow

• Laminar flow

• Single phase only occupying 100% of porosity

• No reaction between fluid & rock

• Homogenous rock

|What are methods of estimating permeability

• Empirical correlation

• Lab measurements

• Well test data

What is wettability

The relative degree to which a fluid will spread on or coat a solid surface in the presence of other immiscible fluid

• it is a function of both rocks and fluids which depends on the compositions of the fluids solid surface

• a wetting phase is one which spreads over the solid and preferentially wets the solid

What are the three flow regimes and their descriptions

Instead-state or transient flow: Transient pressure data without boundary effects

Semi-steady( (pseudo-steady state): Closed no flow boundary

Steady-state: Strong aquifer support or injection wells

What are the classification of reservoir fluids

• Black oil

• Volatile oil

• Gas-condensate

• Wet gas

• Dry gas

What is an FPSO and what does it have

Floating production system which is moored permanently and connected to wells by flexible risers

what it has

• shape of a ship

• Controls well operations

• Required production & processing facilities

• Crude oil storage tanks built into hull

• Oil export by shuttle tanker or pipeline

• No drilling