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Informative material on the basics of Hydrocarbon Exploration.
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HYDROCARBON EXPLORATION
Sedimentary Basin
Sedimentary basin refers to any geographical feature exhibiting subsidence and consequent infilling by sedimentation.
As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification.
SANDSTONE BRECCIA CONGLOMERATE
SHALE
ROCK SALT
FOSSILIFEROUS GYPSUM
COALLIMESTONE
Sedimentary rock types
Relative thicknesses of laminations, beds and strata
Sphericity of grains Texture
Sorting Fabrics
Waterlain beds Mass flow
Sedimentary rock characteristics
Geology
Geophysics
Seismic
Well Logging
By studying these sedimentary beds in outcrops and other surface features, geologists can infer where the underground porous reservoirs and impermeable traps might lie
Understanding of the shapes of the sedimentary rock layers. Early geophysical methods involved gravity-magnetic mapping, measuring the earth's gravity and magnetic responses at a number of points and plotting the results on a map
Geophysicists interpret these results to gain an understanding of the shapes sizes and orientation of rock layers, - stratigraphy and tectonics. To evaluate what kinds of rock are at which depths, how porous the rocks are, and whether there is oil and gas or water in the pore spaces.
Finding oil and gas
GEOLOGICAL
GEOPHYSICAL
GRAVITY
MAGNETIC
SEISMIC
GEOCHEMICAL
SNIFFER
What we look for :GEOLOGIC SETTING
A SIGNIFICANT SEDIMENTARY THICKNESS
FAVOURABLE STRUCTURAL FEATURE
PETROLEUM SYSTEM
Exploration Techniques
Structural elements
Lithology
Paleontological study
Environment of deposition
Stratigraphy
Evolutionary sequence of structure
Geological surveys
Geological field studies
Relative surface variation of Earth's gravitational acceleration over geologic structures
Gravity Magnetic Studies
AEROMAGNETIC RECONNAISSANCE SURVEY
Onland – Seismic surveys (Vibrosis)
Animation courtesy of Elf Aquitaine.
Marine seismic data acquisition
Surface
Layer-1
Layer-2
Layer-3
Arrival
time
0
Depth & Time
ShotReceivers
The seismic trace
Seismic Section (Land)
Seismic section – Deep Water
Semi‐detailed
Detailed 3D
Coarse Grid(reconnaitory)
Seismic imaging
High resolution‐3D
Viewing 3D data in many ways
Xline Sec
tionInline Section
Time SliceChair Display
Seabed Logging
Resistivity Profile
• All geological media have some sort of electrical conductivity.
• Difference in conductivity between shale & sandstone is relatively small when they’re water saturated.
• The conductivity falls markedly when the sandstone is filled with oil.
Seabed Logging
H2OH2O
Water-Filled Reservoir= Low Resistivity
Less Refraction of Wavesto the Receivers
HCHC
Hydrocarbon-Filled Reservoir= High Resistivity
Refraction of Wavesto the Receivers
From Seismic to map
TrapA trap is a geologic or a stratigraphic feature capable of
retaining hydrocarbons. Hydrocarbon traps that result from changes in rock type or pinch-outs, unconformities, or other sedimentary features such as reefs or buildups are called stratigraphic traps. Hydrocarbon traps that form in Geologic structures such as folds and faults are called structural traps
The key components of PETROLEUM SYSTEM (S) are (1) source rocks, (2) timing of generation, (3) migration (4) trap, and (5) seal
Petroleum System
Drilling …..
MUD LOGGING
DITCH SAMPLING
SUBSURFACE PRESSURE MONITORING
HC SHOW
TEMP MONITORING
BLOW OUT PREVENTION
CORING
LWD
MWD
Drilling…
RIG
VERTICAL
INCLINED
HORIZONTAL
EXTENDED REACH WELL
SAKHALIN-1 WELL HORIZONTAL DISTANCE 10 KM.
Well Profiles
Open hole logging – Formation Evaluation
DIRECT INFORMATION -ROCK FRAGMENTS & FLUIDS
Dill cuttings, mud shows
Sidewall samples, Cores or core slices, Production tests, Formation wireline samplers, Dill-stem tests
INDIRECT INFORMATION -WIRELINE LOGS
PHYSICAL PHENOMENON MEASURED PARAMETER
acoustic -waves sonic velocities
acoustic impedance
gamma / gamma scattering electron density
photoelectric cross section
thermal neutron density hydrogen density
thermal neutron decay thermal neutron cross section
neutron activation elemental concentrations
natural gamma radiation API
spontaneous potential membrane potential
electromagnetic waves electric resistivity / conductivity
LOCATE: reservoir DETECT: fluid content
fluid type : gas / oil / waterEVALUATE: lithology
mechanical propertiesgross / net reservoir thicknessporosity permeabilitycapillary propertiessalinity of the wateroriginal hydrocarbon saturationresidual hydrocarbon saturationpercent oil/gas/waterreservoir pressure
Objectives of a Petrophysical Interpretation
Formation Evaluation
Wire line logs - Open Hole
RESISTI VITY
DENSITY
POROSITY
RADIOCATIVITY SPECTRUM
TRANSIT TIME
Well completion
Perforation of reservoir
Reserves are those quantities of petroleum which are anticipated to be commercially recovered from known accumulations from a given date forward.
All reserve estimates involve some degree of uncertainty
PROVED UNPROVED
PROBABLE POSSIBLE
Reserves
Volumetrics
OIIP = Area x thickness x porosity x saturation
FVF
GIIP = Area x thickness x porosity x saturation x Bg
Recoverable Reserves: IIP x Recovery Factor
1. Primary recovery
• Reservoir pressure causes OIL to flow to the surface
•The simplest way of maintaining production flow rates is to use downhole pumps. (15-20%)
2. Secondary recovery
•Secondary recovery methods were developed to improve the recovery factor.The most common method involves flooding the reservoir with water. This involves injecting water into the reservoir to artificially increase the reservoir pressure and press the oil into the production wells (30-40%)
3. Tertiary recovery (EOR = enhanced oil recovery)
•The following methods can be used to improve the crude's flow qualities:
- Injecting steam into a reservoir heats up the crude and reduces its viscosity.
- The same effect can be achieved by pumping in solvents.
•Upto 50 % of the original oil in place can be exploited by means of tertiary recovery
Production
Injection Well
Production Well
Injection Well
1. Water
2. Polymer
Production
Classification of crude oil is often by its relative weight or viscosity ("light", "intermediate" or "heavy");
Refiners may also refer to it as "sweet", which means it contains relatively little sulfur, or as "sour", which means it contains substantial amounts of sulfur and requires more refining in order to meet current product specifications
Classification of crude oil
The world reference oils :
Brent Crude comprising 15 oils from fields in the Brent and Ninian systems in the East Shetland Basin of the North Sea .
Oil production from Europe, Africa and Middle Eastern oil flowing Westtends to be priced off the price of this oil, which forms a benchmark.
•West Texas intermidiate (WTI) for North American oil.
•Dubai used as benchmark for the Asia - Pacific region for Middle East Oil
•Tapis (from Malaysia, used as a reference for light Far East oil)
•Minas (from Indonesia, used as a reference for heavy Far East oil)