Upload
andres-felipe-benavides
View
220
Download
1
Embed Size (px)
DESCRIPTION
IMPORTANCIA DEL RESERVORIO
Citation preview
Important Reservoir Factors
o Gross thickness • The total thickness of the reservoir interval
o Net-to-Gross ratio • The fraction of the gross reservoir thickness
representing porous reservoir rocks
o Porosity • As fraction of the total net reservoir
o Permeability • Impacting the production rates that can be
achieved
o Geometry of reservoir bodies: • Affecting connectivity, and influences the
production rate & recovery factor 3 3. Reservoirs
What we like best:
Very thick
High net/gross massive sandstones
High porosity much room for HCs
High permeability high production rates
High continuity, and no “baffles”
Reservoir Factors are controlled by: o Depositional environment
From terrestrial to deep marine
o Rate of sediment input High sediment input Progradation Lack of sediment input Carbonate deposition
o Relative sea level Rise Regression and accumulation in accommodation space High Progradation into the basin Fall Non-deposition or erosion and by-pass to deep water Stable Lateral fill of accommodation space
N.B Steep slopes narrow shelves with fans & sediment by-pass
o Post-depositional structuration Faulting Differing subsidence rates (accommodation space) Uplift Erosion and unconformities
4 3. Reservoirs
Depositional Environments
5 3. Reservoirs
Clastic Depositional Systems
Clastic Depositional Systems
Clastic Depositional Systems
Sequence Stratigraphy for Dummies Sequence stratigraphy is the study of stratigraphic sequences in a
time framework linked to variations of (relative) sea level.
All cycles in sedimentation result from changes in accommodation space in a depositional setting.
Relative sea-level can be subdivided in 4 phases: Rising – High – Falling – Low
In the sedimentary record we can recognise 3 Systems Tracts: • Transgressive Systems Tract – fast rising sea-level • Highstand Systems Tract – slow rising (late) and high sea-level • Low Stand Systems Tract – falling and low sea-level
Each phase may contain all facies from shallow to deep, but they are: • spatially different, and • have different onlap geometries
9
A very good website with information and illustrations about sequence stratigraphy can be found at:
http://www.sepmstrata.org/seqstrat.html 3. Reservoirs
Eustatic Sea-Level Cycles
JdJ 10
1st Order Cycles > 50-100 MY cycles Resulting from large scale volume changes of
ocean basins related to break-up and formation of supercontinents
2nd Order Cycles 3-50 (10-100) MY Probably caused by changes in oceanic spreading rates
3rd Order Cycles 0.5-3 (1-10) MY Foundation of Seismic Stratigraphy depositional sequences Possibly caused by glacio-eustatic cycles and/or variations in intra-plate stresses
4th and higher Order Cycles <0.5 MY Local autocyclic causes, such as delta switching Milankovitch cycles (Precession: 19-26ky, Obliquity: 41ky, Eccentricity: 95, 125,
400ky)
Sealevel Phanerozoic coastal onlap curve
Vail onlap curve
First-order sea-level cycle
The light blue line is the 1st order sea-level curve
The coastal onlap curve has 2nd order cyclicity Note the flat tops of the coastal onlap curve…
11 3. Reservoirs
Facies change within a depositional sequence Four main parameters influence distribution of facies
belts: 1. Eustacy 2. Subsidence 3. Sediment supply 4. Climate
After Bally et al. JdJ 12
Climate
Eustacy
Subsidence
Sediment supply
Eustacy, Relative Sea-level, Coastal Onlap
A symmetric sea-level curve results in a a-symmetric coastal onlap curve
13
Coastal onlap curve
Stratigraphic Recorded time
B/C D/E F/G
hiatus
hiatus
hiatus
Summation of input functions
time A B D E F G C
Relative changes
of sea-level R
ising Falling
Input functions
time
eustacy
Relative changes
of sea-level R
ising Falling
3. Reservoirs
Changes in sediment supply rate
JdJ 14
Coastal Onlap & Transgression / Regression
Rising sea-level Falling sea-level
Time of sea-level fall
Stillstand
Transgression
Regression
High sediment input
Low sediment input
After B.W. Ross 15
Fast sea-level rise
Slow sea-level rise
3. Reservoirs
Prograding depositional sequence
Coarsening upward progradational (regressive) sequence of fan-delta complex: • Marly shales at the base (slope deposits) • Coarsening/shallowing upward sands (coastal-fluvial/alluvial)
Arrow indicates shaling-out sand unit in distal direction: clear example of facies change within a single depositional sequence
16 3. Reservoirs