Structural Geology inPetroleum Exploration

Oil Exploration Strategy:

Find the TrapsMost common traps are structuresSo exploration often targets the structures inhopes of finding oil

MajorHydrocarbonProvinces inNorthAmerica

Sedimentary Basins

Topics:Petroleum SystemTrapsExploration Methods (seismic)Maui Field ExampleSalt Tectonics

Reading: 1. Outline in website2. Pdf file: Geology for Petroleum Exploration, Drilling, andProduction by Norman J. Hyne, 1984, pages 173-197.

Origin of Petroleum

Oil forms from the decay andtransformation of dead organisms buried insedimentary rocks

Factors required to make an OildepositSource rock- rich in organic matterBurial heating- > maturationReservoir rock- porous and permeableTrap- structural trap stratigraphic trap

Petroleum system

Maturation of Organic Matter

Organic matter in sediments is solid (kerogen)At about 60o C transformation begins Liquid hydrocarbons begin to formAt 120o C gas begins to formAt 140o C organic matter is exhaustedOnly gas forms at higher T

Migration

Source RocksBlack organic-rich marine shalesOrganic matter is preserved low-oxygenwaterRestricted marine basins and zones were water rises from the deep

Migration of oil

Oil is less dense than waterOil will move up by buoyancyOil needs a permeable bed to moveIt will stop when it reaches an impermeable bed

EasternVenezuela

WesternCanada

Oil trapsPermeable reservoir bedImpermeable seal

Porosity

StructuralTraps

Stratigraphic Traps

FaultTraps

Map of theMurre Field

Newfoundland

Salt Traps

Trap Types

Compressional Traps

Traps in Strike-Slip settings

Positive Flower Structures

How to image the subsurface?

DrillingStructural InterpretationSeismic Reflection Imaging Send sound into the rock, and collect theechoes

Seismic Acquisition

3D Seismic Image

Salt

3D Geological Model

Maui Field, New Zealand

Gulf ofMexicoSalt

Offshore Platform

Salt moves driven by buoyancy

Salt density= 2 g/ cm3Salt undergoes no compactionShale Density is initially 40% waterInitial Density = 1.8 g/ cm3Water expelled during compaction Final Density = 2.4 g/ cm3

Sequential Stagesof a Salt Diapir

Seismic Image of a Salt Dome

Sandbox Experiment

Relationship between diapirism and normal faulting

3D Seismic Interpretation of SaltStructures

Extension Above Salt Diapir

Syn-sedimentary Salt Movement