Petroleum Geology (Module PPT) Final Examination

Reservoir rock

Reservoir rock

is a place that oil migrates to and id held underground

Coring

processes used to recover formation samples from petroleum reservoirs

Reservoir rock samples

are used for reservoir description and definition, reservoir characterization and to enhance both geological petrophysical nature of reservoir.

Sidewall sampling tool

can be used to obtain small plugs from the formation. The tool is run on a wireline after the hole has been drilled.

Sidewall cores

are useful for identifying hydrocarbon zones, when viewed under UV light

Whole core

provides larger samples; better and more consistent representation of formation; better for heterogeneous rocks or for more complex lithology

Plugs or sidewall cores

smaller samples; less representative of heterogeneous formations; within 1 to 2% of whole cores for medium-to-high porosity formation

Standard analysis

porosity; horizontal permeability to air; grain density

Special core analysis

vertical permeability to air; relative permeability; capillary pressure; cementation exponent and saturation exponent

Porosity and permeability

both are important properties that are related to fluids in sediment and sedimentary rocks

Porosity

the volume of void space in an sediment and sedimentary rock

Permeability

related to how easily a fluid will pass through any granular material

Total or absolute porosity

is the total void space in the rock whether or not in contributes to fluid flow

Effective porosity

implies the ration of the total volume of interconnected voids Vp to the bulk volume Vb of the rock; percentage of interconnected void space with respect to the bulk volume

Double porous or fracture-porous media

rock having both fracture and intergranular pores

Fracture porosity

is a form of secondary porosity generated by tectonic fracturing of the rock

Micro-porosity

part of the pore space that has a characteristic dimension less than 1 micron

Vugular porosity

is the pore space consisting of cavities or vugs; can occur in rocks prone dissolution, such as limestone, in which case is secondary porosity

Secondary porosity

is the porosity created through alteration of rock, commonly by processes such as dolomitization, dissolution and fracturing

Primary porosity

is the space between grains that were not compacted together completely

Sorting

is the tendency of sedimentary rocks to have grains that are similarly sized

Poorly sorted

sediment displays a wide range of grain sizes and hence has decreased porosity

Well-sorted

indicates a grain size distribution that is fairly uniform

Packing density

the arrangement of the particles in the deposit

Grain size

has no influence in porosity

Compaction

particles are forced into closer packing by the weight of overlying deposits, reducing porosity

Cementation

precipitation of new minerals from pore waters causes cementation of the grains and acts to fill the pore spaces, reducing porosity

Clays

may form by the chemical alteration of pre-existing minerals after burial

Feldspars

are particularly common clay-forming minerals

Clay minerals

are very fine-grained and may accumulate in the pore spaces, reducing porosity

Quartz

relatively soluble when pore waters have a low

Pressure solution

the solubility of mineral grains increases under an applied stress and the process of solution is under stress

Fracturing

• particularly important in producing porosity in rocks with low primary porosity

Density logs

uses radioactive source to generate gamma rays

Neutron log

logging tool emits high energy neutrons into formation

Acoustic (sonic) log

tool usually consists of one sound transmitter (above) and two receivers (below)

Openhole logging tools

most common method of determining porosity

Absolute permeability

the permeability of the porous medium if a single fluid is flowing

Effective permeability

permeability of a fluid if another fluid is present

Relative permeability

effective permeability divided by the absolute permeability

Henry Darcy

hydraulic engineer; the discoverer of Darcy’s law; his law is a foundation stone for several fields of study including ground-water hydrology, soil physics and pet eng.

Original porosity

constituted when the formation was laid

Secondary porosity

history of the rock

Effective porosity

continuous or interconnected porosity

Non effective porosity

discontinuous or isolated porosity

Seismic

define the structure of the subsurface to perform maps

Compressive (P, like primary)

the faster one, the direction of displacement of the particles is parallel to the propagation axis

Shear (S like secondary)

the displacement is perpendicular to the propagation axis

Surface waves or Stoneley

slower, their displacement follow the surfaces where the characteristics are changing

Mud-logging

data acquisition during drilling

Petrophysic

physical properties of the porous network

framework, matrix, cement, pores

Four major components of sandstone

bulk density, sonic (acoustic), compensated form

3 main log types

seismic, mud-logging, core, logging, tests, monitoring

Main ways to get information

sandstones; limestone and carbonate rocks

Examples of reservoir rock:

Reservoirs

are not underground "lakes" of oil; they are made up of porous and permeable rocks that can hold significant amounts of oil and gas within their pore spaces.

Diagenesis

The first stage in the transformation of freshly deposited organic matter into petroleum is called _______. This process begins at the sedimentary interface and extends to varying depths,

Catagenesis

is the stage of thermaldegradation of kerogen that forms oil and gas.

Metagenesis

The metagenesis stage is reached at great depths, or in areas of high geothermal gradients at shallower depths. Metagenesis usually begins at depths of approximately 4,000 meters.

Paraffins

also called alkanes and have the general fomula of CnH2n+2,

Naphthenes

or cycloparaffins are ring or cyclic saturated hydrocarbons with the general formula of CnH2n.

Aromatics

are an important series of hydrocarbons found in almost every petroleum mixture from any part of the world. This series of aromatics is called alkylbenzenes and have a general formula of CnH2n

Primary Migration

expulsion of petroleum from the source rock and also refers to movement of hydrocarbons

Secondary Migration

movement of oil or gas within reservoir

Subsurface Mapping

is a valuable tool for locating undereround features that may form trapso outline the boundaries of a possible reservoir.

Structural Contour Maps

show a series of lines drawn at regular intervals.

Liquid Petroleum

known as crude oil" to distinguish it from refined oil". It is most important commercially.

Natural Gas

which is the lighter fraction of hydrocarbons, can be free or dissolved.

Asphalt, Tar, Pitch

these are solid or semisolid forms of hydrocarbons, the heavy fraction.

Lopatin's TTI V. Lopatin (1971)

recognized the dependence of thermal maturation from temperature AND time. temperatures are weighted with the residence time. This so

Vitrinite Reflectance (Ro)

measures the reflectance of vitrinite

Source rock

refers to the formation in which oil and gas originate

Gravity and Magnetic Surveys

one of the tools used for mineral-bearing ore bodies or even oil-bearing

Geochemistry

ldentify possible source rocks (whole rock): usually black to dark brown in color.

Geologic Fieldwork

Rock identification and sampling

Cross-Sections

Structural, stratigraphic, and topographic information can be portrayed on

Isopach Maps

are similar in appearance to contour maps but show variations in the thickness of the bed.

Lithofacies Maps

show, changes in lithologic character and how it varies horizontally within the formation. This type of map has contours.

Level of organic maturation (LOM)

is based on coal ranks.

Pyrolysis

techniques are performed directly on rock samples and offer the major clues in the systematic analysis of kerogen

The Rock Eval instrument

provides a fast determination of the type and evolution stage of kerogen

Optical Techniques: Transmitted Light Optical

techniques are widely used to characterize type and maturation of organic matter.

Optical Studies: Reflected Light

The method most often used to evaluate the maturation of kerogen and to establish the depth range associated with petroleum generation is vitrinite reflectance.

STRUCTURAL TRAPS

are primarily the result of folding and faulting or both

Simple fold traps (anticlinal)

with axial culmination. The simplest type of trap is formed when a sandstone bed that is overlain by tight shale is folded into an anticline.

Salt domes

Strata around the salt dome curve upvward creating traps against the sealing salt layers.

Growth domes

Domes or anticlines that form during sedimentation when one area subsides more slowly than the surrounding areas.

Normal faults

commonly associated with graben (rift) structures.

Strike-slip faults

these may not be sealed due to incremental movements

Thrust faults

commonly associated with compressional tectonics

Growth faults

typically form in sediments that are deposited rapidly.

Stratigraphic traps

are created by any variation in the stratigraphy that is independent of structural deformation

Primary stratigraphic traps

result from variations in facies that developed during sedimentation.

Secondary stratigraphic traps

result from variations that developed after sedimentation, mainly because of diagenesis.

Hydrodynamic Traps

If porewater flow in a sedimentary basin is strong enough, the oil-water contact may deviate from the horizontal

A reservoir

is a subsurface volumne of porous and permeable rock that has both storage capacity and the ability to allow fluids to flow through it.

Sandstone reservoirs

are generally created by the accumulation of large amounts of clastic sediments which is characteristic of depositional environments such as river channels, deltas, beaches, lakes and submarine fans.

Carbonate reservoirs

are created in marine sedimentary environments with little or no clastic material input and generally ina location between 30° north and south of the equator.

Depth

The physical characteristics of a reservoir are greatly affected by the depth at which they occur.

Shallow reservoir

Created by the folding of relatively thick, moderately compacted reservoir rock with accumulation under an anticline or some trap.