17 Questions
Which of the following is NOT a common sedimentary rock drilled in the oilfield?
Limestones
Which of the following clastic texture characteristics is NOT mentioned in the text?
Grain porosity
According to the Udden-Wentworth scale, which of the following grain sizes is the largest?
Gravel
What is the term used to describe the manner in which particles were laid down and the resulting structure of the inter-pore connections?
Grain fabric
Which of the following clastic texture characteristics is related to the sharpness or curvature of the edges and corners of a particle?
Roundness
What term is used to describe the degree to which a particle approximates the shape of a sphere?
Sphericity
What is the texture designation used to describe a situation where small crystals of calcium carbonate are irregularly scattered without common orientation in a larger crystal of another mineral?
Poikilotopic crystals
Which of the following is NOT a component of (silici)clastics as described in the text?
Orthosparite
In sandstone classification by Pettijohn, what major factor is used to divide sandstones into two groups?
Texture
What is the most common positive effect mentioned for authigenic clays like illite and kaolinite?
Preventing the formation of quartz cement
Which type of cementation in many limestones occupies the majority of the original pore space and is referred to as sparry, drusy, or orthosparite?
Clear, equant calcite spar
What characteristic defines drusy calcite spar in limestones according to the text?
Distinct generations
What are the two types of pore communication within clastics?
Catenary porosity and cul-de-sac porosity
What are the two main components of limestones?
Peloids and intraclasts
Which type of limestone is characterized by equal layers of calcite on pre-existing grains?
Isopachous cement limestone
What process increases porosity in carbonates by 12-13%?
Dolomitization
Which classification system is associated with the porosity in carbonates?
Archie classification system
Study Notes
Clastic Petrology
- Clastic rocks are formed from pre-existing rocks whose constituents were transported by some mechanism
- Most common sedimentary rocks drilled in oilfields are gravels, sands, and clays
- Conglomerates, sandstones, and shales are examples of clastic rocks
Clastic Texture
- Grain size: described using the Udden-Wentworth scale
- Grain shape: depends on size, composition, agent of transport, rigors of transport, hardness, brittleness, toughness, inherited partings, and other random effects
- Grain texture: surface features of particles/grains created during transport and formation of the clastic rock
- Grain fabric: affected by the manner in which the particles were laid down and the resulting structure of the inter-pore connections
Grain Characteristics
- Sphericity: degree to which a particle approximates the shape of a sphere
- Roundness: related to the sharpness or curvature of any edges and corners
- Grain contact: dictated by original packing and degree and amount of any pressure solution
Components of Clastics
- Monocrystalline quartz: 1.0mm grain size, sutured contact, interlocking intra/extraformational clasts of the same type/unassociated sedimentary rocks
- Feldspars: originating from igneous or metamorphic rocks
- Authigenic clays: clays formed in place
- Heavy minerals: detrital minerals with high specific gravity
Sandstone Classification
- Pettijohn classification: based on texture and divides sandstones into two major groups, concerned with mineralogy and presence/absence of matrix
Calcite Cementation
- Poikilotopic crystals: a textural designation denoting a situation where small crystals of calcium carbonate are irregularly scattered without common orientation in a larger crystal of another mineral
- Drusy calcite spar: in many limestones, two distinct generations can be distinguished
Authigenesis and Porosity
- Authigenesis: implies the formation of a mineral during or after deposition
- Clays: most common authigenic clays are illite and kaolinite, which can prevent the formation of quartz cement
- Porosity and permeability: three types of pore communication within clastics
Carbonate Petrology
- Two types of limestones: calcite and dolomite
- Components of limestones: ooids, coated grains, peloids, intraclasts, micrite envelopes, stromatolites, and oncolites
- Classification of limestones: based on grain size, composition, and texture
Test your knowledge on clastic rocks in petroleum geology and sedimentary petrology. Identify the common sedimentary rocks drilled in oilfields and understand clastic textures such as grain size, shape, and fabric. Explore concepts related to conglomerates, sandstones, and shales.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
