CHAPTER 2 (PART 1) Flashcards
•the pressure exerted by the formation fluids on the walls of the rock pores
•a critical parameter because it can affect drilling operations
Formation pore pressure
if the drilling mud pressure is less than the formation pore pressure, it can lead to ___, where formation fluids (oil, gas, or water) uncontrollably flow into the wellbore
blowout
FPP
Formation Pore Pressure
Normal formation pore
pressure also called as
hydro pressure
when the formation pore pressure equals the hydrostatic pressure of a full column of formation water
Normal formation pore
pressure (hydropressure)
Normal pore pressure is usually of the order of
0.465* psi/ft
Abnormal formation pore pressure also called as
geo-pressure
exists in regions where there is no direct fluid flow to the adjacent regions, these regions have impermeable boundaries, preventing fluid flow, trapping it to take a large proportion of the overburden stress
Abnormal formation pore pressure (geo-pressure)
abnormal formation pore pressure ranges between
0.8 and 1 psi/ft
Pressures ABOVE the normal range are called
overpressure
___ is determined through various methods, including well logs, seismic data, and drilling measurements
FPP
Pressures BELOW the normal pore pressure ranges are called ___
subnormal pore pressure
The terms ___ and ___ are used interchangeably because underpressures uncommonly occur in the sedimentary formations (excluding those caused by depletion from oil and gas production).
overpressure and abnormal pressure
What means TVD
True Vertical Depth
Elevated pore pressure s pose a severe risk during drilling when ___ are present and place important constraints on the density pf drilling mud (i.e. mud weights) used during drilling (Mark Zoback, 2007)
hydrocarbons
Hydrostatic pressure in liquid columns
p = 0.052MW × D + po
Some known mechanisms causing Abnormal Formation Pore Pressure (Bourgoyne, 1986)
• Compaction Effects
• Diagenic Effects
• Differential Density Effects
• Fluid Migration Effects
According to (Zoback, 2007), what causes of Abnormal Pore Pressure
• Thermal Expansion
• Depletion
• Undercompaction
• Chemical transformation with water release
• Tectonic Compression
• Hydrocarbon Generation
• Lateral Fluid Transfer
According to (Zhang, 2019), what causes Abnormal Pore Pressure
• Compaction disequilibrium
• Hydrocarbon Generation
• Formation uplift and unloading
• Smectite diagenesis
Compaction disequilibrium, also regarded as ___
undercompaction
In many cases, ___ has been determined to be the primary caused of overpressure, particularly in geologically young rocks.
Compaction disequilibrium (undercompaction)
Areas with abnormally pressured rocks are mainly located in the Tertiary and late Mesozoic sedimentary formations, what is the depositional setting and lithology of it
the depositional setting is dominantly deltaic, and the lithology is dominantly shale
Normal compaction generates ___ in the formation of compaction disequilibrium
hydrostatic pore pressure
When the sediments subside rapidly and the formation has extremely low permeability, the ___, and the remained fluid in the pores must support all or part of the weight of overburden sediments.
fluids are partially expelled
The pores are less compacted, which results in a ___. This generates abnormally high pore pressure, causing porosity to decrease less rapidly than it should be with depth, and formations are in the state of undercompaction or compaction disequilibrium.
higher porosity than the normally compacted formation
• It is the creation of mobile fluids from initially immobile solid kerogen
• Causes fluid volume or porosity increase if fluids are not expelled
Hydrocarbon Generation
The conversion of ___ is the most aggressive overpressure mechanism
kerogen into methane gas
