Glossary
3D three dimensional
Anderson stress states
Reverse Fault, S_{H} > S_{h} > S_{V}, or S_{H}/S_{V} > 1.4 and S_{h} /S_{V} >1
Strike Slip, S_{H} > S_{V} > S_{h}, or S_{H}/S_{V} > 1 and S_{h}/S_{V} < 1
Normal fault , S_{V} > S_{H} > S_{h}, or S_{H}/S_{V} < 1 and S_{h}/S_{V} << 1
Closure Pressure (P_{C}) is picked from fluid injection pressure decline graphs, P_{C} = S_{h}.
Compressional Pulse a globally synchronous compressive event resulting in seismic onlap of anticlines or inversions, generally during basin subsidence.
Extended Anderson stress states
Compressional Strike Slip, S_{H} > S_{V} > S_{h}, or S_{H}/S_{V} >1.2 - 1.4 and S_{h}/S_{V} = 0.925 – 1
Extensional Strike Slip, S_{H} > S_{V} > S_{h}, or S_{H}/S_{V} > 1 and S_{h}/S_{V} = 0.825 - 0.925
Uplift, S_{H} > S_{V} = S_{h}
Loading, S_{V} > S_{H} = S_{h}
Fracture Gradient is defined by Schlumberger as the ‘formation fracturing pressure as a function of well depth’. ‘Frac. Gradient’ is here taken to be the instantaneous shut in pressure (ISIP) read from fluid injection decline graphs, as a function of well depth, i.e., ISIP/D, less than LOP/D (leak-off pressure) and FBP/D (formation breakdown pressure) both of which include the effects of tensile strength, natural fractures and near wellbore fracture complexities.
Hydrostatic stress state occurs when the normal stresses acting on any plane are neutral and the mutually perpendicular components of stress at a point are equal, ie, S_{V} = S_{H} = S_{h}.
Isochore the vertical thickness between two seismic horizons. An isopach is the thickness measured perpendicular to at least one of the horizons.
OP_{P}, is overpressure.
PDG pressure-depth graph.
P_{P}, pore pressure.
PT plate tectonics, the 2 dimensional movement of continental and oceanic plates across the earth’s surface.
PT^{+}, Plate tectonics Plus, the 2 dimensional of PT (above) as well as vertical forces and variations with time (compressional pulses).
S_{H}D (S_{Hmax}) is the direction of the maximum horizontal component of compressional stress (S_{H}) at a point in the Earth.
S_{h}D (S_{hmin}) is the direction of the minimum horizontal component of stress (S_{h}) at a point in the Earth.
S_{h} is the ‘frac gradient’ for weak, low tensile strength rocks (see ‘Fracture Gradient’ and Closure Pressure), i.e., ISIP - P_{C} (=S_{h})= P_{NET} = 0; if P_{NET} is low then ISIP = P_{C}(S_{h}). Note, in this case ISIP/D = P_{C}/D = S_{h}/S_{V}, if S_{V} is 1ppg/ft (10KPa/m).
S_{V} is the load or weight of the rock at the any point in the Earth. It is generally directed vertically and perpendicular to S_{H}D and S_{h}D.
S_{H}M (S_{Hmax} Magnitude) is S_{H}/S_{V} and generally increases with depth in petroleum producing basins.
Stress-isochore a map with extended Anderson stress states produced from PSI’s 4DGeoStress software and plotted on the equivalent isochore.
S_{h}M (S_{hmin} Magnitude) is S_{h}/S_{V} and is equal to the ‘frac gradient’ for weak rocks and can be >110% S_{h}M for harder, Permian rocks with significant tensile strength (T_{O}) in a reverse fault stress regime. |