Petrospec Technologies Tools On-Line Pore Pressure Analysis Software

Overburden Gradient Eaton Exponent Normal Compaction Trend Equation Pore Pressure and Fracture Gradient Natural Gas Density Rectangular Coordinate Transformation Digitize Graphic Image

The overburden gradient, corrected for water depth is computed using these two relations:

Input values needed for the calculations are:

• obg_max maximum theoretical overburden (psi/ft)
• wd is the water depth (feet)
• phi₀ is the initial porosity (decimal)
• nhg is the normal hydrostatic gradient (psi/ft)
• pde is the porosity decay exponent

Calculated values are:

• phi is the porosity (decimal)
• obg is the overburden gradient (psi/ft)

The Eaton Exponent, used for the computation of the pore pressure can be determined using a single relation:

Input values needed for the calculations are:

• val_o is the observed log value
• val_n is the normal log value
• obg is the overburden gradient (psi/ft)
• nhg is the normal hydrostatic gradient (psi/ft)
• EE is the Eaton Exponent

The normal compaction trend is used to determine the normal values of the log data. There are four basic types:

Linear Form:

Logarithmic Form:

Exponential Form:

Hyperbolic Form:

Input values needed for the calculations are:

• Vmin is the minimum log value at the mud line
• Vmax is the maximum log value
• Vcal is the calibration log value
• Dcal is the calibration depth value

Pore pressure is estimated using the Eaton equation:

Fracture gradient is estimated using the following two relations:

Input values needed for the calculations are:

• val_o is the observed log value
• val_n is the normal log value
• obg is the overburden gradient (psi/ft)
• nhg is the normal hydrostatic gradient (psi/ft)
• EE is the Eaton Exponent

• PP is the pore pressure (pounds per gallon)
• FG is the fracture gradient (pounds per gallon)

Equation Exponent, typical values:

• Conductivity = -1.2
• Resistivity = 1.2
• Sonic = -3.0
• Velocity = 3.0

Natural gas density is estimated using the Real-Gas Law:

Input values needed for the calculations are:

• pres is the pressure (psia)
• temp is the temperature (deg F)
• Mp is the mole percent of each constituent (%)

• Natural gas compressibility factor - "Z"
• Specific gravity of the gas (air = 1.0)
• Natural gas density (g/cc)
• Gas pressure gradient (psi/ft)

Coordinates are converted from one coordinate system to another using:

Input values needed for the calculations are:

• X_cal is the input (X,Y) coordinate system calibration point
• Y_cal is the input (X,Y) coordinate system calibration point
• U_cal is the output (U,V) coordinate system calibration point
• V_cal is the output (U,V) coordinate system calibration point
  
• X is the input X coordinate to be transformed into the (U,V) coordinate system
• Y is the input Y coordinate to be transformed into the (U,V) coordinate system

• U is the output U coordinate transformed from the (X,Y) coordinate system
• V is the output V coordinate transformed from the (X,Y) coordinate system

Note: Do not use this transformation worksheet for converting between (X,Y) and (Longitude,Latitude) over large geographic areas.

Load a graphic image in the project directory or upload it from your local computer.

Input values needed for the calculations are:

• X left is the left (X) corner of the image
• X right is the right (X) corner of the image
• Y bottom is the bottom (Y) coordinate of the image
• Y top is the top (Y) coordinate system of the image