Petroleum Engineering Equations & Formulas Part -2

Compressibility of oil

Pressure depletion in the reservoir can normally be assumed to be isothermal, such that the isothermal compressibility is defined as the fractional change in volume per unit change in pressure:

       c = -(1/V) DOT dV/dP  [psi-1] or [bar-1]

       Where:

       dV : derivative of volume
       dP : derivative of pressure
       V  : volume

Generating Expecting Curves TO BE COMPLETED

STOIIP is a term which normalises volumes of oil contained under high pressure and temperature in the subsurface conditions.

GIIP is the equivilant expression for gas initially in place.

GRV is the Gross Rock Volume of the hydrocarbon-bearing interval and is the priduct of the area (A) containing hydrocarbons and interval thickness (H).
      STOIIP = GRV * (N/V) * Φ * So * (1/Bo) [stb]

      GIIP = GRV * (N/V) * Φ * Sg * (1/Bg) [stb]

      GRV = A * H

      Ultimate recovery = HCIIP * Recovery Factor [stb] or [scf]

      Reserves = Ultimate Recovery - Cumulative Production [stb] or [scf]





Fluid Flow near the Wellbore

The difference between the following wellbore pressure (Pwf) and the average reservoir pressure ( P) is the pressure drawdown (ΔPDD).
       Pressure drawdown ΔPDD = P - Pwf [psi] or [bar]

       Where:

       P is Reservoir pressure
       P wf is Flowing wellbore pressure
            

The relationship between the floarate (Q) towards the well and the pressure drawdown is approximately linear, and is defined by the productivity index (PI)
       Productivity Index PI = Q/ΔPDD [bbl/d/psi] or [m3/d/bar]
            

The flowrate of oil into the wellbore is also influenced by the reservoir properties of permeability(k) and the reservoir thickness(h), by the oil properties viscosity(μ) and formation volume factor (Bo) and by any change in the resistance to flow near the wellbore whch is represented bu the dimensionless term called skin (S). For semi-steady state flow behaviour abd radial inflow for the oil into a vertical wellbore is represented by equation 3:



Ultimate Recovery 

In estimating the ultimate recovery (UR) for an oil reservoir, one would need to use the following:
      UR = Area * thickness * (N/G) * Φ * So * (1/Bo) * RF

      Where:

      Φ is porosity
      So is the oil saturation in the pore space
      Bo is the formation volume factor of the oil
      RF is the recovery factor



Oil & gas volumes

STOIIP is a term which normalises volumes of oil contained under high pressure and temperature in the subsurface conditions.

GIIP is the equivilant expression for gas initially in place.

GRV is the Gross Rock Volume of the hydrocarbon-bearing interval and is the priduct of the area (A) containing hydrocarbons and interval thickness (H).
      STOIIP = GRV * (N/V) * Φ * So * (1/Bo) [stb]

      GIIP = GRV * (N/V) * Φ * Sg * (1/Bg) [stb]

      GRV = A * H

      Ultimate recovery = HCIIP * Recovery Factor [stb] or [scf]

      Reserves = Ultimate Recovery - Cumulative Production [stb] or [scf]


Recovery Factory


The recovery factor(RF) defines the relationship between the hydrocarbons initially in place (HCIIP) and the ultimate recovery for the field.
       UR = HCIIP * RF [stb] or [scf]

       R = UR - CP [stb] or [scf]

       Where:

       UR is Ultimate recovery
       RF is Recovery factor
       R  is Reserves
       CP is Cumulative Production


SolutionGas Drive : Water cut


Commonly the water cut remains small in solution gas drive reservoirs, assuming that there is little pressure support provided by the underlying aquifer. Water cut is also referred to as BS&W(Base, Sediment & water) and is defined as:
      Water cut (BS&W) = (water production / oil plus water production) * 100(%)