Reservoir Engineering I - PEB2023

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Questions and Answers

Overburden pressure (OP) is the combined ______ of the formation rock and fluids.

weight

Overburden pressure increases ______ with depth.

linearly

Overburden pressure typically has a pressure gradient of 1 ______/ft.

psi

Hydrostatic pressure is the pressure applied by a ______ at equilibrium.

<p>fluid</p> Signup and view all the answers

Hydrostatic pressure increases in proportion to ______ measured from the surface.

<p>depth</p> Signup and view all the answers

Swc is the ______ or irreducible water saturation.

<p>connate</p> Signup and view all the answers

The ______ is a constant which is positive if the water is overpressured and negative if underpressured.

<p>C</p> Signup and view all the answers

Swc is expressed as a fraction of the ______ volume.

<p>pore</p> Signup and view all the answers

The value of hydrostatic pressure depends on the ______ of the fluid.

<p>density</p> Signup and view all the answers

The hydrostatic pressure gradient for fresh water is 0.433 ______/ft.

<p>psi</p> Signup and view all the answers

Swc is normally between ______ percent of the pore volume.

<p>10-25</p> Signup and view all the answers

For the ______ in any sand to be abnormally pressured, the sand must be effectively sealed off from the surrounding strata.

<p>fluid</p> Signup and view all the answers

The pressure gradients are smaller for ______ because their densities are less than that of water.

<p>hydrocarbons</p> Signup and view all the answers

Boi is the ______ formation volume factor.

<p>oil</p> Signup and view all the answers

Hydrostatic pressure continuity to the ______ cannot be established when the sand is effectively sealed off.

<p>surface</p> Signup and view all the answers

Boi is the ______ volume/stock tank volume.

<p>reservoir</p> Signup and view all the answers

The parameters Ï• and Swc are normally determined by ______ analysis.

<p>petrophysical</p> Signup and view all the answers

Causes of abnormal pressure include temperature change, thermal effects, geological changes, and ______ between waters having different salinity.

<p>osmosis</p> Signup and view all the answers

At a given depth, the ______ pressure can be equated to the sum of the fluid pressure (FP) and the grain or matrix pressure (GP) acting between the individual rock particle.

<p>overburden</p> Signup and view all the answers

The total pressure at any depth, resulting from the combined weight of the ______ rock and fluids, is known as the overburden pressure.

<p>formation</p> Signup and view all the answers

At the ______ the fluids in contact have the same pressure.

<p>fluids' contacts</p> Signup and view all the answers

In the majority of sedimentary basins, the overburden pressure increases ______ with depth.

<p>linearly</p> Signup and view all the answers

Since the overburden pressure remains constant at any particular depth, then a reduction in fluid pressure will lead to a corresponding increase in the ______ pressure, and vice versa.

<p>grain</p> Signup and view all the answers

The pressure gradient in the formula Pw is denoted by ______ divided by ______ water.

<p>dP</p> Signup and view all the answers

The fluid pressure in hydrocarbon columns are dictated by the dominant ______ pressure in the vicinity of the reservoir.

<p>water</p> Signup and view all the answers

The formula for Pw includes a constant term of ______ and another term related to pressure gradient.

<p>14.7</p> Signup and view all the answers

In a perfectly normal case, the fluid pressure at any depth can be estimated first by the ______ pressure connected to the reservoir.

<p>water</p> Signup and view all the answers

Pw = the pressure of the ______ at depth D.

<p>water</p> Signup and view all the answers

(dP/dD)w = the ______ pressure gradient, is dependent on the salinity, and for fresh water has the value of 0.4335 psi/ft.

<p>water</p> Signup and view all the answers

Assumes: continuity of water pressure to the ______ and the salinity does not vary with depth.

<p>surface</p> Signup and view all the answers

Equation is only applicable to ______ hydrostatic pressure.

<p>normal</p> Signup and view all the answers

The pressure at the ______ contact is equal to the pressure in both fluids.

<p>gas-oil</p> Signup and view all the answers

The linear equation for oil pressure above the oil-water contact is Po = 0.35D + ______.

<p>constant</p> Signup and view all the answers

The pressure at the gas-oil contact is calculated to be ______ psia.

<p>2385</p> Signup and view all the answers

The equation of the gas pressure line is Po = 0.08D + ______ psia.

<p>1969</p> Signup and view all the answers

The gas pressure at the top of the structure is calculated to be ______ psia.

<p>2369</p> Signup and view all the answers

The gas pressure at the top of the structure exceeds the normal hydrostatic pressure by ______ psi.

<p>104</p> Signup and view all the answers

When drilling through a sealing shale on the crest of the structure, there will be a sharp pressure ______ on first penetrating the reservoir.

<p>kick</p> Signup and view all the answers

The pressure kick occurs from ______ psi to 2369 psia.

<p>2265</p> Signup and view all the answers

The magnitude of the pressure discontinuity depends on the vertical distance between the point of well penetration and the hydrocarbon _____ contact.

<p>water</p> Signup and view all the answers

If the reservoir only contains gas, the pressure discontinuity will be much _____ for a given vertical distance.

<p>greater</p> Signup and view all the answers

In the example, a well test is conducted at a depth of 5100 ft to determine the gas _____ at that depth.

<p>pressure</p> Signup and view all the answers

The exploration well is penetrating the gas reservoir only and assumes no _____ in the well.

<p>oil</p> Signup and view all the answers

The oil pressure at the depth of 5500 ft is given as 2600 psia, allowing estimation of the oil-water _____.

<p>contact</p> Signup and view all the answers

The gas oil contact is located at 5500 ft deep in the water _____ zone.

<p>oil</p> Signup and view all the answers

Pressure measurements are essential in determining the gas pressure at the gas water _____ at 5281 ft.

<p>contact</p> Signup and view all the answers

Assuming normal hydrostatic pressure, a well was drilled and hit the oil and gas _____ zones.

<p>zones</p> Signup and view all the answers

Flashcards

Swc

Connate or irreducible water saturation expressed as a fraction of pore volume, typically 10−25%.

Boi

The oil formation volume factor, indicating the relationship between reservoir volume and stock tank volume, expressed in rb/stb.

Pore Volume

The total volume of void spaces in a rock that can hold fluids.

Net Bulk Volume (V)

The total volume of the subsurface reservoir, derived from geological and pressure analysis.

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Overburden Pressure

Total pressure at any depth from the weight of the formation rock and fluids, increases with depth.

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Pressure Gradient

Rate at which pressure increases with depth, typically 1 psi/ft in sedimentary basins.

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Fluid Pressure Regimes

Describes the pressure conditions of fluids within a reservoir and its influence on extraction.

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Petrophysical Analysis

Study to determine parameters like porosity (Ï•) and Swc in a reservoir.

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Fluid Pressure Equation

Pw = (dP/dD) * D + 14.7 + C where C indicates pressure state.

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Constant C

C is positive if water is overpressured; negative if underpressured.

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Abnormal Pressure

Occurs when sand is sealed from surrounding strata preventing hydrostatic pressure continuity.

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Causes of Abnormal Pressure

Includes temperature change, thermal effects, geological changes, osmosis between different salinities.

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Hydrocarbon Pressure Regimes

Pressure gradients in oil and gas are smaller compared to water.

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Fluids in Contact

Fluids that touch each other have the same pressure at their interface.

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Hydrostatic Pressure Continuity

The ability of hydrostatic pressure to maintain a continuous profile to the surface.

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Overburden Pressure (OP)

The total pressure exerted by the weight of overlying rock at a specific depth.

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Fluid Pressure (FP)

The pressure exerted by fluids within the pores of the rock at a given depth.

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Grain Pressure (GP)

The pressure resulting from the weight of the rock particles themselves at a specific depth.

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Fluid Pressure Gradient

The rate of change of fluid pressure with depth, influenced by factors like salinity.

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Normal Hydrostatic Pressure

A condition where fluid pressure increases with depth at a predictable rate.

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Abnormal Hydrostatic Pressure

A condition where fluid pressure deviates from the normal rate due to geological factors.

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Water Pressure at Depth (Pw)

The pressure exerted by water at a certain depth, influenced by fluid column height.

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Continuity of Water Pressure

The assumption that water pressure remains consistent and connected all the way to the surface.

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Pressure Discontinuity

A sudden change in pressure when drilling into a hydrocarbon reservoir, affected by distance to water contact.

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Gas Pressure at Depth

The pressure of gas in a reservoir measured at a specific depth, influenced by the gas gradient.

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Hydrocarbon Water Contact

The interface between hydrocarbons and water in a reservoir which affects pressure measurements.

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Gas Gradient

The rate of change of gas pressure with depth, typically expressed as psi/ft.

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Gas Oil Contact

The interface in a reservoir where gas transitions to oil layer, important for pressure calculations.

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Oil Water Contact

The boundary where oil and water meet in a reservoir; important for understanding reservoir behavior.

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Depth of Gas Pressure Measurement

The specific depth where gas pressure is recorded, vital for estimating fluid contacts.

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Estimating Pressure at Contacts

Calculating pressure at specific interfaces (gas-water, oil-water) using known pressure data.

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Hydrostatic Pressure

Pressure from a fluid at equilibrium due to gravity.

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Fresh Water Pressure

Hydrostatic pressure from fresh water is 0.433 psi/ft.

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Saline Water Pressure

Pressure from saline water increases with salinity level.

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Pore Pressure

Pressure of fluids within the pores of rocks.

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Oil-Water Contact Pressure (Po)

The pressure at the interface of oil and water, calculated as Po = 0.45 × 5500 + 14.7 = 2490 psia.

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Equation for Oil Pressure (Po)

A linear equation describing oil pressure above the contact: Po = 0.35D + 565 psia.

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Gas-Oil Contact Pressure

At 5200 ft, pressure must remain equal in both fluids, calculated as 2385 psia.

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Gas Pressure Line Equation

The equation for gas pressure can be noted as Po = 0.08D + 1969 psia.

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Gas Pressure at Reservoir Top

Gas pressure at 5000 ft is calculated to be 2369 psia, higher than hydrostatic pressure.

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Hydrostatic Pressure Comparison

Gas pressure exceeds normal hydrostatic pressure by 104 psi at the top of the structure.

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Pressure Kick During Drilling

When entering the reservoir at 5000 ft, there's a pressure jump from 2265 psi to 2369 psia.

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Reservoir Depth Measurements

Key reservoir depth points include 5500 ft for oil contact and 5200 ft for gas-oil contact.

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Study Notes

Reservoir Engineering I - PEB2023/PFB2023

  • Fluid Pressure Regimes

    • The total pressure at a depth is the combined weight from the formation rock and fluids (water, oil, or gas) and is known as overburden pressure.
    • Overburden pressure typically increases linearly with depth with a gradient of 1 psi/ft.
    • Hydrostatic pressure is the pressure exerted by a fluid at equilibrium due to gravity. It increases with depth proportionally to the fluid's weight.
    • Water salinity affects the value of hydrostatic pressure.
  • Hydrocarbon Volumes Calculation

    • Oil volume in place (OIP) is calculated using the formula: OIP = V¢(1-Swc) (res.vol.)
      • V = net bulk volume of the reservoir rock
      • Φ = porosity (volume fraction of the rock)
      • Swc = connate/irreducible water saturation (fraction of pore volume)
    • Stock tank oil initially in place (STOIIP) is calculated using the formula: STOIIP = n = v¢(1-Swc)/Boi
      • Boi = oil formation volume factor under initial conditions (reservoir volume/stock tank volume).
    • The parameters porosity and water saturation are typically determined by petrophysical analysis
    • Net bulk volume is derived from geological and fluid pressure analyses
  • Reservoir Temperature

    • Earth's temperature increases from the surface to the center
    • Geothermal gradient: heat flowing outwards around 1.6°F/100 ft
    • Local and regional temperature gradients are influenced by factors like lithology and local conditions (e.g., wellbore temperatures).
    • Reservoir temperatures are obtained from wellbore temperature surveys.
  • Lecture Summary

    • Topics covered: Hydrocarbon Volumes Calculation, Fluid Pressure Regimes, Reservoir Temperature
  • What's Next?

    • Reserve Estimation
    • Volumetric Calculation
  • Recommended Textbook:

    • L.P. Dake, Fundamental of Reservoir Engineering, Chapter 1

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