I.Pressure ConceptsI.Pressure Concepts Depth:Depth: Measured Measured

Depth (MD).Depth (MD). True Vertical True Vertical

Depth (TVD).Depth (TVD).

I.Pressure ConceptsI.Pressure Concepts

Force:Force:((((Force = Mass X AccelerationForce = Mass X Acceleration))))

DENISTY:DENISTY:((((= = Mass (or Weight) Per Unit VolumeMass (or Weight) Per Unit Volume))))

PressurePressure

((Is an Expression of Force Per Unit Area))((Is an Expression of Force Per Unit Area))• Hydrostatic Pressure.Hydrostatic Pressure.• Frictional Pressure.Frictional Pressure.• Annulus Pressure.Annulus Pressure.• Well Bore Pressure.Well Bore Pressure.• Differential Pressure.Differential Pressure.• Bottom Hole PressureBottom Hole Pressure..

Pressure ConceptsPressure Concepts Balance:Balance:

((((Refer to the Relation Between the Refer to the Relation Between the Formation Pressure and the Formation Pressure and the

Hydrostatic HeadHydrostatic Head)))) Balanced.Balanced. Under Balanced.Under Balanced. Overbalanced.Overbalanced.

Porosity.Porosity. Saturation.Saturation. Permeability.Permeability. Overburden.Overburden. Formation pore pressure.Formation pore pressure. Compaction.Compaction. Matrix stress.Matrix stress.

II.ROCK PROPERTIESII.ROCK PROPERTIES

1. Porosity1. PorosityMatrixMatrix

PoresPores

Porosity= Porosity= Pore SpacePore Space VolumeVolume Bulk Volume.Bulk Volume.

Porosity GenerationsPorosity GenerationsPrimary porosity:Primary porosity:

•HPP HPP 40%.40%.

• At 10000’, shale porosity At 10000’, shale porosity

reaches reaches 5%.5%.Secondary porosity:Secondary porosity:• Those ones created after initial Those ones created after initial

deposition.deposition.• Either by dissolving or Either by dissolving or

fracturing.fracturing.

2. Saturation2. Saturation• Is that fraction of pore volume that is Is that fraction of pore volume that is

filled with a given fluid.filled with a given fluid.• A A 20%20% sw sw = = 20%20% of the pores are filled of the pores are filled

w/ water & 80% w/ other fluid which may be w/ water & 80% w/ other fluid which may be oil or gas.oil or gas.

3. PERMEAPLITY3. PERMEAPLITY• Is a measure of the ease with which a Is a measure of the ease with which a

fluid willfluid will flowflow through a formation.through a formation.• Q= k*a* (p1 – p2)/v*lQ= k*a* (p1 – p2)/v*l..• K = QVL/A(P1-P2) in millidarciesK = QVL/A(P1-P2) in millidarcies..• The larger the porosity the higher the The larger the porosity the higher the

permeabilty.permeabilty.

4. Overburden4. Overburden• Overburden load:Overburden load:

Is the combined weight of the formation Is the combined weight of the formation matrix and the fluids overlying a matrix and the fluids overlying a formation.formation.

• Overburden pressure:Overburden pressure:Is the pressure exerted by the Is the pressure exerted by the overburdenoverburden load upon underlying load upon underlying formations.formations.

CompactionCompaction

It is It is PRINCIPALYPRINCIPALY a process of a process of mechanical rearrangementmechanical rearrangement

Factors Affecting Compaction Factors Affecting Compaction RateRate

1.1. Rate of deposition.Rate of deposition.2.2. Tectonic forcess.Tectonic forcess.3.3. Formation permeability.Formation permeability.4.4. Lithology.Lithology.5.5. Diagenesis.Diagenesis.6.6. Osmosis.Osmosis.

OverburdenOverburden

Matrix StressMatrix Stress

Pore Fluid Pore Fluid PressurePressure

Overburden Overburden pressurepressure

Matrix StressMatrix Stress

Is the resistance of the formation Is the resistance of the formation matrix to compaction expressed in matrix to compaction expressed in

psi or psi/ft.psi or psi/ft.

Overburden GradientOverburden Gradient

This is an expression This is an expression of the pressure unit of the pressure unit per unit depth. e.g.per unit depth. e.g.

• psi/ftpsi/ft..• ppg..ppg..

5.Formation Pressure5.Formation Pressure

((Is the Fluid Pressure Found Within ((Is the Fluid Pressure Found Within the Pore Spaces of the the Pore Spaces of the

Formation))Formation))• Can Be Expressed As an Average Can Be Expressed As an Average

Vertical Pressure or Equivalent Mud Vertical Pressure or Equivalent Mud Weight. E.G. psi, ppg, G/cc…Weight. E.G. psi, ppg, G/cc…

Normal PressureNormal Pressure

MatrixMatrixPoresPores

Expelled fluid

Formation pressure Formation pressure equalequal in in magnitude to the hydrostatic pressure of magnitude to the hydrostatic pressure of a column of pore fluid that reaches from a column of pore fluid that reaches from the surface to the vertical depth of the the surface to the vertical depth of the

formation.formation.

Normal PressureNormal Pressure

Abnormal PressureAbnormal Pressure

MatrixMatrixPoresPores

Formation pressure Formation pressure greater greater than than the magnitude of the hydrostatic the magnitude of the hydrostatic

pressure of a column of pore fluid that pressure of a column of pore fluid that reaches from the surface to the vertical reaches from the surface to the vertical

depth of the formation.depth of the formation.

Abnormal PressureAbnormal Pressure

1.Concept of Continuous 1.Concept of Continuous DepositionDeposition

This concept assumes that the compaction This concept assumes that the compaction rate of any formation is the same as for all rate of any formation is the same as for all

formations of a given type.formations of a given type.This mean that shales for example This mean that shales for example deposited at different times and buried to deposited at different times and buried to different depths are considered to have different depths are considered to have compacted at the same rate as long as the compacted at the same rate as long as the formation pore pressure remained normal.formation pore pressure remained normal.

2. Pressure Seal2. Pressure Seal((A zone of low permeability acts to ((A zone of low permeability acts to

trap the pore fluids within a trap the pore fluids within a formation.))formation.))..

• May be either physical or chemical.May be either physical or chemical.• Restrict the vertical an lateral movement of Restrict the vertical an lateral movement of

pressure.pressure.• e.g. evaporates, faults ..e.g. evaporates, faults ..

3.Equilibrium.3.Equilibrium.

S = Mv + PS = Mv + PS= overburden.S= overburden.Mv= Vertical matrix stress.Mv= Vertical matrix stress.P= formation pore pressure.P= formation pore pressure.

EquilibriumEquilibrium

Matrix StressMatrix Stress

Pore Fluid Pore Fluid PressurePressure

Overburden Overburden pressurepressure

4.Transition Zone4.Transition Zone

This is an argillaceous This is an argillaceous sequence of gradual pore sequence of gradual pore pressure increase above a pressure increase above a permeable high pressure permeable high pressure

formation.formation.

Causes of Abnormal PressureCauses of Abnormal Pressure Rapid subsidence and sediment Rapid subsidence and sediment

accumulation.accumulation. Thermal expansion.Thermal expansion. Tectonic movement.Tectonic movement. Reservoir altitude.Reservoir altitude. Clay digenesis.Clay digenesis. Repress ring of shallow reservoirs.Repress ring of shallow reservoirs.

Signs of Abnormal pressureSigns of Abnormal pressure Normalized drilling rate (Drilling models).Normalized drilling rate (Drilling models). Change in rotary torque.Change in rotary torque. Change in drag.Change in drag. Shale density.Shale density. Gas analysis.Gas analysis. Flow line temperature.Flow line temperature. Size and shape of cuttings.Size and shape of cuttings. Open hole logs.Open hole logs.

Normalized Drilling RateNormalized Drilling Rate

1.1. Weight on bit.Weight on bit.2.2. Rotary speed.Rotary speed.3.3. Bit diameter.Bit diameter.4.4. Bit type.Bit type.5.5. Rock type.Rock type.6.6. Mud properties.Mud properties.7.7. Differential pressure.Differential pressure.8.8. Hydraulics.Hydraulics.

““d” Exponentd” Exponent

R/60N= (12W/10^6D)^R/60N= (12W/10^6D)^dd-Log(R/60N)=-Log(R/60N)=dd*log (12W/106D)*log (12W/106D)--dd= Log(R/60N)/ log (12W/10^6D)= Log(R/60N)/ log (12W/10^6D)R=rop (ft/hr).R=rop (ft/hr).N= rpm.N= rpm.W=wob (ib)W=wob (ib)D= bit diameter (in).D= bit diameter (in).

Corrected “d” exponentCorrected “d” exponent

Dc = d*(n/mw)Dc = d*(n/mw)NN= normal pp= normal ppMw= mud weightMw= mud weight

Factors Affecting dcFactors Affecting dc

1.1. Bit wearBit wear2.2. Lithologic changeLithologic change3.3. Drastic changes in drilling parameters.Drastic changes in drilling parameters.4.4. Bit types.Bit types.

Flow Line TemperatureFlow Line Temperature

Formation fluids tend to act as thermal Formation fluids tend to act as thermal barriers or insulators which impede the barriers or insulators which impede the

normal flow of heat from the earth’s normal flow of heat from the earth’s core to the surface.core to the surface.

Flow Line TemperatureFlow Line Temperature

Size and shape of cuttingsSize and shape of cuttings

A cutting drilled near balanced A cutting drilled near balanced conditions will be larger and more conditions will be larger and more angular in shape than one which is angular in shape than one which is drilled under conditions of greater drilled under conditions of greater overbalance.overbalance.

Pore Pressure CalculationsPore Pressure Calculations

1.Depth of seal1.Depth of sealFP=Sf-[(Se-n)/(TVDe/TVDf)]FP=Sf-[(Se-n)/(TVDe/TVDf)]FP= fm pressureFP= fm pressureSf= overburden at wanted depthSf= overburden at wanted depthSe= overburden at depth of seal.Se= overburden at depth of seal.N= normal pp.N= normal pp.TVDe= depth of sealTVDe= depth of sealTVDf= fm depthTVDf= fm depth

Pore Pressure CalculationsPore Pressure Calculations

2. Eaton equation2. Eaton equationFP=Sf-(Sf-n)*(DCo/DCn)^mFP=Sf-(Sf-n)*(DCo/DCn)^mFP= fm pressureFP= fm pressureSf= overburden at wanted depthSf= overburden at wanted depthN= normal pp.N= normal pp.DCo= observed dxcDCo= observed dxcDCn= normal dxcDCn= normal dxc

1000

1500

2000

2500

3000

3500

0.1 1 10Dc Exponent

TVD

(m)

NCT

Top Overpressure

ResistivityResistivity1000

1500

2000

2500

3000

3500

0.1 1 10RILD (ohm.m)

TVD

(m)

NCT

Top Overpressure

1000

1500

2000

2500

3000

3500

100 1000Sonic (usec/m)

TVD

(m)

Top of Overpressure

NCT

responsein casing

Cycle Skipping

SonicSonic

III- FRACTURE PRESSUREIII- FRACTURE PRESSURE

Is the pressure needed to Is the pressure needed to make a fracture in a make a fracture in a

formation.formation.• The orientation of the produced The orientation of the produced

fracture depend on the orientation fracture depend on the orientation of the principal stress of the of the principal stress of the fracture point.fracture point.

Principal StressesPrincipal StressesAt any point in the At any point in the formation there formation there exists a stress exists a stress regime consisting of regime consisting of three perpendicular three perpendicular stressesstresses

Sig1 maximum, sig2 Sig1 maximum, sig2 intermediate, sig3 intermediate, sig3 minimum.minimum.

Fracture developmentFracture development

The fracture is The fracture is developed developed perpendicular to the perpendicular to the minimum stressminimum stress

Poisson RatioPoisson Ratio

The ratio of transverse strain to axial strainThe ratio of transverse strain to axial strain V=change in breads/original breadsV=change in breads/original breads

change in length/original lengthchange in length/original length

Fracture pressure Fracture pressure

Fr={V/(1-V)}*(S-P)+PFr={V/(1-V)}*(S-P)+P

Leak off TestLeak off Test

Application of Application of pressure to a pressure to a formation to formation to determine its determine its fracture pressure, fracture pressure, without fracturing without fracturing the formation.the formation.

Frp= MWt + LOPFrp= MWt + LOPTVDt*.052TVDt*.052

Thanks for your attentionThanks for your attention