I.Pressure Concepts

1. I.Pressure Concepts • Depth: • Measured Depth (MD). • True Vertical Depth (TVD).

2. I.Pressure Concepts Force: ((Force = Mass X Acceleration)) DENISTY: ((= Mass (or Weight) Per Unit Volume))

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

4. Pressure Concepts Balance: ((Refer to the Relation Between the Formation Pressure and the Hydrostatic Head)) Balanced. Under Balanced. Overbalanced.

5. II.ROCK PROPERTIES • Porosity. • Saturation. • Permeability. • Overburden. • Formation pore pressure. • Compaction. • Matrix stress.

6. Matrix • Pores Porosity= Pore SpaceVolume Bulk Volume. 1. Porosity

7. Porosity Generations Primary porosity: • HPP 40%. • At 10000’, shale porosity reaches 5%. Secondary porosity: • Those ones created after initial deposition. • Either by dissolving or fracturing.

8. 2. Saturation • Is that fraction of pore volume that is filled with a given fluid. • A 20% sw = 20% of the pores are filled w/ water & 80% w/ other fluid which may be oil or gas.

9. 3. PERMEAPLITY • Is a measure of the ease with which a fluid willflowthrough a formation. • Q= k*a* (p1 – p2)/v*l. • K = QVL/A(P1-P2) in millidarcies. • The larger the porosity the higher the permeabilty.

10. 4. Overburden • Overburden load: Is the combined weight of the formation matrix and the fluids overlying a formation. • Overburden pressure: Is the pressure exerted by the overburdenload upon underlying formations.

11. Compaction It is PRINCIPALY a process of mechanical rearrangement

12. Factors Affecting Compaction Rate • Rate of deposition. • Tectonic forcess. • Formation permeability. • Lithology. • Diagenesis. • Osmosis.

13. Overburden pressure Overburden Matrix Stress Pore Fluid Pressure

14. Matrix Stress Is the resistance of the formation matrix to compaction expressed in psi or psi/ft.

15. Overburden Gradient This is an expression of the pressure unit per unit depth. e.g. • psi/ft. • ppg..

16. 5.Formation Pressure ((Is the Fluid Pressure Found Within the Pore Spaces of the Formation)) Can Be Expressed As an Average Vertical Pressure or Equivalent Mud Weight. E.G. psi, ppg, G/cc…

17. Normal Pressure Matrix Pores Expelled fluid

18. Normal Pressure Formation pressure equal in magnitude to the hydrostatic pressure of a column of pore fluid that reaches from the surface to the vertical depth of the formation.

19. Abnormal Pressure Matrix Pores

20. Abnormal Pressure Formation pressure greater than the magnitude of the hydrostatic pressure of a column of pore fluid that reaches from the surface to the vertical depth of the formation.

21. 1.Concept of Continuous Deposition This concept assumes that the compaction rate of any formation is the same as for all formations of a given type. This mean that shales for example deposited at different times and buried to different depths are considered to have compacted at the same rate as long as the formation pore pressure remained normal.

22. 2. Pressure Seal ((A zone of low permeability acts to trap the pore fluids within a formation.)). • May be either physical or chemical. • Restrict the vertical an lateral movement of pressure. • e.g. evaporates, faults ..

23. 3.Equilibrium. S = Mv + P S= overburden. Mv= Vertical matrix stress. P= formation pore pressure.

24. Overburden pressure Equilibrium Matrix Stress Pore Fluid Pressure

25. 4.Transition Zone This is an argillaceous sequence of gradual pore pressure increase above a permeable high pressure formation.

26. Causes of Abnormal Pressure • Rapid subsidence and sediment accumulation. • Thermal expansion. • Tectonic movement. • Reservoir altitude. • Clay digenesis. • Repress ring of shallow reservoirs.

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

28. Normalized Drilling Rate • Weight on bit. • Rotary speed. • Bit diameter. • Bit type. • Rock type. • Mud properties. • Differential pressure. • Hydraulics.

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

30. Corrected “d” exponent Dc = d*(n/mw) N= normal pp Mw= mud weight

31. Factors Affecting dc • Bit wear • Lithologic change • Drastic changes in drilling parameters. • Bit types.

32. Flow Line Temperature Formation fluids tend to act as thermal barriers or insulators which impede the normal flow of heat from the earth’s core to the surface.

33. Flow Line Temperature

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

35. Pore Pressure Calculations 1.Depth of seal FP=Sf-[(Se-n)/(TVDe/TVDf)] FP= fm pressure Sf= overburden at wanted depth Se= overburden at depth of seal. N= normal pp. TVDe= depth of seal TVDf= fm depth

36. Pore Pressure Calculations 2. Eaton equation FP=Sf-(Sf-n)*(DCo/DCn)^m FP= fm pressure Sf= overburden at wanted depth N= normal pp. DCo= observed dxc DCn= normal dxc

37. Resistivity Sonic

38. III- FRACTURE PRESSURE Is the pressure needed to make a fracture in a formation. • The orientation of the produced fracture depend on the orientation of the principal stress of the fracture point.

39. Principal Stresses At any point in the formation there exists a stress regime consisting of three perpendicular stresses • Sig1 maximum, sig2 intermediate, sig3 minimum.

40. Fracture development • The fracture is developed perpendicular to the minimum stress

41. Poisson Ratio • The ratio of transverse strain to axial strain • V=change in breads/original breads change in length/original length

42. Fracture pressure Fr={V/(1-V)}*(S-P)+P

43. Leak off Test Application of pressure to a formation to determine its fracture pressure, without fracturing the formation. Frp= MWt + LOP TVDt*.052

44. Thanks for your attention