Well Logging: 01 borehole environment
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This document discusses concepts related to well logging. It covers topics like borehole environment, fluid distribution around wells, invasion ratios for different porosity rocks, flushed and uninvaded zones, depth of investigation, formation resistivity, invasion and resistivity profiles, and provides examples of dual laterolog and induction logs through water-bearing and hydrocarbon-bearing zones. The document contains definitions of important parameters and concepts used in well logging and provides explanations for calculating invasion diameters and interpreting well log curves.
Well Logging: 01 borehole environment
- 1. PETE-303: Well Logging Spring 2016 Khaled Abdelgawad Department of Petroleum Engineering KFUPM ENGINEERING Well Logging
- 4. Well QATIF-46 Fluid Distribution around a Well 4
- 5. Well QATIF-46 Borehole Environment 5 h : Bed Thickness hmc : Mudcake Thickness dh : Borehole Diameter di : Diameter of flushed zone. dj : Diameter of Transition zone Shy: Hydrocarbon saturation Sw : Water Saturation Sxo : Flushed zone water saturation Sro : Residual HC. saturation Rm : Mud resistivity Rmc : Mudcake resistivity Rmf : Mudfiltrate resistivity Rs : Adjacent bed resistivity Rt : True formation resistivity Rxo : Flushed zone resistivity Rw : Formation water resistivity
- 6. Well QATIF-46 Question General for the same drilling fluid and layer permeability, invasion diameters are: dj/dh = 2 for ？ porosity rocks dj/dh = 5 for intermediate porosity rocks dj/dh = 10 for ？ porosity rocks High or Low porosity? And why? 6
- 7. Well QATIF-46 Invaded zone (Cont.) For the same drilling fluid: The amount of invasion which takes place is dependent upon the permeability of the mudcake and not upon the porosity of the rock. An equal volume of mud filtrate can invade low porosity and high porosity rocks. The solid particle in the drilling muds bridge and form an impermeable mudcake. 7
- 8. Well QATIF-46 Invaded zone (Cont.) The mudcake then acts as a barrier to further invasion. Because an equal volume of fluid can be invaded before an impermeable mudcake barrier forms, the diameter of invasion will be greatest in low porosity rocks. Low porosity rocks have less storage capacity or pore volume to fill with the invading fluid, and, as a result, pores throughout a greater volume of rock will be affected. 8
- 9. Well QATIF-46 Invaded zone (Cont.) 9 General invasion diameters are: dj/dh = 2 for high porosity dj/dh = 5 for intermediate porosity dj/dh = 10 for low porosity
- 10. Well QATIF-46 Flushed zone The flushed zone extends only a few inches from the well bore and is part of the invaded zone Completely cleared of its formation water (Rw) by mud filtrate (Rmf) The remaining oil is called Residual oil Sro: Residual oil saturation (ROS) Sxo: Flushed zone water saturation 10 Sro = 1 – Sxo Sro Sxo Uninvaded zone Flushed zone
- 11. Well QATIF-46 Uninvaded zone Located beyond the invaded zone. Pores are uncontaminated by mud filtrate and saturated with formation water (Rw), oil, or gas. Water saturation (Sw) of the uninvaded zone is an important factor in reservoir evaluation. Recoverable oil. 11 Shc = 1 – Sw SoR=Shc – Sro =(1-Sw)-(1 - Sxo)=Sxo– Sw Sro Sxo Shc Sw Uninvaded zone Flushed zone
- 12. Well QATIF-46 Depth of investigation 12 A distance that characterizes how far a logging tool measures into the formation from the face of the tool or the borehole wall. The depth of investigation summarizes the radial response of the measurement in one or more directions.
- 14. Well QATIF-46 Formation Resistivity Which of these “Archie Blocks” has the largest resistivity? 14 Rt=100 Rw Rt=25.5 Rw Rt=25 Rw @ a=1 n=2 m=2 > > > = BVW= 0.1 BVW= 0.198 BVW= 0.2 Bulk Volume Water =𝝓 × 𝑺 𝒘
- 16. Well QATIF-46 Invasion and Resistivity Profiles 16 Step Profile Transition Profile
- 17. Well QATIF-46 Invasion and Resistivity Profiles Annulus Profile • The annulus profile represents a fluid distribution that occurs between the invaded • zone and the uninvaded zone and only exists in the presence of hydrocarbons. • In the annulus zone, pores are filled with formation water (RW ) and residual hydrocarbons. 17
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- 19. Well QATIF-46 Example 19 Dual laterolog curves through a water- bearing zone. Rmf ~ Rw
- 20. Well QATIF-46 Example Dual induction log curves through a water-bearing zone. Rmf> 3Rw 20
- 21. Well QATIF-46 Dual induction log curves through a hydrocarbon-bearing zone 21 Rmf> 3Rw