10. Logging While Drilling, Notas de estudo de Engenharia Mecânica

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Well Control

Lesson 10

Logging While Drilling (LWD)

Logging While Drilling

 Sonic Travel Time

 Resistivity and Conductivity

 Eaton’s Equations (R, C, t, d

c)

 Natural Gamma Ray

 Other…

Logging While Drilling

 (^) Any log that infers shale porosity can indicate the compaction state of the rock, and hence any abnormal pressure associated with undercompaction.

Logging While Drilling

 (^) Most of the published correlations are based on sonic and electric log data.  (^) Density logs can also be used if sufficient data are available.

Matthews and Kelly

Normal  t o

-  t n ,  sec/ft g p , psi/ft

Relationships vary from area to area and from age to age But, the trends are the same.  t o

-  t n ,  sec/ft g p , psi/ft

Resistivity and Conductivity

Rock grains, in general, are very poor conductors.  Saline water in the pores conducts electricity and this fact forms the basis for inferring porosity from bulk R or C measurements.

Resistivity and Conductivity

Under normal compaction, R increases with depth.  Deviation from the normal trend suggests abnormal pressure

Resistivity of formation water R w reflects the dissolved salt content of the water, and is dependant upon temperature. Equation shows that R w decreases with increasing temperature, and consequently, decreases with depth.

T 6. 77

T 6. 77

R R

2 1 w 2 w 1

where T and T arein F

o 1 2

Porosity, 

m R aF  1 /  (^) Porosity of water-saturated rock,    (^) If a = 1, and m = 2, then  = F R -0.  (^) So,  = (R o /R w ) -0.  (^) R w in shales cannot be measured directly so R w in a nearby sand is used instead.  (^) R o would tend to increase with increasing depth under normally pressured conditions. See Fig. 2.63.

Example 2.

R

w

estimated from

nearby well.

Estimate the pore

pressure at 14,188 ft

using Foster and

Whalen’s techinque.

So, at 14,188 ft,

F

R

**0. 034

1. 96**   w o R R R F

17 Transition at ~11,800’ Using Eaton’s Gulf Coast correlations,  ob = 0.974 psi/ft or 13,819 psig at 14,188’ Eq. Depth = 8,720’  obe = 0.937 psi/ft or 8,170 psig at 8,720’ p ne

p p = p pe

ob

obe

= 9,703 psig

= 13.16 ppg

Example 2. Matthews and Kelly

Determine the transition

depth and estimate the

pore pressure at 11,500’

Transition is at ~9,600 ft. At 11,500 ft: C o = 1,920, and C n

C

o

/C

n

g p = 0.81 psi/ft (Fig 2.66) Example 2. Fig. 2.