7. applied - ijans - statistical analysis on corrected well-log derived - horsfall - nigeria - opaid

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STATISTICAL ANALYSIS ON CORRECTED WELL-LOG DERIVED TEMPERATURES IN

SOUTH-EASTERN NIGER DELTA

O.I. HORSFALL, E. D. UKO & D. H. DAVIES

Department of Physics, Rivers State University of Science and Technology, Port Harcourt Nigeria

ABSTRACT

Analysis of bottomhole temperature !HT" data from #$ e%ploration &ells in '()ield of south eastern Niger Delta

has been carried out in order to determine appropriate correction method and correction factor &hich can be used to correct

the measured bottom hole temperatures, estimate geothermal gradient, true formation temperatures using the corrected

!HT and to ascertain the accuracy of the corrected !HT data using statistical tool* Horner and +aples methods &ere used

to correct the bottomhole temperatures* The study sho&s that the geothermal gradient of a formation can be effectively

determined by first correcting the measured bottom(hole temperatures* -eothermal gradients computed from the various

&ells indicated that these gradient varies from &ell to &ell* These variations may be attributed to changes in thermal

conductivity of the roc.s &ithin the formation ground&ater flo& etc* The geothermal gradients ranges from $*$#/012m to

$*$3$012m* A regional average vertical geothermal gradient of $*$43012m or 430125m &as obtained from the study area*

The accuracy associated &ith the corrected bottom(hole temperatures !HTs" &as achieved using the students t

distribution at the desired level* At 678 and 668 confidence interval 19" and computed corrected !HTs for +ell A:5(#

is ##3*4; <=*$4 and ##3*4; < #6*#/ Similarly for +ell A:5(4 is##$*/3 < >*4$ and ##$*/3 < 4;*#7* 9t &as observed that the

678 confidence level is more reliable than the 668 since the lo&er limits of the confidence intervals &ill be very far from

the uncorrected bottom(hole temperatures, in principle the lo&er confidence interval limit should be e?ual to or greater

than the uncorrected bottom(hole temperatures* The deviations of the uncorrected bottom(hole temperatures !HTs" from

the corrected !HTs" using both Horner and +aples methods for &ells A:5(# and A:5(4 are σh @ 3*3$, σ& @3*=4 for

A:5(# and σh @ $*4>, σ& @$*=# for A:5(4* ur investigations also sho& that there is a high degree of closeness bet&een

the corrected bottom(hole temperatures !HTs" values of Horner and +aples method*

KEYWORDS: Statistical Analysis on 1orrected +ell(Bog Derived Temperatures in South(Castern Niger Delta

INTRODUCTION

The understanding and strong dependence of temperature study has led to the rene&ed interest in using thermal

data in e%ploration for hydrocarbons, detection of ones of over pressure, basin analysis, stratigraphic modeling of thermal

migration of organic matter, and the study of earths evolution etc*

Temperature &hich is the ?uantitative measure of the tendency of heat to flo& in a given direction* is one of the

primary factors controlling hydrocarbon generation, sediment diagenesis and migration of hydrocarbons and other fluids

N&an.&o, 4$$;"*

Subsurface temperature increases &ith depth due to the outflo& of heat from radioactive isotopes from the centre

of the earth Bo&rie, #66;"* The rate of temperature increase &ith depth is .no&n as geothermal gradient* -eothermal

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Na"#a) Si!(! I*ANS/

ISSNP/: 0123-45246 ISSNE/: 0123-4500

V%). 4, I#! 4, *#( - *#) 0527, 13-78

9 IASET

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S"a"i"ia) A(a)i %( C%!"!$ W!))-L%; D!i<!$ T!=!a"#! i( S%#">-Ea"!( Ni;! D!)"a 45

gradient can be used in the study of regional and sub(regional tectonics, assessment of geothermal resource potential,

indicator of subsurface temperature distribution, 9dentification of prospective areas for oil and gas e%ploration etc*

!orehole temperature is the temperature measured inside the borehole during drilling or &hen drilling has

stopped* !orehole temperature measurement is important in several areas of underground resource investigation and

management chu.o, 4$##"* 9n mineral e%ploration, it aids the detection of massive mineral e%ploration* 9n hydrogeology,

temperature variations can be a .ey element in the understanding of underground &ater flo&*

!ottom hole temperature is the ma%imum recorded temperature from a &ellbore fe& hours after drilling has

stopped* :ost bottom hole temperature measurements only provide t&o or three temperature dataE this ma.es it unreliable

in generating borehole temperature profile, also during drilling, most times temperature data are obtained after the

perturbing mainly cooling" effects have subsided hence correction needed to be applied using circulation time, and time

since circulation has stopped for correcting the original temperature of the logging suit* Provided several logging runs have

been made and data obtained are subFected to corrections, then the true formation temperature can be obtained*

Records sho& that bottom hole temperatures has been used by various authors in the Niger Delta area for

temperature studies A.pabio and CFeda&e, 4$##" used the linear e%trapolation bet&een ambient and bottom hole

temperatures to develop a geothermal gradient map of the Niger delta* !ayram et al*, 4$##" sho&ed in their study that

appro%imate temperature at various depths in different parts of an area can be estimated from temperature gradient map*

N&an.&o and C.ine, 4$$6" used bottom hole temperature study to sho& that differences in geothermal gradients may

reflect changes in thermal conductivity of roc.s, ground&ater movement and endothermic reactions during digenesis*

U.o et al*, 4$$4" &or.ing on the Northern Niger Delta calculated geothermal gradient to vary bet&een #7*4>0125m to

4;*4;0125m* U.o et al*,4$$4" also observed that lithology controls geothermal gradient of a formation*

N&achu.&u, #6;>" stated that the geothermal gradient map could be used in the application of the hydrocarbon concept

for oil e%ploration*

GENERAL GEOLOGIC SETTING

The Niger Delta !asin &hich is one of the &orlds most prolific petroleum producing tertiary deltas and accounts

for about 78 of the &orlds oil and gas reserves is located on the continental margin of the -ulf of -uinea in e?uatorial

+est Africa and lies bet&een latitude /0 and ;0N longitude and 30 and 60C+hiteman, #6=4"* Three lithostratigraphic units

have been identified in the subsurface Niger Delta Short and Stauble, #6>;E )ran.l and 1ordy, #6>;, Avbovbo #6;="*

These stratigraphic units are from the oldest to the youngest, the A.ata, Agbada, and !enin formataions* The A.ataformation Cocene GRecent" is a marine sedimentary succession that is laid in front of the advancing delta* 9t is mainly

uniform under compacted shale &ith colours consisting of dar. grey, sandy, silty shale &ith plant remains at the top*

The shales are rich in plan.tonic and benthonic foraminifera and &ere deposited in shallo& to deep marine environment*

The Agbada )ormation Cocene(Recent" is characteried by paralic interbedded sandstone and Shale &ith a

thic.ness of over 3,$/6m ReiFers, #66>"* The top of Agbada )ormation is defined as the first occurrence of shale &ith

marine fauna that coincides &ith the base of the continental(transitional lithofacies* The base is a significant sandstone

body that coincides &ith the top of the A.ata )ormation Short and Stauble, #6>;"* Some shales of the Agbada )ormation

&ere thought to be the source roc.s, ho&everE CFeda&e et al*, #6=/" deduced that the main source roc.s of the Niger Delta

are the shales of the A.ata )ormation*

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The !enin )ormation is the youngest lithostratigraphic unit in the Niger Delta* 9t is :iocene G Recent in age &ith

a minimum thic.ness of more than >,$$$ ft #,=46m" and made up of continental Sands and sandstones 6$8" &ith fe&

shale intercalations* The sands and sandstones are coarse(grained, sub angular to &ell rounded and are very poorly sorted*

Plan.tonic foramin

METHODOLOGY

B%""%= H%)! T!=!a"#! C%!"i%( M!">%$

9t is evident that measured subsurface temperature from a borehole is al&ays lo&er than the static formation

temperatureE this is because &hen the borehole is being drilled a large ?uantity of the drilling mud is circulated in the

borehole to facilitate the drilling, evacuate the cuttings and stabilie the hole* The adverse effects of this circulation and

other drilling influence li.e thermal properties of the drilling fluids, nature of heat e%change bet&een borehole and the

&ell, duration of drilling, non(e?uilibrium temperature at the time of measurement etc, on the formation &ere the reasons

&hy bottom hole temperature data &as rarely used in geophysical studies* Hence correction of the measured bottom hole

temperature is of utmost importance*

Several methods to correct bottom hole temperatures have been proposed by many authors, such as the correction

made Davies et al*, 4$$;"E Henri.son and 1hapman, 4$$4E nuoha and C.ine, #666 etc*

9n this study the !ottom Hole Temperatures from #$ e%ploratory &ells &ere collected for correction to true or

static formation temperature*

The bottom Hole drilling effects &ere corrected by using t&o different methodsE The Horner Plot and +apleIs

methods*

The Horners Plot method is a concept of a straight line relationship bet&een the measured bottom hole

temperatures and circulation times, &hile +aples method allo&s corrections to be made on individual recorded bottom

hole temperatures*

T>! H%(!? M!">%$

The Horners Plot is a method that relies on a concept of straight line relationship bet&een !HT and the log of ∆t 2

∆tJT"* n e%trapolation of this straight line to cut across the abscissa at #, yields the true static formation temperature*

!HTs versus ∆t 2 ∆tJT" @ # #"

A plot of !HT versus ∆t 2 ∆tJT" on semi log paper is a straight line*

!ecause Bim ∆t 2 ∆tJT" @ # corresponds to Tf *

D. W Wa)! !" a)., M!">%$

+apleet al all e%trapolated that for individual temperatures, the correction factor f s, &hich is applied to the

difference bet&een the measured temperatures and the surface temperature is given as belo&

!HT5 @ TS J f ST: ( TS" G $*$$$#36#K G //6="+aples and Ramly, 4$$#" 4"

f S@ #*3/33e ($*$$76TS1"

3"

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40 O.I. H%+a)), E. D. U@% & D.H. Da<i!

+here,

!HT. @ 1orrected !HT

f S @ 1orrection factor

TS @ Surface Temperature 01"

T: @ :easured Temperature 01"

K @ Depth m"

TS1 @ Time Since 1iculation has StoppedHrs"

After the measured bottom hole temperatures &ere corrected using the various methods statistical analysis &as

carried out to investigate the level of confidence associated &ith those corrected temperatures in each &ells*

Students t distribution &as used to compute the confidence levels for the mean corrected bottom hole temperature

at the desired levels and the 1hi(S?uare for the standard deviation* Cd&ard and Srivastava #6=6E :orris #6;7"

Using coefficient of variation and confidence interval* The desired level used for this study is 678 and 668

intervals* :urray et al*, #6;7"

T>! S"#$!("? " Di"i#"i%(

!HT5 < tcS2L" /"

V=N –K 7"

BHT K ±t

c ( S

√ N −1 ) >"

!HT 5 @ 1orrected !ottom Hole Temperature

t @ 1ritical values or confidence coefficients, &hich depends on the desired level of confidence and the

sample sie

S @ Standard Deviation

L @ Degree of freedom

N @ Sample population*

RESULTS AND DISCUSSIONS

Using the Horner plot and +aples methods to correct for the drilling effects on bottom(hole temperatures !HT",

results &ere obtained &hich are presented in the various tables and figures belo&* The Horners plot assumes a linear

relationship bet&een !HT at a given depth from each of several logging runs against the log of ∆t2∆t J t" &hich is a

dimensionless time* The e%trapolation of this straight line cuts the absisca at # and yields the true static formation

temperature* i*e* !HT5 * +hile the +aples method approach allo&s correction to be made on individual recorded !HT

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data*

Table # sho&s the bottom(hole temperatures !HT" obtained from the ten different &ells and its correction using

the Horners plot method* The table is sho&ing the depths, uncorrected bottom(hole temperature !HT" values, the

corrected bottom(hole temperature !HTh" values, the time since circulation has stopped T", and the length of time that the

borehole &as subFected to the cooling effect of the fluid ∆t"* The effect of this correction is to raise the uncorrected

bottom(hole temperatures to the static formation temperature or very close to the formation temperature of the formation

under consideration*

Table 4* sho&s the corrected bottom(hole temperatures using the Horners method* These corrected values give

the formation temperatures of the various &ells* The corrected values obtained indicates that in all the &ells under study

there is the possibility of hydrocarbon formation since the corrected temperatures falls &ithin the range of temperatures

&here maturation occurs>$0 ( #4$0"*

Table 3 also sho&s the bottom(hole temperatures !HT" obtained from the ten different &ells and its correction

using the +aples method* The table is sho&ing the depths, uncorrected bottom(hole temperature !HT" values, the

corrected bottom(hole temperature !HT&" values, and the number of runs* Similarly the effect of this correction is to raise

the uncorrected bottom(hole temperatures to the static formation temperature or very close to the formation temperature of

the formation under consideration*

Table / sho&s the corrected bottom(hole temperatures using the +aples method* These corrected values also give

the formation temperatures of the various &ells* The corrected values obtained indicates that in &ells A:5(#

G A:5(=, and A:5(#$ under study there is the possibility of hydrocarbon formation since the corrected temperatures falls

&ithin the range of temperatures &here maturation occurs>$0 ( #4$0"* A:5(6 has temperature belo& the range of

maturation and subse?uent formation of hydrocarbon*

Table 7 sho&s the comparison of the corrected bottom(hole temperature values !HTs" using both Horner and

+aples methods* 1areful observation indicates that the difference in the corrected bottom(hole temperature values from

the t&o methods are very close*

Table > sho&s the geothermal gradients computed from the various &ells, these gradients vary from &ell to &ell*

The geothermal gradients range from $*$#/012m to $*$3$012m* A regional average geothermal gradient of $*$43012m &as

obtained from the study area*

Table ; is a statistical table sho&ing the confidence levels of the corrected bottom(hole temperature values using

+aples method the desired confidence levels used are 678 and 668 respectively* The statistical analysis indicated that at

678 confidence level the corrected bottom hole temperature values are reliable* This is evident in the range of values

presented in table ;* The assurance of the corrected bottom(hole temperature values is that, the lo&er limit of the

confidence level should al&ays be e?ual to or higher than the average uncorrected bottom(hole temperature in the

particular &ell under consideration as evident in &ells A:5(4, A:5(7, A:5(6 and A:5(#$ &here the lo&er limit values

of the confidence level is higher than the uncorrected bottom(hole temperature values* 9n essence if the lo&er limit

temperature value is lo&er than the average uncorrected bottom(hole temperature values, then it is advisable to only &or.

&ith the upper limit bottom(hole temperature values* Using 668 confidence level the lo&er limit e%hibited bottom(holetemperature values that are very far from the average uncorrected bottom(hole temperature values*

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44 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Table = sho&s the deviations of the uncorrected bottom(hole temperatures from the corrected bottom(hole

temperatures for both methods, the values obtained sho&ed that deviations of uncorrected bottom(hole temperatures from

the corrected values for both methods are not too far from each method in the various methods*

Table*6 sho&s the coefficient of variations in percentage using both methods*

)igures#* A:5(# ( A:5(#$ presented belo& sho&s the variation of the uncorrected bottom(hole temperature and

corrected bottom(hole temperature &ith depth &ith* The temperatures increases &ith an increasing depth* The red line

indicates the corrected bottom(hole temperature &hile the blue represents the uncorrected bottom(hole temperatures* )rom

the plots it &as observed that the corrected temperature values is higher than the uncorrected temperature as evident in the

red and blue lines* )igures ## G 4$ is sho&ing the Horners plot for &ells A:5(# ( A:5(#$* The general .no&ledge of the

Horners e%trapolation is to substitute '@# in the linear e?uation displayed on the plots to give the static formation

temperatures of various &ells*

)igure 4# is plot sho&ing corrected bottom(hole temperatures &ith depth to give the regional geothermal gradient

&ithin the study area*

Ta)! 2: B%""%=-H%)! T!=!a"#! C%!"i%( Va)#! Ui(; H%(!? M!">%$

" H/TH

/

"TH

/

" "T

/BHT

°

C/BHT>°C

/

;*$$ >*$$ #3*$$ $*73=7 #$/

##/*37##*7$ >*$$ #;*7$ $*>7;# #$;

#6*7$ >*$$ 47*7$ $*;>/; #$6

;*$$ >*$$ #3*$$ $*73=7 #$$

##>*>;##*7$ >*$$ #;*7$ $*>7;# #$7

#6*7$ >*$$ 47*7$ $*;>/# #$==*47 3*$$ ##*47 $*;333 ##>

##7*=>##*$$ 3*$$ #/*$$ $*;=7; #47

#3*7$ 3*$$ #>*7$ $*=#=4 #4=

#*7$ >*$$ ;*7$ $*4$$$ #$4

##4*7/>*$$ >*$$ #4*$$ $*7$$$ #$>

##*7$ >*$$ #;*7$ $*>7;# #$=

;*47 /*$$ ##*47 $*>//$ #$$

#7;*7##$*$$ /*$$ #/*$$ $*;#/3 #$6

#4*7$ /*$$ #>*7$ $*;7;> ##6

;*$$ >*$$ #3*$$ $*73=7 6$

#$$*37##*7$ >*$$ #;*7$ $*>7;# 63

#6*7$ >*$$ 47*7$ $*;>/; 67

;*$$ >*$$ #3*$$ $*73=7 6#

#$#*37##*7$ >*$$ #;*7$ $*>7;# 6/

#6*7$ >*$$ 47*7$ $*;>/; 6>

#*7$ >*$$ ;*7$ $*4$$$ >;

=#*7/>*$$ >*$$ #4*$$ $*7$$$ ;#

##*7$ >*$$ #;*7$ $*>7;# ;3

=*47 /*$$ #4*47 $*>;37 7$

;>*$4##*$$ /*$$ #7*$$ $*;333 7/

#3*7$ /*$$ #;*7$ $*;;#/ 7=

;*47 7*$$ #4*7$ $*7=$$ >$

6$*$=#$*$$ 7*$$ #7*7$ $*>>>; >7

#4*7$ 7*$$ #;*7$ $*;#/3 ;$

I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4




Ta)! 0: C%!"!$ B%""%=-H%)! T!=!a"#! Va)#! Ui(; H%(!? M!">%$

W!)) BHT>C/

A:5(# ##/*37

A:5(4 ##>*>;

A:5(3 ##7*=>

A:5(/ ##4*7/

A:5(7 #7;*7#

A:5(> #$$*37

A:5(; #$#*37

A:5(= =#*7/

A:5(6 ;>*$4

A:5(

#$6$*$=

Ta)! 1: B%""%=-H%)! T!=!a"#! C%!"i%( Va)#! Ui(; Wa)!? M!">%$

W!)) R#( N% D!">=/ BHT°

C/ BHTw°

C/

A:5(# # #37$ #$/ #$7*34

4 4>7$ #$; ##7*3$

3 3$/= #$6 ##6*4$

A:5(4 # ;$$ #$$ #$7*#4

4 44$$ #$7 ##4*#$3 34$$ #$= ##/*$=

A:5(3 # 4#$$ ##> #4$*$$

4 3#$$ #47 #46*6;

3 3;$$ #4= #33*6$

A:5(/ # >$$ #$4 #$/*/6

4 43$$ #$> #$6*/>

3 3>7= #$= ###*//

A:5(7 # #7$$ #$$ #$7*;4

4 47$$ #$6 ##7*>>

3 33$$ ##6 #47*>$

A:5(> # #;$$ 6$ 67*;4

4 3$$$ 63 66*>6

3 37;/ 67 #$4*7>A:5(; # 47$$ 6# 63*$$

4 34$$ 6/ 6>*$$

3 3>7$ 6> 6=*77

A:5(= # >$$ >; ;4*7=

4 4#$$ ;# ;>*77

3 3#$$ ;3 ;=*73

A:5(6 # =$$ 7$ 7/*#/

4 #7$$ 7/ 76*#4

3 4=># 7= >3*$6

A:5(#$ # #4$$ >$ >/*/;

4 4=$$ >7 >6*//

3 33$$ ;$ ;/*/$

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48 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Ta)! 4: A<!a;! C%!"!$ B%""%=-H%)! T!=!a"#! Va)#! Ui(; Wa)!? M!">%$

W!))BHTwC

/

A:5(# ##3*4;

A:5(4 ##$*/3A:5(3 #4=*$$

A:5(/ #$=*/>

A:5(7 ##7*>>

A:5(> 66*34

Ta)! 4: C%("$.,

A:5(; 67*=7

A:5(= ;7*=;

A:5(6 7=*;=

A:5(#$

>6*//

Ta)! 7: C%=ai%( !"w!!( C%!"!$ BHTS Ui(; H%(! a($ Wa)!? M!">%$

W!)) N% H%(!? M!">%$ Wa)!? M!">%$

A:5(# ##/*37 ##3*4;

A:5(4 ##>*>; ##$*/3

A:5(3 #7/*=> #4=*$$

A:5(/ ##4*7/ #$=*/>

A:5(7 #7;*7# ##7*>>

A:5(> #$$*37 66*34

A:5(; #$#*37 67*=7

A:5(= =#*7/ ;7*=;

A:5(6 ;>*$4 7=*;=

A:5(#$ 6$*$= >6*//

Ta)! 8: G!%">!=a) Ga$i!(" i( ">! Vai%# W!))

W!)) N%.G!%">!=a) Ga$i!("

C=

A:5(# $*$3$

A:5(4 $*$4;

A:5(3 $*$4=

A:5(/ $*$43

A:5(7 $*$3$

A:5(> $*$4$

A:5(; $*$4$

A:5(= $*$#>

A:5(6 $*$#3A:5(#$ $*$#/

Ta)! : D!<ia"i%( %+ ">! U(%!"!$ BHTS +%= ">! C%!"!$ BHTS +% B%"> H%(! a($ Wa)!? M!">%$

W!))

´ X

W

w

´ X

>

>

A:5(# >*># 3*=4 >*>= 3*3$

A:5(4 >*#$ $*=# #4*3/ $*4>

A:5(3 /*6> $*;# ##*$; $*/>

A:5(/ 3*#3 $*/7 ;*4# $*4$

A:5(7 >*33 $*/3 =*;7 $*>4

A:5(> >*33 $*;7 ;*>= $*#>

A:5(; 4*#= $*47 ;*/6 $*#>

I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4




A:5(= 7*77 $*4# ##*4# $*4$

A:5(6 /*;= $*/> 44*$4 $*4>

A:5(#$ /*/7 $*$# 7*33 $*33

Ta)! 3: C%!++ii!(" %+ Vaia"i%( C%V/ +% B%"> H%(! a($ Wa)!? M!">%$

W!)) C%V/> C%V/w

A:5(# /6*$$ 7;*;$

A:5(4 4*$$ #3*$$

A:5(3 /*$$ #/*$$

A:5(/ 3*$$ #/*$$

A:5(7 ;*$$ ;*$$

A:5(> 4*$$ #4*$$

Ta)! 3: C%("$.,

A:5(; 4*$$ ##*$$

A:5(= 4*$$ /*$$

A:5(6 #*$$ #$*$$

A:5(#$ $*4$ >*$$

Fi;#! 2: BHT Vaia"i%( wi"> D!"> +% AMK-2


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4 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Fi;#! 1: BHT <aia"i%( wi"> D!"> +% AMK-1



I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4





Fi;#! : BHT Vaia"i%( wi"> D!"> +% AMK-

Fi;#! : BHT Vaia"i%( wi"> D!"> +% AMK-

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75 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Fi;#! : BHT Vaia"i%( wi"> D!"> +% AMK-3


Fi;#! 22: H%(!? P)%" AMK-2

I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4




Fi;#! 20: H%(!? P)%" AMK-0

Fi;#! 21: H%(!? P)%" AMK-1

Fi;#! 24: H%(!? P)%" AMK-4

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70 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Fi;#! 27: H%(!? P)%" AMK-7

Fi;#! 28: H%(!? P)%" AMK-8

Fi;#! 2: H%(!? P)%" AMK-

I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4




Fi;#! 2: H%(!? P)%" AMK-

Fi;#! 23: H%(!? P)%" AMK-3

Fi;#! 05: H%(!? P)%" AMK-25

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74 O.I. H%+a)), E. D. U@% & D.H. Da<i!

Fi;#! 02: P)%" %+ C%!"!$ BHT <!# D!"> "% Gi<! ">! G!%">!=a) Ga$i!(" %+ ">! S"#$ A!a

CONCLUSIONS

)rom the results of the bottom(hole temperature correction and the statistical analysis, the follo&ing observations

&ere made and conclusions dra&n*

• Horner plot and +aples method are effective method for the correction of measured bottom(hole temperatures

!HTs" to static formation temperature of a formation*

• This study has confirmed that the geothermal gradient of a formation can be effectively determined by first

correcting the measured bottom(hole temperatures* The geothermal gradients computed from the various &ells

indicated that these gradients varies from &ell to &ell* These variations may be attributed to changes in thermal

conductivity of the roc.s &ithin the formation ground&ater flo& etc* The geothermal gradients ranges from

$*$#/012m to $*$3$012m* A regional average vertical geothermal gradient of $*$43012m or 430125m &as obtained

from the study area*

• The accuracy associated &ith the corrected bottom(hole temperatures !HTs" &as achieved using the students t

distribution at the desired level* At 67819 and 66819 and computed corrected !HTs for +ell A:5(# is ##3*4;

<=*$4 and ##3*4; < #6*#/ Similarly for +ell A:5(4 is##$*/3 < >*4$ and ##$*/3 < 4;*#7* 9t &as observed that the

678 confidence level is more reliable than the 668 since the lo&er limits of the confidence intervals &ill be very

far from the uncorrected bottom(hole temperatures, in principle the lo&er confidence interval limit should be

e?ual to or greater than the uncorrected bottom(hole temperatures*

• The deviations of the uncorrected bottom(hole temperatures !HTs" from the corrected !HTs" using both Horner

and +aples methods for &ells A:5(# and A:5(4 are

σh @ 3*3$, σ& @3*=4 for A:5(# and σh @ $*4> , σ& @$*=# for A:5(4

• ur investigations also sho& that there is a high degree of closeness bet&een the corrected bottom(hole

temperatures !HTs" values of Horner Plot and +aples method* 9t is also found that there is good agreement

bet&een the various correction methods*

REFERENCES

I=a" Fa"% *CC/: 0.3473 NAAS Ra"i(;: 0.4




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from 1ontinuous temperature logs* -lobal Mourn* of Pure and Applied Sciences, 6O4" 4>7 G 4;#*

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base of neural method C%amples for simavgeotherm area, +estern Tur.ey* 9nt* M* Phys* Sci*, >#" /3(7#

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sedimentary and 9gneous Roc.* M* -eophysics* Res*, ##4, !$74#>

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:e%ico city, seventh &orld petroleum congress proceedings, p #67(4$7

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probability and statistics 4nd edition :c-ra&(Hill*

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Phys* Sci*,>O3#" ;#$>( ;###

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78 O.I. H%+a)), E. D. U@% & D.H. Da<i!

#6;p

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Science and Technology, Port, Harcourt, Nigeria*

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7. applied - ijans - statistical analysis on corrected well-log derived - horsfall - nigeria - opaid

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