Anaerobic corrosion caused by sulfate-reducing bacteria

A N A E R O B I C C O R R O S I O N C A U S E D BY S U L F A T E - R E D U C I N G B A C T E R I A

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A thes is s u b m i t t e d to the F a c u l t y a n d the B o a r d of T r u s t e e s of the C o l o r a d o S ch oo l of M i ne s in p a rt i a l

f u l f i l l m e n t of the r e q u i r e m e n t s for the d e g r e e of M a s t e r of E n g i ne e r i ng , P e t r o l e u m E n gi ne er i ng . Golden, C o l o r a d o Da t e

ZéWûY

8

A B S T R A C T The p u r p o s e of this e n g i n e e r i n g r ep or t is to p r o v i d e a b e t t e r o v e ra l l u n d e r s t a n d i n g on the s u b j ec t of a n a e r o b i c c o r r o s i o n c a u s e d b y s u l f a t e - r e d u c i n g b a c t e r i a (S R B ). It is a c o m p i l a t i o n of s c i e n t i f i c m a t e r ia l f r om the m i c r o b i ol o gy , m e t a ll u rg y , a n d p e t r o l e u m fields. The e ff ec t s of SRB is a t opic of m a j o r c o n c e r n in the p e t r o l e u m i n d u s t r y . T he p r e s e n c e of s u l f a t e - r e d u c i n g b a c t e r i a can resu l t in s u b s t a n t i a l e c o n o m i c l osses and p o l l u t i o n of the

e n v i r o n m e n t . T h e y c a u s e the d e t e r i o r a t i o n of m e t a l s , p a r t i c u l a r l y iron a n d s t e e l , w h i c h can a f f ec t oil a n d gas p i pe li ne s, o f f s h o r e s t r u c t u r e s , w a t e r f l o o d i n j e c t io n

s y s t e m s , oil a n d gas s t o ra g e t a n k s , a n d t u b u la r s to name a f e w . T h e y g e n e r a t e h y d r o g e n s u lf i d e w h i c h can c a us e oil a n d gas r e s e r v o i r s to b e c o m e c o n t a m i n a t e d or 'sour'.

This r e p o r t w ill e x a m i n e the g e n e ra l c h a r a c t e r i s t i c s of s u l f a t e - r e d u c i n g b a c t e r i a . It will e x p l a i n and r e v i e w the c l a s s i c a l a n d a l t e r n a t i v e m e c h a n i s m s of c o r r o s i o n c a u s e d b y s u l f a t e - r e d u c i n g b a c t e r i a . It w ill e xa mi n e the p r o b le m s

t hat o cc u r as a r e su lt of t heir p r e s e n c e . This thesis will

r e v i e w m e t h o d s u s e d to d e t e c t s u l f a t e - r e d u c i n g b a c t e r i a . Finally, it w ill e x am i ne the m e t h o d s that are u s e d to c on t ro l a n d p r e v e n t the g r o w t h a nd a c t i v i t y of

s u l f a t e - r e d u c i n g b a c t e r i a .

TABLE OF CONTENTS Page A B S T R A C T ... iii L I ST OF F I G U R E S ... x L I S T OF T A B L E S ... xii A C K N O W L E D G E M E N T S . ... xiii 1 . I N T R O D U C T I O N ... 1 2. L I T E R A T U R E S U R V E Y ... 4 3. P R O B L E M S A S S O C I A T E D W I T H THE P R E S E N C E OF SRB ... 7 3.1 O F F S H O R E S T R U C T U R E S ... 7 3.2 R E S E R V O I R S O U R I N G A N D P L U G G I N G ... 10 3.3 S T OR A G E T ANKS A N D P I P E L I N E S ... 13 3.4 H Y D R O C A R B O N S ... 15 3.5 C O R R O S I O N OF S T E E L AND O T H E R A L L O Y S ... 16 3.5.1 M i l d S teel or Iron ... 16 3.5.2 S t a i n l e s s S teels ... 17 3.5.3 C o p p e r A l l o y s ... 17 3.5.4 A l u m i n u m A l l o y s ... 18 3.5.5 C o r r o s i o n of A l l o y s in S a l t w a t e r .. 19 3.6 C O N C R E T E ... 20 4 . C A SE S T U D Y ... . 21 iv

Page 5. M E T H O D S OF C O N T R O L A N D P R E V E N T I O N OF SRB ... 27 5.1 B I O C I D E S ... 27 5.1.1 I n h i b i t i o n of G r o w th ... 27 5.1.2 S e l e c t i n g and E v a l u a t i n g a B i o c i d e ... 29 5.1.3 C o n t i n u o u s B i oc i d e T r e a t m e n t V e r s u s Slug T r e a t m e n t ... 32 5.1.4 B a c t e r i a l Kill Tests ... 33 5.1.5 N o n - O x i d i z i n g B i o c i d e s ... 35 5.1.5.1 C h l o r i n a t e d P h e n o l s ... 36 5. 1.5.2 C a t i o n i c C o m p o u n d s ... 37 5. 1.5.2.2 Q u a t e r n a r y A m m o n i u m Salts ... 37 5 . 1 . 5. 2. 2 A mi n e s ... 37 5 .1 . 5 . 2. 3 C a t i on i c P o l y m e r s ... 38 5.1.5.3 A l d e h y d e s ... 38 5.1.5.4 O r g a n o S u lf u r C o m p o u n d s ... 39 5 . 1 .5 .4 .1 T h i o c y a n a t e s ... 39 5 .1 . 5 . 4. 2 S u lf on es a n d T h io n e s ... 39 5 .1 . 5 . 4. 3 T h i o c a r b a m a t e s ... 39 5.1.6 O x i d i z i n g B i o c id e s ... 40 5.1.6.1 C h l o r i n e ... 40 5.1.6.2 C h l o r i n e D i o x i d e ... 41 5.2 C A T H O D I C P R O T E C T I O N ... 41 5.3 U SE OF P R O T E C T I V E M A T E R I A L S ... 45 v

Page 5.3.1 U s e of P r o t e c t i v e C o a ti n g s O n s h o r e ... 45 5.3.2 U s e of C o n v e n t i o n a l A n t i - F o u l i n g P a i n t s a n d N o ve l A n t i - F o u l i n g C o a t i n g s O f f s h o r e ... 46 5.3.3 U s e of S e l f - P o l i s h i n g C o p o l y m e r s O f f s h o r e ... 48 5.3.4 U se of C o p p e r / N i c k e l C l a d d i n g O f f s h o r e ... 48 5.4 C H L O R I N A T I O N A N D A E R A T I O N OF S T A G N A N T W A T E R S ... 49 5.5 U S E O F N O N - A G G R E S S I V E B A C K F I L L ... 50 5.6 U S E OF N O N - M E T A L L I C M A T E R I A L S ... 51 5.7 U S E OF P H Y S I C A L A G E N T S TO K I L L THE SRB ... 52 5.7.1 H ea t ... 52 5.7.2 C o l d ... 52 5.7.3 V i s i b l e L ig h t ... 53 5.7.4 U l t r a v i o l e t L i ght ... 53 5.7.5 N u c l e a r R a d i a t i o n ... 54 5.7.6 E l e c t r o m a g n e t i c R a d i a t i o n ... 54 5.8 S U G G E S T I O N S TO M A I N T A I N A *T R O U B L E - F R E E * S Y S T E M ... . 5 5 6. M E T H O D S O F D E T E C T I O N A N D M O N I T O R I N G OF SRB ... 57 6.1 C O L L E C T I O N O F S A M P L E S ... 58 6.2 S E R I A L D I L U T I O N M E T H O D ... 59 6.2.1 Total V i a b l e C ou nt ... 62 vi

Page 6.2.2 M o s t P r o b a b l y N u m b e r ... 64 6.2.3 D i r e c t C o un t M e t h o d ... 66 6.3 A D E N O S I N E T R I P H O S P H A T E (ATP) T E S T ... 68 6.4 U S E OF M E T A L C O U P O N S ... 69 6.5 A G G R E S S I V E N E S S OF THE S OIL ... 71 6.6 D E T E R M I N A T I O N O F B I O L O G I C A L O R NON-B I O L O G I C A L G E N E R A T I O N OF H Y D R O G E N S U L F I DE ... 72 6.7 M I C R O S C O P Y ... 7 3 6.7.1 L ig h t M i c r o s c o p y ... 74 6.7.2 S c a n n i n g E l e c t r o n M i c r o s c o p y ... 74 6.7.3 T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y .. 75 6.8 C O N C E N T R A T I O N OF O X Y G E N ... 75 6.9 C O N C E N T R A T I O N OF S U L F A T E ... 76 6.10 C O N C E N T R A T I O N OF S U LF I D E ... 76 7. THE S U L F A T E - R E D U C I N G B A C T E R I A ... 77 7.1 C L A S S I F I C A T I O N OF SRB ... 77 7.2 R A N G E OF T O L E R A N C E S FOR THE SRB ... 80 7.2.1 T e m p e r a t u r e ... 80 7.2.2 P r e s s u r e ... 81 7.2.3 S alt C o n c e n t r a t i o n s ... . 82 7.2.4 pH L ev e ls ... 83 7.2.5 R e d o x P o te n t i a l ... 83 7.3 THE R OL E OF THE S U L F U R C Y CL E ... 84 7.4 THE N U T R I T I O N A L R E Q U I R E M E N T S ... 87 vii

Page 7.5 S O UR C E S OF C A R B O N A N D E N E R G Y ... 88 7.6 B I O F I L M S - A M I C R O B I A L E N V I R O N M E N T ... 92 7.7 D I S T R I B U T I O N O F SRB ... 95 7.8 THE E F F E C T S OF SRB A C T I V I T Y IN N A T U R E ... 98 7.9 C H A R A C T E R I S T I C S OF A N A E R O B I C C O R R O S I O N C A U S E D B Y SRB ... 100 8. C L A S S I C I A L A ND A L T E R N A T I V E M E C H A N I S M S OF SRB IN D UC ED A N A E R O B I C C O R R O S I O N ... 102 8.1 A G E N E R A L O V E R V I E W OF E L E C T R O C H E M I C A L C O R R O S I O N ... 102 8.2 THE C A T H O D I C D E P O L A R I Z A T I O N T H E O R Y ( C L A SS IC AL THEORY) ... 104 8.3 A L T E R N A T I V E M E C H A N I S M S TO THE C A T H O D I C D E P O L A R I Z A T I O N T H E O R Y ... 108 8.3.1 Iron S u lf i de (FeS) as a D e p o l a r i z e r ... 109 8.3.2 I ron S u l f i d e (FeS) a n d B a c t e r i a l H y d r o g e n a s e as a D e p o l a r i z e r ... 112 8.3.3 H y d r o g e n S ul fi de (Hz S ) as a D e p o l a r i z e r ... 112 8.3.4 The C o r r o s i v e M e t a b o l i t e T h e o r y ... 113 9. C O N C L U S I O N ... 114 R E F E R E N C E S ... 115 A P P E N D I X A: G E N E R A L M I C R O B I O L O G Y OF THE SRB ... 121 A. 1 M O R P H O L O G Y . 121 A. 1.1 D e s u l f o v ib r i o ... 121 viii

Page A . 1.2 D e s u l f o t o m a c u l u m ... 123 A. 1.3 D e s u l f o b a c t e r ... 126 A. 1.4 D e s u l f o b u l b u s ... 127 A. 1.5 D e s u l f o c o c c u s ... 128 A . 1.6 D e s u l f o n e m a ... 128 A. 1.7 D e s u l f o s a r c i n a ... 129 A. 2 M O T I L I T Y ... 130 A. 3 G R A M R E A C T I O N ... 130 A P P E N D I X B: C U L T U R E M E D I U M S FOR THE G R O W T H OF SRB ... 132 B . 1 M e d i u m B ... 132 B.2 M e d i u m C ... 133 B . 3 M e d i u m D ... 134 B . 4 M e d i u m E ... 135 A P P E N D I X C: G L O S S A R Y 136 ix

LIST OF FIGURES F i gu r e N u m b e r T itle Page 1 S c h e m a t i c r e p r e s e n t a t i o n of b i o f i l m a c t i v i t y on a m e t a l s u rf ac e i m m e r s e d in s e a w a t e r ... 8 2 C a t h o d i c p r o t e c t i o n of a b u r i e d p i p e l i n e u s i ng a m a g n e s i u m s a c r i fi c ia l a no d e ... . 42 3 C a t h o d i c p r o t e c t i o n using a r e c t i f i e r to s u p p l y a c u r r e n t to an inert a no de ... 43 4 A n i l l u s t r a t i o n of the serial d i l u t i o n m e t h o d ... . ... 61 5 The total v i a b l e c ou nt m e t h o d u s i n g

test tubes a n d plat e s ... 63

6 The m o s t p r o b a b l e n u m be r (M P N ) m e t h o d ... 65 7 The d i r e c t c ou n t m e t h o d ... 67 8 V a r i a t i o n in 3 4 S isotope r a tios in b i o l o g i c a l a n d n o n - b i o l o g i c a l SO4 2 ™ r e d u c t i o n ... 73 9 The S u l f u r C yc l e ... ... 86 10 A s i m p l i f i e d d i a g r a m of a n a e r o b i c b i o l o g i c a l d e g r a d a t i o n ... ... 89 11 E l e c t r o c h e m i c a l r ea c ti o n s d u r i n g the c o r r o s i o n of zinc in d i l ut e h y d r o c h l o r i c a c i d ... 103 12 A n i l l u s t r a t i o n of the c l a s s i c a l m e c h a n i s m a n d a l t e r n a t i v e m e c h a n i s m ... 109 13 The i n t e r r e l a t i o n s h i p of the i ro n s u l f i de s .. 110 14 P h o t o g r a p h of m i c r o b i a l i n d u c e d p i t t i n g ... Ill x

Figu re N u m b e r T it l e Page A .1 A m o n o t r i c h o u s D e s u l f o v i b r i o d e s u l f u r i c a n s a n d a s p i r i l l o i d D e s u l f o v i b r i o d e s u l f uri cans ... 122 A. 2 D e s u l f o v i b r i o g i g a s ... 123 A . 3 D e n t i c u l a t e D e s u l f o t a m a c u l u m n i g r i f l e a n s .... 124 A . 4 A p e r i t r i c h o u s D e s u l f o t o m a c u l u m n i g r i f i c a n s .. 124 A . 5 D e s u l f o t o m a c u l u m a c e t o d o x i n s a n d s po r es ... 125 A. 6 D e s u l f o b a c t e r p o s t g a t e i ... 126 A. 7 D e s u l f o b u l b u s p r o p i o n i c u s ... 127 A. 8 D e s u l f o co c c us m u l t i v o r a n s ... 128 A . 9 D e s u l f o n e m a l i m i c o l a ... 129 A. 10 D e s u l f o s a r c i n a v a r i a b i l i s ... 129 xi

LIST OF TABLES T a ble N u m b e r T it l e Page 1 R E S U L T S F R O M THE W A T E R I N J E C T I O N S Y S T E M ... 24 2 R E S U L T S F R O M S A M P L E T AK E N B E N E A T H T U B E R C L E S ON 9Cr - IMo T U B I N G ... 25 3 N U M B E R OF B A C T E R I A P R E S E N T P E R P O S I T I V E B O T T L E ... 61 4 R E D O X P O T E N T I A L A N D C O R R O S I V E N E S S OF THE SOIL ... 71 5 A G G R E S S I V E N E S S O F THE S OI L ... . 72 6 C L A S S I F I C A T I O N A N D SOME C H A R A C T E R I S T I C S OF S U L F A T E - R E D U C I N G B A C T E R I A ... 78 7 O P T I M U M G R O W T H T E M P E R A T U R E ... 81 8 THE C A T H O D I C D E P O L A R I Z A T I O N T H E O R Y ... 106 xii

A C K N O W L E D G E M E N T S

I w o u l d like to t ha n k Dr. J am es W . C r a f t o n for his c on t i n u o u s s u p p o r t a n d g u i d a n c e t h r o u g h o u t m y g r a d u a t e p r o g r a m . I w o u l d like to t hank Dr. B r uc e C r ai g from M e t a l l u r g i c a l C o n s u l t a n t s for b e in g on m y c o m m i t t e e ,

p r o v i d i n g support, a nd for a n s w e r i n g the m a n y q u e s t i o n s that I had. I w o u l d like to t h a n k P r o f e s s o r R o b e r t T h o m p s o n for p a r t i c i p a t i n g on m y c o m m i t t e e . I w o u l d like to thank

D en n is H o r s t m a n (P E T R O L I T E ) a n d Carl C r o n (U N O C A L C o r r o s i o n C e n t e r ) for the i n f o r m a t i o n t he y p r o v i d e d in m y thesis. I w o u l d like to thank D a v i d M a y e r for l i s t e n i n g w h e n I w a n t e d

to talk a b o u t SRB or let off some steam. L a s t , but not

least, I w o u l d like to t ha nk m y p ar en ts for their

o v e r w h e l m i n g s up po r t w h i l e I was in g r a d u a t e school a nd for c o n t i n u o u s l y r e m i n d i n g me t h at r e a l i t y does in d e e d exist o ut s i d e the h a ll s of a cademia.

1. I N T R O D U C T I O N

T h e r e a p p e a r s to be a n e e d to i n te g ra t e all the d i v e r s e s c i e n t i f i c m a t e r i a l on a n a e r o b i c c o r r o s i o n c a u s e d b y

s u l f a t e - r e d u c i n g b a c t e r i a ( S R B ) . W i t h that in mind, this e n g i n e e r i n g r e p o r t a t t e m p t s to p r o v i d e a p e t r o l e u m

e n g i n e e r i n g p e r s p e c t i v e on this s u b j e c t .

T h e r e is an e x t e n s i v e b o d y of l i t e r a t u r e on the s ub je ct of a n a e r o b i c c o r r o s i o n , or s u i f a t e - r e d u c i ng b a c t e r i a (SRB), or some c o m b i n a t i o n , m uc h of w h i c h is w r i t t e n for other t e c h n ic a l b a c k g r o u n d s . Also, the l i t e r a t u r e u s u a l l y d eals w i t h a v e r y n a r r o w a s p ec t of this t o p i c , not a l l o w i n g the r e ad e r to o b t a i n a c le a r o v e ra l l u n d e r s t a n d i n g . T h e r e f o r e , this r e p o r t a t t e m p t s to p r ov i d e a b e t t e r o v er al l

u n d e r s t a n d i n g of s u l f a t e - r e d u c i n g b a c t e r i a (SRB), the

c o r r o s i o n p r o b l e m s that r es u lt f rom t h ei r activity, a n d h o w to d eal w i t h the p r o b l e m s a s s o c i a t e d w i t h t h eir p r e s e n c e .

M i c r o b i a l i n d u c e d c o r r o s i o n (MIC) is a form of c o r r o s i o n that r e su l t s f ro m the p r e s e n c e of a e r o b i c a n d /o r a n a e r o b i c b a c t e r i a , w h i c h leads to the c l a s s i f i c a t i o n : a e r o bi c c o r r o s i o n a n d a n a e r o b i c c o r r o s i o n . A e r o b i c c o r r o s i o n occu rs w h e n o x y g e n is p r e s e n t in the s u r r o u n d i n g e n v i r o n m e n t . A n a e r o b i c c o r r o s i o n o c cu rs w h e n o x y g e n is a bs e nt f r om the s u r r o u n d i n g e n v i r o n m e n t . H o w e v e r , this c l a s s i f i c a t i o n is o n l y u s e d in c o n j u n c t i o n w i th m i c r o b i a l i n du c ed c o r r o s i o n .

The a e ro b i c and a n a e r o b i c b a c t e r i a that are i n v o l v e d in m i c r o b i a l i n d u c e d c o r r o s i o n can u s u a l l y be f o un d in c o e x i s t e n c e a n d one c a n be d e p e n d e n t or i n d e p e n d e n t of the o t h e r ’s p r e s e n c e . SRB are d e p e n d e n t on t hr e e featu r es of t h ei r p h y s i o l o g y ; t h e y are a n a e r o b i c ; t he i r g r ow t h is r e s t r i c t e d to the a v a i l a b i l i t y of the n e c e s s a r y n u t r i e n t s ; a nd t h e y p r o d uc e h y d r o g e n s u l f i d e . SRB are stri c t a n a e r o b e s , in o t h e r words o x y ge n i n h ib i ts t he ir g r o w t h . T h e y c a nn o t u t i l i z e o x yg e n for t heir f or m of r e s p i r a t i o n as do m o st o r g a n i s m s . SRB u t il i ze s ul f at e for t he ir f or m of a n a e r o b i c r e s p i r a t i o n w h i c h in the p ro c e s s r ed uc es the s u lf a te (SO4 2 ~ ) to s ul fi d e (S 2 - ), hence the n am e s u l f a t e - r e d u c i n g b a c t e r i a . In the p r e s e n c e of o x y ge n the SRB r e m a i n in a d o r m a n t state a nd are r ea d y to b e c o m e a c t i ve w h e n the s u r r o u n d i n g e n v i r o n m e n t b e co m es a n a e r o b i c .

E v e n t h ou gh SRB are not a c ti v e in a e r o b ic e n v i r o n m e n t s , w h e n the s u r r o u n d i n g e n v i r o n m e n t b e co m e s s u i t a b l e for g ro wt h th eir a c t i v i t y c a n r es u lt in s u bs t a n t i a l e c o n o mi c losses and p o l l u t i o n to the e n v i r o n m e n t . M a j o r e c o n o m i c losses occur to iron a n d steel s t r u c t u r e s that are b u r i e d in soils or l oc at e d in m a r i n e e n v i r o n m e n t s . T h e y can also :

1) sour a n d plug oil a n d gas r e s e r v o i r s ; 2) g e n e r a t e h y d r o g e n s u l f i de ;

3) c o r r o d e p i p e l i n e s , i n je c t i o n systems, s t o ra g e tanks, d o w n h o l e tubulars, p u m p i ng equipment, o f f s h o r e

s t ru ctures, e t c .

C o r r o s i o n c a u s e d b y SRB is a m o r e e x t e n s i v e p r o b l e m than is c o m m o n l y r e c o g n i z e d in the p e t r o l e u m industry. U nt i l the time c om es w h e n the c o r r o s i o n p r oc e ss is m o r e f u l ly

u nd e rs to od , c o o p e r a t i o n b e t w e e n m i c r o b i o l o g i s t s a nd e n g i ne e rs is e s s e n t i a l in d e s i g n i n g an a p p r o p r i a t e p r o g r a m to c o n tr o l a n d p r e v e n t b a c t e r i a l growth. That m ea ns the e n g i n e e r must h a ve a g o o d u n d e r s t a n d i n g of the m i c r o b i a l a nd m e t a l l u r g i c a l a s p e c t s of the problem.

2. L I T E R A T U R E S U R V E Y J.H. G a r r e t t * 1 > r e p o r t e d the e x i s t e n c e of m i c r o b i a l c o r r o s i o n in 1891 w h e n he o b s e r v e d an i n c r e as e in the r ate of c o r r o s i o n of a l e a d - c o v e r e d c able w h i c h was l i n ke d to b a c t e r i a l a c t i v i t y . M .W . Beijerinck* 2 > d i s c o v e r e d the p r e s e n c e of s u l f a t e - r e d u c i n g b a c t e r i a (SRB) in 1895. In

1903, A. v a n Delden* 3 > r e p o r t e d the e x i s t e n c e of m a r i n e , salt t o l e r a nt s p ec ie s of SRB. In 1910, R.H. Gaines* 4 > w r o t e a p a p e r s h o w i ng e v i d e n c e that "iron b a c t e r i a " a nd "sulfur b a ct e r i a " w e r e , in p a r t , r e s p o n s i b l e for the c o r r o s i o n of b u r i e d ferr o us m e t a l s . T hi s i n c l u d e d b o t h a e r o b i c and

a n a e r o b i c b a c t e r i a . By 1924, it was b e l i e v e d that the p r o d u c t i o n of h y d r o g e n s u l f i d e b y SRB p l a y e d an i m po r ta nt

part in the c o r r o s i o n of b u r i e d ferrous metals. L. Elion* 5 >

d i s c o v e r e d t h e r m o p h i l i c v a r i e t i e s of SRB in 1925. In 1931, M. S t e p h e n s o n a n d L.H. Strickland* 6 > e s t a b l i s h e d t hat SRB (p a r t i c u l a r l y in the g en us D e s u l f o v i b r i o ) c o n t a i n an e n zy m e w h i c h t h e y n a m e d h y d r o g e n a s e , that uses h y d r o g e n to r e d u c e s u lf a te to sulfide. In 1934, at the P r o v i n c i a l W a t e r w o r k s in n o r t h e r n

Holland, C.A.H. v on W o l z o g e n K u h r a n d I.S. v an der Vlugt* 7 > n o t i c e d the c o r r o s i o n of f e rr o us m e ta l s b u r i e d in wet,

a n a e r o b i c , c l a y soils. T h e y o b s e r v e d that iron s u l f i d e was p r o d u c e d not o n l y on the s u r f a c e of the p i p e but in the soil

a r o u n d the c o r r o d e d p i p e . T h e y c o n f i r m e d the p r e s e n c e of SRB a n d s u g g e s t e d that the SRB act as a c a t h o d i c d e p o l a r i z i n g a ge n t b y a c t i n g as a h y d r o g e n a c c e p t o r . T h e y p r o p o s e d that the SRB c o u l d r e mo v e the a t o m i c h y d r o g e n (H ° ) f r om the

p o l a r i z e d c a t h o d e s and o x i d i z e it to e l e c t r o n s a n d p r ot o ns w h i c h was t hen u t i l i z e d to r e du c e s u l f a te to s u l f i d e .

D u r i n g the 1 9 4 0 ’s a n d 1 9 5 0 ’s, C.E. ZoBell, i n v e s t i g a t e d the role of SRB a n d o t he r m i c r o o r g a n i s m s in the p e t r o l e u m i n d u s t r y * 8 > . In 1947, ZoBell* 9 » 1 0 > i n v e s t i g a t e d the

i n j e c t i o n of the D e s u l f o v i b r i o g en us into a r e s e r v o i r to a i d in the r e le a se of h y d r o c a r b o n s as a m e t h o d of s e c o n d a r y oil r e c o v e r y . This p r o c e ss w o r k e d v e r y well in the l a b o r a t o r y but was not a p p l i c a b l e in an oil f i e ld e n vi ro n me nt . He r e p o r t e d three m a j o r d i s a d v a n t a g e s :

1) the SRB c o r r o d e iron a n d steel ;

2) they g e n e r a t e h y d r o g e n s u lf i de w h i c h c o n t a m i n a t e s the r e s e r v o i r ; 3) the SRB t h e m s e l v e s or c o r r o s i o n p r o d u c t s r e s u l t i n g from SRB c a n p lu g the r e s e r v o i r or p e r f o r a t i o n s . F r o m the 1 9 5 0 ’s t h r o u g h the p r e s e n t , J.R. P o s t g a t e * 1 1 > , a m i c r o b i o l o g i s t , has p e r f o r m e d an e x t e n s i v e a n d t h o r o u g h i n v e s t i g a t i o n of SRB. In 1979 he p u b l i s h e d a b o o k e n t i t l e d "The S u l p h a t e - R e d u c i n g B a c t e r i a " . It was the first b o ok

3. P R O B L E M S A S S O C I A T E D W IT H THE P R E S E N C E OF SRB

3.1 O F F S H O R E S T R U C T U R E S

SRB can be f o u n d i n s i de a n d o u t s id e o f f s h o r e s t r u c t u r e s , in w at e r or w a t e r / o i l e n v i r o n m e n t s a n d are u s u a l l y a c ti v e if a n a e r o b i c c o n d i t i o n s exist. The m o s t c o m m o n l y a f f e c t e d a reas on an o f f s h o r e s t r u c t u r e are w a te r i n j e c t i o n systems, oil s t or a ge tanks, c o n c r e t e g r a v i t y s t r u c t u r e s , d r i l l i n g and p r o d u c t i o n systems, a n d b a l l a s t l e g s . O u t s i d e the o ff sh o r e s t r u c t u r e the SRB c an b e f o un d b e n e a t h m a r i n e m a c r o f o u l i n g , in the s e a f l o or s ed iments, s e af l o o r p i p e l i n e s , and in

d e p o s i t e d m a t e r i a l s (d ri l l c u t t i n g s ) a r o u n d the s t r u c t u r e . A g o o d e x am p l e of m a r i n e m a c r o f o u l i n g (b i o f o u l i n g ) occurs w h e n b a r n a c l e s , m ussels, seaweed, etc., b e c o m e a t t a c h e d to

the s t r u c t u r e a n d c r e a t e m a c r o - e n v i r o n m e n t s w h i c h in turn c r e a t e m i c r o - e n v i r o n m e n t s s u i ta b l e for s u p p o r t i n g v ar io u s forms of b a c t e r i a . T h e s e e n v i r o n m e n t s i nc lu d e a n a e r o b i c c o n d i t i o n s that w o u l d s u p p o r t S R B . O n c e S RB a c t i v i t y has s t a r t e d on the s u r f a c e of the m etal the p r o d u c t i o n of s ul fi de in the b i o f i l m w i ll i n c r e a s e the e x te n t of the a n a e r o b i c zone c r e a t i n g a d d i t i o n a l s ites for SRB activity. F i gu r e 1

BULK LIQUID PHASE O x y g e n C o n c e n t r â t F a c u l t a t i v e B a c t e r i a B a c t e r i a F i g u r e 1. S c h e m a t i c r e p r e s e n t a t i o n of b i o f i l m a c t i v i t y on a m e t a l s u rf a ce i m m e r s e d in s e a w a t e r (from M a x w e l l * 1 2 > )

I n side the o f f s h o r e structure, p a r t i c u l a r l y w he re s t a g n a n t c o n d i t i o n s e x is t (b a l l a s t legs, s t o ra g e tanks, etc.)» m e a s u r e m e n t s h av e f ou n d that s i g n i f i c a n t a m ou n ts of h y d r o g e n s u lf i de c a n be g e n e r a t e d b y the S R B . The h y d r o g e n s u l f id e c o n c e n t r a t i o n c an r e ach levels h ig h e n ou g h that m a y p ose a t hr ea t to h u m a n life.

M o s t of these s t a g n a n t a r eas i n i t i a l l y c o n t a i n large v o lu me s of w a t e r a n d o x y g e n w h i c h c r ea t e a f av o ra b l e

e n v i r o n m e n t for the g r o w t h of a er ob i c bacte ri a. A f t e r the o x yg e n is c o n s u m e d b y the a e r o b i c b a c t e r i a the s t ag n a n t c o n d i t i o n s b e c o m e f a v o r a b l e for the g r o wt h of SRB a nd the p r o d u c t i o n of h y d r o g e n sulfide. U n d e r some c o n d i t i o n s b ot h o x y g e n a n d h y d r o g e n s u lf i d e can be o x i d i z e d to form sulf u ri

a c i d b y s u l f u r - o x i d i z i n g b a c t e r i a .

The b i o f i l m d e p o s i t s that are f o r m e d i ns id e the s t r u c t ur e ca n plug filters, valves, pipes, a nd e ve n p lu g the

p e r f o r a t i o n s in the t u b i ng in a w a t e r i n j e c t i o n s y s t e m or in a p r o d u c i n g well.

O u t s i d e the o f f s h o r e structure, a n a e r o b i c c o r r o s i o n is a s s o c i a t e d w i t h m a r i n e b i o f o u l i n g c o u p l e d w i t h the p r e s e n c e of b a c t e r i a or b y b a c t e r i a l a c t i v i t y in the s e d im e nt s

s u r r o u n d i n g the platform. The o r ga n i s m s p r o d u c e d e p o s i t s of g e l a t i n o u s s l ime on the m et a l s ur fa ce w h i c h is the initial stage of b i o f i l m b u i l d u p o u ts i d e the structure. The b i o f i l m m a y c o n t a i n a g g r e s s i v e m e t a b o l i t e s or p r o d u c e d e p o s i t s that c r e a te d i f f e r e n t i a l a e r a t i o n c ells w h e r e the o x y g en

c o n c e n t r a t i o n is h i g h e r at one l o c a t io n of the m e ta l than at a n o t h e r l o c a t i o n of the metal. This c re at e s an anod i c and c a t h o di c a r e a on the m e ta l w h i c h leads to i nt ense l o c a l i z e d c o r r o s i o n on the m e ta l surface. This m a y a d d to the e x i s t i n g c o r r o s i o n p r o c e s s e s that are a l r e a d y occurring.

The rate of c o r r o s i o n for steel in s e a w a t e r that c o n t a in s ac t iv e SRB is 10 to 20 t imes h i g h e r t han in s e a w a t er

a l o n e < 1 3 > . In the s e a w a t e r a r o un d the o u t s i d e of the

o ff s h o re s t r u c t u r e there e xists an i n e x h a u s t i b l e s u p p l y of s u lf a t e for the SRB to utilize. The o f f s h o r e s t r uc t u r e c a n also d i s c h a r g e t r e a t e d p r o d u c e d w a t e r f r om the r e s e r v o i r or dr i ll c u t t i n g s f rom the d r i l l i n g o p e r a t i o n that c o n ta i ns

n u t r i e n t s for the SRB to utilize.

F r o m 170 s e d i m e n t s a mp l es t ak e n in the N or t h S ea it was d e t e r m i n e d that the n u m b e r of SRB was h i g h e s t in the top

l ayers of the s e d i m e n t a n d t he i r n u m b e r s d e c r e a s e d r a p i d l y in

the f irst 20 c m (7.9 in) of depth. B e l o w 20 cm (7.9 in), the

p r e s e n c e of SRB was s p o r a d i c a n d b e l o w 50 cm (19.7 in) v e ry few w e r e d etected. If the s e d i m e n t s were m i x e d the SRB c o u l d be f ound t h r o u g h o u t the e nt i re d i s t u r b e d zone b e c a u s e

n u t r i e n t s from the top zone w o u l d a lso be m i x e d into the d i s t u r b e d z o n e < 14 > .

The a n a e r o b i c c o r r o s i o n p r o b l e m s c a u s e d b y the SRB can d e v e l o p q u it e r a p i d l y . The c o r r o s i o n is u s u a l l y v e r y

l oc a l i z e d a n d tends to be p i t t e d r a t h e r than u n i f o r m l y

c o r r o d e d . T he refore, the d a m a g e to the m et a l c a n o c cu r quite s u d d e n l y a n d u n ex pe ct e d l y.

3.2 R E S E R V O I R S O U R I N G AND P L U G G I N G

In w a t e r i n j e c t i o n s y st e m s (f r e s hw a t e r or s a l t w a t e r ) one of the p r i m a r y c o n c e r n s is the i n t r o d u c t i o n of SRB into the r e s e r v o i r . T h e ir p r e s e n c e c a n r es ul t in r e s e r v o i r plugging, p r e m a t u r e a b a n d o n m e n t of the w el l or field, s o ur i n g of the oil a n d gas, a nd c o r r o s i o n of the p r o d u c t i o n a n d i n j e ct i on e q u i p m e n t . This m a y u l t i m a t e l y r e sult in e f f e c t i v e

p e r m e a b i l i t y a nd a d e c r e a s e in the a m o u n t of r e c o v e r a b l e oil a nd g a s . If s e a w a t e r is i n j e c t e d into the r e s e r v o i r it can be a s s u m e d that the p r o b l e m s m e n t i o n e d a b o v e c o u l d be

a c c e n t u a t e d d u e to the i n t r o d u c t i o n of h i g h levels of s u lf a t e that are p r e s e n t in the s e a w a t e r .

S o u r i n g in the r e s e r v o i r m a y r e s u l t f r om three d i f f e r e n t m e c h a n i s m s : h y d r o g e n s u l f i d e m a y be p r o d u c e d b y the i n t r o d u c e d S R B ; b y f l u s h i n g out p o c k e t s of h y d r o g e n s u lf i de p r o d u c e d b y SRB d u r i n g d i a g e n e s i s ; or b y h y d r o g e n s u lfide that was p r o d u c e d b y a n o n - b i o l o g i c a l m e c h a n i s m * 1 5 > . P l u g g i n g in the r e s e r v o i r c a n be a r e s ul t of the SRB t h em se lv es . In g e n e r a l , t h e ir d i m e n s i o n s are in the o r de r of 3 to 10 m i c r o n s in l e n g t h a n d 1 m i c r o n in d i a m e t e r . W h e n the p o re t h ro a ts in the r e s e r v o i r are s m al l e r t han the size of the SRB p l u g g i n g b y the SRB t h e m s e l v e s c a n o c c u r . The SRB c a n pass t h r o u g h the r e s e r v o i r t h ro u gh f r a c t u r e p l an es or a reas w h e r e the p or e t h r o at s are l a r ge r t ha n the S R B .

T h e r e f o r e , it is t h e n p o s s i b l e to e s t a b l i s h a reas far from

the w e l l b o r e w h e r e the SRB m a y be present. SRB can also plug

the r e s e r v o i r w i t h c o r r o s i o n p r o d uc t s that are p r o d u c e d by their p r e s e n c e a n d b y b i o f i l m b u i l d u p .

S e a w a t e r m a y be h i g h l y c o r r o s i v e w h e n it c o n ta i ns

d i s s o l v e d o x y g e n , therefore, b e f o re it is i n j e c t e d into the r e s e r v o i r it is d e a e r a t e d to remo v e the d i s s o l v e d o xy g en a n d f i l t e r e d to r e mo v e the free s o l i d p a r t i c l e s . As a r es ul t the

t r e a t e d s e a w a t e r b e c o m e s f a v o r a bl e for the S R B > p a r t i c u l a r l y the b a r o t o l e r a n t , m a r i n e D e s u l f o v i b r i o species.

SRB are not a l w a y s a c t i v e in a r e s e r v o i r p r i o r to w a t e r f l o o d i n g . The c o n d i t i o n s c o u l d be ideal for SRB a c t i v i t y but t h ey are not p r e s e n t in the r e s e r v o i r or the SRB are p r e s e n t in the r e s e r v o i r but the s u p p l y of n u t r i e n t s

are not a d e q u a t e for the SRB activity; the pH m a y be too

low; or the r e s e r v o i r t e m p e r a t u r e m a y be too high. SRB m a y be p r e s e n t a n d a c t i v e in a r e s e r v o i r but s u lf i d e p r o d u c t i o n m a y be d e l a y e d or m a y not a p p e a r in the p r o d u c t i o n stream.

SRB a c t i v i t y in a r e s e r v o i r a fter w a t e r f l o o d i n g c o u l d be

a r es u lt of two causes. O ne is SRB b e i n g i n t r o d u c e d into the

reservoir. The s e c o n d is if t he y w er e p r e s e n t p r i o r to

w a t e r f l o o d i n g , an a d e q u a t e s u p p l y of n u t r i e n t s (i.e., s ul fa te from seawater) c o u l d b e c o m e available. S o m e t i m e s r e s e r v o i r w a t e r c a n n o t s u p po rt SRB a c t i v i t y but w h en i n j e c t i o n w a t e r is i n t r o d u c e d into the r e s e r v o i r a nd a l l o w e d to m i x w i th the r e s e r v o i r water, it m a y p r o v i d e c o n d i t i o n s for SRB a c t i v i t y a nd s u l f id e g en er at io n. O x y g e n m a y be i n t r o d u c e d into the r e s e r v o i r that w o u l d p e r m i t a e r o b i c d e g r a d i n g b a c t e r i a to u t i l i z e the h y d r o c a r b o n s a n d p r o d u ce s u b s t r a t e s that c o u l d be u s e d b y the SRB as a c a r b o n / e n e r g y source.

The i n j e c t e d w at e r m a y cool the r e s e r v o i r m a k i n g it

s u i t a b l e for the SRB to g r o w and b ec om e active. In the N or t h

a n d the i n j e c t e d s e a w a t e r m a y d e c r e a s e the t e m p e r a t u r e to 50 °C (122 °F) or l o wer to d i s t a n c e s of 100 m e t e r s (328 feet) from the i n j e c t i o n w e l l * 1 5 > . This s u bs t a n t i a l d e c r e a s e in r e s e r v o i r t e m p e r a t u r e a l l o w s for SRB activity.

It was b e l i e v e d that c h e m i c a l l y p r o d u c e d h y d r o g e n s u lf id e c o u l d o nl y o ccur at t e m p e r a t u r e s a b ov e 150 °C (302 °F) a n d at t e m p e r a t u r e s b e l o w this, the h y d r o g e n s u l f i de w as p r o d u c e d by the SRB. T he r e h av e r e c e n t l y b e e n some m e c h a n i s m s p r o p o s e d that c o u l d a c c o u n t for the g e n e r a t i o n of h y d r o g e n s u lf id e at t e m p e r a t u r e s b e l o w 150 °C. T h e y are: "1) T h e r m a l d e g r a d a t i o n of o r g a n i c s ul fu r c o m p o u n d s in oil at t e m p e r a t u r e s g r e a t e r than 80 0 c (176 °F); 2) t h e r m o c h e m i c a l s ul fa t e r e d u c t i o n at t e m p e r a t u r e s g r e a t e r t h an 80 - 120 °C (176 - 248 °F); and, 3) r e a c t i o n of s u l f at e w i th h y d r o c a r b o n s at t e m p e r a t u r e s b e l o w 80 °C (176 °F) if mass t r a ns f e r is not limited'^ 1 5 > . It is p o s s i b l e to d e t e r m i n e if the s u lf i de was b i o l o g i c a l l y or c h e m i c a l l y g e n e r a t e d (see s e c t i o n 6.6). 3.3 S T O R A G E T ANKS A N D P I PE L I N E S

S t o r a g e tanks p r o v id e ideal e n v i r o n m e n t s for the g r o w th of SRB. O n c e SRB b e c om e a c t i v e in the s t o ra g e tanks it is

v i r t u a l l y i mpossible, to c o n t ro l the g r o w t h of S R B . C ar ef ul m a n a g e m e n t of the s t o r e d h y d r o c a r b o n s is i m p o rt a n t in order to a v o i d a n y p o s s i b l e c o nt a m i n a t i o n , p a r t i c u l a r l y due to the p r e s e n c e of SRB.

U n d e r n e a t h the h y d r o c a r b o n p ha s e in a s t or a ge tank there u s u a l l y exis t s a layer of w a t e r (fresh, salty, or b r a c k i s h water) a n d p o s s i b l y a l ayer of s e d i m e nt s a n d / o r sludge. S u l f a t e r e d u c t i o n can o cc u r in the w a t e r l a ye r a n d / o r s e d im en t a n d the p r o d u c t i o n of h y d r o g e n s u l f i d e can

c o n t a m i n a t e the s t o re d oil a n d / o r gas. O nc e again, if o x ygen is p r e s en t a e r o b i c oil d e g r a d i n g b a c t e r i a c a n p r o d uc e

s u b s t r a t e s for the SRB to utilize. If d i s s o l v e d o x y g e n is a d d e d to the w a t e r zone to i nh i bi t SRB growth, the d e s ig n a l l o w a n c e s m u s t be m a d e to the s t or a ge tank to a l l o w for the i n cr ea se in c o rrosion.

Inside a p i p e l i n e the c o r r o s i o n is u s u a l l y due to b i o f i l m b u i l d u p (plugging) or SRB a c t i v i t y o c c u r r i n g in m i cr o- ni c h e s, crevices, cracks, insi de tubercles, or u n d e r n e a t h the

biofilm. SRB a c t i v i t y on the e x t e r i o r of the p i p e l i n e is s o me t im e s a r es u lt of the p i p e l i n e s b e i n g b u r i e d in c la y or c l a y e y soils. T h is type of e n v i r o n m e n t m a y e v e n t u a l l y b e c o m e w a t e r l o g g e d a n d a n a e r o b i c c r e a t i n g an e n v i r o n m e n t s u i te d for

SRB growth. The c o r r o s i o n p r o b l e m s in this type of

e n v i r o n m e n t can u s u a l l y be d e t e c t e d w h e n e x c a v a t i n g the soil s u r r o u n d i n g the pipe. T h e r e is a smell of h y d r o g e n s ul fide

('rot t en e g g ’ s m e l l ) a nd the soil is s t a i n e d b l a c k (FeS p r e c i p i t a t e ).

3.4 H Y D R O C A R B O N S

S u l f i d e g e n e r a t i o n b y the SRB can sour oil a nd gas in the reservoir, s t or ag e f ac ilities, or any l oc a le w h er e h y d r o g e n s u lf i d e is p r e s e n t w i t h h y d r o c a r b o n s . If d i s s o l v e d s u lf u r is c o n t a i n e d in the c r u de oil the SRB c a n u t i l i z e the s u lfur and g e n e r a t e h y d r o g e n sulfide.

SRB c a n be i n t r o d u c e d into the r e s e r v o i r d u r i n g a c i d i z i n g a n d f r a c t u r i n g p r o g r a m s , w a t e r f l o o d p r o g r a m s , d u r i n g the

d r i l l i n g p r o c e s s , or c o u l d a l r e a d y be in the r e s e r v o i r . T h e y are u s u a l l y e a sy to d e t e c t in m ost w a t e r a nd rock samples o b t a i n e d from the r e s e r v o i r .

It is g e n e r a l l y a c c e p t e d that SRB c a n n o t u t i l iz e

h y d r o c a r b o n s for a c a r b o n / e n e r g y s o u r c e . H o w e v e r , there have b e e n some q u e s t i o n a b l e r e p o rt s to the c o n t r a r y . T h er e have not b e e n a n y r e ce nt m i c r o b i o l o g i c a l s tu di es i n di c a t i n g that h y d r o c a r b o n s can be d e g r a d e d u n de r a n a e r o b i c c o n d i t i o n s . If a n a e r o b i c / a e r o b i c c o n d i t i o n s exist, a e r o b i c oil d e g r a d i n g b a c t e r i a c an p r ov i d e s u b s t r a t e s (fatty acids, a l c o h o l s ) for

the SRB to utilize. "There are o rg anic c o n s t i t u e n t s of c rude

s u b s t r a t e s for [SRB] ,r< 1 5 > . This c a n o c c ur in o i l / w a t e r e m u l s i on s in the p r e s e n c e of oxygen.

3.5 C O R R O S I O N OF S T E EL A N D O T H E R A LL OY S

3.5.1 M i l d S te el or Iron

W h e n m i l d steel or iron is e x p o s e d to c ul t u r es of SRB the m e t a l b e c o m e s c o a t e d w i th a f il m of iron sulf i de (FeS). The

iron s u lf i d e f o r m a t i o n is a r es ul t of the ferrous iron on the m e t a l ' s s u rf a ce r e a ct i ng w i t h the h y d r o g e n s u lf id e g e n e r a t e d

b y the SRB. SRB can g e n e r a t e o t he r forms of s ul fi de s (HS-,

S 2 *) d e p e n d i n g on the pH of the s u r r o u n d i n g e n v i r o n m e n t but the r e a c t i o n a l wa y s p r o d u c e s iron sulfides.

The f il m m a y i n i t i a l l y p r ot e c t the u n d e r l y i n g m e ta l from

the SRB a n d f rom o ther forms of c o rrosion. W h e n the

film weakens, forms a crack, or b e c o m e s detached, the n e w l y e x p o s e d m e ta l b e co m e s s u s c e p t i b l e to an a g g r e s s i v e p i tt i n g attack. This o ccurs b e c a u s e the n e w l y e x p o s e d m e t a l acts as

an a no de a n d the film acts as a cathode. The p i t t i n g a t ta c k

is a g g r e s s i v e b e c a u s e of its a u t o c a t a l y t i c nature. T hat is, the a node (the n e w l y e x p o s e d metal) is quite small w hi l e the

c a t h o d e (the film) is q uite large. The t e n d e n c y is for the

for e l e c t r on s b y the cathode. As a result, the m e ta l pits v e r y r a pi d l y w h i c h c a n p e r f o r a t e the metal.

3.5.2 S t a i n l e s s S t ee ls

The same p r o c e s s i n v o l v e d in the c o r r o s i o n of m i l d steel

or iron o cc ur s w i t h the s t ai n le s s steels. A film of iron

s u lf i de forms a r o u n d the m e ta l w hi ch l a ter can b ec o me

damaged. O nc e the f il m is d a m a g e d c o u p l e d w i t h the p r e s e n c e of SRB an a g g r e s s i v e p i t t i n g a tt a ck can ensue.

S t a i n l e s s stee ls s i t u a t e d in s e a w a t e r that are p r o t e c t e d b y c a t h o d i c p o l a r i z a t i o n (cathodic p ro te c ti o n ) can e x p e ri e n c e a d e c r e a s e in the p r o t e c t i v e effe c ts of c a t h o d i c p o l a r i z a t i o n

w h e n b a c t e r i a are present. This r es ul ts in an i nc re as e in

the rate of c o r r o s i o n (This s u bj ec t is d i s c u s s e d f ur th er in s e c t i on 5.2).

M o n e l s a n d o t he r c o r r o s i o n r es i st a n t a l l o y s are also a f f e c t e d b y SRB in a n a e r o b i c e n v i r o n m e n t s a n d are subj ec t p i t t i n g attack.

3.5.3 C o pp e r A l l o y s

a n d c o p p e r salts r e s u l t i n g from the c o r r o s i o n of c o p p e r w e re

u s u a l l y t oxic to all organisms. This is not the c ase for

b a c t e r i a , p a r t i c u l a r l y SRB, in f a c t , t he y are v e r y r e s i s t a n t to h i g h c o n c e n t r a t i o n s of copper. C o p p e r , b r o n z e s , c o p p e r steels, a n d c o p p e r n i c k e l a ll oy s are s e r i o u s l y a f f e c t e d b y m i c r o b i a l g r o w t h * 1 6 > .

Again, a s u lf i d e f ilm (c u p r ou s sulfide) forms on the s u rf a c e of the m e t al a nd w h e n b r ea k s o c cu r in the f ilm the e x p o s e d a re a s b e c o m e a n o d i c and the s ul f i de film b e c o m e s cathodic. The e x p o s e d a re a s b e c o m e sites for p o t e n t i a l p i t t i n g attack. The c u p r o u s s ul fi d e f ilm can a lso f or m in the d e f e c t s of the c u pr o u s o xi de film. T he se r e gi o ns a p p e a r to act as local a n od e s that p r o m o t e r a p i d c o r r o s i o n d u r i ng p e r i o d s of oxygenation* 1 7 > .

3.5.4 A l u m i n u m A l lo ys

As w i th the steel, p i t t i n g a t t a ck o cc ur s on the a l u m i n u m w h e n it is i m m e r s e d in seawater. The m e c h a n i s m is b e l i e v e d to be a r e su l t of c a t h o d i c d e p o l a r iz a t i on .

SRB in an a q u e ou s p h a s e can incr e as e the rate of c o r r o s i o n of a l u m i n u m from 3 to 100 t i m e s * 17 > .

3.5.5 C o r r o s i o n of A l l o y s in S a l t w a t e r

M o s t c o r r o s i o n s tu di e s p e r f o r m e d in m a r i n e e n v i r o n m e n t s u s u a l l y use a r t i f i c i a l s e a w a t e r or s e a w a t e r that is o l d and s t a g n a n t . This can c r e a t e r es ul ts that are not c o n s i s t e n t wi t h o b s e r v a t i o n s that are m a de in the field. W he n c o r r o s i o n s t ud i e s are p e r f o r m e d c o r r e c t l y in the m a r i n e e n v i r o n m e n t , it has b e e n f o u nd that a l m o s t i m m e d i a t e l y a f t e r the m e ta l is p l a c e d in the s e a w a t e r , a s u r f ac e f il m of m i c r o o r g a n i s m s a t t ac h t h e m s e l v e s to the m e t a l .

Kalinenko< 18 > f o un d that b a c t e r i a l c o l o n i e s f or m ed on aluminum, b r a s s , a n d b r o n z e c o u p on s w h e n i m m e r s e d in fresh s e a w a t e r . He also f ou n d that the b a c t e r i a l c ol on ie s

a c c e l e r a t e d the e l e c t r o c h e m i c a l p r oc e s s of c o r r o s i o n . W h e n the s e a w a t e r is polluted, it is e a si e r for the b a c t e r i a to a t t a c h t h e m s e l v e s to the m e t a l and c o l o n i z e its s u r f a c e . The f o ll o w i n g m e t a l s w e re i m m e r s e d in p o l l u t e d s e aw a t e r to o b s e r v e the l ev el s of b a c t e r i a l c o l o n i z a t i o n : aluminum, b r a s s , c o p p e r , 70/30 c o p p e r nickel, s t a i nl es s steel

(AISI 304), a n d titanium. T i t a n i u m was the m o st d e n s e l y

p o p u l a t e d , f o l l o w e d b y the s t a i n l es s s teel (AISI 304), aluminum, b r a s s , 70/30 c o p p e r nickel, a n d c o p p e r * 1 9 > . A c c e l e r a t e d rates of c o r r o s i o n h a v e a lso b e e n o b s e r v e d on c o pp e r n ic ke l a l l oy s a n d c h r o m e c o n t a i n i n g steels w h en i m m e r s e d in p o l l u t e d seawater* 2 0 > .

3.6 C ON C RE T E

C o n c r e t e is u s e d e x t e n s i v e l y in the p e t r o l e u m i n d u s t r y on o f f s h o r e s tr uctures, for the p l u g g i n g of wells, a n d to form a b a r r i e r b e t w e e n the c a s i n g a nd f o r m a t i o n r o c k . SRB can

g e n e r a t e h y d r o g e n s u l f id e in soils or w a t e r w h i c h c a n m i g r a t e to the a e ro b i c zone w h e r e b a c t e r i a of the g e nus T h i o b a c i l l i o x i d i z e the h y d r o g e n s u l f i d e to s ul f ur i c acid. The s u lf u ri c a c i d then a t t a c k s the conc re te . The h y d r o g e n s u lf id e does not have to be b i o l o g i c a l l y p r o d u c e d to c au s e this d a m a g e , it c an be c h e m i c a l l y p r o d u c e d or n a t u r a l l y o c c u r r i n g .

4. C ASE S T U D Y

A n oil f i el d was e x p e r i e n c i n g u n u s u a l l y h i g h rates of c o r r o s i o n on u n c o a t e d 9% C h r o m e - 1% M o l y b d e n u m (9Cr - IMo)

i nj e c t i o n w e ll tubing. S o m e of the 9Cr - IMo t u bi n g was

s e v e r e l y c o r r o d e d a ft e r 9 to 16 m o n t h s of s e r v i c e . The

e x t e r i o r of the t ub in g c o n t a i n e d l arge pits (1 to 2" by 2 to 6 ” ) c o u p l e d w i th thick s cale deposits. It was i n i t i a l l y b e l i e v e d that the c o r r o s i o n p r o b l e m s were a r e su l t of:

1) m e t a l l u r g i c a l i n c o m p a t i b i l i t y b e t w e e n the 9Cr - IMo a n d the w a t e r in the system;

2) a c t i v e SRB g e n e r a t i n g Hg S u nd e r the c o r r o s i o n d e p o s i t s ;

3) SRB a c t i v i t y o c c u r r i n g in the s t a g n an t a reas of the a n n u l u s .

A m a j o r c h e m i c a l c o m p a n y was c o n t r a c t e d to i d e n t i f y the p l a n k t o n i c a nd s es s i le b a c t e r i a in the i n j e c t io n w at e r and

u n d er the deposits. A n a l y s i s of the f ield w a t e r was

p e r f o r m e d in the f i e l d a n d then later in the l a b o r a t o r y .

Five g a l l o n s of i n j e c t i o n w a t e r was o b t a i n e d a nd sent to the c h e m i c a l company. It was u s e d to m a ke c u l t u re m e d i u m s and d i l u t i o n tubes for p l a n k t o n i c a n d s e ss il e b a c t e r i a counts. The c u l t u r e m e d i u m s w e re m ad e to c u l t i v a t e a e r o b i c b acteria,

a n a e r o b i c b ac te ri a, a n d SRB. The a e r o b i c m e d i u m was m a de up of a p h e n o l red d e x t r o s e b r o t h . T he a n a e r o b i c m e d i u m was m a d e up of a t h i o g l y c o l l a t e b r o t h . The SRB m e d i u m was m ade up of a P o s t g a t e M e d i u m B w i t h acetate.

P l a n k t o n i c b a c t e r i a l e vels in the w a t e r i n j e c t i o n s y st em w e re c o n d u c t e d w i t h the c u lt u r e mediums. A total b a c t e r i a c o u n t was p e r f o r m e d u si ng an ATP P ho to m et e r . The sessile b a c t e r i a l e ve ls w er e d e t e r m i n e d b y s c r a p p i n g c o r r o s i o n

d e p o s i t s off of m et al c o u p o n s that w e re i n s t a l l e d one m o nt h p r i o r .

S p e c i al s e s s il e b a c t e r i a c o u po n h o l d e r s were i n s t a l l e d in s e l e c t e d i n j e c t i o n w e ll s in the system. E a c h c o u p o n h o ld e r c o n t a i n s six r o u n d c o u p o n studs of 0.5 c m 2 s u rf a ce a r e a . The c o u p o n studs w e r e o r i g i n a l l y i n t en d ed to be m a de out of 9Cr - IMo b u t t h ere was not e n ou g h time to m a n u f a c t u r e the special

studs. The studs that w er e u s e d w er e m a n u f a c t u r e d out of

m i l d steel.

D a t a was c o l l e c t e d from i n j e c t i o n w e l l s a n d at the w a t e r i n j e c t i o n plants. The f o l l o w i n g tests w e r e p e r f o r m e d on site :

1) pH level

2) H y d r o g e n s u l f id e c o n c e n t r a t i o n 3) S o lu b le iron c o n c e n t r a t i o n 4) O x y g e n c o n c e n t r a t i o n

5) B i c a r b o n a t e c o n c e n t r a t i o n 6) T e m p e r a t u r e

7) SRB c ou nt

8) A e r o b i c b a c t e r i a c ou n t 9) A n a e r o b i c b a c t e r i a c o u nt

10) Total b a c t e r i a c o u n t using an A T P Phot om et er .

R e s u l t s of the tests f r o m the w a t e r i n j e c t i o n s ys te m f o l l o w in T ab l e 1.

The 9Cr - IMo t ub i ng was p u l l e d from one of the i n j e ct i o n

wells. The e x t e r i o r of the t ub in g c o n t a i n e d scale buildup,

p i t s , a nd tubercles. The t u b e r c l e s (a p p r o x i m a t e l y 1 c m in d i a m e t e r ) w e r e b r o k e n . The c o r r o s i o n p r o d u c t s and f luid c o n t a i n e d w i t h i n the t u b e r c l e w ere r e mo v e d w i t h a syringe. S erial d i l u t i o n was p e r f o r m e d on these s a m pl es to d e t e r m i n e the n u m b e r of a e ro b i c b a cteria, a n ae r o b i c b a c t e r i a , and

s u l f a t e - r e d u c i n g b a c t e r i a . The pits w ere a p p r o x i m a t e l y 1 - 2 m m d ee p a n d h a d a s m oo th l a y e r e d a p p e a r a n c e . The e x p o s e d pit was a c l a s s i c a l e x a mp l e of p i t t i n g c a u s e d b y the p r e s e n c e of S R B . The o t h er c o r r o s i o n p i t s that w e re not SRB i n du c ed were s h ar p a n d jagged. A T P a n a l y s i s was a lso p e r f o r m e d to

d e t e r m i n e the total n u m b e r of b a c t e r i a p r e s e n t . R e s u l t s can be f ound in T a b l e 2.

TAB LE 1. RE SU LT 'S FR OM TH E WA TE R I N J E C T I O N S Y S T E M 1 U".i jD Lu W G O 1 3 jC Cl TJ 'c n G en 1 t o 0 m Cl O c G ro •TJ O X O S= 1 j= O O 6 O C LU 1 to U’l o Cl I— 1 6 i U"l I Cl 6 |Çn 1 o ’ Cl Cl CM G i n i Cl CO CM € O o ro cn i a> i r-- j3 LU U’l CD G m I G G Cl T3 d G C 1 U"i 3 3 Cl c X to Iri o "O T i O 0 G o c LU 1 ü> at LO U'l I— 1 G G 1 U'l 1 cn CD G Cn i e e rf m c Cl Cl O Cl CM g UO C'-J T .A. o 1 CO -Ü Lu U’l o O XI a : i _C 3 Cl "O

i m CTi O Cl CT' Ill I-Vi

to u -o c l LU 1 ÜÔ U'l ai - I G 1 -O U"i ! e Cl o Cl Cl "T z 0 i n i CL to r r o O d r f i 1 "ai z t~ Oi LU Œ o C a H— QC t e XI Œ 1—- h -Lu CC Z 11' _û U’I —1 1— LU 1.0 c o zo z CJ LU o a. U’l w Z 9 r CL LO • ri •i' o o LU Z jD UO TD i.n i z z H— Cl O LU LU Œ CL c CCi LO U'l 1 CD o z CC LO 3D LU • r-t O LU - LU Cl Ci s ÜD —i i cc z CD Cl w CJ LU O CC 1 o 0- Z —1 Ci çr CL ÛD i ]= cc >c LU a z cc LU CL a : i 1 Cl X o 1— LO o 1.0 Œ 'X LO

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F r o m the r e su lt s of the initial tests p e r f o r m e d on the w a t e r i n j e c t i o n system, the a s s u m p t i o n s m a d e p r io r to the tests w e r e c o r r e c t .

1) T he re are c o m p a t i b i l i t y p r o b l e m s w i t h the 9Cr - IMo t ub i ng a n d w a t e r in the s y s t e m . The l arge c o r r o s i o n d e p o s i t s on the e x t e r i o r of the tubi ng is i n di ca t iv e of the i n co m p a ti b il i t y .

2) T h e re is a v e r y large n u m b e r of s e ss i le SRB l o c a t e d u n d e r n e a t h the c o r r o s i o n deposits.

3) T h er e is a l arge n u m b e r of s e s si le SRB a t t a c h e d to the m et al c o u p on s in the s t a g n a n t areas.

The r e su l t s f ro m the A T P test i n d i c a t e d that the total n u m b e r of b a c t e r i a p r e s e n t was c o n s i d e r a b l y l o wer t han the ac t ua l n u m be r d e t e r m i n e d w i t h c u lt u r e mediums. The lower A T P P h o t o m e t e r r e su l t s w er e p r o b a b l y a c o n s e q u e n c e of the solids in the test m e d i u m c r e a t i n g i n t e r f e r e n c e .

5. M E T H O D S OF C O N T R O L A N D P R E V E N T I O N OF SRB

5.1 B I O C I D E S

B i o c i d e s are c h e m i c a l s u s e d to kill, c o n t r o l , a nd p r e v e n t the g r o w t h or a c t i v i t y of m i c r o o r g a n i s m s in i n d u s tr i al or p e t r o l e u m systems. B i o c i d e s are also r e f e r r e d to as

b a c te r i c id e s , m i c r o b i c i d e s (sic), and m i c r o b i o c i d e s . The p r i m a r y o b j e c t i v e s of a b i o c i d e is to kill m i c r o o r g a n i s m s a n d to k e e p c o r r o s i o n p r o d u c t s or solids from f or mi ng d eposits. This w i l l p r e v e n t s u i t a b l e e n v i r o n m e n t s for m i c r o b i a l growth. 5.1.1 I n h i b i t i o n of G r o w t h The c o r r o s i o n p r o b l e m s c a u s e d b y SRB are p o o r l y u n d e r s t o o d a n d t h e y are d i f f i c u l t to m o n i t o r , c o n t r o l , and treat. The a p p a r e n t a b s e n c e of SRB in a s y s t e m does not n e c e s s a r i l y m e a n that the s y s t e m is u n de r c o n t r o l . On the o ther hand, the p r e s e n c e of SRB in a s y s t e m does not

n e c e s s a r i l y m e a n that p r o b l e m s exist. T h e r e f o r e , it is d i f f i c u l t to i m pl e m e n t an e f f e c t i v e b i o c i d e p r o g r a m .

T h e re has b e e n a c o n s i d e r a b l e a m ou n t of r e s e a rc h and t es ting d o ne on the e f f e c t i v e n e s s of b i o c i d e s on S R B . T h er e