Bureau of Mines Report of Investigations/l979

Methane Content and Geology of the Hartshorne Coalbed in Haskell and Le Flore Counties, Okla.

By Anthony T. Iannacchione and Donald G. Puglio

UNITED STATES DEPARTMENT OF T H E INTERIOR

Report of Investigations 8407

Methane Content and Geology of the Hartshorne Coalbed in Haskell and Le Flore Counties, Okla.

By Anthony T. Iannacchione and Donald G. Puglio

UNITED STATES DEPARTMENT OF T H E INTERIOR Cecil D. Andrus, Secretary

BUREAU OF MINES Lindsay D. Norman, Acting Director

This publication has been cataloged as follows:

l a n n a c c h i o n c , Anthonj- 'I' Methane content and geology of the IIartshorne coalbed

in IIaskel l and L e F lore Counties , Okla. (Kcport of inves t iga t ions )

B i b l i o g r a p h y p. 1.4.

Supt. of 1)ocs . no: 1 28.23.

1. C.u.11-(;cology-Oklahoma-llaskell ( 1 0 . 2. Coal-(;eology- Oklahoma-lde Flor? (;o. 3 . ( :oal-Oklahoma-l laskel l (10.-\lethanc content . 4 . Coal-Oklahoma-Le F lore Co.-Methanc content . I. P u g l i o , I). G., joint author. 11. T i t l e . 111. S e r i e s l ln i t ed S t a t e s , Bureau of , \ l ines . Report o f inves t iga t ions .

TN23.U43 LTN805.05) 622l .08~ [662'.622g176677] 79-607051

CONTENTS Page

A b s t r a c t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I n t r o d u c t i o n 1

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S t r a t i g r a p h y 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S t r u c t u r e 8

C l e a t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methane c o n t e n t 9

Method of c a l c u l a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 R e s u l t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2

Summary and c o n c l u s i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Refe rences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

ILLUSTRATIONS

Loca t ion map of s t u d y a r e a showing topograph ic quadrang les . towns. and major r o a d s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Mined-out -a rea map and overburden map of t h e Har t shorne coa lbed . . . . Genera l i zed s t r a t i g r a p h i c column of exposed rocks i n t h e s t u d y a r e a I sopach map o f i n t e r v a l between Lower and Upper Har t shorne coa lbeds I sopach map of t h e undivided Har t shorne and of t h e Lower Har t shorne

coa lbeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I sopach map of t h e Upper Har t shorne coa lbed

Genera l i zed c r o s s s e c t i o n o f t h e Har tshorne Formation through H a s k e l l and Le F l o r e Count ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

S t r u c t u r e c o n t o u r s on t h e b a s e o f t h e Har t shorne coa lbed i n H a s k e l l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and Le F l o r e Count ies

Coal c l e a t o r i e n t a t i o n s of t h e Har t shorne coalbed i n L e F l o r e County Graph showing changes i n gas c o n t e n t of t h e Har t shorne coalbed w i t h

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . changes i n d e p t h Overburden above t h e Har t shorne coalbed . . . . . . . . . . . . . . . . . . . . . . . . . . . .

TABLES

1. Coal i n p l a c e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2 . Methane c o n t e n t v e r s u s overburden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3 . D i s t r i b u t i o n o f methane i n t h e Har t shorne coa lbed .................. 13

METHANE CONTENT AND GEOLOGY OF THE HARTSHORNE COALBED IN HASKELL AND L E FL-ORE COUNTIES, OKLA.

by

Anthony T. lannacchione and Donald G. Puglio2

ABSTRACT

The Bureau o f Mines deve loped d a t a on t h e methane c o n t e n t o f t h e H a r t s h o r n e c o a l b e d , H a s k e l l and Le F l o r e C o u n t i e s , O k l a . The methane c o n t e n t i s c a l c u l a t e d t o b e be tween 1.1 and 1 . 5 t r i l l i o n c u b i c f e e t , based on a n e s t i m a t e of t o t a l c o a l i n p l a c e o f 2 . 4 t o 3 . 2 b i l l i o n s h o r t t o n s . Methane i n c r e a s e s w i t h d e p t h , b u t t h e r a t e o f i n c r e a s e d e c r e a s e s w i t h g r e a t e r d e p t h s . D e g a s i f i c a t i o n i n advance o f mining i s recommended f o r a l l mines o p e r a t i n g a t d e p t h s g r e a t e r t h a n 500 f e e t t o r e d u c e h a z a r d s and methane e x p l o s i o n s , d e c r e a s e mine v e n t i l a t i o n c o s t s , and c o n s e r v e t h e n a t u r a l g a s t h a t would be o t h e r w i s e wasted .

INTRODUCTION

A s p a r t o f t h e Bureau of Mines methane c o n t r o l program, a s t u d y was con- d u c t e d t o d e t e r m i n e t h e geo logy and methane c o n t e n t o f t h e H a r t s h o r n e c o a l b e d i n a n a p p r o x i m a t e l y 1 , 5 0 0 - s q u a r e - m i l e a r e a i n Le F l o r e and H a s k e l l C o u n t i e s , Ok la . ( f i g . 1 ) . Underground mines o p e r a t i n g i n t h e H a r t s h o r n e c o a l b e d have had a l o n g h i s t o r y o f h i g h methane e m i s s i o n s . R e c e n t l y , two mines (Howe mine, Le F l o r e County, O k l a . , and Choctaw mine, H a s k e l l County , O k l a . ) c l o s e d down c o m p l e t e l y o r suspended mining owing t o a combina t ion o f h i g h methane emis- s i o n s and r o o f c o n t r o l p rob lems .

The purpose o f t h i s s t u d y i s t o e s t a b l i s h a s c i e n t i f i c b a s i s f o r p l a n n i n g t h e d e g a s i f i c a t i o n t h a t w i l l b e e s s e n t i a l f o r mining t h e c o a l s a f e l y . Approx i - m a t e l y 900 d a t a p o i n t s were used t o i n t e r p r e t t h e geo logy o f t h e H a r t s h o r n e c o a l b e d and t o e s t i m a t e t h e t o t a l c o a l i n p l a c e . Gas r e s o u r c e s e s t i m a t e d were c a l c u l a t e d u s i n g d i r e c t - m e t h o d a n a l y s e s (913 o f 16 c o a l c o r e s sampled between 1976 and 1978 from d e p t h s of 200 t o 1 ,500- fee t .

I G e o l o g i s t , ~ i t t s b u r g h Resea rch C e n t e r , Bureau o f Mines , P i t t s b u r g h , Pa . 2 ~ e o l o g i s t , P i t t s b u r g h Resea rch C e n t e r , Bureau o f Mines , P i t t s b u r g h , P a . (now

w i t h ~ i c h a e l Baker , J r . , I n c . , C o n s u l t i n g E n g i n e e r s and S u r v e y o r s , Beaver , P a . ) .

3 ~ n d e r l i n e d numbers i n p a r e n t h e s e s r e f e r t o items i n t h e l i s t o f r e f e r e n c e s a t t h e end o f t h i s r e p o r t .

FIGURE 1. - Location map of study area showing topographic quadrangles, towns, and major roads.

The Hartshorne coalbed i n t h e s tudy a r e a i s a h i g h - v o l a t i l e A bituminous t o s emian th rac i t e c o a l , which has been used f o r making coke i n Ind iana , I l l i n o i s , Texas, and Colorado. It i s gene ra l l y f r i a b l e , has c l o s e l y spaced c l e a t , and con ta in s many i n c l i n e d ( shear ) f r a c t u r e s t h a t d i p 45" t o 5 5 " . Ind iv idua l coalbed th ickness ranges from zero t o approximately 6 f e e t , averag- i n g 3 t o 5 f e e t . Overburden ranges from zero a t ou tc rop t o a lmost 7,000 f e e t under Cavanal Mountain i n Le F l o r e County.

I n t he p a s t , t h e c o a l was mined c l o s e t o t h e ou tc rop , a s shown on t h e mined-out-area map ( f i g . 2 ) . However, two newer ope ra t i ons err-~c~ee's Choctaw mine, 1,200 t o 1,400 f e e t deep; and Armco's Experimental Mine No. 1, a d r i f t mine t h a t w i l l even tua l ly be under 1,500 f e e t o f overburden) w i l l be mining down t o and a t t h e bottom of major s y n c l i n a l s t r u c t u r e s , where most of t h e l ea sed remaining coa l r e sou rces l i e .

I Lam SW SIW, Y E M o i , ni* 2 E v m Call a, Na 3,7,9,ll, md W mi ln 3 E m Gad Co.,Na2mi* 4 P m M r Ccal @.,No.lmd2n**r 5MNmGadCa 6 Reese Czal Ca 7Jdn Jma W a l m d 2 l n i m 8 Lona sm SlWl 9 K m u GadCo.

10 Haa Coal Ca, Bdrorh No. I ni* I f HsothuiiRn BromO Gad Co. 1 2 t h ~ Gad Ca,Wa10,1~12,14,E,&~4mdR~ I3 PmamD Cml Co., No. 2 min I 4 Ozut Cool ad n d ~ l n y I5 B k k hnmd Coal CO., No. 6 mi* 16BokaIm SmoWIS CodCo.,OldOli*rNaImi* I7Brrntalschas Gad Co. I 8 U n t m 19Ocbshe GadU,Na8,8M,9,10,U,~Vr,md16mia 20 Darn md Srindk No. l m h 21 ~ q t m G a d C o . , N o . l m d L 2 ~ 22 Supera Smd:eb% Cad Co., No. 29 mir

2 4 ~ i t l i m a cad C o . , b . l m 25 Reera Cwl Ca B W . J couoh W C o . 27Tems Cod Co, No. 2 d 4 h 28LceosqUa Gadmd yi*lp U , N o . l a d 2 ~ k ~ 29Lincdn Poar Ca, Wa4mim 3x0 Wby cadCa,No.3mi* 31 Muln Cod md Colrr Co., No. 7 4 9minr 32- Cml md Co* U., b . 8 m i * ~ ~ m m d r ~ ~ n n l ~ ~ a d m d ~ o l u c a , m . ~ a d ~ ~ 34DaaBomcR GadCa,b.4mi* 35hlwf f l ls Cmla,Wa4md5mLmr 36Hn mi* 37SIanQnl todlhlil! to. 38Heovaa S d m b s Gad Co. 39ChDmvGadmd Mbiq Co.

lCTNE D E E P m s 4 0 E m Gad Co., E-l No. I mi* 4 1 Kcrr -UMe Gad Co.. C h o * a mi*

FIGURE 2. - Mined-out-area m o p and overburden map of the Hartshorne coalbed.

S t r a t i g r a p h y

ACKNOWLEDGMENTS

The a u t h o r s thank S . A . Friedman of t h e Okla- homa Geologica 1 Survey f o r p r o v i d i n g c o r e l o g d a t a , mine maps, and review of t h e manuscr ip t . S p e c i a l coopera- t i o n was p rov ided by person- n e l from Kerr-McGee Coal Corp. and Amco I n c . Pre l im- i n a r y i n v e s t i g a t i o n s i n t h i s a r e a (10) by former Bureau of Mines employee Gary W . Murr ie were of c o n s i d e r a b l e h e l p i n comple t ing t h i s s t u d y .

GEOLOGY

An examinat i o n of t h e geology of t h e Har tshorne coa lbed was necessa ry because o f h igh v a r i a b i l i t y i n t h e d e g r e e s of d i p , a r e a s of complex f a u l t i n g , v a r i a t i o n i n t h i c k n e s s of overburden , and t h e r e g i o n a l s p l i t t i n g of t h e Har tshorne i n t o a n upper and lower coa lbed . A l l of t h e s e geo log ic f a c t o r s shou ld be cons idered i n t h e d e s i g n of d e g a s i f i c a t i o n programs i n t h i s a r e a .

The Har t shorne coa lbed i s c o n t a i n e d w i t h i n t h e t iar tshorne Formation ( f i g . 3 ) and i s s t r a t i g r a p h i c a l l y t h e lowest minable coalbed i n t h e Arkoma b a s i n . The coa lbed i s commonly o v e r l a i n a n d / o r u n d e r l a i n by t h e Har tshorne Sandstone (5, 8 , 11).

Atoka Formation

I n t h e e a s t e r n and s o u t h e r n p o r - t i o n s of t h e s t u d y a r e a , t h e Har t shorne coa lbed i s d i v i d e d i n t o two beds known a s t h e Upper and Lower Har ts ,horne (8) . The Har t shorne i s c o n s i d e r e d d i v i d e d wherever t h e p a r t i n g w i t h i n t h e c o a l -

a

E P! cn

6 .- c e - % cn C C

8

bed exceeds 1 f o o t i n t h i c k n e s s ( 4 ) . F i g u r e 4 shows t h e s e p a r a t i o n between

4 2 (3

8 ,

cn 0, .- 5 c .e g *-

% O f ! V ) $ Y

23

I

t h e s e two impor tan t c o a l u n i t s . A r e a l d i s t r i b u t i o n and coa lbed t h i c k n e s s o f t h e undivided H a r t s h o r n e , t h e Lower H a r t s h o r n e , and t h e Upper Har t shorne a r e shown i n f i g u r e s 5 and 6 .

Boggy Formation

I I

Savanna Formation

a

Mc Alester For mat ion

I I

Hartshorne Format ion

The coalbed s p l i t s a l o n g a n i r r e g - u l a r n o r t h e a s t -southwes t "hinge" l i n e , w i t h t h e i n t e r v a l between t h e two benches t h i c k e n i n g t o t h e southwest ( f i g . 4 ) . The maximum s e p a r a t i o n between t h e Lower and Upper Har t shorne coa lbeds i s approx imate ly 115 f e e t w i t h i n t h e Heavener 15-minute quadran- g l e , Le F l o r e County ( f i g s . 1 and 4 ) . Three c o r e h o l e s i n t h i s same a r e a i n d i c a t e t h e p resence o f a 1 - foo t - t h i c k , s h a l e y "wild" coa lbed approx imate ly 70 t o 90 f e e t above t h e Lower H a r t - shorne c o a l b e d .

The Har t shorne Formation i s com- p r i s e d o f complex l a y e r s of c o a l , s h a l e , s i l t s t o n e , and sands tone ( f i g . 7 ) . We b e l i e v e t h e s e sediments a r e p a r t o f a p rograd ing d e l t a i c com- p l e x t h a t c o n t a i n s a d i s t r i b u t a r y channe l sys tem, l e v e e and overbank d e p o s i t s , i n t e r d i s t r i b u t a r y bay s e d i - ments, c r e v a s s e s p l a y s , and p e a t swamps much l i k e t h e environments

FIGURE 3. - Generalized stratigraphic col- found today on the River lJrnn of exposed rocks i n the s t u d y area. D e l t a complex a s d e s c r i b e d by F i s k ( 3 ) . -

The Har t shorne Formation i s o v e r l a i n by t h e McCurtain Sha le Members o f t h e McAlester Formation and i s u n d e r l a i n by t h e s h a l e s , s i l t s t o n e , and sand- s t o n e s of t h e Atoka Formation. The Hartshorne Formation ranges i n t h i c k n e s s from a minimum o f 35 f e e t i n t h e L a f a y e t t e 7-112-minute quadrangle t o a p p r o x i - mately 300 f e e t i n p o r t i o n s of t h e n o r t h e r n Po teau E a s t and s o u t h e r n S p i r o 7-112-minute quadrang les ( f i g . 1 ) . The b a s e o f t h e Har t shorne Sandstone d e f i n e s t h e b a s e o f t h e fo rmat ion , and t h e t o p o f t h e undivided Har t shorne coa lbed o r o f t h e Upper Har t shorne coa lbed d e f i n e s t h e top o f t h e fo rmat ion .

SEOUOYAH COUNTY

MUSKOGEE COUNTY

A -N- ' A

LEGEND V ~ g o o I ~ t -3 rn4 fee t

-1 I to 2 feet 4 r o 5feet B m j 2 o3feet 5 t o 6 f e e t

Drill hole location _,-- Dividing line between Hartshorne (undivided) coalbed

and Upper and Lower Hartshorne coalbeds Note :

Solid pattern indicates isopach of Lower Hartshorne coalbed,and stripe pattern indicates isopach of Hartshorne

I 0 4 C- -8

I Scale, miles

~ - ,. . , .. . . ..

FIGURE 5. - lsopach map of the undivided Hartshorne and of the Lower Hartshorne coalbeds.

SEWN COUWTY

HASKEU

LEGEND ~ 0 l o l f C u 0 3 b 4 f e e t

=I b2feet 4 b S f w 1

~ 2 1 0 3 f e e l m5b6fert

Drill Me beoti _,.-Dividng l i betueen HarMKwn,

(udividsd) codbed and Upper adLamrHotshomecodkd,

FIGURE 6. - lsopach map of the Upper Hortshorne coalbed.

A A' McAlester Formation

Harts tame b r m a t i i

Atoka Formation

Formation McAWr I

Atoka Formation

LEGEND

coal

Shale

a Sandstone

HASKEU COUNTY

cross section th&h study area

FIGURE 7. - Generalized cross section of the Hartshorne Formation through Haskell and L e Flore Counties.

Localized thickening of the Hartshorne Formation is generally associated with the thickening of the Hartshorne Sandstone. In the Poteau East and south- ern Spiro 7-1/2-minute quadrangles, this sandstone comprises the entire Hart- shorne Formation, where ancient fluvial channels apparently eroded away the Hartshorne coalbed (figs. 5-6). Regional thickening of the Hartshorne Forma- tion is generally associated with the thickening of the interval between the Lower and Upper Hartshorne coalbeds (fig. 4).

Structure

The study area is located within the Arkoma basin. This large synclino- rium is comprised of synclines and faulted anticlines. The most prominent synclinal folds in the study area include the Cavanal, Panther Mountain, and Sans Bois (fig. 8), which form broad synclinal mountains. Dominant anticlinal axes folds are the Milton, Backbone, and Kinta (fig. 8). There are large- displacement faults paralleling the axes of these anticlines. The synclinal and anticlinal axes trend in easterly and northeasterly directions. Dips

FIGURE 8. - Structure contours on the base of the Hartshorne coalbed in Haskel l and L e Flore

Counties.

r a n g e from n e a r l y h o r i z o n t a l a t t h e bottom o f t h e Cowlington s y n c l i n e a t t h e s i t e o f t h e Choctaw mine, t o s t e e p l y d i p p i n g beds t h a t approach t h e v e r t i c a l i n p l a c e s a l o n g t h e M i l t o n a n t i c l i n e a s obse rved a t Grea t ~ a t i o n a l ' s s t r i p mine n e a r McCurtain ( f i g . 1 ) .

I n t e n s e f a u l t i n g o c c u r s a l o n g major a n t i c l i n a l s t r u c t u r e s and w i t h i n t h e complex W h i t e f i e l d u p l i f t (11) o f n o r t h - c e n t r a l H a s k e l l County ( f i g . 8 ) . The W h i t e f i e l d u p l i f t , a broad a n t i c l i n o r i u m , i n c l u d e s s e v e r a l s m a l l f o l d s and f a u l t s . The o l d e s t s t r a t a i n t h e s t u d y a r e a be long t o t h e Atoka Format ion and a r e exposed w i t h i n t h e W h i t e f i e l d u p l i f t and a l o n g t h e a x e s o f t h e M i l t o n and Backbone a n t i c l i n e s .

C l e a t

C l e a t d i r e c t i o n s were measured a t s t r i p min

LEENO 2 Anticline 1 M i b strip mirs x Syncbe 28okm NaK)stripmins 4Fadtwnhdiectmddp 3 outcrop -O'Outcrop lire d limtsbm F6nmth 4 Rock k&md No. I strip mine

1 Primary d i i o n 5 Howe deep mine 1 Secondary diection 6Roodart

FIGURE 9. - Coal c leat or ientat ions of the Hartshorne

s and s u r f a c e exposures o f c o a l ( f i g . 9 ) . C l e a t d a t a were t h e n ana lyzed u s i n g a method d e v i s e d by Diamond ( 2 ) . R e s u l t s of t h e s e a n a l y - ses show t h a t t h e d i r e c t i o n o f f a c e c l e a t r anges from N 32" W t o N 17" W , which i s p e r p e n d i c u l a r t o s t r u c - t u r a l t r e n d s i n t h e a r e a . The f r i a b i l i t y o f t h e H a r t - s h o r n e coa lbed i s due t o c l o s e s p a c i n g of c l e a t and t h e f r e q u e n t o c c u r r e n c e o f s h e a r f r a c t u r e s w i t h d i p s o f 45" t o 55" w i t h i n t h e c o a l - bed . D i r e c t i o n a l pe rmeab i l - i t y c h a r a c t e r i s t i c s o f coa lbeds a r e g e n e r a l l y dependent on t h e o r i e n t a t i o n o f t h e s e c l e a t f r a c t u r e s ( 7 ) . -

METHANE CONTENT

Methane i s a lways p r e s e n t i n c o a l . Wi th in t h e s t u d y a r e a , methane gas con- s t i t u t e s a s e r i o u s p o t e n t i a l s a f e t y haza rd f o r a l l f u t u r e deep mining. Methane con- t e n t o f coa lbeds i s a func- t i o n o f d e p t h and rank (6 , 1 2 ) . Methane e m i s s i o n s xn - c o a l mines a r e c o n t r o l l e d by p o r o s i t y , f r a c t u r e pe rmeab i l - i t y , and gas p r e s s u r e .

coalbed in L e F lo re County.

Method of C a l c u a l t i o n s

S i x t e e n d e s o r p t i o n samples from d i f f e r e n t c o a l c o r e s c o l l e c t e d w i t h i n t h e s t u d y a r e a were ana lyzed f o r methane c o n t e n t u s i n g t h e Bureau o f Mines d i r e c t - method t e c h n i q u e . T h i s i n f o r m a t i o n was t h e n used t o c o n s t r u c t t h e g raph shown i n f i g u r e 1 0 . Equa t ion 1 i s t h e l i n e a r l e a s t - s q u a r e s e q u a t i o n r e p r e s e n t i n g t h e changes i n gas c o n t e n t w i t h d e p t h f o r t h i s coa lbed i n t h e s t u d y a r e a .

A

Y = -27.88 + 6.25 ( I n X), (1)

where X = overburden ( f e e t )

and ? = expec ted methane c o n t e n t ( ~ r n ~ / ~ ) .

T h i s e q u a t i o n has a c o r r e l a t i o n c o e f f i c i e n t o f 0 .908 w i t h t h e d a t a . The a r e a between t h e dashed l i n e s shown i n f i g u r e 10 i n d i c a t e s t h e range o f expec ted g a s c o n t e n t , u s i n g t h e d i r e c t method, o f c o a l s c o l l e c t e d a t v a r i o u s d e p t h s a t t h e 95-pc t conf idence l e v e l .

h

Y.27.882 + 6.251 (log x )

R* = 0.908

22

20

FIGURE 10. - Graph showing changes in gas content of the Hartshorne coalbed wi th changes in depth. R~ = correlat ion coeff ic ient.

1 I I I I 1 1 I 1 I I I I 1 (

- I / & & - - / / -

/ /( - / I

- 18-

I /

- 16 -

0 - \

14- 0 - -

' 2 - - - W -

lo- - 8 - v, 8 - - a - u

6 - - -

4 - - -

2 - - -

J

0 200 400 600 800 F0 1,600 DEPTH, feet

/ To c a l c u l a t e t h e t o t a l volume of methane contained wi th in t he coalbed i n t h e s tudy a r e a , i t was necessary t o e s t ima te t h e amount of t o t a l coa l i n p l a c e w i th in t h e va r ious depth i n t e r v a l s i n d i c a t e d i n t a b l e 1. This was accom- lpl ished by over lay ing t h e overburden map ( f i g . 11) wi th t h e coa l isopach maps o f the Hartshorne coalbed ( f i g s . 6 -7) .

TABLE 1. - Coal i n p l ace

The d i f f e r e n t methane con ten t s f o r t h e va r ious depth i n t e r v a l s were c a l - c u l a t e d by plugging t h e median depth value f o r each overburden i n t e r v a l i n t o t h e X v a r i a b l e of equa t ion 1. The Y v a r i a b l e of t h i s equa t ion i s t h e gas con- t e n t of t h e coa l i n cubic cen t imeters of methane per gram of c o a l . The equiva- l e n t cubic f e e t o f methane pe r t on o f c o a l i s obta ined by mul t ip ly ing t h e Y v a l u e by 32. Minimum and maximum methane con ten t s were ob ta ined by mu l t i p ly - i n g t h e minimum and maximum tonnages of coa l t imes t h e methane con ten t f o r each of t h e va r ious overburden i n t e r v a l s (equa t ions 2 and 3 ) .

Overburden, f e e t

0 -500. . . . . . . . . . . . . .

500-1,000. . . . . . . . . .

1,000-1,500 . . . . . . . . 1,500-2,000. . ...... 2,000-3,000 ........

Tota l . . . . . . . . .

( Minimum methane con ten t ( f t 3 ) a t XX = [min coalbed th i cknes s of a x ]

I

x [acreage w i t h i n XX]

x [z ,aoo f t 3 / t o n ] x [YxJ . (2)

( Maximum methane conten t ( f t 3 ) a t XX = [max coalbed th ickness of Zx]

Percent of t o t a l coa l

19

29

27

15

10

100

Mi l l i on s h o r t tons

I

x [acreage wi th in XX]

x [1,800 f t 3 / t o n ] x [YX]. (3)

Hartshorne (undivided) Min 149 Max 221 Min 368 Max 487 Min 365 Max 475 Min 158 Max 204 Min 49 Max 61 Min 1,089 Max1,448

I n t he se equa t ions , Xx = overburden i n t e r v a l ( 0 t o 500 = X I , 500 t o 1 ,000 = X2, 1,000 t o 1,500 = X,, 1,500 t o 2,000 = X,, and 2,000 t o 3,000 = X,); Yx = aver - age methane conten t of Xx; and Z = coalbed th ickness i n f e e t ( 1 t o 2 f e e t = Z1,

1 2 t o 3 f e e t = Z 2 , 3 t o 4 f e e t = Z,, 4 t o 5 f e e t = Z, , and 5 t o 6 f e e t = 2,).

Upper Hartshorne Min 122 Max 178 Min 108 Max 165 Min 76 Max120 Min 37 Max 60 Min 48 Max 75 Min 391 Max598

Lower Hartshorne Min 174 Max. 238 Min 228 Max 290 Min 198 Max 252 Min 160 Max 198 Min 141 Max 176 Min 901 Max1,154

FIGURE 11. - Overburden above the Hartshorne coalbed.

Resul t s

The Hartshorne coalbed i n Haskel l and Le F lo re Counties i s es t imated t o con ta in 1.1 t o 1.5 t r i l l i o n cubic f e e t of methane. Table 2 l i s t s t h e gas p o t e n t i a l f o r t h e Hartshorne coalbed a t var ious overburden i n t e r v a l s w i t h i n t h e s tudy a rea . Methane d i s t r i b u t i o n wi th in each of t h e var ious overburden i n t e r v a l s ( t a b l e 3) i n d i c a t e s t h a t 58 p c t of t he t o t a l gas i n t h e coalbed occurs a t depths from 500 t o 1 ,500 f e e t . This i n t e r v a l a l s o conta ins approxi- mately 56 pc t of t h e t o t a l coa l i n p l ace ( t a b l e 1) and i s t h e expected depth range of most f u t u r e underground mining operat ions.

TABLE 2 . - Methane c o n t e n t v e r s u s overburden

Overburden, f e e t

0-500 . . . . . . . . . . .

500-1,000. . . . . . .

1,000-1,500 . . . . .

TABLE 3 . - D i s t r i b u t i o n of methane i n t h e Har t shorne coa lbed

Average 1 Est imated methane c o n t e n t ,

1 ,500-2 ,000 . . . . .

2,000-3,000. . . . .

13 .5

16.7

SUMMARY AND CONCLUSIONS

Methane c o n t e n t

1 8 . 8

21.0

Overburden, f e e t

0-500 . . . . . . . . . . . 500 -1,000. . . . . . .

. . . 1 ,000-1 ,500 . . 1 ,500 -2,000. . . . . 2,000-3,000. . . . .

Using d a t a ga thered from c o r e l o g s , mine maps, o u t c r o p s , and desorbed

cm3Ig

6 . 6

b i l l i o n c u b i c f e e t

432

534

c o a l c o r e samples , t h e gas r e s o u r c e s of t h e Har t shorne coa lbed i n H a s k e l l and Le F l o r e Count ies a r e c a l c u l a t e d t o be between 1 . 1 and 1 . 5 t r i l l i o n c u b i c f e e t .

~t~ /ton

211

Undivided Har t shorne

Min 32 ( Max 47

602

672

Methane d i s t r i b u t i o n , p c t

These d a t a were based on a n e s t i m a t e d t o t a l c o a l i n p l a c e of between 2 . 4 t o 3 . 2 b i l l i o n t o n s .

Min 47 Max 71

in 195 Min 40 IMax 253 1 Max 64

Undivided Har t shorne

6 31 38 1 8

6

The Har t shorne coa lbed has i n d i c a t e d d i p s r a n g i n g from h o r i z o n t a l t o v e r t i c a l and i s i n t e n s e l y f a u l t e d . Overburden ranges from z e r o a t t h e o u t - c r o p t o n e a r l y 7,000 f e e t . The coa lbed i s f r i a b l e w i t h p r i n c i p a l c l e a t o r i e n t a t i o n s developed p a r a l l e l and p e r p e n d i c u l a r t o r e g i o n a l s t r u c t u r a l t r e n d s , and i t a l s o c o n t a i n s a secondary s h e a r c l e a t sys tem. S t r a t i g r a p h i - c a l l y , t h e Har t shorne coa lbed s p l i t s i n t o a n upper and lower coalbed and ranges i n t h i c k n e s s from z e r o t o approximately 6 f e e t .

Upper Har t shorne

Min 26 Max 37

Min 99 Max 125 Min 106 Max 135 iMin 95

Max 123

2:

Methane c o n t e n t of t h e Har t shorne coalbed i n c r e a s e s w i t h d e p t h , b u t a t a d e c r e a s i n g l o g a r i t h m i c r a t e s o t h a t t h e maximum methane c o n t e n t w i l l p robably n o t exceed approximately 700 f t 3 / t o n a t 3,000 f e e t of overburden. D e g a s i f i c a - t i o n i n advance of mining i s recommended a s p a r t of a complete mine deve lop- ment p l a n f o r mines o p e r a t i n g a t dep ths g r e a t e r t h a n 500 f e e t t o reduce methane emiss ions i n mine workings . Also , t h e r e i s t h e added p o s s i b i l i t y of commercial gas p r o d u c t i o n from a d e g a s i f i c a t i o n system ( I ) , - conserv ing t h i s gas t h a t would o therwise be ven ted i n t o t h e a tmosphere .

Lower Har t shorne

Min 37 Max 50

Upper Har t shorne

15 28 24 14 19

Min 23 Max 36

Min 32 Max 5 1

Min 96 Max 119

Min 95 Max 119

Lower Har t shorne

9 23 24 22 22

T o t a l

9 27 31 19 4

REFERENCES

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