Shutter of the Artesanian Well Gushing Abandons in Monzoungoudo, Benin

GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 SHUTTER OF THE ARTESIAN WELL GUSHING ABANDONS IN MONZOUNGOUDO, BENIN Babilas HOUNTONDJI, F ançois de Paule CODO, Ma in Pépin AINA Uni e si y o Abomey-Cala i (UAC), Labo a o y o Wa e and En i onmen al Sciences and Techniques (LSTEE), Benin E-mail: babilass ock@yahoo. , depaule2003@yahoo. , ma nickson@yahoo. ABSTRACT The a esian well o Monzoungoudo has been abandoned since 2005. The non-mas e y o a esianism sp inging up a his wa e poin cons i u es a was e o he esou ce and has caused en i onmen al damage. I is a ques ion o an uncon olled low o he a esian well induced by he dep essu iza ion o he aqui e , esul ing in a po en ial loss o capaci y o neighbou ing wells and con inuous low o he well a he mou h o i s casing. In con ac o he eco e ed wa e wi h he su ounding soil, i may gene a e local looding, gullying, soil subsidence, he o ma ion o sinkholes and cause damage o he in as uc u es loca ed nea by. In addi ion, he wa e om he a esian aqui e on he su ace mig a es o he Monzoun Ri e , while anspo ing suspended pa icles o con aminan s encoun e ed on i s pa h. The ecei ing en i onmen o his wa e could hen be a ec ed by an inpu o u bid wa e o a ious con aminan s. All hese easons jus i y he alidi y o his s udy, which p oposes o add ess he echnique o plugging he abandoned a esian wells o Monzoungoudo in o de o s op o con ol he gushing wa e . Keywo ds: Abandons; A esian well; Cap i e aqui e ; Gushing; Monzoungoudo; Shu e . 1 INTRODUCTION In he locali y o Monzoungoudo in Benin, a la ge p opo ion o he d inking wa e consumed comes om wa e eco e ed om he pe meable unde g ound soils called "aqui e s" [1, 2]. To collec wa e in his locali y, a well is usually d illed in he unconsolida ed deposi s, a a ying dep hs. Depending on he hyd ogeological con ex o his locali y, he aqui e exploi ed by he ex ac ion o g oundwa e is in e cep ed a g ea dep h. The wells in his locali y show a gushing beha iou [3] (Fig.1), ha is o say ha he wa e le el in he well exceeds he g ound su ace. To ully unde s and wha an a esian gushing well is, one mus unde s and he hyd ogeological con ex in which he well is loca ed [4]. We a e alking o an aqui e , o a pe meable, po ous geological o ma ion, allowing g oundwa e o low and wi hd aw. I is a geological o ma ion made up o unconsolida ed g anula ma e ials (sand, g a el). The aqui e in ques ion is a cap i e aqui e . The cap i e aqui e has a low pe meabili y co e ing (clay) p o iding p o ec ion agains pe cola ion o su ace wa e o agains any sou ce o su ace con amina ion o g oundwa e . The base o his poo ly pe meable co e co esponds o he oo o he aqui e [5]. No e ha he wa e lowing wi hin a cap i e aqui e is usually p essu ized, i.e., he piezome ic su ace ( he le el eached by he wa e in a well open o he a mosphe e) is usually highe han he oo o he aqui e . Since he a esian well o Monzoungoudo canno be con olled (Fig. 2), his explains he abandonmen o he wo k and i s sealing. The objec i e sough in he con ex o his wo k o illing he a esian well gushing om Monzoungoudo is o eco e he hyd ogeological condi ions o he o iginal aqui e , ha is o say, he condi ions inhe en in he aqui e p io o he d illing o wells, so as o a oid he po en ial nuisances o he gushing. 108 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 Figu e 1. A esian well [3] Figu e 2. Cons an low o wa e om he abandoned well in Monzoungoudo [2] 2 MATERIALS AND METHOD 2.1 Sealing p ocedu e In he con ex o his wo k, he gushing o wa e is obse ed a ound he pe ime e o he well, be ween he casing and he su ounding soil. Acco ding o he decision-making p ocess leading o he plugging o a spou ing well [6] (Fig. 3) he pe ime e o he well should be sealed p io o he plugging wo k. To do his, se e al app oaches can be conside ed. These me hods consis , in pa icula , o he exca a ion o eaming o he ou side o he well, ollowed by he illing o his exca a ion wi h a low pe meabili y ma e ial (ben oni e in g anules, cemen -ben oni e g ou , e c.). Depending on he con ex , i may be jus i ied o a oid sealing wo k on he ou side o he casing and o di ec ly injec dense g ou (sealing agen ) inside he well. Fo example, i he composi ion o he su ounding soils is in pa e y loose, i i essen ially shows he p esence o la ge-diame e agg ega es o i he low gushing ou side he casing is impo an , he ecommended sealing wo ks may wo sen he si ua ion. P io o injec ion wo k, he hyd os a ic p essu e o be alle ia ed mus be assessed. To do his, he heigh o he wa e column be ween he aqui e oo (L) and he piezome ic le el (H) mus be known (Fig. 4). The o al leng h o his wa e column will p o ide he hyd os a ic p essu e o comba when selec ing he g ou . This o al leng h can be achie ed in a numbe o ways, bu he mos common me hods equi e he ins alla ion o back-up casing o he ins alla ion o a p essu e gauge a he wellhead. 109 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 Figu e 3. Decision-making p ocess leading o he plugging o a spou ing well 2.1.1 P epa a ion Since he spou con ol de ice ins alled a he head o he a esian gushing well a Monzoungoudo is damaged (Fig. 5), be o e emo ing i , i is necessa y o ensu e ha you ha e he necessa y equipmen o con ain he low om he well and he po en ial upwelling o he well sealing ma e ial. Figu e 4. Layou o a gushing well o measu ing he piezome ic su ace 110 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 Figu e 5. Damaged wellhead equipmen [𝟐] 2.1.2 Piezome ic le el and p essu e a g ound le el Fi s , he piezome ic le el o he well mus be de e mined (Fig. 4). The piezome ic le el ep esen s he heigh abo e he g ound su ace a which he wa e le el would be s abilized (in equilib ium wi h a mosphe ic p essu e). To de e mine his le el, i su ices o measu e he heigh o he s abilized wa e le el in ela ion o he g ound su ace (H). To ob ain he alue o he piezome ic le el, he ecommended me hods consis o : • Ex ending he casing un il he wa e le el s abilizes in he casing; • O equipping he well head wi h a p essu e gauge. This second op ion measu es he hyd os a ic p essu e a he end o he casing while he low is blocked. 2.1.2.1 Calcula ion me hod by adding ex a casing Ex ension o he casing can be achie ed by adding sec ions o s eel pipe un il he head o he casing exceeds he piezome ic le el. Howe e , conside ing he sp inging na u e o he well, i may p o e o be simple o equip he well wi h a pneuma ic shu e wi h bypass pipe as shown in Figu e 6, o wi h a mechanical shu e wi h by-pass (Fig. 7) and o p o ide hem wi h an ex a casing as an ex ension o he exis ing casing. The leng h o his ex a casing mus exceed he le el o he piezome ic su ace (Fig. 4). No e ha he diame e o he ex a casing has no impac on he measu emen o he piezome ic le el since he hyd os a ic p essu e (p) which causes he wa e o ise in he casing is he p oduc o he densi y o he liquid (ρliquid), he g a i a ional o ce (g) and he heigh o he wa e column abo e he measu ing poin (h) [4]. 𝑝 = 𝜌𝑙𝑖𝑞𝑢𝑖𝑑 × 𝑔 × ℎ (1) whe e: P is p essu e [ba s], g is G a i y accele a ion g [m/s2] o [N/kg], and h is wa e column [m]. Once he piezome ic su ace has s abilized in he back-up casing (s opping he low), he heigh (H) be ween he piezome ic su ace and he g ound le el can be measu ed (Fig. 4). This column o wa e abo e g ound le el is commonly called an "a esian wa e head". The a esian wa e head can hen be con e ed o equi alen p essu e o ob ain he wa e p essu e ha would be measu ed a g ound le el. The con e sion can be done as ollows [7]: 111 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 1 m wa e = 1.42 psi (9.8 kPa), o (2) 1 pi wa e = 0.433 psi (2.99 kPa) (3) Figu es 8 and 9 espec i ely con e he heigh o a wa e column (in me e s o ee ) in o a p essu e alue o he in e na ional sys em o he impe ial sys em. 2.1.2.2 Measu emen me hod using a manome e The manome e measu emen me hod consis s o i ing a manome e o he well head and eading he p essu e measu emen di ec ly he e. The e a e se e al op ions o a anging a wellhead so ha a p essu e gauge can be ins alled. Figu e 10 shows one ype o de ice o plugging he well while measu ing he p essu e a he end o he casing. The p essu e ead on he manome e (Pm) ep esen s he p essu e ha would be ead a he base o he wa e column be ween he piezome ic le el and he manome e (Fig. 11). To ob ain he alue o he p essu e a g ound le el, i is impo an o: • measu e he heigh o he manome e (Hm) om he g ound; • con e his heigh (Hm) in o p essu e by Fo mulas 2 o 3; • and add his alue o he p essu e measu emen ead on he manome e (Pm) o ob ain he o al p essu e a g ound le el. Figu e 6. Pneuma ic shu e wi h bypass ha can be i ed on a cen al casing o measu ing he piezome ic su ace Figu e 7. Mechanical shu e wi h bypass ha can be i ed on a cen al casing o measu ing he piezome ic su ace 112 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 Figu e 8. P essu e equi alence cha as a unc ion o hickness o he wa e column Figu e 9. P essu e equi alence cha as a unc ion o hickness o he wa e column 113 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 I necessa y, his alue can be con e ed back o an a esian wa e head using Fo mulas 2 o 3 (see abo e), so as o ob ain he heigh o he piezome ic su ace ela i e o he g ound. This in o ma ion will be equi ed in he p ocess o selec ing he g ou o be injec ed in o he well. Figu e 10. Well head i ed wi h a shu e i ed wi h a p essu e gauge Figu e 11. Calcula ion o he piezome ic le el using a manome e 114 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 2.1.3 Hyd os a ic p essu e a he aqui e oo To ob ain he hyd os a ic p essu e a he oo o he aqui e , ha is o say he hyd os a ic p essu e o be comba ed, he dep h (L) co esponding o he di e ence be ween he oo o he aqui e and he su ace o he g ound mus be added (Fig. 11), a he dis ance be ween he g ound su ace and he piezome ic le el (H). Subsequen ly, his sum (H + L) can be con e ed in o p essu e by Fo mulas 2 o 3. The dep h (L) is measu ed du ing d illing and he in o ma ion is usually a ailable in he d illing epo o any wa e wi hd awal ins alla ion. 2.1.4 Selec ion o g ou To selec he ype o g ou ha will be pou ed in o he well in o de o comba he hyd os a ic p essu e and pe manen ly seal he well, he hyd os a ic p essu e alue ob ained mus be dis ibu ed o e he dep h (L). Thus, we ob ain a p essu e pe uni o leng h wi h which i is possible o combine di e en ypes o g ou . Table 1 gi es a non-exhaus i e lis o p oduc s ecommended in he li e a u e. Table 1. Hyd os a ic p essu e o di e en ypes o g ou [𝟖] G ou Densi y P essu e pe uni leng h (kg/L) (lbs/gal) (kPa/m) (psi/pi) Thixo opic cemen (4 gal wa e /sack*) 1.98 16.5 19.45 0.86 Pu e cemen (5.2 gal wa e / sack) 1.87 15.6 18.32 0.81 Pu e cemen (6.0 gal wa e / sack) 1.80 15.0 17.64 0.78 Ben oni e g ou (30% solids) 1.25 10.4 12.22 0.54 Ben oni e g ou (20% solids) 1.14 9.5 11.08 0.49 G anula ben oni e/polyme slu y (15% solids) 1.10 9.2 10.86 0.48 Ben oni e d illing luid ( iscosi y 38 sec) 1.08 9.0 10.63 0.47 Wa e 1.00 8.3 9.73 0.43 * wi h cemen ic ion educe / luid loss addi i e 2.2 The da a necessa y o he plugging o he a esian well o Monzoungoudo 2.2.1 Geome y and hyd odynamics o he a esian well o Monzoungoudo The da a conce ning he geome y and hyd odynamics o he bo ehole a e g ouped oge he in Table 2 and mainly conce n he echnical da a o he hyd aulic bo ehole ca ied ou in he illage o Monzoungoudo and which a e p o ided by he Gene al Di ec o a e o Wa e o Benin (DGEau). 2.2.2 Li hological sec ion o he a esian well o Monzoungoudo The a esian well gushing om Monzoungoudo c osses all he geological o ma ions in he s udy a ea. I is a o a y d illing, which p oduced cu ings [9]. The in e p e a ion o he cu ings made i possible o ecognize he geology o Mouzoungoudo and o ca y ou he log and he li ho-s a ig aphic sec ion. The li hological sec ion e eals a su ace sedimen a y le el be ween 0 and 1m hick, o med o opsoil. Then, be ween 1 and 3 m he e is a o ma ion o la e i ic clay. Be ween 3 and 15 m yellow clay sp eads ou . Be ween 15 and 57 m he e is plas ic clay. Be ween 57 and 75 m we ind shell limes one. 115 GeoScience Enginee ing Vol. 67 (2021), No. 3 h p://gse. sb.cz pp. 107–118, ISSN 1802-5420 DOI 10.35180/gse-2021-0057 Table 2. Geome ic cha ac e is ics and hyd odynamic pa ame e s o he a esian spou ing well o Monzoungoudo [1] Be ween 75 and 135 m we ind clayey limes one. Be ween 135 and 184 m we ind mo e o less calca eous py i ic clay. Be ween 184 and 201 m we ind an al e na ion o clay and limes one. Be ween 201 and 214 m we ind sandy clay. Be ween 214 and 244.18 m we ind ine and medium-g ained whi e qua z sand. Figu e 12 shows he c oss sec ion o he Monzoungoudo well. 3 RESULTS AND DISCUSSION In his pa , we will p esen he esul s ob ained o he choice o g ou as well as o i s placemen in he well. 3.1 Resul s: Choice o g ou The a esian well spou ing Monzoungoudo a i s piezome ic su ace (H) which is 3 me e s om he g ound su ace in e cep ed he oo o he aqui e a a dep h o 184 me e s (L) om he g ound. The heigh o he wa e a he op o he aqui e (H+L) is he e o e 187 me e s, which is equi alen o a calcula ed p essu e o 1832.6 kPa (using Fo mula 1). Then, o know he p essu e pe uni o leng h o be used in he selec ion o he g ou , he hyd os a ic p essu e calcula ed a he op o he aqui e (1832.6 kPa) mus be di ided by he leng h o he wa e column sepa a ing i om he g ound su ace (L=184 m). Thus, a alue o 9.96 kPa/m is ob ained. The nex s ep is o selec a g ou whose densi y will coun e an equi alen o g ea e hyd os a ic p essu e, as shown in Table 1. He e, a "ben oni e d illing luid ( iscosi y 38 sec)" g ou would be accep able. 3.2 Discussion: Placing he g ou in he well 3.2.1 Filling o he sec ion o he well open o he aqui e The po ion o he casing open o he aqui e mus be illed wi h clean sand. Howe e , be o e s a ing any illing, i is impe a i e o con i m he dep h o he well by an in-si u measu emen . This measu emen will con i m he posi ion o he bo om o he well and especially he absence o objec s o esidues obs uc ing he well. In he e en ha he dep h measu ed on he si e is lowe han he da a collec ed be o e he wo k ( o al dep h a ailable in he d illing epo ), i is ecommended o inspec he well using a came a, so as o de e mine he sou ce o he obs uc ion, and o ule on he possibili y ha his obs uc ion does no in e e e wi h he wo k o plugging he well, in pa icula wi h he placemen o he g ou . I is only a e he illing o he open sec ion o he aqui e is comple e ha he sealing o he well can begin. Rega dless o he ype o aqui e used, illing mus be ca ied ou using an ine ma e ial (silica sand, clean g a el, e c.) so as o ill, a a minimum, he en i e sec ion o he open well o he op o he aqui e and minimize he loss o g ou in he aqui e (Figs. 13A and 13B). Geome ic cha ac e is ics and hyd odynamic pa ame e s om he a esian well o Monzoungoudo Se ings Values Well dep h H (m) 244.18 Well diame e D (m) 0.126 Flow Q (cm3 /s) 2000 G a i y accele a ion g (m/s2 o N/kg) 9.81 Wellhead p essu e p2 (ba s) 4.16 Absolu e pipe oughness ε (mm) 0.12