Adapting oil and gas drilling techniques for the mining industry with dewatering well placement technology

Transcription

1 Adapting oil and ga drilling technique for the mining indutry with dewatering well placement technology by A. Rowland*, M. Beter, M. Boland, C. Cintolei, and J. Dowling** Synopi Although increaing R&D pent to develop original technologie will benefit the mining indutry, adaptation of appropriate exiting technologie from other indutrie can be a more cot-effective alternative. Schlumberger Water Service, now WSP Paron Brinckerhoff, ha undertaken a 6-year programme aeing the adaptation of oil and ga (O&G) drilling and geophyical characterization technique to a range of mining application, including dewatering. Conventional dewatering ytem for open pit mine generally ue vertical borehole that target hydraulically productive zone within an orebody. The drilling and completion of vertical dewatering borehole can be complicated by mine planning contraint, where optimum hydrogeological target are not acceible from the available drilling location. A thee borehole are often located within the operating open pit, they can interfere with the mining operation and the ability to carry out ignificant dewatering ahead of mining i limited. Dewatering Well Placement Technology (DWPt) i WSP Paron Brinckerhoff next-generation mine dewatering olution aimed at addreing the limitation of conventional dewatering ytem through placement of permanent, high-performance dewatering well in optimum orientation beneath an open pit uing largediameter directional drilling technology commonly ued in O&G. Ideally, well collar are located outide of the mine operating area, reulting in improved compatibility between the dewatering ytem and mine plan. Recently drilled and contructed pilot directional dewatering well in hard rock mining environment in the USA and Mexico have demontrated that DWPt offer ignificant benefit for groundwater inflow control and value to mining operation compared to conventional open pit mining dewatering practice. Keyword open pit mine, dewatering, well placement, directional drilling. Introduction The management of groundwater inevitably become an integral part of open pit operation a they eventually encounter groundwater. Depending on the condition, thi management may take the form of proactive dewatering through the ue of borehole. In uch ituation, a robut and effective dewatering ytem can be vital for maintaining lope tability and afety, and enabling the minimization of tripping ratio. Furthermore, effective dewatering remove groundwater from the operating area in the bae of a pit and help to reduce wear- and tear-related cot on mining equipment, along with reduced haulage cot owing to the reduced haulage of wet ore and wate (Dowling and Rhy-Evan, 2015). The impact on the mining operation from poor dewatering often include: Wet drilling and blating, requiring more expenive blating agent and reduced fragmentation efficiency Wet working benche, which increae equipment wear and introduce additional afety rik factor Inundation of the pit floor and low mine advancement Reduced geomechanical performance of pit lope that, in ome cae, lead to the deign of more conervative lope angle reulting in higher trip ratio and deferral or lo of ore (Figure 1). Although condition vary widely, where wall tability and reducing groundwater inflow are the main dewatering objective, conventional dewatering i normally implemented with a combination of: (1) in-pit vertical pumping well to remove groundwater from the formation and lower groundwater level within the ultimate pit hell, (2) pit perimeter well to intercept and remove groundwater moving toward the mine, and (3) a erie of ump and urface pump to remove tanding and near urface groundwater (Dowling and Rhy-Evan, 2015) (Figure 2). Thi tend to be effective for ore depoit in moderate to high permeability etting where productive zone are preent and within the reach of conventional drilling technique. Adapting innovation The petroleum indutry ha faced many of the ame challenge a thoe currently facing the mining indutry, epecially in term of declining grade and a precipitou decreae in large, eaily acceible dicoverie (McCartney and Anderon, 2015). However, in order to addre thi, the O&G indutry ha maintained ignificant invetment in reearch and development (R&D) (McCartney and * Piteau Aociate, South Africa. Kumba Iron Ore, South Africa. WSP Paron Brinckerhoff, United Kingdom. Anglo American, Chile. ** Piteau Aociate, USA. The Southern African Intitute of Mining and Metallurgy, ISSN Thi paper wa firt preented at the New technology and innovation in the Mineral Indutry Colloquium, 9 10 June 2016, Emperor Palace, Johanneburg, South Africa. The Journal of the Southern African Intitute of Mining and Metallurgy VOLUME 117 MARCH

2 Adapting oil and ga drilling technique for the mining indutry Figure 1 Many large open pit operation are eventually impacted by the inflow of groundwater, requiring proactive dewatering ytem Figure 2 A conceptual layout of a conventional dewatering ytem in a hard rock, fractured environment. Some or all of the variou apect illutrated may be included in any given ytem, and often a combination i deployed baed on local requirement (Dowling and Rhy-Evan, 2015) Anderon, 2015). R&D pend a a percentage of revenue average around 0.5% for the major oil companie, and i higher than 2% for the main ervice companie (McCartney and Anderon, 2015). In contrat, R&D pend in the mining indutry ha previouly been pegged in the media at a little a one-tenth of that in the O&G indutry. Directional drilling a a whole i conidered a mature technology with widepread acceptance and commonplace ue in the O&G, utilitie, and infratructure indutrie. However, directional well placement in hard rock mining ha a very limited track record and wa previouly unteted for dewatering application in an open pit mine. The geological and geomechanical environment, ize and cale of equipment, flow and production pumping regime, and the aociated well deign requirement are ignificantly different, requiring ubtantial adaptation and modification. However, WSP Paron Brinckerhoff and Freeport-McMoRan recognized that the principal benefit of directionally drilled dewatering well are highly applicable to open pit mine dewatering (Dowling and Rhy-Evan, 2015). Crucially, the ue of directional drilling enable: Enhancement of hydraulic contact between multiple fracture zone and the production well or well Acce to permeable water-bearing zone unreachable with vertical drilling Poitioning of the well-head permanently outide of the planned mine operating area. The combined impact of the benefit lited above ha been hown to reult in a tep-change improvement in dewatering well efficiency, performance, and overall effectivene of the mine dewatering programme, reulting in ignificant cot and rik reduction. Improvement that have been demontrated by pilot programme in the USA and Mexico are: Increaed well yield due to the deign trajectory, interception of ub-vertical tructure, and enhanced hydraulic contact. Improved well runtime with the well-head located outide of operating area, thereby avoiding interference between dewatering infratructure and mine operation High well yield and improved runtime leading to a tep-change increae in long-term volume of groundwater produced from the dewatering programme Reduced number of well-head intallation with aociated burden of procurement, implementation, and in-pit operation interaction. Recognizing the limitation of conventional dewatering practice and the potential value of improved dewatering, WSP Paron Brinckerhoff and Freeport-McMoRan have collaborated to develop, tet, and implement a new generation of high-performance mine dewatering well ytem, combining mine hydrogeology and dewatering expertie with croover technology of O&G directional well placement (Dowling and Rhy-Evan, 2015) (Figure 3). Subequently, the ucce of variou pilot programme at Morenci with Freeport McMoRan led Kumba Iron Ore (KIO) to approach WSP Paron Brinckerhoff to conduct a technical feaibility tudy (TFS) for the evaluation of directional well placement to improve dewatering effectivene at their Sihen operation in South Africa. Adaptation of exiting technology require a deep undertanding of the goal of the adaptation, a well a the technology to be adapted. For example, the directional placement of a well to a pre-planned trajectory involve complex interactive conideration of multiple factor, including the ore depoit geology, geological tructure and geomechanical environment, the range of performance for directional tool, downhole urveying, and the ability to control and teer the well to the target (Dowling and Rhy- Evan, 2015). The trade-off between alternative option, rik factor, the final dewatering goal, and overall value to the mine operation are integral to the matrix of planning, deign, and implementation deciion. By adapting thee technique from the O&G indutry, WSP Paron Brinckerhoff and Freeport-McMoRan developed a mine dewatering project integration matrix, which wa ubequently implemented at the Freeport-McMoRan Morenci copper mine in Arizona, with the previouly mentioned TFS having been done for KIO Sihen operation. Proof of concept To date, two directionally placed dewatering well have been uccefully implemented at Morenci a part of the Garfield open pit mine dewatering programme. An initial well wa contructed on a proof-of-concept bai and commiioned in early April The well ite wa located on the wet wall of the open pit, outide of planned mining limit. The borehole wa teered underneath the centre of the planned pit on a pre-planned directional trajectory. Attaining a meaured depth of approximately 700 m, the well intercepted hydrogeological target aociated with major northeat-trending geological tructure and hydrogeological compartment. After completion, the well wa equipped with an oilfield-tyle high-lift, lim-hole electrical ubmerible pump ytem deigned to minimize well drilling and contruction hole diameter while permitting high production pumping rate for variable head preure condition (Figure 4). The well initially produced between 150 m 3 /h and 160 m 3 /h, which 232 MARCH 2017 VOLUME 117 The Journal of the Southern African Intitute of Mining and Metallurgy

3 Adapting oil and ga drilling technique for the mining indutry Figure 3 3D viualization of directional well placement trajectorie beneath the Garfield pit at the FreePort McMoRan Morenci Copper Mine, USA with January 2014 phreatic urface hown. The trajectory on the left (Well C) i the proof-of-concept well completed in April 2013, while the trajectory on the right (Mammoth Well) wa completed in January The cro-ection run from NNW to SSE (Dowling and Rhy-Evan, 2015) Figure 4 The collar of the firt directionally placed well at Morenci, permanently plumbed and operating outide the footprint of the Garfield Pit wa at the high end of the planned production, and i five to ten time greater than the previouly intalled conventional, vertical in-pit well. The well wa immediately commiioned into the active dewatering programme and during the firt year operated at 96% availability. Due to the combination of high production rate and high availability, it effectively produced up to two order of magnitude more groundwater than any of the pre-exiting in-pit vertical well and exceeded the combined groundwater production from the ret of the dewatering ytem, compried of ix vertical production well (Dowling and Rhy-Evan, 2015). Following the ucce of the firt well at Morenci and another ucceful well in Mexico, Freeport-McMoRan in partnerhip with WSP Paron Brinckerhoff commiioned an additional programme to contruct a econd well collared on the pit perimeter of the eat high wall. The target for the econd well wa a et of northeat-trending geological tructure and lower permeability compartment. With a more aggreive drill bit trajectory, deign modification were made during implementation to control rik while attaining the planned hydrogeological target. Reult from early tage of operation indicate the well to be a high-performance highvalue dewatering aet (Dowling and Rhy-Evan, 2015). Since initiation of the programme at Morenci, monitoring data ha hown a ditinct acceleration in the rate of the groundwater level reduction in the open pit. A number of piezometer located within and around the edge of the pit have hown a foot (60 90 m) decline in tatic water elevation (Dowling and Rhy-Evan, 2015). South African example The Sihen iron ore mine, Kumba Iron Ore flaghip operation, i currently the larget open pit iron ore mine in Africa, and one of the larget open pit mine in the world at almot 14 km in length (Kumba Iron Ore, 2016a). Total annual production at Sihen i approximately 35 Mt, with the mot recent value being kt in the firt quarter of 2016 (Kumba Iron Ore, 2016a). Additionally, up to 190 Mt of wate i removed annually from the open pit (Kumba Iron Ore, 2016b). Thi large-cale mining operation target a high-grade haematite orebody with grade of ignificantly more than 60% Fe and a ought-after lump content that command higher price on the global teel market (Atrup, Hammerbeck, and van den Berg, 1998). Sihen currently conit of four operating area that have been excavated to near or below the natural groundwater urface (Schlumberger Water Service, 2014). A a reult of the relatively hallow pre-mining groundwater level, dewatering activitie have been ongoing ince the beginning of mining operation, with a erie of vertical inpit and perimeter pumping well targeting productive geological formation within the mine area (Schlumberger Water Service, 2014). The groundwater regime and rate of mining require that dewatering pumping operate on a continuou bai. The abtraction rate of the overall mine dewatering ytem i approximately m 3 /h a of November 2015, from a total intalled capacity of approximately m 3 /h (Nel and White, 2015). Of the four operating pit, the GR35 pit i currently the deepet and i mining at 950 m above ea level (mal) from an original urface elevation of approximately mal. Leading up to early 2014, dewatering operation at GR35 pit faced ignificant challenge related to lithology, tructure, and operation, including: Typically 2 to 4 dry well are drilled before a highyielding water trike i interected at the required depth The drill rig at ite could not drill beyond water trike of 250 m³/h. Dewatering borehole were therefore contructed below target abtraction a a reult of their limited depth of penetration Due to highly fractured formation, exploration borehole are not reamed and production well are drilled a few metre away. During production drilling the rik of miing the water-bearing tructure encountered in the exploration well cloe by i ignificant due to the vertical orientation of tructure The preence within the pit of dewatering, exploration, and production borehole and the aociated The Journal of the Southern African Intitute of Mining and Metallurgy VOLUME 117 MARCH

4 Adapting oil and ga drilling technique for the mining indutry dewatering infratructure interfere with the active mining front and pit operation Interruption to dewatering operation from mining activitie reulted in ignificantly reduced utilization of the production borehole and a conequent quick rebound of the groundwater ytem due to high connectivity and hydraulic conductivity. In order to addre the challenge raied above, WSP Paron Brinckerhoff wa approached to conduct a prefeaibility tudy (PFS), and ubequently a full technical feaibility tudy (TFS) on the ue of directional well placement to replace or augment the exiting ytem in GR35 pit. The PFS concluded that directional well placed outide of the final pit hell, targeting chert (CH), banded iron formation (BIF), and ub-vertical tructure would intercept fracturing that would yield ignificant amount of groundwater and lead to effective dewatering of the CH, BIF, and haematite (HEM) rock ma. Baed on thi and conidering pumping ytem, drilling, and completion diameter, a yield of about 360 m 3 /h from a ingle directionally placed well wa determined to be an achievable abtraction target (Schlumberger Water Service, 2014). The collar location for the drill pad wa propoed by Sihen baed on the following criteria (Figure 5): Location outide the planned final GR35 pit hell Eay acce for the drill rig and ancillary ervice Outide area identified for contruction of future wate dump and therefore the pad could be ued for future directional well if required. During the TFS, 14 different directional well configuration were aeed, with the Plan 11 and Plan 14 trajectorie elected for detailed engineering deign and coting. Detailed engineering deign work wa carried out in order to define the feaibility of drilling the Plan 11 and Plan 14 well uing engineering input from a number of group within Schlumberger, including: Smith Bit: drill-bit election, rate of penetration (ROP) calculation Drilling and Meaurement: directional drilling plan, bottom hole aembly (BHA) and caing deign MI Swaco: drilling fluid plan for hole cleaning Drilling Tool and Remedial: turbine and mud-motor election Artificial Lift: ubmerible pump deign. Plan 11 provided a bae cae a it involved aement of drilling of all of the main lithologie preent at GR35, at a range of drilling diameter from 24 inche to 8½ inche, with a ignificant directional component, and completion of a long horizontal production zone within the well that would involve ignificant challenge and rik. Apart from aeing the technical feaibility of drilling the well, thi propoed trajectory alo allowed the cot implication of focuing the drilling on the dolomite unit, a oppoed to the hallower chert and BIF, to be aeed. On the other hand, Plan 14 (Figure 6) preented a impler well trajectory, which would require le directional drilling to achieve it target placement beneath the GR35 pit. Thi wa aeed to have a higher probability of ucce, epecially conidering that thi would be the world firt directionally placed dewatering well drilled in iron ore formation. Thi plan allowed the lower rik aociated with the directional drilling component to be aeed againt the cot and rik implication of drilling predominantly within the harder and more fractured chert and BIF unit. Eventually, the Plan 14 trajectory wa elected a the preferred option A cot-benefit analyi wa carried out to compare the current approach to dewatering at Sihen, baed on the ue of vertical in-pit well, and the cot aociated with developing a dewatering programme baed on DWPt. In addition, a number of intangible benefit aociated with the DWPt approach were identified, and although the cot benefit of thee were not aeed their value wa to be conidered in aeing the DWPt approach. Thee intangible benefit, which are applicable for other Sihen open pit and nearby mine (Kolomela), included: Improved in-pit afety environment due to reduced peronnel movement in the pit related to dewatering activitie, and reduced in-pit infratructure aociated with dewatering Simplified mine planning due to removal of the need to incorporate dewatering infratructure and maintenance in-pit Improved dewatering leading to: More efficient and cheaper blating. The reduced block ize reulting from more effective blating will in turn reduce the need for cruhing, grinding, and potentially drying of material and double-hauling Reduced mining equipment maintenance due to lower humidity and acid rock drainage (ARD) generation at the mining front Improved ore tranportation efficiency due to the reduction in the volume of water carried in ore Dewatering infratructure that will remain in ue after backfilling of the GR35 pit, thu upporting ongoing ite-wide dewatering upporting GR80 pit. Overall, multiple conventional vertical well dewatering cenario were evaluated againt the choen DWP plan. The value for lot revenue were calculated on the bai that benche that could not be mined a a reult of high groundwater level and/or change to the mine plan a a reult of inufficient dewatering would be lot. The value of ore contained in the variou benche a per the mine plan would a a reult be defined a lot revenue. Thee were decribed a follow: Scenario 1: Mot Likely conventional dewatering continue a planned and two benche in the bae of the pit are lot Scenario 2: Leat Likely a bet-cae cenario where conventional dewatering continue a planned and no benche are lot Scenario 3: Wort Cae a wort-cae cenario where conventional dewatering continue a planned but four level in the bae of the pit are lot Scenario 3: DWP the planned DWP i executed uccefully and all level in the pit are mined. The reult of the trade-off analyi indicated that although the etimated capex for continued vertical well dewatering wa le than that of the propoed DWPt plan, the cot differential wa offet by the etimated cot aving related to more efficient dewatering, and the reulting reduction in wet mining and water haulage. Additionally, in the event that the GR35 mine plan could not be met a a reult of contraint related to the conventional dewatering ytem (uch a evaluated in Scenario 1 and 3), high-grade ore repreenting up to US$80 million in revenue could have been lot. Figure 7 how the relative cot calculated for the variou cenario, clearly indicating that the greatet economic rik lie with potential lot revenue aociated with lot benche a a reult of the inadequacy of the conventional dewatering ytem. The lot revenue value ued in the cotbenefit analyi were calculated at iron ore price of US$50 to US$56 per ton, depending on the acceible volume of fine and lump ore remaining for each bench in the GR35 pit according to the mine plan at the time. 234 MARCH 2017 VOLUME 117 The Journal of the Southern African Intitute of Mining and Metallurgy

5 Adapting oil and ga drilling technique for the mining indutry The Journal of the Southern African Intitute of Mining and Metallurgy VOLUME 117 MARCH Figure 5 GR35 pit with the location of the DWP collar and drill path hown relative to critical tructure and urface infratructure

6 Adapting oil and ga drilling technique for the mining indutry Figure 6 The final Plan 14 directional well trajectory and propoed contruction Figure 7 Chart howing the reult of the cot-benefit analyi conducted for the Sihen GR35 DWP project TFS. The graph clearly how that the cot aociated with DWP are lower than all other cenario, including the Leat Likely, but epecially relative to the Mot Likely and Wort Cae cenario Conidering that the cot-benefit analyi wa conducted uing depreed iron ore price in the ame range a the current iron ore price, the trade-off analyi demontrate the clear economic benefit of deploying DWPt for the GR35 pit at Sihen. However, the ignificant decline in iron ore price and iron ore market fundamental in 2014/15 reulted in a marked lowing of the rate of vertical advance in GR35 pit and ignificant change to the mine plan. Thi enabled dewatering of the pit at a lower rate uing the exiting conventional dewatering ytem and reulted in DWPt being indefinitely delayed for the GR35 pit. However, ince KIO remain committed to deploying the latet technologie at their Sihen and Kolomela operation in an effort to increae productivity and efficiency (Mining Review Africa, 2016), DWPt a a concept ha been retained to addre the potential dewatering requirement for other deep pit at Sihen and Kolomela hould condition warrant it. Concluion A the mining indutry i driven to exploiting ore reource that are deeper and in more inacceible area than ever before, ytem previouly thought to be robut olution are increaingly being expoed a ub-optimal a mine get deeper and larger. The ue of vertical dewatering well i uch an example, a the bet hydrogeological target cannot alway be reached from the available drilling location. Additionally, a drive to increae efficiency and productivity throughout the indutry further puhe operation to reduce in-pit dewatering infratructure and to improve the overall effectivene of dewatering ytem in the mot cot-effective manner poible. A hown in thi paper, the adaptation of mature directional drilling technologie ha brought ignificant benefit to ome of the larget open pit operation through the deployment of directional well placement technology. It i expected that a pit continue to get larger and deeper, and le in-pit pace i available, the ue of thi technology will become more common a it i accepted a a cot-effective method for dewatering. Reference ASTRUP, J., HAMMERBECK, E.C.I., and VAN DEN BERG, H Iron. The Mineral Reource of South Africa. Wilon, M.G.C. and Annhaeuer, C.R. (ed.). Handbook 16. Council for Geocience, Pretoria, South Africa. pp DOWLING, J. and RHYS-EVANS, G Oilfield directional well placement technology ued for mine dewatering. Mining Magazine. May p. 28. KUMBA IRON ORE. 2016a. Operation. our-buine/operation.apx [Acceed 21 April 2016]. MCCARTNEY, J. and ANDERSON, M Mining innovation why tart from cratch. Mining Magazine. December p. 48. KUMBA IRON ORE. 2016b. Kumba Iron Ore Limited production and ale report for the quarter ended 31 March apx [Acceed 21 April 2016]. MINING REVIEW AFRICA Kumba ay technology a company game-changer. [Acceed 11 May 2016]. NEL, E. and WHITE, T Groundwater report, November Kumba Iron Ore Limited, Kathu, South Africa. 21 pp. SCHLUMBERGER WATER SERVICES Technical feaibility tudy for dewatering well placement technology at the GR35 Pit, Sihen Mine. Report no R2v11. Johanneburg, South Africa. 129 pp. SCHLUMBERGER WATER SERVICES Pre-feaibility aement of the ue of dewatering well placement technology at the GR35 Pit, Sihen Mine. Report no R1v1. Johanneburg, South Africa. 62 pp. u 236 MARCH 2017 VOLUME 117 The Journal of the Southern African Intitute of Mining and Metallurgy