Download pdf - Packer Testing Program Design and Managementpackertest.com/files/511.pdf · Packer Testing Program Design and Management Eric E. Swanson¹ and Brian C. Titone

Golden CO; USA IMWA 2013“Reliable Mine Water Technology”

Wolkersdorfer, Brown & Figueroa (Editors) 73

IntroductionCharacterizing groundwater flow systems in amodern hard rock mining environment is acomplex and challenging task. The hydrogeol-ogy of many mineral deposits typically com-prises complex lithology and alteration zoneswhich can be dominated by multiple fracturesets acting as flow barriers or conduits. Manymining projects are located in complex geolog-ical environments and are pushing depth lim-its below the capabilities of traditional fieldmethods. As the economic, engineering andenvironmental constraints of mine design be-come increasingly restrictive, the demand foradvanced types of testing to supporting thesedesigns increases. Increasingly, mine designsare now including pore water pressure decaydeterminations, advanced dewatering tech-niques, and modes of integrating sustainableenvironmental practices as required by regu-latory agencies, lending entities, and as bestmanagement practices at the corporate level.The costs, time and resources budgeted to gen-erate advanced mine design data sets are alsolimited. This current environment necessi-tates innovative tools and field techniques that

“do more with less.” Wireline hydraulic packertesting embodies this by facilitating discreteinterval hydrogeological data acquisition as aprogrammatical addition to existing orplanned core drilling programs.

MethodsBasic packer testing techniques are discussedin Nielsen (1991). Unlike traditional pumpingtests, packer testing generates a series of dis-crete interval permeability values along thelength of a borehole, which typically decreasewith depth. Defining the relationship betweenpermeability and depth in a statistically mean-ingful manner allows this relationship to beprojected across the site to support mine de-watering and refilling, impacts assessment,and groundwater or geotechnical modeling ef-forts.

Core drilling programs are one of the prin-ciple means of collecting a variety of datatypes at deeper depths in a modern miningoperation. Packer testing during core drillingoperations can be performed with a variety ofdifferent equipment types. Optimized for coredrilling, wireline hydraulic packers deploy

Packer Testing Program Design and Management

Eric E. Swanson¹ and Brian C. Titone²

¹AquaLithos Consulting, Principal Consultant, 5360 Cole Circle, Arvada, CO 80002 [email protected]²Orogen HydroGeo, Principal Consultant, 6232 Kilmer Loop #203, Golden, CO 80403

[email protected]

Abstract Hydraulic testing using wireline deployed water-inflated packers is becoming a com-mon practice for groundwater characterization at mining sites. Packers, designed for diamonddrilling, allow for faster, deeper, and more accurate types of testing conducted concurrentlywith existing coring programs. Designing and managing these testing programs requires plan-ning, flexibility, and consideration of available methods and equipment options. This presen-tation explores and provides critical examination of advantages and disadvantages of the fol-lowing options: 1) single or straddle packer testing, 2) injection, shut-in, withdrawal or fallinghead techniques, 3) discrete interval or cumulative testing, and discusses design considerationfor planning a testing program.

Keywords IMWA 2013, packer testing, hydrogeology, Lugeon, wire-line packer system

IMWA 2013 Golden CO; USA“Reliable Mine Water Technology”

Wolkersdorfer, Brown & Figueroa (Editors)74

through the drill rods without inflation linesor cables, are removed using the rig’s wireline,and operate using the rigs water pump. Wire-line hydraulic packers are also inflated withwater, which greatly increases the depth capa-bilities over systems that require compressedgasses to inflate.

Single Element Testing Typical packer testsare conducted using a single packer element.The testing interval using a single packer sys-tem is bounded by the bottom of the boreholeand the packer seated just below the drill bitabove the bottom of the hole. To conduct thetest the packer is lowered and inflated, water iseither injected or withdrawn from the intervalwhile flow rates and pressures are recorded,the packer deflated and removed, and thendrilling of the next interval commences. Thisprocess is repeated until the entire borehole istested in a series of discrete tests. Limitationsto this method include the need to test imme-diately after the drilling a targeted test interval,which requires the packer testing team tostandby while drilling takes place. This is alsocalled “concurrent testing” as it is conductedduring the drilling process.

Double Element Testing Wireline packersystems can also be deployed as a double orstraddle packer system where two inflatable el-

ements are used and separated by a series ofextension pipes that allow both packers to beinflated. Testing is performed on the intervalbetween the two packer elements by injectionor withdrawal (Fig. 1). Typically, straddle packersystems are used to characterize discrete inter-vals at the completion of a borehole by run-ning a series of tests across selected zones ofinterest in the borehole, or across the entireborehole length in a series of sequential tests.One major risk is having unstable holes col-lapse on the lower packer causing equipmentto be damaged or stuck.

Cumulative Testing Single packer tests per-formed at borehole completion are termed“cumulative tests”, and are performed by plac-ing the packer at various depths either startingat the top or bottom of the borehole. Cumula-tive tests always use the bottom of the bore-hole as the lower boundary of the test intervaland the packer as the upper boundary. Sincethe test intervals are a series of overlappingzones, these tests are not considered discreteand resulting data must be mathematicallyprocessed to determine unique permeabilityvalues and remove the overlap effect. Themajor limitation to this approach is that zonesof higher permeability at depth can mask thepermeability determinations for the upper

Fig. 1. Example of testing types and data results

Injection Withdrawl Straddle*Falling Head

Flow

Rat

e

Pressure

Injection

Dep

th to

Wat

er

Time

Withdrawl

Dep

th to

Wat

er

Time

Falling Head

* Straddle packer configuration can be used with any

testing meth od



tests. Cumulative tests performed at hole com-pletion and are sequential unlike concurrenttests which requires less standby time.

Types of Hydraulic TestsThe main types of hydraulic tests performedwith the packer are: 1) injection or Lugeon, 2)withdrawal or airlift, 3) shut-in, and 4) fallinghead (Fig. 1). Each of these tests has the samenet goal of determining permeability; how-ever, the type of test to be performed is de-pendent on the estimated permeability, equip-ment availability and logistics, and dataobjectives. Each type of test has advantagesand disadvantages, accuracy limitations, andtime constraints. The decision on what type oftest to perform can be made in the planningstages or as a situational decision by the fieldteam. A conservative approach is to design aprogram that has the capabilities and flexibil-ity to perform all types of tests; however, thiscan be logistically challenging and expensive.An expedient approach is to assume testingwill be performed via a single method, al-though this may sacrifice data quality.

Injection Testing Injection tests are themost commonly conducted type of packertest. These tests are performed by injectingwater at a constant pressure and recording theflow rate. If several pressure steps are used, theprocedure is termed a Lugeon test (Lugeon1933). Varying the pressure over several stepsis relatively simple and adds a qualitative un-derstanding of the downhole conditions, par-ticularly in a fracture flow setting. The pres-sures used during an injection or Lugeon testmust be high enough to induce flow, but lowenough to ensure that hydraulic fracturing ordilation of existing fractures (hydro-jacking)does not occur, as this artificially increases theformation permeability. Typically, hydrofrac-turing or hydro-jacking does not occur indeeper tests, but may be a major limitation inshallow, fragile or soft formation conditions.Furthermore, if testing is performed in bore-holes filled with cuttings or drill fluids such aspolymer or bentonite drill muds, a rapid plug-

ging response can occur which can lead to anunderestimate of the permeability. Beforestarting injection testing, the borehole is usu-ally flushed with clean water for a period oftime to remove drill fluids from the testing in-terval. Both pressure and fluid flow rates aremeasured at the surface during the test on reg-ular intervals; however, downhole pressuretransducers can be used to accurately deter-mine true interval pressures and increase ac-curacy. Advantages of injection testing are thatthe tests can be performed and analyzed rela-tively quickly, and require relatively basicpacker testing equipment. These types of testsare limited in accuracy by the upper and lowervalues of the test interval transmissivity. Inlower transmissivity intervals, accuracy is re-duced due to potential system leakage and theinability to accurately measure very low flowrates. In higher transmissivity intervals, accu-racy is constrained by frictional loss across thepacker, and the inability to build sufficienttesting pressures. In situations where high in-terval transmissivities limit injection testingaccuracy, the test interval can be shortened orthe type of testing can be changed to with-drawal tests.

Withdrawal Tests Withdrawal tests withthe packer system consist of rapidly removingand measuring water from the test interval fora period of time and then observing the result-ing recovery of the interval water level to nearstatic conditions. This type of test is per-formed in intervals that have transmissivitiesthat are too high for injection testing, such asopen fracture zones, or highly fractured zonesin the shallow portions of a borehole. Thismethod is also called an airlift test when themethod of water removal is compressed air.This type of test is essentially a rising head testbecause the analysis involves observing headrecovery data after fluid removal is completed.One advantage of withdrawal tests is that theycan be completed in borehole fluids other thanwater, such as bentonitic mud, polymers andbrine, as the method removes these fluids dur-ing the test. In situations where a heavy mud



has been used and significant borehole skinconditions occur, withdrawal tests may be thebest method, even in moderate or low perme-ability intervals. However, airlift tests cancause borehole instability because of the re-moval of bentonite from the borehole walls.Since these tests require the analysis of a waterlevel recovery curve, higher accuracy resultsare obtained when recovery is greater than90 % of static conditions which can take signif-icant time. Logistically, airlift withdrawal testsalso require more resources such as a high ca-pacity air compressor, airlift discharge heads,downhole air pipe, and transducers. However,since high permeability zone data is usuallyimportant project data, such measures aregenerally warranted.

Falling Head Tests Falling head tests areperformed in a packer isolated interval bycharging the rods with water and measuringthe resulting water level decline until a near-static condition is observed. This test is typi-cally done immediately after the injection test.These tests are the most simple of all types ofpacker tests in terms of equipment, as only apacker, pressure transducer or water levelprobe is required. However, in low transmis-sivity conditions, falling head tests can take asignificant amount of time to complete, whichrequires drill rig standby expenses. Addition-ally, it may not be possible to run a falling headtest in zones with a naturally high intervalwater level, as there may not be enough roomin the rods to induce sufficient driving headfor a good-quality falling head test. Finally,falling head tests through drill mud and cut-tings may induce a plugging response thatcould result in an underestimate of the perme-ability of that zone. In high transmissivity con-ditions, a falling head test may not work effi-ciently due to the inability to rapidly vent airfrom the drill rods as water is initially placed.Falling head data can also be gathered after aninjection test as a back-up or secondary meansof analysis, as the drill rods are already chargedwith water and data acquisition is simple if adownhole transducer has been deployed.

Shut-in Tests In intervals with very low per-meability or artesian conditions, shut-in typetests can be useful. A shut-in test is performedby pressurizing the testing zone, activatingdownhole or up-hole shut-in valve, and thenmonitoring the pressure decay using an up-hole gauge or a downhole transducer. Sincethis test is essentially a zero flow test, it can re-move accuracy error related to low flow meas-urements obtained in injection tests and fromborehole storage effects. As with withdrawaltests, shut-in tests require more time to com-plete and are thus more expensive consideringdrill rig standby rates. Although these tests by-pass flow measurement related error, they canalso be affected by apparatus leakage error,particularly if an uphole shut in system isused. Typically, the range of permeabilitiesquantified by this method is below that of con-cern at most mining operations; howeverquantification of extremely low permeabilitiesmay be required for some project objectives.New equipment has allowed Shut-in tests to bedone easier and with more accuracy than everbefore (Adams and Richards 2012).

Testing Program DesignData Objectives Detailed planning for a packertesting program is probably the most impor-tant and cost-effective activity. Table 1 showssome guidelines for packer program design.The primary consideration in performing apacker testing program is having detailed dataobjectives and a clear end goal for the pro-gram, which surprisingly, is often overlooked.If the packer testing campaign is in support ofa groundwater or geotechnical model for ex-ample, then a preliminary model using histor-ically available data should be constructed inorder to refine and optimize the overall pro-gram objectives. The data objectives should bedefined by the modeling team and the endusers of the data. Data objectives include itemssuch as assessment of the data density needs,including both vertical and horizontal distri-butions of tests. In an ideal program, the dataneeds drive the location, depths, type and



number of tests to be performed; an over-abundance of data is an unnecessary expendi-ture. Similarly, a statistically inconclusive dataset may require retesting – a major setback ifdrill rigs and key equipment and personnel aredemobilized. Often the data objectives are setby a third party, such as a regulatory body,third party reviewer, or a stakeholder represen-tative; in these cases it is recommended thatall parties come to an agreement on data ob-jective prior to the design of the program andinitiation of field activities.

Design Considerations Once the data objec-tives for a packer testing program are defined,the packer testing program planning canbegin. Elements to consider are: 1) the type,number and capabilities of the drilling equip-ment intended to be used; 2) the depth, loca-tion, inclination and diameter of each bore-hole to be drilled; 3) timing and scheduling ofthe packer testing; 4) staffing as well as train-ing plans for the personnel performing thetesting; 5) expectations regarding equipment,including procurement, logistics, and trans-

portation; 6) other hydrogeological activities,such as well installations, water level monitor-ing, transducer installations.

There are several different approaches toexecuting a packer testing campaign. Typically,packer testing is an activity that is added on toan existing exploration or geotechnical designprogram, thus certain portions of the cam-paign may already be fixed, such as the drillinglocations and hole angles. Other times, con-straints such as limited drill rig availability, keystaff availability, weather or access issues maycome into play. Based on these constraints, thepacker testing program may be designed as ashort but intensive campaign consisting ofmultiple drill rigs and a large testing crew,other times the program may be a long dura-tion operation, where sporadic tests and a sin-gle drill rig are used.

Generally, the best results occur whenpacker testing is performed concurrently withdrilling and when using a single packer config-uration. Since this type of testing is relativelyfast, a typical experienced packer testing crew

Table 1. Program Design ConsiderationsControl



can handle two to three drill rigs, moving gearbetween them, and testing as time allows. Oc-casional delays may occur but these are smallin comparison to the advantages. Smaller ca-pacity drill rigs in under-developed countriestypically average 20 to 40 m of core drilling perday, when conditions such as mechanicalbreakdowns and logistical delays are factoredin. A highly trained packer crew can typicallyperform two injection tests per shift, or oneairlift test. In such a setting, with three operat-ing drill rigs, it is reasonable to assume thattesting could take place on 30 m intervals ineach borehole. Since one drill rig is usuallymoving, installing casing, under maintenance,or drilling in rock that is outside the data ob-jectives; it is reasonable to assume that a singlepacker kit plus a day and night testing crewcould handle up to three drill rigs. If other ac-tivities are required of this crew, such as wellinstallation, data analysis, access, equipmentand supply sourcing; the maximum numberof rigs drops considerably.

Staffing and Scheduling Staffing of packertesting programs is a key issue requiring care-ful planning. Packer testing can be performedby external consultants, specially trained drillcrews, or by in-house staff after receiving train-ing. Some packer testing crews consist of a sin-gle experienced individual, while others crewsmay have two or three inexperienced or juniorpeople. Typical drilling operations and packertesting campaigns are a 24/7 continuous oper-ations, so both a day and night crew is usuallyrequired. Crew duration is typically 3 to 5weeks; even the most seasoned field crewmember become ineffectual after this periodof time. Generally, the most cost effective mixof personnel for a packer testing campaign isa blend of lower cost juniors, some locallysourced laborers, and at least one highly expe-rienced individual that can troubleshoot andsupervise staff. In many instances, when deal-ing with consultants, it is more efficient tohave the project manager on-site so that plan-ning and logistical difficulties are rapidly re-solved. Packer testing, while simple in concept,

can be exacting work that requires an experi-enced operator to supervise and troubleshootissues that junior or inexperienced operatorsmay have trouble managing. Underestimatingthis may result in poor data quality as well aspotentially long rig standby times and associ-ated costs.

ConclusionsRecent innovations in packer systems has re-duced cost and increased accessibility for ver-satile, deep testing equipment. Incorporatinga wireline hydraulic packer testing programinto a core drilling program is advantageous inthat it enables the acquisition of discrete inter-val hydraulic testing during exploration, geot-echnical, infill or other core drilling opera-tions. Although it does require someadditional equipment and personnel, the costadvantages of including this type of testinginto an existing core drilling campaign far out-weigh those associated with a standalone, ded-icated hydrogeological drilling and testing pro-gram.

The types of testing, packer configurationand test scheduling are flexible program de-sign elements. In designing a packer testingprogram, these elements must be optimizedto both meet the data objectives of the pro-gram and minimize overall budget. It is impor-tant to get the advice of a packer testing expertfamiliar with this type of testing to help designa successful program.

AcknowledgementsThanks to Brent Johnson of Interralogic formanuscript review.

ReferencesAdams J, Roberts R (2012). Advances in hydrogeologic

testing of mineral exploration boreholes. – In: Mc-Cullough CD, Lund MA, Wyse L: IMWA Symposium.– p. 357 – 364; Bunbury, Australia.

Lugeon M (1933) Barrage et Géologie. Dunod. ParisNielsen DM (1991). Practical Handbook of Ground

Water Monitoring, Second Edition. CRC Press 1991.