Producing  Producing  Average  Vertical  Porosity  K  Water  Oil  BHT  Initial  Fm Value  GOR  GAS  Reservoir 

Interval  Fields  TVD  Thickness                 Saturation  Gravity BHP  Factor Gravity  Drive 

       (Ave., Ft)  

(%)  

(md)  

(%)  

(oAPI)  

(oF)  

(psia)              

"A" Zone Only  18  10475  4  13.9  4.7‐30  27  38.4‐44  228 4100‐5265 

1.43  877  0.856  Solution Gas‐Water Drive 

"A" & "B" Zones  8  10954  9.4  13.8  8.6  43  42.3‐45  243 5153‐5312 

1.55  843    Solution Gas 

"B" Zone Only  9  10805  12  12.8  4.8  44  39‐43.6  244 4960‐5240 

1.51  709    Water Drive/Solution Gas 

 

 

Producing  Producing  OIP  Primary  EUR 

Interval  Fields 

         Recovery

      (MBO)     (MBO) 

"A" Zone Only  17  844  17.7  221 

"A" & "B" Zones  6  879  22  286 

"B" Zone Only  9  590  20  137 

July 2009 9

IntroductionGas development started along the east flank of theWillistonBasin (primarilyRenvilleandBottineauCounties) in1908whenthe North Dakota Gas Company began drilling wells near thetown of Westhope (Harrison, 1978, oral communication). Oilproduction began in this area in 1952when a randomwildcatwell (#1EdwinBerentson, SWSESec. 21, T163N,R79W)drilledby the ZachBrooksDrilling Companydiscovered theWesthopeField. The discovery of theWesthope Field resulted in furtherexploration,development, andultimately significantproductionalongtheeasternflankoftheWillistonBasin(fig.1). Currentlyproduction is restricted tovarious intervalswithin theMadisonGroup(Mississippian)andoverlyingSpearfishFormation(Triassic).ThereareafewunsuccessfultestsdeeperthantheMadisonalongthisportionofthebasin. This paperwillexamine the futureoilandgaspotentialof theBirdbearFormation(Devonian)innorth-centralNorthDakotaandits relationship to recent exploration and production from thesouthwestportionofNorthDakotaalongtheBicentennial,BeaverCreek,andRoosevelttrend.

Birdbear FormationThe Birdbear Formation lies on top of theDuperow Formationand beneath the Three Forks Formation in the central part oftheWilliston Basin or beneath the Lodgepole Formation alongthemargins of the basinwhere the Three Forks is not present(Foradditionaldetailsseethestratigraphiccolumnonpage28).Oilandgashasbeenproduced fromtheBirdbearFormation inSaskatchewan andMontana since the early 1960s (Ehrets andKissling,1985;Martiniuket al.,1995)andinNorthDakotasince1978.

TheBirdbear Formationwasdepositedabout350million yearsagoduringtheDevonianPeriodwhenNorthDakotawassituatedjustsouthoftheequatorontheslowlymovingnorthwardNorthAmerican tectonic plate. TheWilliston Basin ofNorthDakotawaspartofanembaymentthatextendedthroughSaskatchewanand Alberta to the open sea beyond. This embayment wasrepeatedlyfloodedbyfluctuatingsealevels,themaximumextentof which decreased throughout Birdbear time. This gradualdecline inmaximumsea levels resulted in the lowerportionoftheBirdbearFormationbeingdominatedbydepositsofshallowmarine limestone and dolostones whereas the upper portionof the Birdbear is dominated by onshore deposits containinganhydrite.ThepresenceoftheevaporitemineralanhydriteanddolomitizedlimestoneintheonshoredepositssuggestthatduringthistimeNorthDakotaperiodicallyexperiencedarid conditionssimilar to themodern sabkhaenvironmentof thePersianGulf.Thisdepositionalhistory ledtothedevelopmentofporousandpermeable dolostones encased in impermeable anhydrite andfine-grainedcarbonates.Tiltingofthesereservoirsbybasement-related faults and multi-stage salt solution collapse structuresallowfortheformationoftrapswherethereservoirdolostonesaredrapedoverorpinchoutalongtheflanksofstructuralhighs.OilintheBirdbearFormationisalsotrappedinextensivelydolomitizedstromatoporoidbanks(stromatoporoidsareanextinctcarbonatesecretingorganismsimilarinsomerespectstomodernsponges)and biostromes (“reefs”) that lie immediately below a layer ofinterbeddedanhydriteandtidalflatcarbonates(fig.2).

Birdbear Formation in North-Central North Dakota – Additional Production Potential

Julie A. LeFever

Table 1. SummarytablesofbasicBirdbearFieldinformationpresentedtotheNorthDakotaIndustrialCommission.

10 DMR Newsletter

Bicentennial-Beaver Creek-Roosevelt TrendProductionfromtheBirdbearFormationoccursalongatrendthatextends throughBillings,McKenzie, andGoldenValley counties(fig.1).Alongthistrend,Birdbearproductionfromverticalwellsisobtainedfromadolostonereservoirknownasthe“B”horizon.The “B” horizon is from 8 to 20 feet in thickness and containsan average of 16% porosity with between 4 to 10 millidarciespermeability. Producible traps are formed where the “B”horizonoverliesstructuralhighsand iscappedby impermeableanhydritesoftheoverlying“A”zone(Table1)(SperrandBurke,2005;McClellan,2006). Additional production is sometimes possible where porousdolostones pinchoutwithin the anhydrites of the overlying “A”zone. “A” zonedolostones are 2 to 4 feet thickwith pay zone

porosities that average 14%with permeabilities in the 4 to 30millidarcy range (Table 1). A detailed analysis of this area ispresentedbyBurkeandSperr(2005).Economicproductionfromvertical testsof theBirdbearFormation is typically restrictedtodepthsof less than10,800 feet. However,economicquantitiesofoilcanbeproducedfromtestsdeeperthanthiswhena4,500footlonghorizontallegisaddedtoanexistingverticalwell.Thepotentialofgoodproductionfromthe“A”zone,thestratigraphicnatureofthetrappingmechanism,andthepossibilityofmultiplepayhorizonssuggests thatsignificantBirdbear reservesmaybefoundelsewhereinWillistonBasin.

North-Central North DakotaTherocksoftheBirdbearFormationinthenorth-centralportionof theWilliston Basin are similar to those that produce along

Figure 1. MapshowingthedistributionofBirdbearwells(blackdots)throughoutthe Williston Basin. Producing EastFlank Fields in Bottineau County (blueborder) and along the Bicentennial–Beaver Creek–Roosevelt trend (redborder)arehighlighted. Colors indicatewhichhorizon isproducing:DarkBlue–Madison; Yellow – Madison-Spearfish;Green – Spearfish; Brown – Birdbear“A”; Light Blue – Birdbear “B”; Purple– Birdbear “A”& “B”, Red – FieldswithBirdbearTests.

0 200GR

0.3 -0.1Density Porosity

0.3 -0.1Neutron Porostiy

0.2 2000Deep Resistivity

0 12GR

0 250Deep Resistibity

0 200GR

30 -10Density Porosity

30 -10Neutron Porosity

0.2 2000Deep Resistivity

0 200GR

0.3 -0.1Density Porosity

0.3 -0.1Neutron Porosity

0.2 2000Deep Resistivity

1080

0

1040

0

6700

4200

33-007-01446-0000NWSE Sec. 9, T143N, R102W

BTA Oil Producers20101 JV-P Cooper #1

KB = 2,455 ft

33-025-00005-0000SENW Sec. 22, T149N, R91W

Mobil Producing Co.Pegasus Div Solomon Bird Bear #F-22-22-1

KB= 2,102 ft

33-075-01286-0000SWSE Sec. 10, T160N, R86W

Eagle Operating, Inc.E-M Leland #10-15

KB=1,824 ft

33-009--02068-0000SENE Sec. 20, T161N, R77W

Eagle Operating, Inc.E-M Johnson #20-8

KB=1,484 ft

Three Forks Formation

Duperow Formation

Bird

bear

Form

atio

nzone “A”

zone “B”

A

A’

Index Map

ND

A A’

WillistonBasin

New Text

1060

010

700

0 200GR

0.3 -0.1NPOR

0.3 -0.1DPHZ

0.2 2000AHT90

0.2 2000AHT60

0.2 2000AHT30

0.2 2000AHT20

33-007-01448-0000Aviara Energy Corporation

#30-2 StateSWSE Sec. 30, T143N, R102W

Roosevelt Field

Bir

db

ear

Form

atio

n

Cycles123

A

B

Pay Zone

Pay Zone

July 2009 11

theBicentennial–BeaverCreek–Roosevelttrend.Acrosssectionthroughthesetwoareasdemonstrates that theunitsareeasilytraceable across the basin (fig. 3). The north-central areawaschosenforstudyonthebasisofwellcontrolandtheavailabilityof cores. Thirteen cores provide insight into the distribution ofthe various depositional environments that formed the rocks(lithofacies)thatrepresentthegeologichistoryofthisformation.The lowermostportionof theBirdbearFormation is aplatformfacies that immediately overlies the Duperow Formation. Itconsists of 30 to 43 feet of burrow mottled to nodular limemudstone to wackestone containing gastropods, brachiopods,

rugose (horn) corals and other skeletal debris. Commonlyfracturedandoilstainedinthisarea,fluidmovementhassolutionenhanced existing pinpoint and vuggy porosity, in addition toprovidingfractureporosity(Martiniuketal,1995).Theplatformfaciesisoverlainbyabiohermalfaciesconsistingofalightbrownanhydriticlimemudstonetowackestone.Itisgenerallymassiveandmaybeburrowedornodularbedded.Reachingamaximumof27feet,theserockshaveporositiesrangingfrom8to19.5%withpermeabilitiesashighas3.3millidarcies.

Thebasalportionofthebiohermalorbankfaciesinnorth-centralNorthDakotaisalightbrown,tomediumbrown-greydolomiticlimestonecontainingfossil fragments(bioclastic)thatareeithersurroundedbyorare“floating”inmud-sizedcarbonatesediment(packstone to wackestone). Fossils including Thamnopora, Amphipora, laminarandhemisphericalstromatoporoids,rugosecorals, brachiopodsand crinoids areabundant. Theporosity isvuggy, solution enhanced or moldic where skeletal material ispresent(fig.4).

Themainbiohermconsistsofalimewackestoneandboundstonethat is comprised predominantly of laminar, bulbous, anddigitate stromatoporoids. Other fossils include rugose corals,Thamnopora, Amphipora, and colonial corals (Syringopora).Porosities range from 6 to 19% with permeabilities up to 237millidarcies. Intergranular, moldic, intraparticle, pinpoint andvuggy are the common types of porosity andmay ormay notbesolutionenhanced. This isoverlainbya limewackestoneto

Figure 3. Cross-section from Roosevelt Field, Billings County, toBottineauCounty.Potentialproductivezones(blueandgreen)thatarepresentinthesouthwestportionofthestatearecorrelativeacrossthebasin.ThetypesectionfortheBirdbearFormationisrepresentedbytheMobilProducingCo.–PegasusDivSolomonBirdBear#F-22-22-1(Sandberg andHammond, 1958). The cored section for thatwell isindicatedbythehatchurestotheleftoftheGammaRaylog.Thelowerdashedlinereferstothetopofaplatformfaciesthatprovidesforthedevelopmentofthepotentiallyproductiveoverlyingbiohermalorbankfacies(Martiniuketal.,1995).

Figure 2. WirelinelogfromaproducingwellinsouthwesternNorthDakotawitharepresentativesectionoftheBirdbearFormation.Theconventionalproducinghorizonisinformalunit“B”andwhereproductive,consistsofstromatoporoidandbiohermalbanksindicatedingreen. Informalunit“A” isthefocusofthispaperandconsistsofan interbeddedsequenceofanhydritesanddolostonesanditsproducinghorizonindicatedinblue(modifiedfromBurkeandSperr,2006).

A - 4272 ft

D - 4314 ft F - 4311 ft

C - 4293 ftB - 4282 ft

E - 4306 ft

0 200GR

0.45 -0.15Density Porosity

0.45 -0.15Neutron Porosity

0.2 2000LLD

4300

33-009-01723-0000NENW Sec. 30, T162N, R78W

Citation Oil & Gas Corp.Ardis Holen #21-30

KB = 4500 ft

Thre

e Fo

rks

FmD

uper

owFm

A

B

platformfacies Bi

rdb

ear F

orm

atio

n

ABCDEF

12 DMR Newsletter

grainstone.Localizedmudstonesarealsopresentinthearea.FossilsincludeAmphipora, Thamnopora,rugoseand Syringopora corals, ostracods, and brachiopods.Thisportionshowssimilartypesofporositytothelowersection but with lower porosity and permeabilitiesprobablyduetolimiteddolomitization.Theintervaliscommonlyheavilyoilstained(Martiniuketal.,1995).

The equivalent to the “A” zone in this area ischaracterizedbyaninterbeddedsequenceofmassive,chickenwire, or nodular mosaic anhydrite with thinshale partings. Interbedded within the anhydritesequence are massive dolostones, very fine-grained(microsucrosic)dolostones,algallaminateddolostones,andmottledlimemudstones.Thecarbonatesequenceis oil stained and commonly contains intergranular,intercrystallineandsolutionenhancedvuggyporosity.

Exploration and Development PotentialSignificant potential exists for production from theBirdbearFormationontheeastflankof theWillistonBasin. Thisportionof thebasin iswellknownfor itssalt tectonics. Newburg and SouthWesthopefieldsarelocatedontheupdipsideofaprominentsynclineresulting fromthedissolutionandcollapserelatedto

thePrairiesalt(AndersonandHunt,1964;LeFeverandLeFever,1991).Theactivityinthisareahasproducedthenecessary structure todevelop the correct faciesrelationships forproduction from the “B” zone. Thismaybetiedfurthertothetrappingmechanismrelatedto two stage salt dissolution and collapse as seen inproducingareasinnortheasternMontanaandsouthernSaskatchewan.

Coresalsosuggestthatfluidshaveenhancedporosityand permeability. This may provide a diagenetic-stratigraphic trapwhereenhancedreservoirbedsaretrappedupdipbytighterfacies.Also,thereisadditionalpotential in horizontally drilling the thin dolostonebedsofthe“A”intervalasexhibitedbythewellalongthesouthwestportionofthebasin.

References CitedAnderson,S.B.and J.B.Hunt,1964,DevonianSalt Solution

in North-Central North Dakota, in W. Leskela, J.Brindle and S.H. Harris, eds., Third InternationalWilliston Basin Symposium: Billings GeologicalSociety, North Dakota Geological Society andSaskatchewanGeologicalSociety,p.93-104.

Figure 4. TheCitationOil&GasCorp.–ArdisHolen#21-30wellinBottineauCountyisdisplayedinthisfigure.ThisBirdbeartestshowssimilarintervalstothewellspresentinthesouthwestpartofthestate.Theportionofthewellcoredisindicatedbythehatchuresontheleftsideofthediagram.Indescendingorder:A(4,272ft)–mediumgreymassiveanhydrite;B(4,281ft)–thindolostoneinterbed;C(4,293ft)–localizedcollapsefaciesinthiswellduetothedissolutionoftheunderlyingPrairiesalt;D(4,300ft)–thelimewackestonetograinstonewithtabularstromatoporoidsofthebioherm;E(4,305ft)–thelimewackestonetoboundstonesectionofthebioherm;and,F(4,310ft)–thebasalportionofthebiohermorbanklithofacies.

A

B

C

D

E

F

July 2009 13

Burke,R.B.andT.J.Sperr,2006,BirdbearFormationLithofaciesinWest-CentralNorthDakota:SomeCharacteristicsandInsight:DMRNewsletter,vol.33,no.1,p.17-21.

Ehrets, J.R. and D.L. Kissling, 1985, Deposition, Diagenesis andPaleostructural Control of Duperow and Birdbear (Nisku)Reservoirs, Williston Basin: in Rocky Mountain CarbonateReservoirs–ACoreWorkshop,SEPMWorkshopNo.7,p.183-216.

LeFever, R.D. and J.A. LeFever, 1991, Newburg and South WesthopeFields, in Foster, N.H. and E.A. Beaumont, eds., StratigraphicTrapsII,AtlasofOilandGasFields:AAPGTreatiseofPetroleumGeology,p.161-188.

Martiniuk, C.D., H.R. Young, and J.A. LeFever, 1995, Lithofacies andPetroleum Potential of the Birdbear Formation (UpperDevonian), Southwestern Manitoba and North-CentralNorthDakota: in L.D. VernHunter and R.A. Schalla, eds., 7th

InternationalWillistonBasin Symposium1995Guidebook, p.89-102.

McClellan, T.S., O. Skinner, and B.Miller, 2006, Birdbear “A’ DolomitePlay:EconomicExploitationofaThinCarbonateReservoirwithHorizontalDrilling,WillistonBasin,NorthDakota:RMS-AAPGMeeting,Billings,MT,OralPresentation

Sandberg,D.A.andHammond,G.R.,1958,DevonianSysteminWillistonBasin and central Montana: AAPG Bulletin, v. 42, p. 2293-2334.

Sperr, Jay, T. and R.B. Burke, 2005, The Birdbear Formation (Nisku) ofWestern North Dakota: Another Emerging Williston BasinHorizontalPlay,inMeetingProgram2005RMS-AAPG,Jackson,WY,p.49.

New Web Subscription Service Option

TheOilandGasDivisionoftheDepartmentofMineralResources announces a new web subscriptionoptionthatisdesignedtobettermeettheneedsofmineral interestowners. Theoriginal subscriptionserviceisnowlistedas“PremiumServices”andthenewoptioniscalled“BasicServices”.

The basic services will give subscribers access tomonthlyproductionandsalesvolumesforallwellsand units on a monthly basis, which will assistmineral owners in verifying the accuracy of theirmonthly royalty statements. A summary of basicwell information can be foundon the scout ticketpagewhichwillalsocontainalinktothecompletescannedwellfileinAdobePDFformat.Thewellfilecontains the permit application form, completionreports, geological reports, details of work-overs,andcopiesof lettersandothercorrespondencetoandfromtheoperatorsofeachwell.

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includedinthebasicserviceplusdigitalandimagewelllogs,productiondeclinecurves,coreandthin-section photographs, state-wide well productionfor each month, a stripper well determinationtool, and unitization statistics about all units thathave been formed in North Dakota. Field orderscanbeaccessedthroughthemain indexorby fulltextsearch.Theassociatedscannedcasefilesandhearing audio are also available for download.ThereisalsoaGISmappingtoolforresearchinggasanalysisdatathroughacooperativeeffortbetweenthe PCOR Partnership and the ND Department ofMineralResourcesandishostedontheUNDEERCwebsite.

Thecostofthe“BasicService”is$50peryearandthecostofthe“PremiumService”is$175peryear.Formoreinformationonsubscribingtotheseservices,go to https://www.dmr.nd.gov/oilgas/agreement.pdfandfollowtheinstructionsonthewebsiteuseragreement.