Niobrara Chalk Beds, South Dakota, Yankton CountyPhoto Credit: Samuel Calvin, 1873-1911 uiowa.edu

Introduction to the Niobrara

Brief Geologic Overview and Impact on

Completion Strategy

• Development History• Geology• Variety of Current Completion Strategies• Completion Challenges We Must Address

Outline

• History & variety of fields associated with the Niobrara– 1876: Florence Field near Canyon City CO (associated Pierre Shale)– Boulder Field. McKenzie #1-21 produced from 1902 to ~2005 (Pierre)– Salt Creek– Tow Creek– Teapot Dome– Twin Buttes & Shell Creek (13,000 to 15,000 ft gas)– Shallow biogenic gas - W KS, W NE, and E CO >3,000 wells– DJ Basin (comingle Niobrara, J Sand and Codell) >20,000 active wells– 2009: EOG’s Jake horizontal well, 1750 bopd; 680 bopd month 2

• 20 to >2000 ft thick. Found at surface to 24,000 ft deep• Thermal maturity varies

– Oil, thermogenic gas, condensate, or biogenic gas• We need to be specific when talking about “the Niobrara”

Niobrara Background

Late Cretaceous, 90 Ma

Ron Blakely, Northern Arizona University http://jan.ucc.nau.edu/~rcb7/90moll.jpg

Late Cretaceous, 100 Ma

Ron Blakely, Northern Arizona University http://jan.ucc.nau.edu/~rcb7/90moll.jpg

Finn, USGS, DDS-69-D

Oscillating sea levelsCritical to understanding

Niobrara deposition

Sample Strat Column

Showing Benches

DJ: Wattenberg Field

200 ft thick at 7,000 ft depth

Sonnenberg 2002, CSM

Western Colorado

>2000 ft thick at 11,000 ft depth

Relative extent and locationplus some recent Niobrara activity

Base Map:ArcGIS

Bakken

Niobrara

Fluid Types & Depth RangeOil, gas/condensate, biogenic gas

Surface (outcrop) to 24,000 ft

Whiting (Cody Shale)

True Oil, Barrett

Samson, Termo, Cypress, Quicksilver

Delta, Laramie, Antero, EnCana

EOG, Chesapeake, Baytex, Helis, Resolute

DJ Basin:EnCana, EOG, Noble, Slawson,

Chesapeake, SM, Anadarko, Pine Ridge, Lario, Carrizo, PDC, Marathon, Voyager,

Rubicon, Whiting, Cirque

El Paso

Pioneer, El Paso, Manzano

St Mary, RKI, QEP , Noble, MDU, Rexx, East(Shell), TARC,CHK,MBI(Anadarko)

Laramie, EOG, Bonanza Creek, Wellstar

At least 60 different operators in Niobrara

play

Age equivalent to Austin Chalk

UnderlyingSecond White Specks ~

Favel ~ Greenhorn

Medicine Hat, First White Specks

Age equivalent to Mancos Shale

Examine Outcrops!

Watney, Kansas Geological Survey

Next image near Lyons

Examine Outcrops!

From PTTC/RMAG field trip flyer, Gustason, Deacon

Photo from the Portland Cement Quarry near Lyons, CO

Outcrop of “A” bench. • Typically considered a brittle

formation, sandwiched between ductile shales

• Even minor structure can lead to natural fracturing

AAPG Explorer, Nov 2010, Durham

• Outcrop of “C” bench between Boulder and Lyons.

Noble Analyst Day June 3 2010

Variation of Reservoir Conditions

Watney, Kansas Geological Survey and Pollastro

• Kansas– 40-50% porosity– 0.2 to 3 mD. >0.5 mD at shallow depths– Biogenic gas from thermally immature chalk

• Wattenberg– Four 20-30 ft thick chalk benches– <10% porosity in some areas – Fractures mineralized with calcite, quartz, or gypsum– <<0.1 mD at 3000 – 8000 ft depth– Thermogenic gas and condensate

• Silo– Five chalk benches; develop the “B”, 25-35 ft thick– <6-8% porosity but open vertical natural fissures– <0.01 mD matrix perm at 7800 ft depth– Oil, 35-38 API, 500-1000 scf/bbl GOR

Why are refracs necessary in vertical DJ wells?

Pagano, 2006. See also 134330 for discussion of refrac mechanisms

– Gas Condensate wells in DJ Basin – up to 5 restimulations– Initial fracs used low concentrations of sand

Increase in Horizontal Drilling

Tom Bratton, SLB

Challenge:Limited Intersection between Wellbore and Fracture

Horizontal Well with Transversely Intersecting Frac: Enormous fluid velocity and near-wellbore connection is key!

Woodford Shale Outcrop

Some reservoirs pose challenges to effectively breach and prop through

all laminations

Our understanding of frac barriers and kv should

influence everything from lateral depth to frac fluid type, to implementation

Narrower aperture plus significantly higher stress in

horizontal steps?

Failure to breach all lamina?

Will I lose this connection due to

crushing or embedment of proppant?

Challenge: Effective Frac Design

• Design issues– Role of bentonite layers– Degree of proppant embedment– Fluid sensitivity

• Development near urban and residential areas– Increased scrutiny regarding completions and wellsite stewardship

• Water availability– In SE Wyoming, may govern development pace

Some Additional Challenges

• Extensive play, long history– Many different challenges across play

• Historic Completion Strategies– Notorious “low cost” development with minimal data gathering– More than 5000 refracs have been necessary in the DJ– Horizontal well completion strategy/optimization is equally poor

• Opportunities– Transverse fractures require different optimization approaches

• Must accommodate flow convergence near wellbore• Horizontal wells depend on durable vertical fracs to drain laminated reservoirs

– Reduce or eliminate need for frequent restimulation– Enormous opportunities for improvement

Niobrara Summary