Title: The Art of Logging Horizontal Niobrara Wells in the Denver Basin
Author: Janet Marks, Halcon Resources
Publication: The Outcrop, March 2013, p. 8, 10, 14-21, 26-29, 32-37
Ms. Marks has a BS from the University of Illinois and MS from the University of Wyoming. She formerly performed mudlogged/well site geology on 33 horizontal wells throughout the Denver Basin for Columbine Logging from 2010-2012.
She would like to thank Columbine Logging and the various operators for the time spent drilling Niobrara wells that allowed her to gain this knowledge.
This article was part of a presentation for the AAPG-RMS in Grand Junction, September 2012.
Relatively recently, horizontal drilling into basin centered, continuous source rocks has exploded. Without pre-planning of the well path, it is easy to deviate from the formation sweet spots during drilling. Seismic and wellbore control are examined prior to drilling t the borehole to anticipate any faults. Using all the available data, the well site geologist helps make timely critical decisions on the borehole path when drilling fast in real time.
Calling the top of formations while drilling vertically and landing the intermediate casing within the exact part of the desired formation is important. After drilling horizontally out of the intermediate casing, it is necessary to know what bed within the formation the bit is located in with respect to the target zone. The target is generally a 5-20 foot thick layer that has the greatest porosity, least gamma, and/or highest resistivity.
The well site geologist uses various tools to log critical geological data during real-time drilling of wells to provide formation evaluation, monitor drilling performance and determine the location of the bit in the pay zone.
The following article shows examples from the stratigraphic section drilled to the Niobrara target as well as through the target interval.
During the time of Niobrara deposition (Upper Cretaceous; late Turonian-earliest Campanian), the continents experienced highstand eustatic sea levels worldwide resulting in shallow epicontintental seas including the Western Interior Sea. To the west i in the Cordilleran region, the Sevier orogeny was causing subduction, volcanism and mountain building. Siliciclastic sedimentation and subsidence occurred in the western portion of the seaway. To the east was a relatively shallow shelf that was terrigenous sediment starved. Widespread pelagic and hemipelagic carbonate sedimentation rich in coccolith and planktonic foraminifera were deposited.
Cretaceous Transgressive/ Regressive Cycles
Stratigraphy and Type Log
Sharon Springs – Ardmore bentonite marker with double peak high gamma and brilliant mineral fluorescence, very little effervescence with HCI, hot shale, anoxic, platy, dark gray to black shales, bituminous, large pieces on the shale shaker, 15-30’ TVD above top of Niobrara, not thick but drilling at a high angle
Top of Niobrara – violent effervescence with HCI indicating calcareous, lighter in color than the Sharon Springs, smaller pieces, 15-30’ TVD thick unnamed marl
A Chalk – not as clean as B Chalk, few fossils if any, some bentonite, mottled, lighter color, 10-30’ TVD thick
A Marl – large framboidal pyrite crystals and bentonite bed, little or no fossils, truly a marl, darker and higher gamma than chalks, silty, organic rich, 35-60’ TVD thick
B Chalk – cleaner than A or C Chalks, white specks, some fossils, target zone in lower half, mottled, lighter color, trace to some bentonite, base has some fossils + Inoceramus prisms, 25-35’ TVD thick
B Marl – more interbedded with chalk, bentonite with pinpoint disseminated pyrite, abundant fossils especially near the bottom with Inoceramus prisms, darker and higher gamma than chalks, silty, organic rich, 35-50’ TVD thick
C Chalk – interbedded with marl-especially in the top, some fossils, Inoceramus prisms, target zone also in lower half, 30-40’ thick
Chalks – 70-110 API gamma; Marls – 120-150 API gamma
Gilbert, G.K. 1895, Sedimentary Measurement of Cretaceous Time, Journal of Geology, V.3, p. 121-127.
Hattin, Donald E., 1981, Petrology of the Smoky Hill Member, Niobrara Chalk (Upper Cretaceous), in Type Area, Western Kansas, AAPG B65 5, p. 831-849.
Kauffman, Earl G., 1977, Geological and Biological Overview: Western Interior Cretaceous Basin, RMAG, MG14, 3-4, p. 75-99.
Kauffman, Earl G., 1977, Second Day, Upper Cretaceous Cyclothems, Biotas and Environments, Rock Canyon Anticline, Pueblo, Colorado, RMAG, MG14, 3-4, p129-152.
King, Phillip B., 1959, 1977, the Evolution of North America, Princeton University Press, 197 p.
Longman, Mark W., Barbara A Luneau and Susan M. Landon, 1998, Nature and Distribution of Niobrara Lithologies in the Cretaceous MG35 4, p. 137-170.
Scholle, Peter A. and Richard M. Pollastro, 1985, Sedimentology and Reservoir Characteristics of the Niobrara Formation (Upper Cretaceous), Kansas and Colorado: Rocky Mountain Carbonate Reservoirs, a Core Workshop: SEPM Core Workshop 7, p. 447-
Sonnenberg, Stephen A., 2011, The Niobrara Petroleum System: A New Resource Play in the Rocky Mountain Region, Chap. 1 of Estes-Jackson, Jane E. and Donna S. Anderson, RMAG Revisiting and Revitalizing the Niobrara in the Central Rockies, p. 13-32.
Witner, John, 2010, personal communication, Columbine Logging.