An Assessment of Selected Rate-Decline Models for Horizontal Oil Wells in the Niobrara Formation
- John P. Seidle (MHA Petroleum Consultants Inc) | Deborah Irene Savimaki (MHA Petroleum Consultants Inc)
- Document ID
- Society of Petroleum Engineers
- SPE Unconventional Resources Conference and Exhibition-Asia Pacific, 11-13 November, Brisbane, Australia
- Publication Date
- Document Type
- Conference Paper
- 2013, Society of Petroleum Engineers
- 1.6 Drilling Operations, 5.7 Reserves Evaluation, 5.2.1 Phase Behavior and PVT Measurements, 4.6 Natural Gas, 5.6.1 Open hole/cased hole log analysis, 5.1.1 Exploration, Development, Structural Geology, 1.6.6 Directional Drilling
- Niobrara, Rate Decline, Horizontal
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Horizontal well development targeting the Niobrara formation in the Denver-Julesburg (DJ) Basin in Colorado and Wyoming is gaining development momentum as the price of gas in the US has fallen and liquid rich plays have come into high demand.
The low permeability Cretaceous age Niobrara formation is commonly encountered as three benches of naturally fractured limestones, marls and calcareous shale. The advent of horizontal drilling has allowed exploitation of this previously overlooked target in the DJ Basin.
Thermal maturity varies across the DJ basin, resulting in a variety of reservoir fluids in the Niobrara including dry gas (biogenic and thermogenic), wet gas, condensate, and oil. Two of the main oil fields in the DJ Basin are the Silo field, in Laramie County Wyoming, and the Wattenburg field, which is predominantly in Weld County, Colorado.
Oil has been produced out of the DJ Basin since 1901, however successful horizontal well development is still relatively recent in both fields. With the increased interest in Niobrara development, rate-decline analysis is used extensively by operators to estimate reserves and to evaluate potential locations for future drilling.
Various published models are available for rate-decline analysis. Arps rate-decline relationship has been the most widely used model, however subsequent authors have developed models modifying Arps, or in the case of unconventional and naturally fractured formations, developed completely new models, like Duong, for rate-decline analysis.
This paper will utilize production data for wells in Wattenburg and Silo fields to assess how appropriate different models are for rate-decline analysis in the naturally fractured Niobrara Formation.
In 2012, Colorado produced nearly 8 million barrels of oil, the highest since 1956, due to increasing production from the Niobrara formation in the DJ Basin. This significant increase in production demonstrates the significance and ramp-up in production for this formation and with over 1,000 active horizontal Niobrara well permits, development is not going to slow down soon. As more acreage is converted to horizontal well development across the entire play, companies are relying on rate-decline analysis for reserves, to develop type curves to predict future well performance and to drive economic evaluation.
The DJ Basin stretches across the southeast Wyoming, southwest Nebraska and northeast Colorado. The Niobrara has three benches that are all being developed with horizontal wells, however the initial focus was the thicker "B?? bench. The limestones in the formation tend to be naturally fractured, and the shales are a source rock. The Niobrara formation generally has porosity in the range of 10-14%, with permeability estimates less than 0.1mD, which makes fractures, both naturally occurring and through wellbore stimulation, critical to achieve commercial flow rates.
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