Unconventional Resource Play Evaluation: A Look at the Bakken Shale Play of North Dakota
- Stuart Alan Cox (Marathon Oil Co.) | David Cook (Marathon Oil Co.) | Kenneth Dunek (Marathon Oil Co.) | Gerald R. Daniels | Connie Jo Jump (Marathon Oil Co.) | Robert David Barree (Barree & Assocs. LLC)
- Document ID
- Society of Petroleum Engineers
- SPE Unconventional Reservoirs Conference, 10-12 February, Keystone, Colorado, USA
- Publication Date
- Document Type
- Conference Paper
- 2008. Society of Petroleum Engineers
- 2.2.2 Perforating, 5.5.8 History Matching, 7.4.3 Market analysis /supply and demand forecasting/pricing, 5.8.4 Shale Oil, 5.6.3 Pressure Transient Testing, 1.6 Drilling Operations, 5.5 Reservoir Simulation, 1.14 Casing and Cementing, 5.7.2 Recovery Factors, 5.7.5 Economic Evaluations, 5.6.4 Drillstem/Well Testing, 5.6.5 Tracers
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Unconventional resource plays can provide a long-term supply of oil and gas to help supplement the North American energy demands. However, obtaining a good economic return from these developments can be challenging. A successful entry into an unconventional play requires careful pre-entry analysis in order to develop meaningful production profiles and set realistic expectations. Wells completed in unconventional plays typically exhibit limited drainage areas and produce a majority of recoverable reserves at low rates. Due to the limited flow capacity of these reservoirs typical development strategies include some form of horizontal completion.
When considering a potential entry into a "new?? resource play there are a number of important questions that must be answered such as "What is an appropriate range of initial production rates and reserves for the development??? or "What is the most cost effective completion method??? and "How will post drill completion efficiency be determined???. This paper will present one operator's approach to answer these questions for its entry into the Bakken Shale development of North Dakota. The paper focuses on the effective use of existing public information to frame expectations for the development. It will also present the completion design considerations and initial implementation results from the development.
The initial production from the Bakken Formation of North Dakota began in 1950's as a back up zone should other primary targets fail to be productive. The play experienced two further development periods. The first development phase was comprised of vertical completions. According to public records a total of 145 vertical wells were drilled in North Dakota and completed from 1953 to 1991.
These wells were completed in the entire Bakken interval and have a cumulative production of approximately 11 MMSTB. On average the historical vertical wells had an initial production rate of 28 BOPD and are expected to recover 85 MBOE per well.
The second phase of development began in 1987. During this phase 225 horizontal wells were drilled targeting the upper Bakken Shale interval. On average the upper shale horizontal wells had an initial production of 86 BOPD and a projected ultimate recovery of 145 MBOE. Figures 1 and 2 show the initial production and the historic EUR distributions for North Dakota Bakken wells.
The economic results of the first two stages of development were marginal. However the successful results demonstrated by the Middle Bakken development of the Elm Coulee field in Montana have prompted a further round of development in North Dakota. A careful review of the historical results of the prior development work can provide valuable insight into the potential performance of this new Bakken development. One should not assume that the success demonstrated in Montana will be automatically duplicated in North Dakota.
The Bakken reservoir of North Dakota is comprised of an upper shale member underlain by sandstone/siltstone members bounded by the lower shale member. Figure 3 is a type log of the geologic section1. The current development is focused on the Middle Bakken interval. Typically this interval is approximately 30 feet thick. Table 1 summarizes the average reservoir properties of the Middle Bakken interval.
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