--> Examination of the Tyler Formation's Exploration and Development History using Current Source Rock and Reservoir Maps

2014 Rocky Mountain Section AAPG Annual Meeting

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Examination of the Tyler Formation's Exploration and Development History using Current Source Rock and Reservoir Maps


The Tyler Formation contains two separate petroleum systems: a northern, basin-centered petroleum system that contains organic-rich marine shale within the lower Tyler section, and a southern petroleum system containing organic-rich limestone beds in the upper Tyler. The southern petroleum system has yielded >99% of Tyler production to date with a 60 year history of exploration and development along the southern margins of the Williston Basin (southwestern North Dakota). Exploratory drilling has recently been initiated to test the southern Tyler petroleum system's potential as a resource play. Reexamining the previous 60 years of Tyler activity with current geologic maps and information regarding source rocks and conventional reservoirs will provide insight into current and future exploration efforts. Production began from the Tyler in 1954 with Amerada-Northern Pacific Railway's Dan Cheadle Unit #1 located in southern Billings County, southwestern North Dakota. Since the Dan Cheadle discovery, over 85 million barrels (BBLS) of oil have been produced from the Tyler Formation from 298 productive wells to date. Most of the productive Tyler wells have been vertical with a handful of horizontal completions. Based on productive wells drilled, the peak years of Tyler activity occurred during 1964–1975 when 117 successful Tyler wells were drilled (approximately one new productive well per month). Peak production occurred during the middle 1960's through the late 1970's when Tyler production totaled between 200 and 300 MBO per month. Water injection began in the early 1970's for enhance oil recovery and to date has injected ∼228 million BBLS water into Tyler reservoirs versus 143 million BBLS of recovered water. Since the end of 1997, Tyler production has steadily decreased with only 20 additional productive wells being drilled and completed. Most of the Tyler production to date has come from a series of bar-type sandstone bodies that trend approximately east-west and are collectively referred to as the Dickinson-Fryburg trend. Most of these sandstone bodies form isolated, oil-saturated porosity pods. Interpreted as either barrier and/or back-barrier sandstones deposited along shore, productive pay sandstone usually displays 10–20% porosity with permeability values of several hundred millidarcies. Organic-rich, argillaceous limestone beds overlay, as well as sometimes underlay, these productive sandstone reservoir bodies and have locally sourced Tyler hydrocarbons. Changes in the quantity and quality of Tyler source rocks across the Dickinson-Fryburg trend controls the amount of hydrocarbon charge within these isolated sandstone reservoirs. In areas where there is high source rock to reservoir ratio, fluid overpressure (pre-production) is often present and production yields oil with low water cuts (prior to water injection).