Reservoir Characterization of a Carbonate Reservoir in the Williston Basin, North Dakota-Winnipegosis Formation

Abstract

The Winnipegosis Formation is a carbonate of Middle Devonian age and is overlain by the Prairie evaporite acting as the cap rock in the Williston Basin. The Winnipegosis Formation has produced significantly larger quantities of hydrocarbon in Canada than the United States. Winnipegosis production in North Dakota has been limited to very few fields in which only a few wells produced the majority of the hydrocarbon. The production differences between Canada and the United States have raised questions about the geological and petrophysical factors controlling production from this formation. The majority of the production from the Winnipegosis comes from reservoir rock that has not been plugged with salt. Salt plugging of the prolific carbonate reservoirs is known to be the reason for failure for many wells when salt is the main cap rock. The main purpose of this study was to integrate geological and petrophysical workflows in order to better characterize carbonate reservoirs with a focus on salt plugging as a major production controlling component. Discrepancies occurring between available data from producing and dry wells in the Winnipegosis Formation in North Dakota were addressed, where resistivity logs admit suitable hydrocarbon saturation in both. Further study includes comparison of well logs, core data and micro-scale images from prolific and poor producing fields in North Dakota. It was found that the depositional environment is the main contributing factor on the reservoir quality and production from the Winnipegosis Formation along with the overlying Prairie Formation. Porosity and permeability distribution in the Winnipegosis Formation is highly controlled by the depositional facies through the basin and later affected by salt plugging. The petrophysical study shows that salt plugged porosity degrades reservoir quality and production from the formation. Log analysis data and high resolution core images proves the presence of salt plugs in the reservoir.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015