Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Understanding Controls on Produced Fluid Properties at Pinedale
(1) Innovation, Research & Development, Shell Projects and Technology, Houston, TX.
(2) Upstream Solutions, Shell Projects and Technology, Houston, TX.
(3) Onshore Gas, Shell Upstream Americas, Houston, TX.
(4) Onshore Gas, Shell Upstream Americas, Calgary, AB, Canada.
(5) Onshore Gas, Shell Upstream Americas, Denver, CO.
The Pinedale anticline is one of the best-known tight gas accumulations in the Rocky Mountains. Fluids are reservoired in the Upper Cretaceous Lance and Mesaverde formations, which comprise fluvial and overbank sands, interbedded with carbonaceous shales and thin coal layers. Production is predominantly dry gas with some condensate. The objective of this study was to determine the origin of the produced fluids and which factors control their distribution and properties, via an integrated geochemical and basin modeling study. Gas, condensate and produced water samples were collected from 31 wells together with core and Isotube gas samples from the Jensen 6-11 well. Some of the wells were re-sampled six months later to assess changes in fluid composition during production. Hydrocarbon fluids were subjected to rigorous geochemical analysis, including, detailed molecular and isotopic characterization. The brines were also well characterized, with additional trace element and isotopic analysis performed. These results reveal a deep kitchen source for the gas. However, much of the condensate appears to be derived from shales and coals within the reservoir, which spans the conventional maturity oil window from ca. 0.7 to 1.2% VR. Thus, the hydrocarbon accumulation at Pinedale is hybrid in nature, comprising dry gas which has migrated in to the structure and condensate sourced from the reservoir formation. This study also reveals how charging mechanisms, interaction of separate fluid phases within the reservoir, and fracture intensity have influenced the observed chemistries and associated fluid properties.