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4D seismic monitoring of CO₂ flood in a thin fractured carbonate reservoir

EnCana Corporation, Calgary, Alberta, Canada

Corresponding author: guoping.li@encana.com

The first 20% of the full text of this article appears below.

The miscible CO₂ flood in Weyburn Field is a massive process for enhanced tertiary oil recovery and greenhouse gas sequestration, the largest of this kind ever in western Canada. This field, a mature Paleozoic carbonate pool of 1.4 billion-barrel reserves, has had nearly 48 years of conventional production history, mostly through waterflooding. Since October 2000 and in an effort to arrest production decline and improve recovery, the field operator has pipelined 5095 MMcf of CO₂ each day as by-products of a coal gasification operation in North Dakota, and pumped it into the 30-m fractured reservoir at a mean depth of 1450 m. Over a 25-year project life, an estimated 14 million tons of the greenhouse gas, which would otherwise be vented into the atmosphere, will be injected and stored in the field's producing formations.

A variety of engineering, geochemical, geologic, and geophysical efforts have been made to monitor flood conformance, optimize sweep efficiency, and assess the reservoir capacity to sequester CO₂ over a long time. The comprehensive monitoring program, conducted jointly by EnCana Corporation and the IEA CO₂ Monitoring and Storage Research Project (a consortium of industry and government partners), has applied technologies such as chemical tracers, hydrogeology and geochemistry sampling, multicomponent (3C and 9C) time-lapse seismic surveying (surface 4D, 4D VSP, and crosswell), in addition to production fluid composition and volume analyses. In this article, we will present some 4D P-wave results obtained from our 3C time-lapse surface acquisitions to demonstrate seismic capabilities for effectively monitoring the progressive movements of miscible CO₂ flood fronts.

	Geology and production history

 
Weyburn Field in southeast Saskatchewan covers about 180 km² and is one of several large oil fields discovered along the Mississippian subcrop belt on the flat northern flank of the intracratonic Williston Basin (Figure 1). Medium gravity crude oil (29° API) . . . [Full Text of this Article]