With partial funding from the U.S. Department of Energy Class I Oil Program, a research team headed by the Utah Geological Survey conducted a reservoir characterization study, designed a field demonstration program, and is beginning the recompletion of a second well in the Bluebell oil field of the Uinta Basin, Utah.

The Bluebell field is productive from the Tertiary Green River and Wasatch Formations. The productive interval consists of thousands of feet of interbedded fractured clastic and carbonate beds deposited in a fluvial-dominated deltaic lacustrine environment. Wells are typically completed by perforating 40 or more beds over 1,000 to 3,000 vertical feet, then acid stimulating the entire interval. This technique is believed to leave many potentially productive beds damaged or untreated.

The project demonstration will show how to improve primary oil recovery using better completion techniques. The demonstration consists of three parts: (1) recomplete a well using multi-stage, high-diversion, low-friction acid treatments over a gross interval of 1,500 feet; (2) in a second well test, stimulate and test again three or more beds individually to determine the effects of the stimulation on each bed; and (3) drill and complete a new well.

Mechanical problems with the first demonstration prevented the operator from carrying out the acid-frac as planned and the results obtained from the recompletion cannot be considered typical for a well in the Bluebell field but some useful data was gathered. Interpretation of the dipole sonic, thermal decay, and radioactivity tracer logs used in the demonstration show that: (1) many fractures are confined by bed boundaries, (2) fractures distribute acid beyond the perforated interval, and (3) many of the beds that are not perforated appear to be as depleted as the beds that are perforated.

The second part of the demonstration will occur during the fall of 1997. The second demonstration will use the reservoir characterization study and advanced cased-hole logs to identify three or more key beds in the demonstration well. The objectives of the second demonstration are to: (1) identify “pay” within the complex heterogeneous reservoir using reservoir characterization and advanced logging techniques, (2) improve the efficiency of the completion by isolating and stimulating on a bed scale, and (3) compare the economics of interval-scale versus bed-scale completion techniques. The results of the second demonstration will be presented May 1998 at the AAPG Annual Convention in Salt Lake City, Utah.