Eric Davidson

Delayed-Release Acid System for Cleanup of Al Khalij Horizontal Openhole Drains

The full-length paper describes a new approach that uses a slow-acting stimulation treatment for damage removal and stimulation. The stimulation treatment comprises a starch enzyme to degrade the most troublesome polymer and an organic compound that reacts with the carrier brine to release organic acid in situ over a period of several hours. The system has been used recently in the Al Khalij field in Qatar with openhole lengths ranging from 162 to 576 ft and treatment volumes ranging from 125 to 725 bbl.

Development of the Alba Field-Evolution of Completion Practices, Part 1: Openhole Screen-Only Completions to Gravel Pack

The Alba reservoir (located in the central North Sea) is a highly permeable, unconsolidated sand body with lenses of reactive shales within the reservoir sand. From the initial decision to exploit the field with horizontal wells, there has been an evolutionary approach to selecting the most appropriate drilling fluid and completion technique. Field development has been marked by a drive to increase productivity and reduce the total cost of the ownership of the asset. The major challenges in completing wells in this field involve sand control and inhibition of reactive reservoir shales. Initially, completions were prepacked screens in open hole, and the fluid used to drill the reservoir section was oil-based mud (OBM). Productivity was lower than expected, but improvements were achieved by switching to sized salt water-based mud (WBM) and initiating a very stringent quality-control procedure for the drilling and completion fluids. However, screen failure occurred within 2 to 3 years of production startup, and the wells almost invariably sanded up. More recent changes have involved a switch to sized calcium carbonate WBM and openhole gravel packs. Because the geology of the Alba field dictates that there is almost always some shale exposed in the openhole reservoir section, it was found that the gravel-carrier fluid needs to be equally as inhibitive as the drill-in fluid. Since 1998, 13 openhole gravel packs have been successfully completed, with high flow rates and no history of sand production in all cases. This paper deals with the performance of the various techiques applied and details the best practices derived for optimum productivity and screen longevity.