Abstract

Chevron presently employs two new completion methods to control steam injection into multisand reservoirs in the California Vertical Expansion steamflood areas. The two methods, parallel tubing injection and limited entry injection, are used to improve the steam utilization and to reduce the need to drill new injection wells.

One of the methods used previously is concentric injection in which steam is injected down two concentric pipes placed inside the wellbore and thereby distributed to two separate sands. This method, however, proved unsatisfactory because one of the strings became plugged due to scale buildup. As a result, injection into both sands at desired rates was not possible. For this reason, the concentric injection method is no longer used. Instead, parallel tubing injection and limited entry injection methods are currently used by Chevron.

Since Chevron began the vertical expansion steamflood program in 1984, over 180 injection wells have been drilled and completed with parallel tubing. Thirty-nine existing injection wells have been retrofitted with dual downhole steam chokes. Temperature and production data indicate that the parallel string method can distribute steam between the drive intervals as desired. The limited entry injection method was successful in improving the production performance but was not totally effective in distributing steam into various sands as desired. More tests are underway to improve the method effectiveness.

This paper presents the conceptual details of the two new completion methods and discusses the advantages of these methods over those previously employed. The results of a numerical modeling study and Chevron's operating experience with the two new methods are also discussed.