Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
Field studies of wells on the Nesson Anticline in North Dakota have shown that cement placed during original primary cementing operations in many of the wells has now deteriorated to the point that zone isolation no longer exists. In their present condition, they cannot be stimulated or used successfully as injection wells. Squeeze cementing has proved highly uneconomical because many repeated stages are required. Even with repeated stages, success ratios have been extremely low. This paper describes a replacement cementing-technique developed to remove deteriorated cement and replace it with new cement. While developed for Nesson Anticline wells, the technique should prove successful in other areas where similar problems exist. problems exist
Many of the wells producing front the Madison formation along the Nesson Anticline in North Dakota had declined as early as 1963 to a point where they would no longer produce their allowable. Some stimulation was started at that time. In 1966, however, North Dakota allowables were raised, and a great number of the wells were treated with large volumes of acid to increase the production. The majority of these wells treated on vacuum. Little or no increase in oil production resulted from the treatment, although there was often a large increase in water production. Wells which required surface pressure to displace the acid showed good increases in oil production.
It was suspected that channels existed in the primary cement in the wells which treated on vacuum and that the acid was not entering the desired producing zone. The wells which treated with pressure were believed to have the primary cement intact. Acid was confined to the desired zone and reservoir penetration with the acid provided good production increases.
