Optimizing productivity and recovery in highly deviated cased wellbores hasevolved and improved over the years but still presents economic and technicalchallenges. The success of a workover depends on the perforating andstimulation techniques employed. This paper reviews the history of a successfulperforating and foam diversion strategy developed for a multilayered carbonatereservoir in Norman Wells. The technical and procedural considerations forcoiled tubing applications are discussed with references to recentworkovers.
The Norman Wells Kee Scarp Formation is a limestone reef located 450 meterssubsea. The Kee Scarp was discovered in 1920 when an oil seepage was drilledalong the north shore of the Mackenzie River. The reservoir is approximately115 meters thick and is pooled in a 25 by 8 kilometer area under the Mackenzie.It is located approximately 120 kilometers south of the Arctic Circle and isthe only producing carbonate reef in the Northwest Territories.
The reef is Middle Devonian in age, roughly time equivalent to the Swan Hillsreefs of west-central Alberta. It is subdivided into a non-porous basalplatform and an overlying porous reef section. The reef is capped by the Canol Formation and can be subdivided into two distinct facies belts. The marginfacies typically has the highest porosity and permeability with good verticalcontinuity. The reef interior or lagoonal facies is typified by low porosityand permeability and very low vertical continuity.
The reef has three major sedimentary cycles initiated with a shoaling ('5')unit and progressing into a differentiated reef (R') unit. These cycles arefurther subdivided into a total of nineteen cycles. The nomenclature todescribe the Kee Scarp is, from base to top: the S I A to C, R I A to E, followed by the S2A to B, R2A to G and capped by the S3A to B. The reef wasflooded prior to R3 deposition. Across much of the reef 5 interior the nineteencycles behave as individual flow units since the cycles are capped by tight, muddy tidal flat facies causing poor vertical flow. Along the reef margin andforeslope, vertical continuity between cycles is good due to the more porousnature of the facies. The 19 cycles form the basis of the workover strategy in Norman Wells and are shown in Figure 1.
The field currently produces 4800 m3/d of 38 ° API sweet oil and 250m3/d NGL through 165 producing wells. It is supported by 9000m3/d of fresh and produced water through 156 injection wells in a 5spot pattern waterflood. The majority of the wells are deviated and are locatedon the banks of the Mackenzie River six artificial and two natural Island. Thepatterns have a 2:1 aspect ratio to take advantage of natural fractures whichare predominantly oriented in a N 26 ° E trend and located in the upper thirdof he reef (R2 and S3). Each pattern is approximately 250 meters by 500 meters.Porosity in the reservoir ranges from 2 to 24% with an average of 8.4%.
