Actual production data of Winter Field were examined for production rates, oil cut, cumulative oil produced and reserves per well in relation to well length. The log oil cut vs. cumulative oil production per well of groups of wells plots showed that the reserves at a 2% oil cut was the same despite the different lengths of these wells. Published data were next examined to establish the relationship between well length and reserves. It is obvious that the relation between reserves as a function of well length is not a linear relationship for the entire well length examined. This relation shows that as the well length increases from 200 m to roughly 500 m there is a linear increase in reserves. The slope of the line is less than one (0.7); as the length increases beyond 600 m there is very little increase in the reserves. This could explain why the Winter wells all have the same reserves. These groups of wells varied in length from 574 m to 1,110 m; that is, they are all in the length range (greater than 500 m) that gives the maximum reserves(1). In order to verify this conclusion and utilize it to increase the reserve from existing and future wells a series of well workovers and treatment programs were carried out. Newly drilled wells were completed in such a way as to use the conclusions and recommendations of these programs. Introduction The Winter field (Figure 1) has been developed utilizing horizontal wells to produce heavy oil (13.7 API oil of 2,800 – 3,800 cp. viscosity) in a 12 m thick Cumming Sand underlain by a very strong aquifer. The oil cut vs. oil cum. per well plots for each phase (wells drilled in a specific year) are shown in Figure 2. It is obvious that the reserves per well at an economic oil cut of 2% are essentially the same for the different phases. It is interesting to notice that the average well length for the different phases ranges from 574 m to 1,111 m. Data for over 250 horizontal wells producing oil over water reservoir in Saskatchewan published in SEM publication were analysed and the reserves as a function of length are shown in Figure 3. This figure illustrates the non-linear nature of the relationship between reserves and well length. For example a well of 200 – 300 m length has a reserves of 9,000 m3 while a well of 1,000 – 1,100 m has a reserves of 15,000 m3; rather than the 30,000 – 40,000 m3 expected in a linear correlation. Detailed analysis of every well in the Winter Field was carried to identify potential reasons for better or worse performance. A series of water shut-off treatments and workovers were carried out. External casing packers were utilized for formation isolation and proved to be effective. Finally, the information gained from all of the above is being tested in some of the 1995 drilling program through a new completion practice targeting reserves maximization with minimum effect of initial rate.