Evolution of Production Practice And Reservoir Management of the Winter Field

Abstract 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 ", ere 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 relations 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 I (0.7); as the length increases beyond the 600 m there is very little increase in the reserves. This could be an explanation for the Winter wells showing the same reserves as the groups of wells examined varied in length from 574 m to 1110 m; they are all in the length range (greater than 500 m) that gives the maximum reserves. In order to verify this conclusion and utilize it to increase the reserve from existing and future wells a series of well work over's and treatment programs were carried out. New drilled wells were completed in such a way that uses the conclusions and recommendations of these programs. INTRODUCTION The Winter field (Figure I) has been developed utilizing horizontal wells to produce heavy oil (13.7 API oil of 2800–3800 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 574m to 1111m. Data for over 250 horizontal wells producing oil over water reservoir in Saskatchewan published in SEM publication were analyzed 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 9000 m3 while a well of 1000–1100 m has a reserves of 15000 m3; rather than the 30–40Em3 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-offs treatments and work over's 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.