The technical and economic feasibility of slant drilling Valhalla Doe Creek water injection wells from central pads was investigated and it was found to be a practical and economic alternative. Slant drilling commenced in September, 1984 and 23 wells have been completed. This paper includes ananalysis of the advantages and disadvantages of cluster dri11ing from central pads; a comparison of slant and directional drilling applicability; a discussion of project planning considerations; a review of drilling procedures, problems, and solutions; and an examination of drilling performance to date. Although some drilling problems were more complex than anticipated, slant drilling is believed to have an economic advantage over vertical drilling at Valhalla based On immediate tangible benefits.
The technique of slant drilling, which is relatively new to Western Canada, differs from conventional directional drilling in that the well is spudded at an angle and then drilled toward the target. It offers the potential of greater horizontal displacements on shallow wells than conventional directional drilling and is well suited to "cluster" drilling: infil1 drilling from central pads. There has been some development of slant drilling in Canada during the past four years, primarily in shallow wells in the soft formations of eastern Alberta and western Saskatchewan.
Petro-Canada''s Valhalla project is slant drilling''s first application to a waterflood scheme and represents the first use of slant drilling in the harder formations of north-western Alberta.
The Valhalla field is located 42 km north-west of Grande Prairie, Alberta as shown in Figure L Conventional oil is produced from 43 wells in the Valhalla Doe Creek "C" Sand at an average vertical depth of 750 m. The pool was discovered in 1981 and is scheduled to go on waterflood in 1985. The waterflood project requires the drilling of 37 water injectors in an inverted five-spot pattern on 32 ha spacing.
The feasibility of directionally drilling the injection wells from central pads was investigaten. In the general case, four well s could be drilled from each surface pad. It was economically desirable to locate the surface pads on existing production well leases.
Cluster drilling from central pads offers several advantages over individual vertical wells. The two modes of 32 ha Field development are compared in Figures 2 and 3 for vertical wells and cluster drilling respectively for a sample one square mile segment of the field. Figures 4 and 5 show a similar comparison for future 16 ha development. Cluster drilling provides the following benefits (refer to Figures 2,3,4 and 5):
Surface land requirements are reduced. The total area to be leased and the number of leases required are decreased. All of the Valhalla pads are located on existing production well locations and in most cases, no additional land was required. There are resulting savings in initial lease payments and annual rent.
Road and lease construction requirements are reduced. No new access roads were required and site preparation involved building minor extensions onto 12 locations rather than building 37 new drilling Sites.