In mature areas well construction costs are the primary obstacle in the development of marginal fields. Implementing more targets into one well path can reduce the exploratory risk. Horizontal wells can help to reduce development costs. However, these wells represent a major cost factor. To reduce horizontal well costs a new casing and completion philosophy, saving the intermediate casing string across the build up section was worked out. Substantial savings result from reduced logging and casing program. Moreover, the concept provides utmost flexibility to actual production requirements. Applying the new concept well costs can be reduced by approximately 30%.
An example of a recently drilled super slanted appraisal well is given. To improve project economics several secondary targets were included in the well path. To even more reduce well costs, starting from the kick off point the well was drilled in one run, with one bit and one bottom hole assembly. Unfortunately the primary target did not come in. But especially under these conditions the concept proved to be most economical.
In mature hydrocarbon provinces new geological concepts can allow for an economic revival of exploration and production activities. However, since the areas have been highly explored in the past only small reservoirs or compartments of already existing reservoirs can be expected to be found. But existing infrastructure, such as pipelines and production facilities would make even small finds attractive. In this light it is of vital importance to reduce risk and costs in HC exploration and production.
The application of new techniques can provide a better understanding of the depositional framework and can result in the establishment of a new and more complex geological model (Fig. 1). Whereas in the past the reservoirs in the Vienna basin for example were considered to be more or less allocated to a flat anticline the new model incorporated small and differently located channels and lobes within the reservoir. It is obvious that a vertical well would not penetrate all horizons in a favorable position.
To cope with theses requirements new well construction concept had to be developed. On the one hand horizontal wells horizontal wells can reduce development costs and increase overall recovery, on the other hand the geological risk can be reduced by incorporating several targets into one well path. However, these wells represent a major cost factor in a low cost environment. To further reduce drilling costs a new casing philosophy was established.
The New Casing and Completion Philosophy
To develop a field with a horizontal producer usually a pilot well is drilled first, to determine the actual depth of the reservoir. Consequently, the hole is plugged back and side tracked. The build up section is cased off and the horizontal section drilled to the required length (Fig. 2). In order to minimize well construction costs the question arose if it would be possible to skip the casing string across the build section and to avoid the need of a pilot hole.
To minimize well construction costs a super slanted well was considered to identify the reservoir depth, prove the extent of the reservoir and to serve as a producer as well. A slanted well trajectory would provide enough flexibility to adjust the planned well path to actual vertical reservoir depth and to appraise the extent of the structure. Moreover, skipping the intermediate casing string would allow to slim down the casing program.