| dc.description.abstract | One of the challenges encountered when planning wells in shallow reservoirs in the arctic is the development of a plan to drill a relief well. According to NORSOK such a plan is required to be in place prior to the initiation of drilling. In the case of a blowout, the relief well should intersect the wellpath of the blowing well at a 90º angle in order to be able to drill through its casing. A shallow reservoir is in this thesis defined as a reservoir no deeper than 500mBML, and data from the Wisting field in the Barents Sea has been used for calculations. Reaching these types of reservoirs at a 90º inclination using conventional straight conductors require build-up rates of up to 5.2º/30m. By allowing the conductor to be curved from seabed, the reservoir depth at Wisting may be reached using a build-up rate of 4º/30m.
A relief well is normally drilled by setting a straight conductor and then drilling consecutive sections vertically, until a desired kick-off depth is reached. When doing this operation in a shallow reservoir, the desired kick-off depth is ideally at seabed. The soil strength immediately below seabed is generally not sufficient to support the lateral forces required to initiate directional drilling. By modifying field proven methods of wellhead foundation and conductor installation; the Conductor Anchor Node and conductor hammering, a method enabling the conductor to be curved from seabed is developed.
The possibility of reaching shallow reservoirs horizontally also enables production wells to be developed with increased drainage. In order for the drilling method to be applicable for production wells, it needs to be economically feasible.
Another challenge associated with well development in the arctic is the harsh surface conditions. Marginal fields may also require the use of satellite wells in order to be economically feasible. The proposed solution is therefore planned as a subsea completion.
With this in mind, this thesis proposes a method for installing a curved conductor using as much existing field proven technology as possible in combination with transportation and installation vessels with lower costs and quicker response times than for drillships and rigs.
In order for the conductor to be hammered along a predetermined curved trajectory, a means to guide the conductor is required. By installing a Conductor Anchor Node with such a guide, in the form of an internal curved pipe, the initially straight conductor may be hammered along this trajectory, forcing it into curvature. This modified Conductor Anchor Node is aptly named a Conductor Anchor Guide , or CAG.
In order for the conductor to remain straight as it exits the CAG, and to avoid extreme shear forces in the CAG when inserting the first conductor section, a pre curved conductor section, referred to as a J-curved conductor is used.
Driving analysis of the proposed solutions for offshore clay and three other formation strength scenarios is carried out using a simulation routine developed in conjunction with this thesis. The simulation routine calculates the axial stress distribution in the conductor as well as the blow count, yielding a maximum penetration depth for the various conductor dimensions in given soil condition. The results from these simulations are used to calculate required CAG dimensions, as well as to propose a casing program for the specific cases.
The casing program and CAG dimensions are in turn used to investigate the possibility of handling by smaller vessels, in an effort to propose a cost efficient solution with low response time.
The solution is found to show promising results in terms of both technical and economic feasibility, while at the same time complying with NORSOK requirements regarding plans to drill a relief well. Further analysis and verification of the simulation procedure is, however, required for a complete solution proposal. | en |
