Extended reach, ERD, wells are those wells where the wellbore is kicked off from vertical near the surface, inclination is built to allow sufficient horizontal displacement from the surface to reach the target zone some distance away, and the angle is again built to near horizontal. The wellbore is then extended horizontally into the reservoir. This technology allows the operator to reach portions of the reservoir at a much greater distance than possible with conventionally drilled directional wells, and allows greater contact between the reservoir and the wellbore.
Multilateral wells are wells in which a single wellbore is drilled to a pre-determined depth, then multiple branches are drilled out from the original wellbore. These laterals may extend in opposite directions from each other in the same zone, or they may be drilled into different zones or formations. As with extended reach wells, multilateral wells allow much more contact with the target formation than vertical wellbores. These technologies allow the reservoir to be depleted with fewer wells than with vertical or conventional directional wells.
When kicks or other well control events occur during the drilling of extended reach and multilateral wells, conventional well control procedures are usually attempted. Many assumptions that are made during well kill operations (e.g. negligible annular friction, straight line drillpipe pressure decline, etc.) may not be valid in these long or multiple wellbores. Surface casing and drillpipe pressures during well kill operations will be considerably different than vertical and conventional directional wellbores. Kicks from a single lateral from a multilateral well will undoubtedly have some effect on well kills. Other phenomena that need to be studied and compared (but not limited to) are:
- Kicks without drillpipe in the hole (or one of the laterals).
- Kick migration in multiple laterals and near horizontal wellbores.
- The effect of the compressibility factor, z, on casing and drillpipe pressure.
- The effect of the compressibility of the drilling fluid and formation.
These differences and the effects that they have on well control operations have not yet been fully studied and compared between ERD, and multi-lateral wells and more conventional wells.
We propose to perform an assessment of the state of the art in well control for extended reach and multilateral wells. This project will be performed by completion of four inter-related tasks described below.
Task 1 – Perform a literature search of the state of the art in well control for vertical, directional, horizontal, extended reach, and multi-lateral wells. This will include land drilling operations, and offshore drilling operations utilizing both surface BOP stacks from platforms and jack-up rigs as well as from floating rigs.
Task 2 – Modify an existing Windows-based well control simulator that has been developed by Dr. Jonggeun Choe for use in more conventional wellbores to model extended reach and multilateral wells. To our best knowledge, there are no known well control simulators that will model multilateral wells.
Task 3 – Use the simulator to evaluate, compare, and contrast the current well control procedures utilized for vertical, directional, horizontal, extended reach, and multi-lateral wells. These simulations will include land, shallow water, intermediate water, deep water, and ultra-deepwater. A wide range of pore pressure and fracture gradients, well depths, varying geometries, and formation fluid types will be modeled. These results will be presented to the MMS and the petroleum industry via workshops and conferences.
Task 4 – Based on the results of the simulation study, recommendations will be made to improve well control for any situations that warrant improvement, especially for the extended reach and multilateral wells. The simulator will again be used to validate the procedures.
Deployment of Results
The results of this project will be conveyed to the MMS and the petroleum industry via a final report written to the MMS, thesis written by the graduate students, industry workshops, presentations made at conferences, and through publication in trade journals.
The MMS and the industry will be provided with newer and safer well control procedures for kicks taken while drilling extended reach and multilateral wells.
The MMS and industry will have a better understanding of wellbore pressures during well control operations for kicks taken while drilling extended reach and multilateral wells.
A user friendly Windows based well control and hydraulics simulator which will model ERD and multilateral wells, as well as more conventional wellbores, will be provided to the MMS (at no additional charge) and the petroleum industry at a price to be determined. The industry will be able to use this simulator in training in the safe handling of kicks, as well as in well planning.