Advanced Well Design: Cost Efficiency and Acceptable Safety Level
Authors: Vefring Erlend H. , Rommetveit Rolv 
Published: December 2007

Drilling operations will be performed under ever more challenging conditions. Operators must plan to cope with shallow gas, wells with extremely high pressures and temperatures (HPHT), horizontal wells through various formations and pressure regimes, and extreme water depths with difficult weather conditions. There is also a pressure from the management to reduce costs by implementing new, slimmer well designs. Traditional design methods for casing setting depths are conservative. Advanced kick simulators represent the physics/process much better than traditional single bubble kick models, and are not as conservative. This makes a design with longer casing sections and slimmer wells possible, still within safe margins.

Examples on use of the Kick simulator for various conditions are given. and cost reductions which have been achieved are presented.

Introduction

The costs associated with an uncontrolled blow-out may be enormous, in money as well as in environmental damages. In addition danger for personnel safety is involved. The whole petroleum industry will have a major setback if a blow-out occurs. Hence, it is imperative to continue efforts to reduce risk levels related to serious well control incidents, for the new and challenging conditions we will drill under. Advanced kick simulators will have an important role to play in this.

The drilling industry needs to cope with challenging conditions in the future.

Shallow gas drilling has been a concern for quite a number of years. Careful evaluation of seismics has avoided a number of incidents. In addition safer drilling procedures including drilling of pilot holes have been implemented, so that a shallow gas flow today most often does not represent a major danger.

Horizontal well drilling is playing an increasing role in the development of reservoirs in the North Sea and elsewhere. To cope with well control situations that may arise, knowledge of typical problems in such wells, as well as proper planning using kick simulators is important.

Drilling in arctic regions (Barent Sea) is also very demanding. Environmental issues are major concerns in these areas, and kick prevention and safe control has a very high priority. High Pressure and High Temperature drilling in the North Sea is still in the frontier of technological development. The small margins between pore and fracture pressure in combination with complicated mud properties and temperature limitations on equipment, is making drilling in these extreme conditions demanding.

Deep water drilling is now on the agenda west of Shetland as well as on the Norwegian Continental Shelf (Voring plateau and Me-basin). Harsh weather conditions in the North Sea make deep water drilling and development more demanding than in South-American (and Gulf of Mexico) waters.

Slim hole drilling is in the development phase, and is being promoted for onshore drilling in remote as well as urban, sensitive areas. In addition also offshore slim hole drilling, or rather slimmed down drilling is developed today.

The drive for more cost-effective drilling promotes slimmed-down exploration drilling. The transient pressure effects are much larger in slim annuli, and small changes to a slimmed-down well casing programme may lead to sections similar to traditional slim hole sections.

Also, for the future we will see a combination of several "extreme well types", for example HPHT slimmed down drilling or deep water slimmed down drilling.

Maintaining, or even improving safety levels in these drilling operations is a big challenge, and advanced kick simulators will play an important role for the future.