DEA-155 – A Probabilistic Approach to Risk Assessment of Managed Pressure Drilling Offshore

Project Summary

DEA-155 – “A Probabilistic Approach to Risk Assessment of Managed Pressure Drilling Offshore”

Date Submitted:  2-19-04

Technical Area:  ExplorationProduction

Sponsor:  ConocoPhillips

Title: A Probabilistic Approach to Risk Assessment of Managed Pressure Drilling Offshore (Follow link to original PowerPoint presentation)

Submitted by:

Mohr Engineering,

Stress Engineering Services,

Mohr Engineering Division,

13602 Westland East Blvd.,

Houston, TX  77041-1205  USA,

(281) 469-2177 – Office,

(281) 469-2217 – Fax

Principal Investigator(s):  Ken Malloy,, (281) 723-2414 – Cellular

Click here to download the JIP letter of intent in PDF format (72 kb)

Business Impact:

Statistical studies developed by Dodson from the offshore drilling database maintained by the MMS demonstrate consistent problematic areas for concern. Over 650 gas wells were studied from the period of 1993 to 2002. All of these wells were drilled in a conventional manner – that is overbalanced. On these subject wells, stuck pipe, kicks, and lost circulation accounted for 1/3 of all the downtime during drilling operations.

About 24% of all drilling days are spent fighting hole problems, these hole problems negatively influence ROP by 30% and impact the cost per foot by an additional 23%, increase the days to TD by 26%. The trouble costs attributed to hole problems is staggering. The common denominator is that all of these wells are drilled in an overbalanced, open system environment, sometimes far in excess of what is required to maintain hole stability and well control.

We would like to encourage the DEA to undertake a risk analysis to help determine if advances in current drilling technology can help mitigate a significant amount of this trouble time. We have basically been drilling wells in an overbalanced environment in an open vessel since the days of Spindletop.

Managed Pressure Drilling is not a new concept but it is a slight departure from what we have historically been taught in well control school. MPD is drilling overbalance while maintaining near constant bottom hole pressure using a combination of mud density, equivalent circulating density and casing back pressure. To accomplish this task, pressure balance is maintained in a closed system.

In the days of Spindletop, we did not have the sophisticated tools that we have today. They did not have the elaborate choke manifold systems we have today, they did not have microprocessor control, they did not know how to use equivalent circulating density to their advantage, and they certainly did not have rotating control devices to drill in a closed loop system. These tools alone do not laydown a massive footprint, nor do they demand an exorbitant capital outlay. But they offer fine micro-flux control.

Various studies have concluded that we cannot continue to drill in the conventional, overbalanced, open-system environment and produce wells in reservoirs where the BHP cannot productively recover from the insult of massive infiltration due to overly high overbalanced mud columns.

Managed Pressure Drilling is a step change in drilling operations. But to get there we must undertake a risk analysis study comparing conventional overbalance drilling in an open system with managed pressure drilling that is modestly overbalanced but controlled in a closed system. We need to assure ourselves and the regulatory bodies that the managed pressure drilling technologies have sufficiently advanced to ensure safe, productive, and efficient drilling operations.

An effective probabilistic risk analysis study requires the knowledgeable body of experts to qualitatively assess and define the risks. Later after the risks are defined, the knowledgeable body convenes again to determine qualitative risk, where Risk = Probability x Severity. The risks are then ranked and compared.

The Managed Pressure Drilling Subcommittee of the IADC Underbalanced Operations Committee is an existing internationally knowledgeable body of experts that are capable of differentiating the risks between conventional overbalance drilling in an open system with managed pressure drilling that is modestly overbalanced but controlled in a closed system.

In a recent Managed Pressure Drilling Forum, this IADC subcommittee has agreed to be the custodian of the common body of knowledge available to the industry on the subject of MPD. As already mentioned, it is an international body where everyone is welcome to participate whether one promotes MPD or not. From personal experience, I can tell you that the discussions are quite lively. There is no fear that the fox is guarding the hen house.

As soon as funding is appropriated every effort will be made to fast-track the project. This MPD subcommittee meets every quarter. Its next meeting is in Netherlands in mid-March. Although the fuse is short, should funding be appropriated the subcommittee could be prepped for the Qualitative Assessment (Phase I) for its May meeting in Houston. Carry over work will proceed over subsequent quarterly meetings. Polling for Quantitative Assessment (Phase II) would follow close on the heels of Phase I. Once the objectives are realized, a report can be written and discussed in the March, 2006 MPD subcommittee meeting. With timely funding, the results could be presented at the annual DEA summer meeting in June, 2006.