Feb. 1, 2000
Increasingly, the word "underbalanced" is being heard in technical conversations around the industry.

Herd mentality in an under-balanced state

Increasingly, the word "underbalanced" is being heard in technical conversations around the industry. As the attractive benefits of constructing wells in a pressure-under-balanced state continue to impress decision-makers, conversations surrounding this topic are taking on more of a "when will we," instead of a "how do we" tone.

Successful, failure-free operation on land is driving supporting interest even higher.

Forty percent of all land wells are now drilled in an under-balanced state. The lower permeabilities encountered in most onshore reservoir rocks offer an ideal environment for utilizing existing rotating pressure control equipment. Offshore well examples obviously are not as numerous, but 33 offshore wells have been drilled to date, using under-balanced drilling (UBD) techniques. All of these were drilled from jackups and drilling vessels in shallow water. Deepwater vessels have limited experience using UBD techniques. Higher geologic permeabilities, unproven subsea rotating pressure control equipment, and a general uneasiness, surrounding UBD techniques in deepwater environments, work against UBD implementation. Comfort zones with the available technologies in UBD applications are the reason for the lack of UBD activity in deepwater. This is soon to change with a series of deepwater tests being performed by a joint industry project, including Petrobras, Mobil, and Amerada Hess off the coast of Brazil. Conventional single-phase mud and nitrogen-mud systems will be tested in this first quarter (2000) in 293 meters of water. Rotating, pressure control-head equipment will be supplied by Williams Tool Company.

Successful completion of this project will most certainly start a rush to be the next user of these technologies in other regions around the world. The oil and gas industry exhibits a notorious "herd mentality." One successful operation, and everyone is going to want to reap the benefits of UBD, and a more damage-free reservoir.

Don Hannegan, Vice President of Williams Tool Company, one of the experts and a current champion of UBD technology, posed an interesting question in an extended conversation we had recently about UBD and its role in the short and long-term futures of the oil and gas industry.

Hannegan asked: "Why drill with uncertainty?" (which we currently do while drilling in an over-balanced situation) The first reactionary answer most often heard is that "there is no uncertainty, if operating in an over-balanced state." In this editor's opinion, if this is true, then why do we as an industry spend so much time circulating out formation influxes - some potentially catastrophic? It seems that we've simply accepted the fact that, as a necessary evil, a formation influx may occur and has to be dealt with accordingly. The key word here is "may." "May" implies some amount of doubt.

Hundreds of millions of dollars have been spent in various sectors of the oil and gas industry to reduce doubt in decision-making and operational processes. All of this investment to improve predictability, yet we still "drill with a certain amount of doubt." There is a legitimate argument that drilling in an over-balanced state helps counter any problems resulting from that potential doubt, and this is the way we've done it as an industry for most of the 20th century.

With the available technology in the early days of the oil and gas industry, this was most likely the safest alternative. However, in no doubt, countless wells have suffered debilitating wellbore formation damage due to excessive over-balanced drilling and completion techniques.

As we explore deeper for potential reserves, costs continue to rise. Recovering those costs in a reasonable amount of time is of utmost importance. From a production/reservoir engineer's perspective, one of the key areas improvement can be made to recover these costs, is keeping formation damage as low as possible, and getting the most from the reservoir's natural producing potential. Enter another alternative - performing well construction in an under-balanced state.

One implication of drilling in a near- or under-balanced state is that the process requires constant attention. In an under-balanced state, the doubt mentioned above is not present. A pressure control situation is present constantly, requiring more focused attention on the process to insure safe operation. This is a change from the current practice, where fluid weight is increased and we all breathe a little easier - for a short time, and then the same question has to be answered again.

How many times in our industry has fluid weight been raised so drilling can continue safely, while key drilling personnel are away from the drilling operation, performing other tasks or simply getting much needed rest? While an alternative for maintaining a comfortable safety margin, it is not the best alternative for preserving reservoir production potential.

In some situations, this short duration of excessive over-balance conditions can cause irreparable formation damage, and lower the ultimate total pay-out of the well. This implies a change in the way we think about the drilling process. To support this change, improvements in real-time monitoring have to be addressed.

Changing long time habits and practices is hard to justify in some situations. For example, how long ago did the industry face the question, "Will a top drive system be fully capable of handling a well control situation effectively?" Experience with conventional kelly drive systems made it hard for some people in the industry to accept, without doubt, that a top drive system was fully capable of dealing with a well control situation.

It took some time for the "comfort zone" surrounding top drive system use to sufficiently shift thinking from "will it work" to "what other good benefits can it give us?" The same comfort zone expansion will occur with UBD technologies, the question is: how long will it take?

This shift in thinking means a better acceptance of the fact that there is always another alternative. Evaluation and qualification of that alternative is the hard part, and only achieved as fast as the surrounding human-factor, comfort zone grows. A key part of this human-factor is education and work force knowledge.

A mass re-education of the work force will most certainly be required, and initiatives are already in progress to educate industry personnel in the mechanics and engineering aspects of UBD. It has been stated by more than one of the industry's experts, that a complete re-training of the industry will be required to effectively prepare the workforce for UBD operations. Well control in a near- or under-balanced state basically flips the wellbore inside-out. Conventional well control methods will not apply anymore. One major university has already expressed interest in offering a curriculum for industry engineering and offshore operations personnel.

Another method of educating the industry comes in the form of technical conferences. The recent International Conference on Horizontal Well and Emerging Technologies in Houston was an excellent mechanism to frame discussions in a wide range of well construction topics. Focused presentations in UBD made up about one-fourth of the papers presented, indicating a heightened industry interest in this technology.

The building blocks are falling into place for increased use of UBD techniques. Information gathering for more detailed analysis is underway, as those in drilling operations already know. The standard IADC Morning Drilling Report has been modified to include a section just for UBD parameters. This information will be used for research and evaluation of UBD operations and techniques, further expanding the evaluation process. Three different joint industry programs are pursuing solutions for conventional drilling practice limitations in ultra-deepwater. Expect even more discussions on "under-balanced" drilling techniques.