Rotary steerable technologies changing ERD trends

As rotary steerable tool technologies evolve, and more tool alternatives hit the market, unique applications continue to be developed. The most obvious application is extending drilling depths beyond conventional steering limitations. But, the "push-the-envelope" philosophy, which is omnipresent in our industry, has resulted in creative applications for these technologies. A look at extended reach drilling (ERD) drilling trends in the 1990s provide some insight into where, and how far, they can go.

Interesting industry trends in the 1990s show a majority of ERD wells with horizontal departures in the range of 10,000-15,000 ft. The second and third highest number of wells are in the 5,000-10,000 ft and 15,000-20,000 ft ranges, respectively (see Mason).

The horizontal departures (Dep) and true vertical depth (TVD) of these wells show a general "shallowing" trend over the 1990s, thus increasing the Dep/TVD ratio. This increase in the Dep/TVD ratio is most likely due to the increase in conventionally steered, horizontal, and multi-lateral drilling techniques in the early to mid-1990s. Older fields realized extended production life from more wellbore exposure within marginal reservoirs. This concept was heavily exploited on land and in older offshore shallow-water reservoirs.

Prior to the 1990s, deeper wells with Dep/ TVD < 2 were the industry standard. In the 1990-1998 period, a gradual trend to more shallow wells (shorter TVD) developed, and Dep/TVD ratios in the 3-5 range.

Global offshore activity increased during this period, contributing more data points to the interpretation. This contribution by offshore extended reach wells during this period were dominated by straight and low-to-moderate slant exploratory holes, pushing the TVD values greater.

With this in mind, a mis-interpretation can easily be made, due to the below-rotary-table (bRT) scale and greatly increased water depth of these wells. Data points of these wells will plot more to the lower center of the graph. The cluster of data points in the 10,000-20,000 ft range and along a Dep/TVD = 1.5 line, are representative of this trend.

If a linear progression of future activity into deeper waters is assumed, then a trend downward and to the right of the graph should develop (see highlighted area). Expect future wells also to continue to push the Dep/TVD > 5. New techniques are being developed every day with these tools, allowing a little extra hole to be drilled.

An abrupt stop in horizontal departure at about 27,000 ft was observed at the end of 1995 (see Mason). Two important events occurring in the 1996-1998 time frame contributed to this anomaly:

• Existing drilling technologies were approach ing a critical limit.
• A sharper increase in activity in greater depths occurred.

The industry, in healthy shape at this time, saw a considerable number of offshore extended reach projects being drilled. Conventional steerable drilling assemblies were the dominant drilling technique of choice. The limitations of these conventional assemblies were finally limiting the drilling process, instead of contributing to it. At this point, rotary steerable technologies began to emerge as a possible solution for this problem.

As another indication of how the industry is using this technology, one service provider noted an increased utilization rate for rotary steerable technology in 1998 and 1999. This is significant, considering the industry experienced an activity downturn in the same time period.

Reference

C.J. Mason, SPE, A. Judzis, SPE; BP Exploration; SPE, Paper No. 48942

North Sea drilling/completion fluids www sites

In the September issue, Offshore Magazine published the 1999 Drilling/Completion Fluids Directory. Included in the survey were two columns, HOCNF Classification, and PLONOR Listing Available. There has been some confusion among the survey contributors and readers concerning the applications for this information.

These classifications are specific to the UK and Norwegian North Sea petroleum-operating regions, with the PLONOR Listing strictly a UK guideline. Governmental regulations controlling the use of petroleum industry specific fluids and chemicals in this region are stringent, when compared to other operating regions around the world. To assist readers that may operate in this region, the following web address can be viewed for a more detailed explanation.

Guidelines on how the OCNS (Offshore Chemical Notification Scheme) is determined by CEFAS (Centre for Environment, Fisheries and Aquaculture Science), and what documen-tation is needed when a product is submitted for evaluation are available at these sites:

• www.cefas.co.uk/ocns/ (OCNS Explanation)
• www.cefas.co.uk/productsframeset.htm (HOCNF and PLONOR Listing Explanations)

Forgetting fundamentals reminder to industry

The biggest loss in the recent Mars Climate Orbiter burning up as it entered orbit, was not the loss of the orbiter itself, but the loss of communication between project planners and programmers during project design. A simple programming error of conflicting metric and English measurement units caused a financial loss of $125 million dollars, let alone the loss of valuable data and information the orbiter was to collect.

This should be considered a harsh wake-up call for industries operating in a worldwide marketplace, and especially the oil and gas industry. The industry has operated with metric and English (oilfield) units for decades, and has always seemed to be able to correct for the proper units with little effect on operations.

But how many times have you looked at a log from some rig in the middle of nowhere, and find yourself asking: "Is this meters, or feet in the depth track?" This is just one example. Numerous others have happened to most of us at some time or other.

As processes become more automated and run behind the scenes, the chance of a "mis-communication" becomes even more possible. Maybe it's time for our industry, specifically in the U.S., to take another hard look and move more aggressively to a common set of units.