Mitchell

When NOT to Research

If you are reading this executive summary, chances are you are a researcher. I am equally guilty. So, when is it appropriate not to use our tendency to research a subject? I have composed a short list for your consideration:

1. The Really Simple Problem: This is a problem you can write and solve on a single sheet of paper without thinking too much. I guess you might even be embarrassed to research this problem.
2. The Textbook Problem: You remember this problem as something you studied in undergraduate school, and you remember the textbook. Look it up in the index. I guess you might call this research, but really, only one reference?
3. Codes, Standards, and Legal Requirements: You are required by law to work the problem according to the regulations. Sorry, no original thought allowed here. What if you think the code is wrong? Well, maybe the legal department of your company can get you a variance. I’m sure they will be sympathetic.

In this issue, there are eleven drilling papers and only a single completions paper. Perhaps the most controversial paper in this issue is The Role of Knowledge, Tools, and Systems for Drilling Analysis. This paper proposes a methodical structure to embody current expertise for the analysis of drilling data. The authors assert that several key aspects of the analysis of drilling data are not clear. Under this scenario, it seems that more effort is needed to unify current approaches to analyze drilling data (i.e., within the scope of common goals, theories, methods, and tools that can support the decision-making process). With more and more data being acquired at the wellsite, the drilling engineer is left with the problem of making effective use of this data. This paper presents a step in that direction.

The next five papers form a "mini" tubular symposium. Near-Surface External-Casing Corrosion in Alaska: Cause and Mitigation--The identification of shallow external surface casing corrosion raised concern about reliance on the casing as a barrier during normal operation of North Slope wells. Understanding the corrosion mechanism was a substantial step forward in prevention and mitigation of the consequences of corrosion damage, which led to practical approaches to provide an alternative to workover repairs. Casing-Collapse Strength Reduction Under Lateral Loads From Yielding Shales in the Daqing Oilfield—Casing failure has been found in nearly 20% of production wells in the Daqing Oilfield, and is one of the most costly problems in the field. A mechanistic model was developed to relate the lateral load to radial and longitudinal deformation of well casing. They found that the model predicts that casing collapse resistance declines sharply with the radial deformation of the casing and that casing collapse resistance declines slightly with the length of the deformation. Strain-Based Design of Tubulars for Extreme-Service Wells—Strain-based design utilizes material capacity beyond its elastic range to overcome a number of economic and technical hurdles encountered in conventional load-based designs. The results in this paper suggest that designs incorporating larger-than-average plastic-strain amplitudes can tolerate multiple loading cycles. This conclusion offers a plausible explanation for the low failure rates in thermal projects where moderate localization effects are known to contribute to cyclic plastic deformation. In the general context of well design, this conclusion presents an opportunity for reducing well costs by using lower strength materials and accommodating more cyclic plastic deformation. Tubing Buckling--The State of the Art--The first analysis of helical buckling was published by Lubinski in 1962. In the nearly 50 years since that publication, a number of developments have extended those results to deviated wells, interactions with packers, and frictional loads. This paper summarizes the current state of the art, provides a comprehensive bibliography of buckling papers, discusses limitations of the current models, and states future development needs. First Hyperstatic-Riser Joint Field Tested for Deep Offshore Drilling--The riser is one of the key elements for deep offshore drilling. However, the total weight of the system increases rapidly with the water depth in the same way as the required tensioning capacity. A new technology developed for integrating riser joints reduces, by up to 30%, the weight of the system. It consists in joining together all the pipes constituting the riser (main pipe and peripheral lines) in such a manner as to share the axial tension between all of them. This "hyperstatic" working mode provides an axial-load sharing between all riser lines. The paper details numerical and experimental works carried out to develop this hyperstatic integration.

Real-Time Digital Interpretation of Subsea-Blowout-Preventer Tests--A computer-based method expedited interpretation of pressure data during subsea-blowout-preventer (BOP) tests. This reduced the time and cost of current subsea BOP-testing practices in a safe and objective manner. Stressed-Shale Drilling Strategy--Water-Activity Design Improves Drilling Performance--Nonaqueous drilling fluids are often chosen to drill troublesome shale formations in an effort to minimize wellbore-instability problems. However, experience in the Gulf of Mexico has indicated that when drilling in highly faulted areas, oil- and synthetic-based fluids do not always prevent wellbore destabilization. A detailed laboratory investigation using preserved shale core and drilling information have confirmed that the water activity of drilling fluids is often much lower than necessary. This study has shown that when drilling faulted or fractured shale the correct, not higher, salt content in drilling fluids will reduce wellbore collapse problems and improve drilling performance. Quantification of Overbalance-Induced Invasive Damage and the Estimation of Equivalent-Skin Effect on Production--An important premise of underbalanced drilling (UBD) is the productivity improvement it delivers through mitigation of invasive damage. Characterization and quantification of such damage, therefore, becomes a prerequisite for assessing the value delivered by UBD. In this work, the authors use a novel approach that combines dynamic microscale-reservoir simulations calibrated to special core tests to model the extent of invasive damage, and its impact on flowback during production. The use of these results in designing an optimal drilling and completion plan to lock in the value of UBD is demonstrated for the two field cases. Wellbore-Stability Study for the SAFOD Borehole Through the San Andreas Fault--This paper presents a wellbore stability study of the SAFOD (San Andreas Fault Observatory at Depth) research borehole located near Parkfield, central California. As logging-while-drilling (LWD) acoustic-caliper data and real-time hole-volume calculations both showed that relatively little failure occurred while drilling through the SAF; the predicted mud weight was successful in drilling a stable borehole. However, once the pore pressure in the bedded and fractured rocks crossed the threshold for shearing the fracture planes, wellbore failure occurred. Successful Drilling of Oil and Gas Wells by Optimal Drilling-Fluid/Solids Control--A Practical and Theoretical Evaluation--This paper describes in detail the theory and field examples on how wear arise on the shaker-screen cloth. This knowledge has been used to increase the solids control efficiency at the same time as the screen wear has been reduced by more than 90% in several field cases where 17 ½-in. sections have been drilled with oil-based muds.

The single completions paper: Bokor--A New Look at Sand Production in a Mature Field--Certain questions have to be answered before completing a well in a weak sandstone reservoir: will sand production be an issue, now or as the reservoir depletes? The industry has become aware that oriented perforations can prevent sand, and they also generally give higher production rates than a screen or gravel pack would give in the same well. Clearly, there is a need to reliably predict under which circumstances the technique of oriented perforating can prevent sand production. This study showed which completions were feasible in each of the Bokor reservoirs, depending on wellbore and perforation orientation.