Executive Summary

Robert 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 toresearch a subject? I have composed a short list for your consideration:

  1. The Really Simple Problem: This is a problem you can write and solveon a single sheet of paper without thinking too much. I guess you might even beembarrassed to research this problem.
  2. The Textbook Problem: You remember this problem as something youstudied in undergraduate school, and you remember the textbook. Look it up inthe index. I guess you might call this research, but really, only onereference?
  3. Codes, Standards, and Legal Requirements: You are required by law towork the problem according to the regulations. Sorry, no original thoughtallowed here. What if you think the code is wrong? Well, maybe the legaldepartment of your company can get you a variance. I’m sure they will besympathetic.

In this issue, there are eleven drilling papers and only a singlecompletions paper. Perhaps the most controversial paper in this issue is TheRole of Knowledge, Tools, and Systems for Drilling Analysis. This paperproposes a methodical structure to embody current expertise for the analysis ofdrilling data. The authors assert that several key aspects of the analysis ofdrilling data are not clear. Under this scenario, it seems that more effort isneeded to unify current approaches to analyze drilling data (i.e., within thescope of common goals, theories, methods, and tools that can support thedecision-making process). With more and more data being acquired at thewellsite, the drilling engineer is left with the problem of making effectiveuse 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 andMitigation--The identification of shallow external surface casing corrosionraised concern about reliance on the casing as a barrier during normaloperation of North Slope wells. Understanding the corrosion mechanism was asubstantial step forward in prevention and mitigation of the consequences ofcorrosion damage, which led to practical approaches to provide an alternativeto workover repairs. Casing-Collapse Strength Reduction Under Lateral LoadsFrom Yielding Shales in the Daqing Oilfield—Casing failure has been foundin nearly 20% of production wells in the Daqing Oilfield, and is one of themost costly problems in the field. A mechanistic model was developed to relatethe lateral load to radial and longitudinal deformation of well casing. Theyfound that the model predicts that casing collapse resistance declines sharplywith the radial deformation of the casing and that casing collapse resistancedeclines slightly with the length of the deformation. Strain-Based Design ofTubulars for Extreme-Service Wells—Strain-based design utilizes materialcapacity beyond its elastic range to overcome a number of economic andtechnical hurdles encountered in conventional load-based designs. The resultsin this paper suggest that designs incorporating larger-than-averageplastic-strain amplitudes can tolerate multiple loading cycles. This conclusionoffers a plausible explanation for the low failure rates in thermal projectswhere moderate localization effects are known to contribute to cyclic plasticdeformation. In the general context of well design, this conclusion presents anopportunity for reducing well costs by using lower strength materials andaccommodating more cyclic plastic deformation. Tubing Buckling--The State ofthe Art--The first analysis of helical buckling was published by Lubinskiin 1962. In the nearly 50 years since that publication, a number ofdevelopments have extended those results to deviated wells, interactions withpackers, and frictional loads. This paper summarizes the current state of theart, provides a comprehensive bibliography of buckling papers, discusseslimitations of the current models, and states future development needs.First Hyperstatic-Riser Joint Field Tested for Deep OffshoreDrilling--The riser is one of the key elements for deep offshore drilling.However, the total weight of the system increases rapidly with the water depthin the same way as the required tensioning capacity. A new technology developedfor 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 pipeand peripheral lines) in such a manner as to share the axial tension betweenall of them. This "hyperstatic" working mode provides an axial-loadsharing between all riser lines. The paper details numerical and experimentalworks carried out to develop this hyperstatic integration.

Real-Time Digital Interpretation of Subsea-Blowout-Preventer Tests--Acomputer-based method expedited interpretation of pressure data duringsubsea-blowout-preventer (BOP) tests. This reduced the time and cost of currentsubsea BOP-testing practices in a safe and objective manner. Stressed-ShaleDrilling Strategy--Water-Activity Design Improves DrillingPerformance--Nonaqueous drilling fluids are often chosen to drilltroublesome shale formations in an effort to minimize wellbore-instabilityproblems. However, experience in the Gulf of Mexico has indicated that whendrilling in highly faulted areas, oil- and synthetic-based fluids do not alwaysprevent wellbore destabilization. A detailed laboratory investigation usingpreserved shale core and drilling information have confirmed that the wateractivity of drilling fluids is often much lower than necessary. This study hasshown that when drilling faulted or fractured shale the correct, not higher,salt content in drilling fluids will reduce wellbore collapse problems andimprove drilling performance. Quantification of Overbalance-Induced InvasiveDamage and the Estimation of Equivalent-Skin Effect on Production--Animportant premise of underbalanced drilling (UBD) is the productivityimprovement it delivers through mitigation of invasive damage. Characterizationand quantification of such damage, therefore, becomes a prerequisite forassessing the value delivered by UBD. In this work, the authors use a novelapproach that combines dynamic microscale-reservoir simulations calibrated tospecial core tests to model the extent of invasive damage, and its impact onflowback during production. The use of these results in designing an optimaldrilling and completion plan to lock in the value of UBD is demonstrated forthe two field cases. Wellbore-Stability Study for the SAFOD Borehole Throughthe San Andreas Fault--This paper presents a wellbore stability study ofthe SAFOD (San Andreas Fault Observatory at Depth) research borehole locatednear Parkfield, central California. As logging-while-drilling (LWD)acoustic-caliper data and real-time hole-volume calculations both showed thatrelatively little failure occurred while drilling through the SAF; thepredicted mud weight was successful in drilling a stable borehole. However,once the pore pressure in the bedded and fractured rocks crossed the thresholdfor shearing the fracture planes, wellbore failure occurred. SuccessfulDrilling of Oil and Gas Wells by Optimal Drilling-Fluid/Solids Control--APractical and Theoretical Evaluation--This paper describes in detail thetheory and field examples on how wear arise on the shaker-screen cloth. Thisknowledge has been used to increase the solids control efficiency at the sametime as the screen wear has been reduced by more than 90% in several fieldcases where 17 ½-in. sections have been drilled with oil-based muds.

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