Cheatham

Simply The Best

Recently a reader wrote to suggest how SPE Drilling & Completion (SPEDC) should deal with technology issues related to the Macondo blowout. Suggestions included development of industry standards for design of deepwater wells and competency tests for drilling engineers working on subsea wells. Both are excellent ideas but neither falls within the scope of SPEDC. Another suggestion was to solicit papers written specifically to address the Macondo blowout. Technical papers obviously fall within the scope of SPEDC, but soliciting papers for a specific topic is unprecedented. Nevertheless, change is possible and could be an improvement. A fair question, therefore, is: Should specific topics be solicited for our journal? To consider this change, let’s review the way paper topics are currently determined.

The mission of SPEDC is to publish the best papers about drilling and completing oil and gas wells. General guidelines for potential topics appropriate for SPEDC are provided on the website http://www.spe.org/about/governance/discipline_categories.php. Authors may submit papers on these topics directly to SPEDC. Roughly 10% of papers we receive are direct submissions.

Most papers submitted to SPEDC (approximately 90%) originate at SPE conferences. As a result, the conference themes chosen by SPE committees influence topics in SPEDC. For example, consider the suggestion by our reader who wanted to see papers published on the Macondo blowout. In October, SPE will convene its first Deepwater Drilling and Completions Conference. We expect some of these papers will be submitted to SPEDC and eventually be published after peer approval. Also, the 2011 SPE/IADC Drilling Conference in Amsterdam has two technical sessions focused on deepwater technology. Therefore, there are ample opportunities for authors to submit papers on the Macondo blowout or other deepwater topics.

This issue contains three papers on deepwater topics. Our first paper, Validation of Blowout-Rate Calculations for Subsea Wells, is a timely topic in relation to the Macondo blowout. But, this paper was presented at an SPE conference in August 2008 and peer approved in January 2010--long before the blowout occurred. Therefore, credit for topic selection goes to the author.

In fact, ultimately, it is authors who choose the topic for their paper. True, there are general guidelines provided by SPE. But in the final analysis, it is up to you and me as individual SPE members to write excellent technical papers about the important topics of the day.

The role of individual SPE members in relation to technical papers was aptly described by H.M. Krause, Jr. in the July 1963 Journal of Petroleum Technology (Krause 1963):

"The individual member who considers himself a professional has the obligation to (1) financially support his professional society and the publication of important literature concerning his profession, (2) keep up with the literature so that he may avoid technological obsolescence, and (3) contribute technical papers to the literature, building on the knowledge which has been given to him by his predecessors."

This view is as valid today as it was when it was written nearly 50 years ago. It reinforces the philosophy that individual SPE members are responsible for writing technical papers on the important issues.

In summary, SPEDC exists to publish the best papers on essentially any topic related to drilling and completing oil and gas wells. Broad guidelines are provided for suitable topics through the SPE website and SPE conferences. In the end, however, individual SPE members determine what topics are important. In my view, that is how it should be.

Associate Editors

We would like to give our heartfelt thanks to three Associate Editors whose terms are coming to an end: Pål Skalle, João Carlos Plácido, and Dan Scott. Each has provided outstanding service to our journal. Happily, they will continue to serve as technical editors.

Congratulations to Deepak Gala who was recently elevated from the ranks of outstanding technical editors to associate editor. We welcome Deepak to his new role in charge of managing reviews for papers on managed pressure drilling.

Now to the papers: This issue contains fourteen papers on the following topics: deepwater (three papers), cementing/zonal isolation (four papers), and seven general papers on drilling.

Deepwater

Our first paper, Validation of Blowout-Rate Calculations for Subsea Wells, appears to be directly applicable to the Macondo subsea well that blew out on April 20. The author explains how calculations of blowout rates in subsea wells are more complex than for onshore or platform wells because of the significantly greater pressure at the seabed. Previously, a simulator was developed and validated for onshore and platform wells. The present work extends the simulator to subsea wells by comparing model predictions to field data from an offshore gas well drilled underbalanced. We hope the subsea blowout-rate simulation described here has been applied to the Macondo well. Better still would be for such a comparison to be published.

Encountering bitumen (called "tar" by some other authors) in deepwater subsalt wells continues to be an expensive problem for the industry. A USD 100 Million "Rock": Bitumen in the Deepwater Gulf of Mexico offers new insights that could lead to effective strategies for managing future bitumen encounters. Laboratory tests were conducted on bitumen samples obtained from a Green Canyon well that experienced costly problems from bitumen. Rock mechanics properties measured at elevated temperature and pressure conditions provide useful insights into the material behavior of bitumen. The authors related these laboratory results to numerical modeling and field observations that bitumen encountered at different depths can behave very differently. This paper is essential reading for those involved in deepwater subsalt wells. It would really be great if other operators with experience drilling bitumen contributed to online discussion of this paper at the SPEDC website.

In deepwater reservoirs, openhole gravel packing is often used for sand control. Water packing is a commonly used method for gravel-packing long, horizontal wells. Low fracture gradients found in deepwater fields can limit the maximum pressures achievable during gravel packing. Exceeding fracture pressure represents a major risk factor because too high pressure causes premature screenout and an incomplete gravel pack. Mechanical means and lightweight gravel are existing solutions to this problem. An Alternative Method of Dealing With Pressure: Friction Reducer for Water Packing of Long Horizontal Open Holes in Low-Fracturing-Gradient Environments introduces a new solution--friction reducers. Friction reducers are commonly used in slickwater applications, but before the present work, friction reducers were incompatible with heavy brines used in water packing. This paper shows results of successful full-scale laboratory testing of the new friction reducer, which can be used as an alternative or in combination with existing methods to extend application to longer horizontal wells.

Cementing / Zonal Isolation

Cements are designed to provide zonal isolation over the life of a well and beyond. Various stresses imposed during the life of a well can cause even a well-designed and properly placed conventional cement to crack or develop microannuli. The result can be loss of zonal isolation. A recent approach has been to use self-healing cements containing additives that swell on exposure either to aqueous fluids or hydrocarbon and seal off any fluid-flow paths. Many successful jobs have been performed using these cements with apparent success, at least in the short term, even in gas fields. The problem with these designs is that the swelling of additives is fluid specific and requires exposure to wellbore fluids. Self-Healing Cements That Heal Without Dependence on Fluid Contact: A Laboratory Study introduces cement that will self heal without exposure to fluids. Demanding laboratory studies were successfully passed by the novel cement, which contains a new class of elastomeric materials. This paper provides an interesting study of a promising new technology.

When a well is permanently abandoned, it is plugged to provide long-term zonal isolation. Laboratory and Field Validation of a Sealant System for Critical Plug-and-Abandon Situations describes a novel sealant system designed to avoid internal shrinkage that occurs using conventional cements. The sealant was proven in laboratory tests to expand without external water contact. A solid case history is presented that demonstrates the expanding cement has been successful in preventing any casing pressure in gas wells close to habitations for several years.

In recent years, swellable packers have proven valuable in achieving zonal isolation for specific applications, such as multiple zone openhole completions and horizontal wells where cementing can be problematic. Effect of HCl Acid and Brines on Water-Swelling Packers describes laboratory qualification testing on commercially available packers exposed to hydrochloric acid, potassium formate, and sodium chloride. Tests showed that all packers successfully swelled in aquifer water and low-salinity brines and held a differential pressure of 2,000 psi. However, none of the packers successfully maintained a seal after exposure to 15% HCl, which is the preferred stimulation method for the field being studied. Additional results, guidelines for field application, and future plans are detailed in the paper.

The fourth and final paper on cementing is Characteristics of Oilwell Cement Slurry Using CMC. It describes a thorough laboratory evaluation of the potential for using carboxymethylcellulose (CMC) to design a new type of cement slurry for oilwell applications. The primary benefits of CMC are its ability to meet multiple requirements for cements such as early high compressive strength, reduced permeability, and reduced free water. Another potential benefit is the wide availability of CMC around the globe, which may make it economically attractive for some applications.

General Drilling

Managed pressure drilling (MPD) and automated drilling are two hot topics that are combined in Control Requirements for Automatic Managed Pressure Drilling System. A primary focus for MPD is narrow margin drilling, which requires accurate pressure control. This paper lays out some key needs for automatic control of downhole pressure by topside chokes during MPD operations. Results from application of automatic MPD in a North Sea well are discussed. The short-term control requirements for automatic choke control are described for normal drilling operations, such as making connections involving starting/stopping pumps and moving the drillstring, and for "failure" operations, such as gas kicks, mud loss to the formation, and a blocked choke. The requirement to stay within tight margins are achievable now for offshore rigs except for floating rigs operating in harsh weather with severe heave motion (large pressure variations occur when the drillpipe is hung stationary in the rotary table for a connection). The paper also includes some ideas for the future of intelligent drilling operations with increasing automation. Anyone interested in MPD or automated drilling should consider this paper a must read.

Drilling At The Limit--Can Your Top Drive Handle It? discusses technical aspects of top drive load rating and clarifies the usable load capacity of a top drive in real-world conditions. The paper explains why a single load rating traditionally associated with a top drive does not give a complete picture. Different load paths exist for hoisting and drilling, which involve different components of the top drive. Relevant API documents for hoisting equipment (SPEC 8C) are compared to those for drillstem components having threaded connections (SPEC 7 and RP 7G). The paper shows two other load ratings must be considered for a complete understanding of top drive capabilities: (1) rotary-shoulder connection, and (2) swivel bearing. The material presented in the paper should be useful for engineers in selecting or maintaining rig equipment and for drilling engineers involved in challenging wells that may push the limits of the top drive.

Pipe rotation is understood to be a major factor affecting hole cleaning for water and oil-based muds. But, there have been no published studies of the effect of pipe rotation on foam drilling until now. Experimental Study and Modeling of Cuttings Transport Using Foam With Drillpipe Rotation reports experiments conducted using a full-scale, high-pressure/high-temperature eccentric annular test section to study effects of pipe rotation, foam quality and velocity, and downhole pressure and temperature on cuttings transport and pressure losses in a horizontal wellbore. It was found that pipe rotation significantly decreases cuttings concentration and reduces frictional pressure loss. A mechanistic model and computer simulator were developed for practical design and field applications. It can predict cuttings concentration, bed height, and pressure drop during horizontal foam drilling with various pipe rotary speeds, eccentricities, foam qualities, and velocities under different pressure and temperature conditions. Comparisons between the model predictions and experimental results agreed within 15 percent in most cases. This paper is a must for anyone interested in underbalanced drilling.

Are you ready to learn something new about mathematics and how it can be applied to designing well paths? A New Well-Path Design Using Clothoid Spiral (Curvature Bridging) for Ultra-Extended-Reach Drilling is a mathematical tour de force that proposes a new formulation for well path designs using clothoid spiral, or curvature bridges. Traditional well planning methods result in curvature and torsion discontinuities in transitions between the build and tangent sections or the tangent and drop sections. The new method uses curvature bridges, or transition curves called clothoid curves, to avoid these discontinuities. Consequently, the clothoid method is predicted to result in lower stresses on the drillstring, lower torque and drag, and lower strain energy when compared to the traditional method. Two examples are used to illustrate the theory and compare the new and conventional methods. Complete mathematical formulations are provided for anyone interested in applying clothoid curves, which the author claims are superior for drilling extended-reach and ultra-extended-reach wells.

Hydrajet Testing Under Deep-Well Conditions Points to New Requirements for Hard-Rock Perforating presents results of laboratory tests using different jetting pressures and abrasives. The paper concludes that jetting in deep formations can be much more difficult than in shallow formations. The need for higher jetting pressures at high ambient pressures is demonstrated. Increasing jetting pressure is shown to improve jet performance although harder, heavier, and larger abrasives seem to improve jetting performance as well. The paper states that more tests are to be performed to determine each of the effects independently.

Oil-based muds improve drilling performance in some applications. However, they may impede resistivity-logging tools (wireline and logging while drilling) because of their high resistivity. Formation resistivity determination is the measurement of resistance to the electric current flow through the formation. Often, logging devices are sensitive to the electrical properties of both the wellbore environment and the formation. Hence, knowledge of electrical resistivity and permittivity of oil-based muds is useful to improve determination of formation resistivity. Experimental Study of Electrical Properties of Oil-Based Mud in the Frequency Range from 1 to 100 MHz presents laboratory experiments that measured electrical resistivity and dielectric permittivity of 19 oil-based muds as a function of frequency and temperature with varying oil and salt content and varying oil/water ratio. The analysis shows that the electrical properties of oil-based muds exhibit behavior similar to published results for water-saturated rocks. Future work is recommended to investigate the effects of pressure.

Collapse strength is a critical property in determining appropriate application of expandable oil country tubular goods (OCTG). Our final paper is important because it describes a new method for developing an equation for the design collapse strength of any expandable pipe product. Collapse tests were conducted on expanded pipe and found not to match API 5C3 collapse formulas, even with adapted plastic collapse formulas and reduced yield strength. A Design Strength Equation for Collapse of Expanded OCTG is based on the combination of collapse test data and theoretical modeling. It uses a statistical approach that is fully consistent with that used for conventional OCTG as described in ISO and API publications. The procedure developed in this paper may be used by manufacturers to develop design strength equations for specific expandable-pipe products.

That wraps up this issue. On behalf of your entire Editorial Review Committee, thank you for your continued support of SPE Drilling & Completion.

Curtis Cheatham
cheatham@spemail.org

Reference

Krause, H.M. Jr. 1963. The Society's Obligation to the Permanent Literature of Petroleum Engineering. J Pet Technol  15 (7): 728-729. SPE-551-PA. doi: 10.2118/551-PA.