Cheatham

Executive Summary

Curtis Cheatham, Weatherford International

60,000 and Counting

Social media is changing the landscape of many aspects of our lives. In some cases, the rate of change is hard to keep up with--at least, it is for me. But the richness of the new learning experiences offers exciting and rewarding opportunities to all of us.

Recently, Glenda Smith, SPE's senior manager of technical publications, sent me a link for a discussion thread from the SPE group in LinkedIn. Although LinkedIn is the social medium that I use the most, I had been unaware of the value offered by its groups until Glenda wised me up. I joined the SPE group and was quickly sold on the merits of the discussion threads because they contained near real-time views of SPE member about topics I care about.

This particular thread discussed the difficulty in searching the SPE library to find the highest-quality papers on a specific subject. Today, the SPE library is contained in OnePetro, which SPE operates and supports on behalf of itself and other societies and organizations, such as the International Petroleum Technology Conference, the Offshore Technology Conference, the National Energy Technology Laboratory, the Society of Exploration Geophysicists, the Society of Petrophysicists and Well Log Analysts, and the World Petroleum Council.

The exchange of thoughts in the thread was stimulating and built a strong case for action. A key problem noted by one person was that the sheer volume of papers in OnePetro generally yields search results with too many papers to be manageable. Another person wrote that, in the good old days, we could search the SPE library and read every paper we found on a particular subject. But he asserted those days are gone because of the explosion of papers in recent years as the number of regional and topical conferences has seen dramatic growth. It should be noted that the surge in new conferences was created consciously to better serve the burgeoning SPE global membership, which currently stands at more than 104,000 members.

I shared the view that there has been a large increase in SPE papers published in recent years even though I had no idea how many papers SPE has published throughout its history. So, with the help of SPE staff, I researched OnePetro and found the cumulative number of papers published by SPE at the end of each decade, as shown in Fig. 1. For example, at the start of 1970, SPE had published roughly 4,170 papers since its inception. By 2010, it had published approximately 53,500 papers. As of this writing, the total had reached approximately 61,000 papers (data not shown in figure).

The figure shows tremendous growth in the cumulative number of papers published by SPE. The oldest paper I found was published by SPE in 1885, The Geology of Natural Gas by Charles A. Ashburner. He was a geologist for the Pennsylvania Survey. [Actually, the American Institute of Mining Engineers (AIME) published this paper as the legacy society for SPE. The Petroleum Branch of AIME became a full-fledged society in 1957 as the Society of Petroleum Engineers.]

But, the data also show the rate of change of papers published has not experienced a dramatic increase in the last few decades. In fact, the rate of change has been fairly steady since about 1930. During the 1920s, SPE published 171 papers, which brought its cumulative total to 211 papers at that time. This represented an increase in the cumulative total by a factor of 5.3 compared to the 40 papers published by the end of the previous decade; see Fig. 2.

Fig. 2 shows the increase in cumulative papers published over the previous decade since 1930. Starting in 1940, the figure shows the total number of papers published by SPE has essentially doubled each decade. Therefore, the rate of change has been more or less steady for a long time.

OK, so now we know what the data show us: There has, in fact, been a large increase in cumulative papers published by SPE each decade since 1930. Furthermore, data in the current decade indicate this growth is continuing. The question remains: What should be done to help us conduct effective OnePetro searches? Back to the SPE group discussion thread, one suggestion was that anyone who downloads a paper from OnePetro should rate the paper, similar to the way other databases such as Netflix work. You watch a movie, and, when you are finished with it, the system automatically sends you an email message that allows you to click a link and rate that movie. Voila! Nothing could be simpler, right?

Well, like many things, it is not actually that simple to apply this method to OnePetro. The thread also covered some practical problems with this approach. What is the incentive for someone to rate a paper after they have downloaded it? How do we deal with the fact that many papers are downloaded using corporate or university subscriptions? What could be done about rating bias, meaning that what one person thinks is top notch another person may find serious flaws in?

One person who weighed in this thread even wrote the formula that the Internet Movie Database uses to calculate an overall rating based on all ratings. While this serves the needs for movie watchers, our Society of Petroleum Engineers would need to develop a formula or algorithm for rating paper quality to meet the needs of its members and fellow societies that use OnePetro.

A key to helping us rate papers is to make the process as easy as possible, a la the Netflix technique for sending a link to users. Thus, anyone who has downloaded a paper from OnePetro would have the opportunity to rate it. These ratings would be combined into an overall rating that would help guide other users when that paper appears in a OnePetro search.

Carrying this analogy a bit further, Netflix allows its subscribers to rate any movies they choose, including, but not limited to, ones they have rented recently. As an additional aid, subscribers can answer questions that provide information about their personal likes and dislikes. This information is used to predict a rating for movies the subscriber has not seen (or rated). For example, I like action movies and comedies, but suspense thrillers are not my cup of tea. Therefore, I tend to rate action movies higher than the average but I rate suspense thrillers much lower than average. To make an analogy to technical papers, I would rate papers related to drilling optimization and directional drilling higher than those on other topics. And I may choose to input my preference for theoretical papers and case histories. The benefit to Netflix subscribers--and potentially to OnePetro users--is that they are given their own personalized rating customized to their own likes and dislikes for each movie. In my experience, this personal subscriber rating can deviate significantly from the overall rating. When I search for movies, I do use the overall rating but I also pay attention to my personal rating. This can help me zoom in on movies that I may like even though most folks did not. It would be great to have similar capability for searching OnePetro for my own highest-quality papers. Such an approach could be used to help reduce ratings bias and provide incentive for us to rate papers.

In conclusion, it appears there is a major opportunity to improve the effectiveness of OnePetro searches. Fortunately for us, the SPE staff is well aware of this, as indicated by Glenda's involvement in the discussion thread. Finally, this experience also indicates to readers that social media can play a role in effecting change in our Society of Petroleum Engineers to the benefit of all members.

Associate Editor

We welcome Bernard Piot as a new Associate Editor. He will manage reviews for cementing and related topics. Bernard was promoted from the ranks of Technical Editor, and we are thrilled to have him working in his new capacity.

Now to the papers. This issue contains 14 papers and a bonus of two reprints.

Two on reservoir characterization and navigation
Five on completion design and execution
One on cementing
Two on drilling and completion fluids
One on drilling systems automation
One on managed pressure drilling
One on coring
One on drill-bit technology
Two classics on PDC bit whirl

The following countries have a major focus in at least one paper: Canada, onshore Texas, onshore United States, Gulf of Mexico, and the North Sea.

Reservoir Navigation and Characterization During Drilling

Reservoir characterization using underbalanced drilling (UBD) is possible because the wellbore pressure is lower than the reservoir pressure. Consequently, UBD offers the opportunity to gather important information about the reservoir not available using conventional overbalanced drilling or even managed-pressure drilling with reduced overbalance margin. Our first paper, Reservoir Characterization Begins at First Contact With the Drill Bit compares well-testing techniques developed for underbalanced drilling with conventional methods. UBD was piloted as a means to achieve the required lateral lengths for reserves capture and meet production targets. Three analysis methods are compared and show close agreement, which lends credence to the UBD interpretation method espoused here. Reservoir analysis while drilling was useful in assessing formation pressure and determining productive intervals, which allowed optimizing stimulation-treatment strategy. This paper is a fascinating read and teaches SPE Drilling & Completion readers much about reservoir characterization methods available through application of UBD.

We want more case histories. That’s what readers tell us every year when they are kind enough to respond to our annual survey. Our second paper delivers a solid case history on the hottest topic in the industry, unconventional reservoirs. Reservoir-Navigation System and Drilling Technology Maximizes Productivity and Drilling Performance in the Granite Wash, US Midcontinent is a good read for those interested in landing and steering in sweet spots of unconventional wells.

Completion Design and Execution

These days, the cost of the completion in unconventional wells is one of the highest costs of the well and, in some cases, rivals the drilling cost. Yet completion engineers are constrained to using only surface wellhead rates and pressures and, on occasion, downhole pressures as their main sources of information. To address such limitations First Downhole Application of Distributed Acoustic Sensing for Hydraulic-Fracturing Monitoring and Diagnostics reports the latest addition to the growing toolbox of fiber-optic techniques in exploration and production. Downhole applications are reported for field examples from Shell Canada’s tight-sand and shale-gas fields for real-time monitoring of setting bridge plugs and shooting perforations. The measurements are shown to be capable of capturing the dynamic changes throughout the hydraulic-fracture treatment. The broad frequency content enables discrimination between perforation clusters that are active during the acid-injection stage vs. perforation clusters that are taking most of the fluid and proppant throughout the job. The technology described in this paper is still in its early form, but it has the potential to lead to improvements in design and execution of hydraulic-fracturing treatments to drive down completion costs and lead to increased well productivity and ultimate recovery.

Are you interested in best practices in completion techniques in shale gas reservoirs? A Technical and Economic Study of Completion Techniques in Five Emerging US Gas Shales: A Woodford Shale Example looks at the Barnett Shale, the Haynesville Shale, the Marcellus Shale, the Woodford Shale, and the Antrim Shale. The paper strives to determine optimal completion techniques for each gas shale basin. Based on economic models, it develops a flowchart and computer program that was validated with published case histories in SPE literature. Because completion is the key to success in many shale gas plays, studies such as the one presented in this paper could accelerate the transfer of best completion techniques to new shale gas plays around the world.

The Lower Tertiary Wilcox formation is renowned worldwide for the elephant fields discovered in recent years. Most experience in the Gulf of Mexico is focused on pumping frac packs into high-permeability formation for sand control. But Designing Multistage Frac Packs in the Lower Tertiary Formation--Cascade and Chinook Project focuses on shifting from deepwater Gulf of Mexico emphasis on soft-rock frac packs to hard-rock hydraulic-fracturing completions. As described in the paper, this focus is similar to what is done in the Wilcox formation onshore in south Texas. The secondary objective was to design a sand control completion to eliminate proppant flowback in screenless hard-rock-fracturing completions. The paper is another excellent case history that will be essential reading for anyone interested in fracturing completions, especially under high pressure.

Our previous paper provided a case history for Petrobras’ Cascade and Chinook hydraulic fracturing completions. Reduction of Perforating Gunshock Loads describes a software tool used to design well perforations in cased-hole completions, which the paper states has been used in many deepwater high-pressure perforation jobs, including Petrobras' Cascade and Chinook. The primary objective of using the software is to assist designing and planning the perforation of high-pressure wells by minimizing risk of damaging completion tools by perforating gunshock loads, thereby reducing equipment costs and time losses.

Openhole packers have been used for many years. In recent years, new variants have appeared and their applications have increased--for example, swelling elastomer packers and related hybrid packers. The Evolution of the Role of Openhole Packers in Advanced Horizontal Completions: From Novel Technology to a Critical Key to Success is recommended for readers interested in learning about the history and present-day applications for openhole packers.

Cementing

Polymers are used in cement slurries for several functions, such as solids suspension, fluid-loss control, and free-water reduction. Unfortunately most viscosifying polymers suffer from shear thinning at bottomhole temperatures, especially under shear. Adding sufficient polymer to overcome the loss of desirable properties at elevated temperature can result in increased friction losses during pumping, which can be challenging for instances of narrow margins between pore pressure and fracture gradient. Chemical Modification of Biopolymers to Design Cement Slurries With Temperature-Activated Viscosification--A Laboratory Study describes a significant improvement by the development of polymers that do not cause excessive slurry viscosification on the surface but gradually increase the slurry viscosity as it reaches downhole temperatures. The maximum viscosity is reached at the time the slurry becomes static behind the casing (as least in the ideal situation). Our reviewers felt this paper is a must read for anyone who works with cement, which is pretty much all our readers, right?

Drilling and Completion Fluids

It has been known for decades that fluid penetration from water-based muds into shale formations causes swelling and can lead to wellbore instability. Decreasing Water Invasion Into Atoka Shale Using Nonmodified Silica Nanoparticles presents laboratory data showing the positive effect of adding commercially available, inexpensive, nonmodified silica nanoparticles to water-based drilling muds and their effect in reducing water invasion into shale. The results of this new technology could offer a powerful and economical means of reducing wellbore-stability problems in shale formations. The paper states that such water-based drilling fluids are being developed. Further, it speculates that similar nanoparticles could be an effective component in fracturing fluids to minimize fluid invasion into shale formations.

A major operator is investigating doubling the existing natural-gas supplies stored in the UK by gas injection into a depleted field. Several major technical hurdles exist when drilling into severely depleted reservoirs, such as differential sticking, major losses of drilling fluids, and hole collapse. Protect and Then Inject: Optimized Well Fluids Successfully Drill Depleted Reservoirs To Store Gas describes a data-acquisition campaign to gather geological and production testing data involving extensive coring, well testing (injectivity testing), and a comprehensive formation-evaluation program of a pilot well drilled in the southern North Sea. A key question is how to drill in a well in a severely depleted field and then be able to inject natural gas into the reservoir? Typically, oil-based drilling fluids would be used in drilling a depleted well, but this can result in a drastic reduction in the subsequent ability to inject gas into the formation because of the internal filter cake formed during drilling (permeability loss). The paper describes the laboratory tests using candidate drilling fluids and remediation treatments. The results of the study led to the conclusion that the project is feasible.

Drilling-Systems Automation

Drilling Automation: Presenting a Framework for Automated Operations aims to put drilling automation into a general framework by using a "modes of automation" approach. The term "modes of automation" refers to different degrees of automation, which is a deciding factor in the work role of both the driller and the automation system. For each increased mode of automation, the work distribution between the automation system and the driller changes. The paper discusses the human/machine interaction at each mode of automation. The role of the driller in a highly automated environment is discussed along with drilling automation in poor downhole conditions. If you are interested in reading more about envelope protection, closing the loop, multilevel control structures, feedback control, supervisory control, and autonomy, then this paper is for you.

Managed-Pressure Drilling

An essential part of an automated managed-pressure-drilling (MPD) control system is the hydraulics model, which is used to estimate downhole pressures. In an automated MPD system, the automation of the choke manifold is performed by a control system usually consisting of two main parts: a hydraulic model that estimates the downhole pressure in real time and outputs a desired choke pressure according to a desired downhole pressure set point and a feedback control algorithm that automates the choke manifold to maintain the desired choke pressure. In previous publications, authors have developed advanced hydraulics models that capture many aspects of the drilling-fluid hydraulics. However, according to Simplified Hydraulics Model Used for Intelligent Estimation of Downhole Pressure for a Managed-Pressure-Drilling Control System, a main drawback is the resulting complexity of these models, which requires expert knowledge to set up and calibrate to achieve a high-end solution. In practice, much of the complexity in such models does not contribute to improving the overall accuracy of the pressure estimate simply because conditions in the well change during MPD operations and there are not enough measurements to keep all of the parameters of an advanced model calibrated. As an alternative approach, this paper presents a model based on basic fluid dynamics that the authors claim is able to capture the dominant hydraulics of an MPD system. Using results from MPD operations in the North Sea and experiments at a full-scale drilling rig, the paper demonstrates how the model can be calibrated automatically using existing measurements to achieve a level of accuracy comparable to that of a calibrated advanced hydraulics model.

Coring

Methane hydrates offer the possibility of massive new potential energy resources. A key step in this quest is to gain knowledge on formation properties below the seafloor. Development of a Continuous Directional Coring System for Deep-Sea Drilling describes a system designed to obtain continuous core sample at depths 7000 m below the seafloor. Directional control is required because formations at this depth become sufficiently competent to cause wellbore deviation. Tests showed core could be successfully retrieved through bent housing angles up to 1.5° but not higher. This paper is an interesting read about how a directional drilling system was designed using a 1.5° bent housing motor on the coring bottomhole assembly to achieve maximum dogleg severities of 5.7° per 100 ft.

Drill-Bit Technology

This paper provides a fascinating history of polycrystalline-diamond-compact (PDC) cutters related to fracture and fatigue. Fracture and Fatigue of Polycrystalline Diamond Compacts reports extensive laboratory testing that led to several important conclusions. The results show that fracture on one side of a PDC cutter does not affect the strength of the opposite side of the same compact (aka cutter). Therefore, PDCs whose fractures or wear-flat areas are relatively small can be salvaged from old bits, rotated 180°, and reinserted into new bits with the result being a virtually new compact, thus extending the life of compacts. Readers may wish to read the two classic papers discussed in the next section and then come back to this gem afterward.

Classic SPE Drilling & Completion Papers

In this issue, we introduce a new feature, the reprinting of classic papers. The purpose is to highlight an outstanding paper that changed our industry. Each issue will contain a paper from the past that has stood the test of time.

To start off, we are actually providing two papers that were originally published in the same issue of SPE Drilling Engineering (the precursor of SPE Drilling & Completion). Both papers were presented at the 1989 SPE Annual Technical Conference and Exhibition and published in the December 1990 journal. SPE 19571, Bit Whirl--A New Theory of PDC Bit Failure, and SPE 19572, Development of a Whirl-Resistant Bit, should be read as companion papers.

PDCs were introduced to the oil and gas industry in the early 1970s by General Electric. Research was conducted over the next decade that resulted in a wide range of bit designs provided by at least a dozen different drill bit companies. PDC bit companies sprang up overnight, which was followed by a somewhat slower shakeout during the 1980s.

As with any new technology, mistakes were made and lessons were learned. Two key problems were identified with using these new PDC bits that had not previously been observed with roller-cone bits: stick/slip and backward whirl. Today, these two dysfunctions are well known and, to some extent, even well understood. The industry presents maps (or graphs) showing where stick/slip and whirl are likely to occur as functions of weight on bit and rotary speed. Various bit designs are offered to mitigate these harmful dynamic dysfunctions.

But in the late 1980s, the root cause of backward bit whirl was not well understood. Nor were there robust solutions in existence. The two classic papers in this issue changed the industry forever because they explained the root cause and offered a solution to the problem of backward bit whirl. The authors worked at Amoco Production Company Tulsa Research Center, which contributed some of the most important research and development that our industry has seen. I encourage you to read other papers from these same authors and their colleagues from Amoco; it will be worth it. Meanwhile, enjoy these two classics.

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