Curry

I have finally come to acknowledge what those around me have known for years—if I have any talent, it is for worrying. If it were an international sport, I could worry for Britain. The list of things I can find to worry about is often endless. My primary school teacher knew me well when she cast me as the white rabbit in the school production of Alice in Wonderland. The opening words “I’m late, I’m late, I’m late” came only too easily to me then, as they still do now. But now, they apply to this editorial, for which Shashana Pearson-Hormillosa, our wonderful staff editor, is ever so gently and patiently chasing me. And it is this editorial that sparked my current round of worries, some of which are real and some imaginary. After each editorial is finished and dispatched to the SPE office, I breathe a sigh of relief, and almost immediately start worrying about what I could possibly write in the next one, and how I can possibly avoid being late this time.

Several of our current Review Chairpersons are nearing the end of their third year in post, having nobly agreed at this time last year to work on, beyond their initial 2-year term of office. I fully expect them to decide this year that it is time to retire, to spend time with their families and on their paid jobs. I know there are very capable replacements currently working for our Review Committee as Technical Editors (TEs), but I still worry. Will I be able to persuade good TEs to step into the breach? And, if so, will we be able to find good TEs to replace their empty posts? 

Last week, I returned to Texas after 10 days in Europe. I monitored the weather reports every day I was away, worried that the grass in my garden needed watering. At the first opportunity after my return, I gave the grass a thorough soaking. I needn’t have worried. The next day, a severe thunderstorm dropped 2 in. (50 mm) of rain in a few hours, leaving me to worry about flooding.

The storm unleashed vast amounts of energy,convincing evidence that the world has no shortage of energy, just a shortage of accessible,controllable, and usable energy. The possibility of returning to nuclear power is being debated in a number of the world’s larger economies. The oil industry rightly worries about “the big crew change.” As my mirror confirms each morning, we have an aging work force. We have not been recruiting, training, and retaining sufficient staff to replace those who will probably retire in the coming years, at a time when we face growing demands for our technical skills. But, we face far less of a challenge than does the nuclear power industry. Many of the professionals who designed and built the last round of nuclear power plants in the U.S.A., the U.K., and quite a few other Western countries, have already retired. Nations in Asia and the Middle East have more active nuclear power programs than do we. France is almost alone in the Western world in having maintained its commitment to nuclear power. Will access to nuclear power technology become as potent a geopolitical factor as access to hydrocarbon reserves? Yet another worry.

At least we do not have to worry about access to drilling and completion technology. The papers in this issue, and indeed the review committee’s workload, are testament to our willingness as an industry to share our knowledge and technology.

The gas fields of south Texas have been produced for more than 50 years. Wells drilled there now penetrate many low-permeability pay sands, some of which are severely depleted, while others are still at their high, virgin pressures. As pressure differentials became too great for lost-circulation-material pretreatments and cement squeezes to control the inevitable lost circulation, mud weights were reduced, causing much of the wellbore to be drilled underbalanced. Although it was usually possible to drill the well to total depth in this condition, it was deemed impractical to trip to run production casing. Underbalanced Drilling With Casing Evolution in the South Texas Vicksburg does just what it says in the title. It describes the technique developed to enable wells to be drilled and completed. Drilling underbalanced with casing or a liner has become the contingency procedure adopted against lost circulation. By enabling smaller casing programs and avoiding the use of drilling liners, it has reduced well costs by approximately 30%. The authors also note the factors that will limit its applicability elsewhere.

Drillstrings do not often fail, but the consequences can be severe when they do. As the authors of An Innovative Design Approach to Reduce Drillstring Fatigue point out, fatigue and corrosion fatigue account for the majority of drillstring failures. As I know from my days working on nuclear power plant integrity, a great deal of information about component and defect geometries, material properties, loading history, and the environment is needed to make a realistic prediction of fatigue life in service. In most cases, the drilling engineer designing a drillstring simply does not have access to all that information. This paper introduces a comparative-design approach to address this problem. It uses two dimensionless indices to normalize many of the factors affecting fatigue life that are generally unknown to the drillstring designer. These allow quantitative comparisons of the fatigue resistance of drillstring-design alternatives, based on what the drilling engineer does know.

Well-control analyses and procedures were developed many years ago for vertical wells. More and more of the wells we drill today have extended reaches with high final inclinations, are horizontal, or have multiple lateral branches. Well-Control Analyses on Extended-Reach and Multilateral Trajectories describes the results of a number of computations performed to investigate how pressures at surface and downhole following a kick differ in these sorts of wells from those seen in a vertical well. As the bottomhole inclination increases away from vertical, so the shut-in casing pressure decreases approaching the shut-in drillpipe pressure. This can make it difficult to determine the kick-fluid density from pressure measurements alone. The choke pressure at surface can rise, even without kick expansion, once the kick gains vertical height on being circulated through the build section of a high-angle or horizontal well. Controlling a multilateral well with more than one kicking wellbore must be confusing because the shut-in drillpipe pressure is influenced by the kick volume and formation pressure for each of the unruly wellbores. The problem is compounded by the fact that the drillpipe can be in only one branch at any one time. The others have to be controlled without the benefit of circulation to their hole bottom. The authors suggest considering the use of additional pump pressure to compensate for hydrostatic-pressure reduction resulting from kick migration and expansion in the branches without drillpipe. Finally, they present simple recommendations for adjusting a conventional vertical-well drillpipe pressure-reduction schedule so that it can be used for directional and horizontal wells.

A drilling rig is essentially a machine for pumping, turning, and hoisting. Its hoisting abilities are usually most severely tested when running a long casing string. The operator of the Gulf of Mexico Thunder Horse project was rightly concerned that the peak loads they anticipated when running casing could challenge conventional landing equipment and techniques. Slip-based equipment imposes crushing loads on the landing string, to the extent that the slip-crushing capacity of the landing string is usually the load-limiting factor. Unfortunately, this is not easy to predict with any great confidence. An initial investigation indicated that it would not be possible to improve conventional slips sufficiently to achieve the desired levels of safety and reliability. So, a new system was developed with the explicit goal of stopping the landing system from being the limiting factor when running heavy casing loads. The elevator and spider combination it uses supports the full landing-string load without contacting the outer diameter of the loading string, thereby removing any concern about slip crushing. 2,000,000-lbf Landing-String Developments: Novel Slipless Technology Extends the Deepwater Operating Envelope describes the development, manufacture, and testing of a slipless landing system, with a load capacity equal to the 2,000,000-lbf capacity of the derrick on the rig working on the Thunder Horse project. The authors report that their system successfully handled the 1,700,000-lbf hookload needed to free a stuck casing string.

Drilling gas wells through depleted formations is something of a theme for this issue. Gas wells in the San Juan basin in New Mexico are routinely drilled with air to avoid losing circulation into the severely depleted Mesa Verde formation. Unfortunately, the potential for lostcirculation problems in these wells does not end when drilling does. Air drilling leaves an airfilled hole and some specific challenges for subsequent cementing operations. The Use of Lightweight Cement Slurries and Downhole Chokes on Air-Drilled Wells discusses these challenges and describes the technique one operator has adopted to obtain primary-cementing success. With no liquid to slow its descent, cement will initially free fall down the casing, leading to high surge pressures at the hole bottom that can initiate fracturing and consequent lost circulation. The absence of mud when drilling leads to an absence of mud filter cake during and after drilling. This can cause the cement slurry to lose water to the unprotected formation. A downhole choke in the float collar restricts the rate at which cement flows into the annulus, thereby limiting surge pressures. A combination of silica fume additive and gilsonite lost-circulation material also contributes to a reduced occurrence of lost circulation while cementing, reducing the need for remedial jobs and, thereby, reducing the overall cementing costs.

I expect, like me, many readers have heard of reverse circulation while drilling—that is, pumping down the annulus between drillstring and wellbore, through the bit, and back up to surface inside the drillstring. It is a technique sometimes used in large-diameter holes if achievable flow rates are not sufficient to lift cuttings out of the well through the annulus. I have to confess, I had not heard of reversecirculation cementing until I read High-Temperature Wells With Lost-Circulation Demands and Reverse-Circulation Techniques Using Foamed-Cement Systems: Two Case Histories. As the authors show, reversecirculation cementing can reduce the pressure on the formation during cement placement, thereby reducing the risk of fracturing the formation and a consequent failure to achieve the desired cement top. One of the challenges when cementing a high-temperature well with conventional techniques is the concentration of retarder needed in the lead cement to prevent setting in the high temperatures found near the hole bottom. Once the same highly retarded cement gets to the intended top-of-cement depth, the prevailing temperature is usually much lower, with the inevitable, but undesirable, consequence of a long wait before the cement has set sufficiently for operations to resume. Placing the cement down the annulus means it does not (or should not, anyway) experience any temperature higher than that in its intended final resting place. This paper describes the technique of reverse-circulation cement placement and illustrates its potential benefits with two very different case histories: a deep well in Wyoming with a history of lost-circulation problems and a shallower geothermal well in California with an anticipation of problematically high temperatures.

Development projects offshore Brazil are increasingly targeting deepwater heavy-oil fields. These require long horizontal intervals to achieve economic production rates. Sand control is a major issue here, but the combination of low fracture gradients and horizontal sections exceeding 2000 m (6,600 ft) in length makes pressure control during sand placement critical—pump too hard and the formation will fracture, not hard enough and the gravel pack will not end up where you want it. Experimental and Theoretical Simulation of Gravel-Pack Displacement in Extended Horizontal-Offshore Wells describes a mechanistic model developed to simulate the entire operation of gravel packing a horizontal well. As the authors noted, gravel packing is a bit like drilling in reverse. When drilling, you pump fluids to stop beds of drilled solids from building up in the horizontal section, whereas in gravel packing, you pump with the intent of forming a bed of solids along the horizontal section. So, the authors have adopted a model one of them developed to analyze cuttings transport for use in their simulation of gravel packing. This paper describes the model and validates it by comparing its predictions with results from full-scale experiments and from field operations. Finally, its use as a design tool is illustrated by analyzing several different options for gravel packing a 2000-m horizontal section in a well drilled in 2000-m water depth.

The deepwater Genesis field in the Gulf of Mexico was the first field-development project to use spar technology for its drilling, completion, and production operations. A total of 14 frac-packed wells has been drilled to date. Completion and Well-Performance Results, Genesis Field, Deepwater Gulf Of Mexico provides an interesting comparison of what the operators planned to do, and what actually happened, during the development program. For example, plans for dual completions on later wells were abandoned in light of well-control challenges. Instead, single wireline-selective completions were installed on the last four wells drilled. One of the key lessons from the project is that the spar structure proved a safe and reliable structure for the field’s development. The authors present a number of other lessons related to perforating, completion, and production operations, and some relating to the use of an online-learning system. Not only did this help time management during the project, but it also allowed other project teams elsewhere in the world to share the knowledge gained by the Genesis team—as does this paper.

As ever, comments are welcome: david.curry@bakerhughes.com.