Abstract: We address the problem, proposed by Gerth, of verifying that a simplified version of the lazy caching algorithm of Afek, Brown, and Merritt is sequentially consistent. We specify the algorithm and sequential consistency in TLA+, a formal specification language based on TLA (the Temporal Logic of Actions). We then describe how to construct and check a formal TLA correctness proof.

Abstract: The stick-slip phenomenon has been identified in the industry as an inefficient and often damaging drilling vibrational condition. Numerous studies, predominantly focusing on measurements of drillstring torque. have detailed the nature of this phenomenon, and have shown its detrimental effects on drill-string components and especially on PDC bits. Using surface rotary motor current, drilling contractors and surface logging companies have attempted to monitor drillstring torque so as to recognize and correct for this torsional instability. Recent MWD tool developments using downhole drilling rotational speed have established a superior method to identify stick-slip and establish its severity. Measuring actual rotational behavior of the lower BHA gives a better insight to the torsional movement of the drill bit during the drilling process, without the problems involved when inferring this behavior from the surface torque readings, obtained at the opposite end of the drillstring. This paper describes the method of determining the stick-slip behavior downhole from magnetometer readings. The sensors are sampled at a high enough frequency to compute near-instantaneous values of downhole drillstring rotation, and variations in the RPM are then used to establish the incidence and severity of stick-slip. This information is telemetered to the surface and provided to the driller in order to allow for real-time changes in drilling parameters to correct for this mefficiency. Also presented in the paper are several examples using actual field data that detail stick-slip behavior and demonstrate how real-time information about downhole RPM variations can help to reduce the problems associated with this torsional drilling dysfunction.

Abstract: Historically, wellbore instability problems have been mainly attributed to the physico-chemical interaction between the rock and the drilling fluid, especially when this is a water-based fluid (WBM). However, recent studies have shown that these chemical effects may be irrelevant in comparison with other energetic events which are present during the drilling operation of a well. Excessive drillstring vibration has been identified as such an event that can cause a great amount of damage to the wellbore. Although some studies present clear mdications that the reduction of drillstring vibration has led, in many occasions, to an improvement on instability problems, still today this item only deserves attention from equipment divisions, aiming at reducing drillstring fatigue problems. The main objective of this paper is to show the clear existing relation between excessive drill string vibrations and serious well instability problems. It is shown, in energetic terms, that drillstring vibration, when having enough lateral amplitude to hit the wall, is responsible for irreparable damage to the borehole. Simple ways of quantifying vibration effects in terms of energy are presented. The paper also presents field measurement data, obtained with surface vibration sensors, which clearly allow identification and correlation between vibration problems and wellbore instability, through the comparison of these vibration records with caliper logs.

Abstract: Underbalanced drilling (UBD) has proven to increase reservoir productivity in several areas around the world. Due to the advantages gained by using this technology, offshore application has also been increasing lately, but it has been restricted solely to fixed platforms. However, with the deepwater drilling trend in the industry, it is imperative that this technology becomes technically and economically viable for application from floater units as well. This paper presents the design and planning of an offshore well to be drilled with aerated-fluid technology. Although the operation is not planned to be underbalanced, the well will be the first one to be drilled from a floating vessel using aerated fluid technology. The paper describes the approach taken to overcome the challenges posed, including the involvement of several companies in a Joint Industry Project to speed up the learning process and the steps related to critical areas, mainly hydraulics and equipment. The article finally discusses the most important points that still need improvement to make UBD a reality in offshore operations from floating units.

Abstract: Wells drilled in the deepwater Gulf of Mexico often experience problems with shallow abnormal pressured sands. Successfully drilling through these sands has been an industry wide problem. Shallow water flow problems have caused the industry to junk wells prior to evaluation of any or all well objectives and prevented using discovery and appraisal wells as producers. Shallow water flow problems also caused the loss of the wells at the first Ursa Tension Leg Platform (TLP) site. The Ursa field is located in the deepwater, 3800' water depth, Mississippi Canyon area of the Gulf of Mexico where shallow water flow problems have been severe. The sediments at Ursa contain massive, wet sands that are pressured above a normal seawater gradient at a very shallow depth below mudline. Different techniques have been used while drilling the discovery, appraisal, and development wells to attempt to successfully prevent and control shallow water flow problems. The severe shallow water flow problems at Ursa have been successfully overcome and the shallow batch set drilling program was completed at the second TLP site in mid-1998. Eleven wells, which required five casing strings, have been successfully drilled to below the base of the shallow water flow zones. This paper will discuss the problems encountered during exploratory, appraisal and development drilling at the Ursa field.

Abstract: A new technology utilizing a Single Step Specific Enzyme Breaker (SSSEB) process has been applied for the removal of damage caused by drill-in fluid on horizontal wells. This technique has resulted in significant improvements in well performance. Previous SEB (Specific Enzyme Breaker) technology, as it applies to xanthan, starch and carbonate drill-in fluid, focused primarily on a two step process for removal of horizontal well drill-in fluid filter cake damage; an initial SEB treatment for starch or xanthan polymer removal followed by a second treatment of acid for calcium carbonate removal. This new SSSEB method provides an effective one step system for removing both the starch polymer and calcium carbonate components of drill-in mud filter cake formed during horizontal open hole operations. Case history information and laboratory data are presented to validate the effectiveness of the SSSEB formulation on the degradation of the filter cake formed when a starch, xanthan and calcium carbonate drill-in fluid is utilized. Previous laboratory and field data have demonstrated the effectiveness of SEB technology for degrading starch polymer. The new SSSEB method utilizes the identical starch specific enzyme product used in previous SEB treatments; however, it also employs a buffered, organic acid fluid. The organic acid reacts with the calcium carbonate portion of the filter cake as the enzyme simultaneously acts on the starch polymer. Compared to conventional high strength mineral acid systems (such as hydrochloric acid) often used for calcium carbonate filter cake removal, the SSSEB acid solution reduces the risk of fluid emulsions, formation acid sensitivity issues, secondary precipitate problems as well as safety and environmental issues. The system is also relatively slow-reacting which is important for the effective placement of the breaker fluid across the entire horizontal interval and allows for uniform filter cake deterioration. The most noticeable economic benefit resulting from the application of the Single Step Specific Enzyme Breaker system is increased production of hydrocarbons. The SSSEB technique also offers savings on rig and related charges, chemical costs and operational charges by allowing for wells to be placed on production more rapidly and not requiring follow up acid work.

Abstract: The contribution of the paper is two-fold. We give a set of properties expressible as temporal logic formulas such that any system satisfying them is a sequentially consistent memory, and which is sufficiently precise such that every reasonable concrete system that implements a sequentially consistent memory satisfies these properties.Then, we verify these properties on a distributed cache memory system by means of a verification method, based on the use of abstract interpretation which has been presented in previous papers and so far applied to finite state systems. The motivation for this paper was to show that it can also be successfully applied to systems with an infinite state space.This is a revised and extended version of [Gra94].

Abstract: During casing running, risks of accidents with the stabber, the stabbing board and around well centre are still existing. In order to reduce the risks of accidents and to streamline the process a new Casing Running Tool is developed. The basic idea of this device is that the Top Drive is used as a torque wrench and that several functions are integrated. A flush mounted spider is used. Integrated in this device are fill up and circulating functions, the power tong function, the top stabbing function and the casing hoisting function. The risk for accidents will be significantly reduced. The driller's operation is simplified and the casing running time is reduced. The Casing Running Tool incorporates additional features, such as the possibility of pushing and rotating the casing string while circulating. The reduction of casing running time, personnel, and risk of accidents create value and HSE benefits. A first prototype is being developed. Design constraints that can be recognised at this stage of the development of the tool are mainly related to mechanized connection making. Both a theoretical and experimental approach are taken in order to define the design constraints. In the development of the Casing Running Tool a step by step approach is chosen. All subsystems are designed as add-on equipment. The Casing Running Tool paves the way to a complete automation of the drilling process.

Abstract: A self-stabilizing algorithm is presented in this paper that finds the bridges of a connected undirected graph on a distributed or network model of computation after O(|E|n2) moves. The algorithm is resilient to transient faults and does not require initialization. In addition, a correctness proof of the algorithm is provided. The paper concludes with remarks on the time complexity of the algorithm.

Abstract: When designing distributed systems, one is faced with the problem of verifying a refinement between two specifications, given at different levels of abstraction. Suggested verification techniques in the literature include refinement mappings and various forms of simulation. We present a verification method, in which refinement between two systems is proven by constructing a transducer that inputs a computation of a concrete system and outputs a matching computation of the abstract system. The transducer uses a FIFO queue that holds segments of the concrete computation that have not been matched yet. This allows a finite delay between the occurrence of a concrete event and the determination of the corresponding abstract event. This delay often makes the use of prophecy variables or backward simulation unnecessary.An important generalization of the method is to prove refinement modulo some transformation on the observed sequences of events. The method is adapted by replacing the FIFO queue by a component that allows the appropriate transformation on sequences of events. A particular case is partial-order refinement, i.e., refinement that preserves only a subset of the orderings between events of a system. Examples are sequential consistency and serializability. The case of sequential consistency is illustrated on a proof of sequential consistency of a cache protocol.

Abstract: Predicting the directional tendency of a bottomhole assembly (BHA) is a key element in improving the efficiency of the directional drilling process. Finite element models attempt to represent the detailed physical interactions between the BHA and wellbore while drilling. However, effective use of such models has been hindered by parameters that are difficult to quantify, particularly the strength of the formation and variations in hole gauge. Details of over 6400 BHA runs made in the Gulf of Mexico from 1994 through 1997 were used in a systematic statistical analysis and combined with intelligent use of the tendency models to yield information that is not readily apparent in single runs of the software. This information can then be used as a predictive tool to minimize the effects of the parameter uncertainties, and to isolate and calibrate those variables to which the models are sensitive. From these studies the most representative values for formation stiffness and hole over-gauge were obtained for various areas within the Gulf region. We describe a methodology using this combination of advanced modeling and statistical analysis to provide more reliable predictions of BHA tendency and to give an indication of the conditions where such predictive techniques can be effectively applied.

Abstract: I introduce and discuss sequential consistency, a relaxed memory model, and define what it means for a protocol to implement sequential consistency. Then, I introduce the lazy caching protocol of Afek, Brown and Merrit [ABM93] and formalize it as a labeled transition system.

Abstract: Ultra-deepwater drilling activity is at an all time high. Recently, there were only two rigs rated to, and actually working in, water depths greater than 6,000 ft. Soon there will be over twenty. This increase will involve new deepwater operators and bring a large number of new people to deepwater. This paper presents some of the problems that have occurred in deepwater operations under the assumption that an understanding of what can go wrong is the best way to avoid problems. It will identify these problems and discuss the critical topics of rig positioning, environmental considerations, BOP control, riser management, well control, wellbore construction, production problems, and personnel training and safety.

Abstract: The paper describes the ongoing development of an electrically powered bottom hole assembly for use in coiled tubing drilling (CTD) applications. Electric coiled tubing drilling (E-CTD) offers many distinct advantages over conventional CTD which are considered in more depth within the paper. These may be summarised to include: ○ Drive power provided independent of fluid flow ○ High tolerance of energised drilling fluids - ideal for underbalanced drilling - ideal for subsea drilling applications ○ High temperature operation ○ Flexible control of electric power with instantaneous feedback for closed loop drilling and optimisation of drilling efficiency ○ Motor operation is scalable. The same drive may be used for auxiliary actuation, e.g. orientation, active traction and formation testing. ○ Real-time transmission of data to surface using power cable ○ Extended longevity of motor ○ Reduced vibration (affects gyro placement, reliability of other equipment, eg NMR magnets) ○ Reversible direction of rotation (passive or active traction capabilities) It is these advantages that have driven the development of the electric BHA in a European Drilling Engineers Association [DEA(E)] joint industry project. This paper reviews prototype bottom hole assemblies from phases 1 and 2 of the project. Surface components, the electrical transmission system and its consequences for an integrated drilling package are also considered. Phase 2 of the project, currently ongoing, has delivered a purpose-built, electric downhole motor (EDM) design suitable for drilling a 3.75 hole. This motor is currently being incorporated into an electric BHA which incorporates pressure, temperature and vibration sensors. The proposed test program is reviewed with some earlier results presented from phase 1 for illustrative purposes. The ultimate goal of this project is to integrate the electric motor into a 'smart'. closed-loop drilling system. It is envisaged that, based upon feedback from near-bit sensors, such a system would be able to automatically adjust drilling parameters to optimise drilling performance. The paper concludes that not only is electric coiled tubing drilling a practical and effective alternative to conventional CTD, but that the system delivers many additional benefits.

Abstract: In the Valhall field in the North Sea, significant resources have been identified in the flanks of the field. In this situation the reservoir targets are the main driver for the wellbore trajectory planning. Even if all of the traditional drilling parameters have been addressed and the well can be drilled on paper, the wellbore can experience wellbore stability problems (lost circulation, stuck pipe, tight hole). These wellbore problems can gradually progress or suddenly occur. The problems may be aggravated by mud properties or mechanical interaction between the rock and the drilling assembly. Wellbore stability models, using offset drilling information, indicated early in the planning process at Valhall that the drilling of extended reach wells in the field was going to be a challenge. This challenge is the result of a narrow safe operational mud pressure window that narrows progressively with increasing wellbore sail angle. This theoretical window upper bound is given by lost circulation. The lower bound is given by the onset of wellbore collapse. This narrow window leaves hardly any room for the surge and swab pressures associated with pipe movement and pump changes. The flank locations require sail angles close to 75 degrees in the overpressured unconsolidated claystone of Tertiary age. The record well to date had a build and hold trajectory at 74 degrees. On this record well around 3 MM USD was spent on fighting wellbore stability problems (around 750 hours). Since traditional wellbore stability analyses have already indicated a high risk of instability, and some wells have been successful, while others not, consideration was given to developing new tools to assist in the well planning in the overburden. We wanted to look at potential heterogeneous rock strength changes that could not be picked up using offset well information in the planning. The approach was to develop a more detailed geological model for the overburden with geologic formation top surfaces and 3D seismic coherency data. In this 3D data cube the drilling problems encountered on the offset wells were correlated along the wellbores. The 3D data presentation was done in a standard visualization software (GEOVIZ). The paper will present the geomechanical theory behind wellbore stability problems in faultzones and fractured rock mass, how the geologic model has been developed and how the visualization software is used to select a wellbore trajectory with the lowest risk of wellbore instability problems. Several case histories are included to illustrates the potential this methodology has for reducing unscheduled events due to wellbore instability problems while drilling the wellbore from the seafloor to the reservoir. Potential for further improvement is highlighted.

Abstract: In this paper we present a proof of the sequential consistency of the lazy caching protocol of Afek, Brown, and Merritt. The proof will follow a strategy of stepwise refinement, developing the distributed caching memory in five transformation steps from a specification of the serial memory, whilst preserving the sequential consistency in each step. The proof, in fact, presents a rationalized design of the distributed caching memory. We will carry out our proof using a simple process-algebraic formalism for the specification of the various design stages. We will not follow a strictly algebraic exposition, however. At some points the correctness will be shown using direct semantic arguments, and we will also employ higher-order constructs like action transducers to relate behaviours. The distribution of the design/proof over five transformation steps provides a good insight into the variations that could have been allowed at each point of the design while still maintaining sequential consistency. The design/proof in fact establishes the correctness of a whole family of related memory architectures. The factorization in smaller steps also allows for a closer analysis of the fairness assumptions about the distributed memory.

Abstract: For the past nine years, the drilling industry has used the Permeability Plugging Apparatus (PPA) to assist in evaluating and resolving differential sticking and lost circulation problems which may arise while drilling depleted, weak or fractured zones. The increasing use of open hole completions in horizontal wells also means that more attention has to be paid to the cake forming properties of drilling fluids. The PPA is a high pressure, high temperature filtration device designed to evaluate fluid loss and spurt loss of drilling fluids under filtration conditions that more closely approximate those encountered downhole than the filter paper normally used. Although filtration occurs under static rather than dynamic conditions, pressures as high as 5000 psi (34,500 kPA) and temperatures of up to 500°F (260°C) may be investigated. The main feature of the PPA is the use of ceramic disks as the filtration medium. These are available in a wide range of porosities and permeabilities to match those properties of the formation much better than filter paper can. There are currently five PPA types with different pressure ratings that are in use in the laboratory and the field. In response to concern about the safe use of these devices, and the reproducibility of the data generated with them, the American Petroleum Institute initiated a program to investigate these issues, and to produce a standardized test procedure. The new API procedure addresses the safety issues of the PPA cell designs. Further, to provide consistency between users, the procedure outlines a new method of calculating spurt loss and total filtrate volume parameters based on the test data. The new procedure has been used, both in the laboratory and the field, to evaluate seepage loss additives as well as traditional lost circulation additives. Case histories are provided which demonstrate successful use of the device in evaluating lost circulation material and in the prevention of differential sticking problems while drilling depleted zones as well as designing pills for severe lost circulation.

Abstract: In recent years, limited advances have been made in drill pipe recovery services technology. Depending on the size, weight per foot, and type of pipe stuck in the well, the options available to separate the pipe string, have remained the same for over a decade. These include: 1. String shot/back off 2. Chemical Cutter 3. Jet Cutter 4. Metal Severing Tool The most commonly used tool is the string shot/back off, which involves applying left hand torque to the pipe string at the neutral weight. The explosive produces and intense hammer blow and allows the joint to be unscrewed at the desired connection. The most difficult part of this procedure is determining the neutral weight at the depth of the back off attempt and the amount of torque required at that point. The back-off is a preferred method because it leaves a clean top on the down hole fish. This saves time in the fishing operation, which is critical to a successful fishing job. However, as wells become more deviated or well conditions become more severe, the back-off method can become less effective. This paper introduces new technology for disengaging pipe located above the point where the drill string assembly is stuck. The system uses a solid combustible mixture which produces sufficient heat to separate drill pipe, leaving a clean top on the remaining down hole fish. The sytstem is safe to store, transport and handle at temperatures up to 660°C. It's solid combustible mixture does not ignite due to pressure, shock or impact, under normal conditions.

Abstract: A lime-free, high-temperature invert emulsion drilling fluid has been developed and applied successfully on 53 wells in the Gulf of Thailand (GOT). The subject drilling program included 24 wells in a field with static bottom hole temperatures (BHT) of 400°F. The fluid is run with a pH of less than 7.0, which is accomplished with the introduction of I lb./gal of citric acid and the elimination of the alkaline source (lime). The fluid was mainly developed in search for a high quality drilling mud resistant to heat degradation, therefore allowing stable borehole conditions under which to execute the open hole wireline logging program. The fluid was also developed in part to allow the possibility of logging CO 2 formation gas at the surface by utilizing a conventional mud logging unit. The ability to log CO 2 gas with surface equipment would help eliminate wireline RFT sampling runs. This could provide significant savings during the course of an extensive drilling program. The paper will discuss the development of the lime-free emulsifier package, the introduction of a new HTHP fluid loss reducer (stable in excess of 450°F) and low-end rheology modifier, the extensive lab testing, the introduction of the system to the GOT and the drilling of 53 wells. Data from 250-plus GOT slimhole wells using invert systems were studied prior to the introduction of the new system. The numerous problems that prompted the investigation for a new cost-effective fluid system will be discussed.

Abstract: This paper shows how the theory of Communicating Sequential Processes (CSP) can be used to establish that a protocol guarantees sequential consistency. The protocol in question is an accepted design based upon lazy caching; it is an ideal example for the comparison of different formal description techniques.

Abstract: With the conventional drilling technique, a general rule-of-thumb establishes that the surface and intermediate casing strings are to be run in holes with a diameter of up to 6-7 in, larger than the casing. This rule is based on the fact that: 1. it is difficult to drill a straight vertical well with conventional technologies; 2. the larger the casing diameter the stiffer the casing string. The clearance between casing and open hole is then reduced to about 1 for the deeper sections, because of the higher flexibility of the casing strings. This paper presents the Lean Profile, an innovative drilling technique which aims at maintaining 1 clearance throughout the whole casing program, leading to a slimmer well profile but keeping the same size for the production casing string. To achieve this it is mandatory to adopt suitable drilling technologies that will be deeply discussed in the paper. The Lean Profile has been successfully applied to some wells drilled from on-shore clusters with parallel vertical sections long as much as 2,000 meters. The drilling environment is challenging with problems such as formations' tendency to deviate from the vertical trajectory, wellbore instability and circulation losses. In this operating scenario the Lean Profile provided for dramatic time and cost reduction. In fact, the halving of the rock volume involved in the drilling process resulted in an outstanding drilling performance (-40% on drilling time with respect to standard technology), less material consumption and less waste production. The Lean Profile is part of the drilling strategy for some 30 wells in the Val d'Agri, southern Italy, with interesting cost saving opportunities. This paper summarizes experiences and results from the field along with engineering considerations.