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A directional well can be divided into three main sections--the surface hole, overburden section, and reservoir penetration. Different factors are involved at each stage within the overall constraints of optimum reservoir penetration. Most directional wells are drilled from multiwell installations, platforms, or drillsites. Minimizing the cost or environmental footprint requires that wells be spaced as closely as possible. It has been found that spacing on the order of 2 m (6 ft) can be achieved.
Introduction Directional drilling is defined as the practice of controlling the direction and deviation of a wellbore to a predetermined underground target or location. This section describes why directional drilling is required, the sort of well paths that are used, and the tools and methods employed to drill those wells. A directional well can be divided into three main sections--the surface hole, overburden section, and reservoir penetration. Different factors are involved at each stage within the overall constraints of optimum reservoir penetration. Most directional wells are drilled from multiwell installations, platforms, or drillsites. Minimizing the cost or environmental footprint requires that wells be spaced as closely as possible. It has been found that spacing on the order of 2 m (6 ft) can be achieved. At the start of the well, the overriding constraint on the well path is the presence of other wells. Careful planning is required to assign well slots to bottomhole locations in a manner that avoids the need for complex directional steering within the cluster of wells. At its worst, the opportunity to reach certain targets from the installation can be lost if not carefully planned from the outset. Visualizing the relative positions of adjacent wells is important for correct decisions to be made about placing the well path to minimize the number of adjacent wells that must be shut in as a safety precaution against collisions. The steel in nearby wells requires that special downhole survey techniques be used to ensure accurate positioning. This section is generally planned with very low curvatures to minimize problems in excessive torque and casing wear resulting from high contact forces between drillstrings and the hole wall.
While traditional definitions classify short-, medium- and long-radius lateral wells by angle build rates, the technology now employed to achieve those build rates suggests an industry definition which characterizes lateral wells not only in ten-ns of wellbore geometry, but in engineering terms as well.
In proposing such a definition. this paper examines new developments in downhole technology, focusing on short- and medium-radius systems to show how choice of drilling hardware can determine the type of curve drilled, as well as how it is planned and completed.
New horizontal well-planning techniques developed in light of recent hardware improvements are also discussed, while technical innovations still in development are noted.
Field results of recent lateral wells present examples of problem-solving, since a detailed discussion of lateral problem-solving, since a detailed discussion of lateral applications exceeds the scope of this paper. Concluding remarks suggest areas for further development to improve economics and performance in lateral drilling.
Renewed interest in lateral drilling centers on the economic and technical advantages of drilling horizontal holes from vertical wellbores to enhance oil and gas production. Because lateral drilling allows a large portion of wellbore to remain In a sinale zone of interest, a greater area of /one can be exposed. In addition, lateral drilling allows multiple holes from a single wellbore for completion of more than one formation or pay zone.
Therefore, lateral drilling may be defined as Implementation of a horizontal or near-horizontal wellbore designed to take optimum advantage of the three dimensional geometry of a reservoir.
A well can be further classified as a "short-," "medium-," or "long-radius" lateral depending on the designed build rate of the hole angle and hence. the radius of the curve it describes.
New developments in lateral drilling tools and well-planning techniques have refined methods of achieving the geometrical specifications of each type of lateral well, suggesting a broader definition which defines lateral drilling in engineering terms.
For brevity, a detailed discussion later in this paper is limited to short- and medium-radius technology, describing how the drilling system used determines the type of curve drilled, and thus "defines" a lateral well as short-, medium- or long-radius.
TYPES OF LATERAL WELLS
Long-Radius, For achieving extended reach off of platforms. and in applications where large horizontal displacement is needed, long-radius lateral techniques drill a directional well that builds inclination at 2 to 6deg./ 100' (30m), with a horizontal section extending up to 3000' (914m).
HORIZONTAL DRILLING-A NEW PRODUCTION METHOD J. C. Bosio, ElfAquitaine, France; R. W. Fincher, Eastman Christensen, USA; J. F. Giannesini, Horwell, France; and J. L. Hatten, Eastman Christensen, USA. Abstract. Vertical, or deviated, oil wells cross a production formation for only short distances. Horizontal wells, however, are capable of remaining within a reservoir for distances up to several hundred metres in an effort to enhance production possibilities. - special flexible equipment is used to drill lateral completions with rapid build rates; - modified conventional hardware is used to drill medium-radius horizontal wellbores; and - conventional directional drilling equipment is utilized to drill horizontais with long radii of curvature. A state-of-the-art discussion covers configurations and drilling procedures for each method. Applications are discussed. with information on why and when horizontal completions should be considered. A table comparing the limitations of each is also included. Horizontal drainholes can be placed in reservoirs using one of three methods: Résumé. Un puits vertical, ou dévié ne traverse un gisement que dans sa dimension la plus faible. Un puits horizontal peut se maintenir pendant plusieurs centaines de mètres dans le gisement, ce qui permet d'augmenter fortement sa capacité de drainage. - par une complétion latérale, forée avec un équipement spécial flexible, permettant un rayon de courbure faible, - par forage latéral à rayon de courbure moyen, utilisant un train de forage légèrement modifié, - en forant avec un matériel standard, ce qui entraîne un plus grand rayon de courbure. I1 existe trois façons d'obtenir un drain horizontal: Chaque méthode est décrite et elles sont comparées, dans l'état actuel de leurs capacités respectives. Les différents cas d'application possibles sont envisagés du point de vue amélioration de la production, les puits horizontaux pouvant être considérés comme une nouvelle méthode de récupération améliorée, la récupér- ation géométrique. 1.
Vertical or deviated oil wells cross a production formation for only short distances. Horizontal wells, however, are capable of remaining within a reservoir for distances up to several hundred metres in an effort to enhance production possibilities. The idea is not new. The concept of drilling horizontally into a reservoir to enhance production has intrigued innovators since the late 1920s'. In the mid-to-late 1950s numerous short-radius horizontal boreholes were drilled in the US to pro- mote additional drainage in tar sands and other low- pressure, easy-to-drill, formations. Most of these drainholes were less than 1OOft (30m) in total length273. There also is documented evidence of horizontal boreholes being drilled in the USSR during this same period435. It has only been since 1979 that conventionally drilled long drainholes have had favourable economic results, thus renewing the interest of the
THE STATE OF THE ART AND THE FUTURE OF HORIZONTAL WELLS Jacques Bosio, Deputy Research and Development Director, Elj- Aquitaine, Tour Elf, Cédex 45,92078, Paris la-Défense, France. Abstract. If the idea of horizontal wells dates back to the beginning of the century, a significant economical success has been obtained for the first time in 1982 only. Since then, horizontal wells have become a standard tool of the petroleum engineer. Most drilling problems have been mastered and drilling costs are down to a very reasonable level compared to vertical wells. Moreover, measurements in horizontal wells, their interpretation, as well as completion methods and equipment, are available so that reservoir engineers can design a better drainage architecture for their reservoirs. The use of horizontal wells is no longer limited to desperate cases, or to very specific cases like reservoirs with a strong coning problem, or fractured reservoirs. Whether for oil or gas, onshore or offshore, for production or injection, pilot operations have now been successfully conducted on many types of reservoirs, quite often fol- lowed by industriai applications. The present extensive development of the Austin Chalk, in Texas, is an example of what can be achieved with this new approach. At a time when reservoir characterization and cost reduction are the main concern of the petroleum engineer, horizontal wells are the ideal tool and their use is likely to expand far beyond what was envisaged a few years ago. Some experts even claim that by the year 2000, 40 to 50% of the wells drilled in the world will be horizon- tal. Résumé. Si i'idée de forer des puits horizontaux date du début du siècle, ce n'est qu'en 1982 qu'un succès économique significatif a été obtenu pour la première fois. Depuis lors, les puits horizontaux sont devenus un outil classique de la panoplie des ingénieurs du pétrole. La plupart des problèmes de forage ont été maîtrisés et les coûts ont été ramenés à un niveau raisonnable par rapport à ceux d'un forage vertical. De plus, les mesures dans les puits horizontaux, leur interprétation ainsi que les méthodes de complétion et les équipements adaptés sont maintenant disponibles, si bien que l'ingénieur de gisement peut concevoir une meilleure architecture de drainage pour ses gisements. L`utilisation de puits horizontaux n'est plus limitée à cas désespérés ou à des cas très spécifiques, comme les gisements à fort risque de coning ou les gisements fracturés. Que ce soit pour du pétrole ou du gaz, sur terre ou en mer, pour la production ou l'injection, des opérations pilotes ont été réalisées avec succès sur de nombreux types de gisements, bien souvent suivies d`applications industrielles. Le développement extensif actuel des Austin chalks au TEXAS est un bon exemple de ce qui peut être réalisé avec cette nouvelle approche. Au moment où la caractérisation des gisements et la réduction des coûts constituent l