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Horizontal drilling required approximately 15 years to evolve into a mature technology. During this time, the petroleum industry witnessed amazing feats of extended-reach technology, updip horizontal drilling, rotary-steerable technology, and now directional drilling with casing. Horizontal drilling became feasible in the 1980s with the emergence of measurement-while-drilling downhole survey tools. Horizontal drilling continues to be a powerful application for exposing more reservoir per motherbore (multilaterals), increasing productivity from tight rock, acquiring exposure to multiple subsurface compartments, producing heavy-oil reservoirs (with steam-assisted gravity drainage), and managing waterdrive reservoirs. It is a particularly strong application in clean sandstones with low-vertical-permeability barriers. However, horizontal drilling also can address thin-layered petroleum traps with poor-to-low horizontal permeability. Horizontal completions are limited only by the imaginations of those who drill horizontally. There soon will be a day when one builds a curve considerably below the level of the lateral and places a subsurface pump below the level of production. How many of Earth's petroleum reservoirs are shallow, have no reservoir pressure, cannot be drilled vertically economically, and yet will respond to gravity drainage in a horizontal wellbore? Horizontal and Complex-Trajectory Wells additional reading available at the SPE eLibrary: IPTC 10966 "Reservoir-Screening Methodology for Horizontal Underbalanced-Drilling Candidacy" by T. van der Werken, SPE, Weatherford, et al. SPE 102678 "Analyzing Under performance of Tortuous Horizontal Wells: Validation With Field Data" by M. Kerem, SPE, Shell Intl. E&P B.V., et al. SPE 101129 "Development of Small- and Medium-Sized Oil Fields Through Horizontal Wells—The Way Ahead" by R.D. Tewari, SPE, Greater Nile Petroleum Operating Co., et al. SPE 92804 "Coiled-Tubing Reverse Circulation—An Efficient Method of Cleaning Horizontal Wells in a Mature Pressure-Depleted Field" by P. Santhana Kumar, SPE, Petroleum Development Oman, et al.
Multi-Lateral Horizontal Drilling Problems & Solutions Experienced Offshore Abu Dhabi. Abstract ZADCO's Offshore oil field which is a stacked reservoir system was considered as one of the optimum candidates for horizontal drilling applications. The flourishing of horizontal drilling technology has completely changed the development strategy criteria of the reservoirs. In early 1989, horizontal drilling was experimented in ZADCO's Offshore field, which became an essential part of the new reservoir development program. Eighty five horizontal wells were successfully drilled and completed. A rapid development in horizontal profile was achieved in ZADCO's Offshore field using the latest horizontal drilling technology to drill complex Multilateral horizontal wells: Multilateral in different directions from parent well bore, Multilateral with two branches in one thin reservoir, Multilateral with Stair-step/traverse trajectories to minimize drilling through tight barriers and to delay water breakthrough. Several problems were encountered while planning, drilling, completing & stimulating the complex multilateral horizontal wells such as:–Maintaining zonal isolation among the various reservoirs. –Minimizing the drilled footage through tight barriers/poor facies, to control sweep efficiency and to delay water breakthrough by drilling stair step or traverse hole trajectory –Anchor-stock utilization. Drilling multilateral horizontal wells with low departure target.–The development of thin & tight oil reservoir –Minimizing casing cement bond failure by drilling multilateral holes from one window. –Target centralization within multilateral sections in different directions –Stimulation of multilateral barefoot completion. The paper will focus on the solutions of above problems experienced in the multilateral horizontal wells implemented in the field offshore Abu-Dhabi. Introduction This field, which is one of the largest oil producing fields in the Middle East, is situated in offshore Arabian Gulf about 80 km North West of Abu Dhabi Emirate island. The field was discovered in 1963, development started in 1977 by utilizing conventional drilling methods. Horizontal drilling was introduced in 1989 and an extensive multilateral drilling was implemented in the last two years. The concept of using horizontal wells to improve recovery and controlling sweep efficiency was introduced in the oil industry since 1920s. In recent years thousands of horizontal wells have been drilled world-wide to achieve this concept at a lower monetary investment. The extensive experience of steerable drilling system and remarkable improvement in horizontal drilling technology, encouraged ZADCO to drill complex multilateral horizontal wells. P. 844
This paper was prepared for presentation at the 1999 SPE Asia Pacific Improved Oil Recovery Conference held in Kuala Lumpur, Malaysia, 25–26 October 1999.
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In the gas field of Zuidwal, situated in one of the most environmentally sensitive areas of the Netherlands, a total of nine wells were drilled, three of which were horizontal. Due to the nature of the location, and its gas-bearing formation with layers of different reservoir characteristics, the operator adopted special programs and procedures, which provide the focus of this paper. provide the focus of this paper. 2
In 1969, Elf Petroland B.V., in partnership with Total Marine Exploitie partnership with Total Marine Exploitie Maatschappij B.V., Eurafrep Nederland B.V., Corexland B.V. and Cofraland B.V., was granted an exploration license in the Waddenzee located between Harlingen and Texel (fig. 1). The first exploration well, Zuidwal 1, was drilled in 1970, and revealed the presence of gas at a depth of 2000 m presence of gas at a depth of 2000 m (6560 ft). After appraisal, Elf Petroland B.V. and partners submitted an application for a partners submitted an application for a concession in 1971. Examination of the application required an exceptionally long time as it coincided with an increased awareness of the ecological significance of the Waddenzee. The Zuidwal concession was finally granted in 1984 and the cooperation agreement with Energie Beheer Nederland was signed in 1986. Drilling commenced in September 1987 and was concluded in February 1989.
To maintain the production plateau, a second set of wells was initially planned to be drilled around 1992. However, by drilling three of the nine as horizontal wells the operator would be able to postpone or possibly eliminate this second campaign (fig. 2). This was of considerable interest in the environmentally sensitive Zuidwal area, and would be possible due to significant improvements in gas deliverability from the horizontal wells when compared to vertical/deviated wells. The operator chose a very particular "staircase" profile for the three subject wells (fig. 3-4). Implementation and significant results achieved thereby are described in detail.
3 RESERVOIR ENGINEERING ASPECTS
Because this topic has been covered by numerous papers (ref.1), it will be only briefly discussed here. In vertical or deviated gas wells, the gas velocities are very high near the wellbore. The resulting turbulence causes additional pressure loss proportional to the square of the flowrate. The flow rate (Q) can be expressed as a function of the differential pressure as follows
p static - p flowing = AQ + BQ
The effect of this turbulence is not negligible, it may represent half of the total pressure drop. However, with a long horizontal completion interval, the gas velocities are much lower, and the turbulence effect can be significantly reduced.
This theory is complicated in the Zuidwal field by the anisotropy of the pay zone. The Vlieland Sandstone reservoir shows layers of variable porosity (10% to 21%) and permeability (1 - 100 md). The two best layers, called IIA and II FGH, which production amounts to 80% of the total, are unfortunately only 6 m (20 ft) and 12 m (39 ft) thick, respectively. The strategy then, was to establish long horizontal completion intervals in these two "good" layers with limited horizontal displacement in the poorer zones. This reservoir completion objective seemed viable using a "staircase" wellbore trajectory through the completion interval.
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