Horizontal Sidetracks Research Articles

Study of the horizontal sidetracking efficiency using hydrodynamic modeling (on the example of a Kazakhstani field)

One of the modern approaches for the effective development of small deposits is the construction and operation of wells with a complex architecture: horizontal wells (HW), sidetracks (BS, BGS), multilateral wells (MLW). Sidetracking makes it possible to reanimate an old well that is in an emergency state or inactivity for technological reasons, by opening layers that have not been previously developed, bypassing contamination zones, or watering the formation. This study examines the possibility of using horizontal sidetracks in the operating wells of the field of the Zhetybai group. To select the optimal length of the horizontal sidetrack of the wells, graphs of the dependences of the change in flow rate versus length of the horizontal well were built, taking into account the pressure losses due to friction. It can be seen from the dependence of NPV versus length of the horizontal wellbore that the maximum NPV is achieved with a horizontal wellbore length of 100 m. A further increase in the length of the horizontal wellbore leads to a decrease in NPV. This is due, firstly, to a decrease in oil prices, and secondly, interference of wells, a small number of residual reserves, and a small oil-bearing area. As a result of a comparison of technical and economic criteria, the optimal length of a horizontal wellbore is from 100-300 meters. Comparison of the flow rates of vertical wells and wells with horizontal sidetracks showed a clear advantage over the latter in all respects.

Прогноз емкостных свойств пород по данным буровой механики в процессе роторного бурения скважин с горизонтальным окончанием

Прогноз емкостных свойств пород по данным буровой механики в процессе роторного бурения скважин с горизонтальным окончанием

Annular Ledge Formation Method Allows Sidetracking in Multilateral Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19350, “Effective Annular Ledge Formation Sidetracking in Multilateral Wells in the Vostochno-Messoyakhskoye Field,” by Andrey Voronin, Messoyakhaneftegaz, and Nikolay Abaltusov, SPE, and Anton Vershinin, Weatherford, et al., prepared for the 2019 International Petroleum Technology Conference, Beijing, 26–28 March. The paper has not been peer reviewed. Copyright 2019 International Petroleum Technology Conference. Reproduced by permission. Multilateral drilling technology offers a highly effective method of enhanced oil recovery in fields characterized by complicated geological structures. This paper describes the analysis of sidetracks drilled in an open hole by an annular ledge formation method with a downhole motor in multilateral wells. Introduction Currently, industry growth requires development of fields with complicated geology. Drilling single-bore horizontal holes for these fields is insufficient, to say nothing of drilling vertical or directional wells. Multilateral wells with multiple horizontal sidetracks are drilled with increasing frequency. The competition between downhole motors and rotary steerable systems (RSS) in multilateral-well drilling is fierce. In the complete paper, the authors describe deployment of a method previously only available with RSS that provides advantages to downhole-motor use: annular ledge formation, which involves sidetracking in an open hole. In the case study described, a conventional motor is used without additional electronics. Conventional sidetracking methods in an open hole with the use of motors involve sliding. During sidetracking, the sliding is aggravated additionally by a low rate of drillstring movement. If side-tracking with the conventional method is impossible, then usually a special sidetracking bit is installed and the motor-bend angle is increased. Such measures result in additional time and financial expenditure. The annular ledge formation method allows for sidetracking in an open hole with the use of a standard bottomhole assembly (BHA) with a motor, which also will be used for drilling a lateral. The key feature of this method lies in the fact that, during sidetracking, the drillstring is constantly rotating, which allows avoidance of the problems related to sliding. When sidetracking with the use of this method, the ledge is formed over the entire circumference of the borehole, not only on the bottom wall. But, when sidetracking deeper, a trough is formed on the low side of the hole and the upper side remains unaffected. Because of this, the annular ledge formation method is described by the authors as sidetrack with rotation. The authors discuss the deployment of this method in the Vostochno-Messoyakhskoye field when drilling multilateral fishbone wells. The complete paper presents a detailed discussion of the method and different situational approaches to its use. Vostochno-Messoyakhskoye Field The field is the northernmost developed onshore oil field in Russia in the Tazovsky region 250 km from the Arctic Circle in the Arctic climatic zone. The field is developed with horizontal production and injection wells along a horizontal section length of approximately 1000 m. The geology of the reservoirs is complicated with a large gas cap. In terms of geological conditions, the PK 1-3 pay zone is irregular within the field and is represented by loose sandstones both uniform and horizontally layered. The oil-bearing formations are isolated.

Первые результаты бурения боковых горизонтальных стволов на пласты тюменской свиты Красноленинского месторождения

Первые результаты бурения боковых горизонтальных стволов на пласты тюменской свиты Красноленинского месторождения

О методах снижения прихватоопасности при бурении наклонно направленных скважин с горизонтальным окончанием

О методах снижения прихватоопасности при бурении наклонно направленных скважин с горизонтальным окончанием

Scenario approach for increasing efficiency of wells operation with the horizontal termination

The aim of this work is to reveal causes of unprofitable horizontal tailing-in well operation, their further ranking according to the degree of influence, and developing reactive and pro-active measures on increasing efficiency of wells in operations as well as planned wells. During this work the retrospective analysis of horizontal termination well operation stock (horizontal well, horizontal sidetrack, horizontal drainhole well), and the analysis of current state were carried out. The influence of the conducted wellbore interventions on economic efficiency of well operations was estimated. According to the results, obtained in the research, the main direction of works on increasing efficiency will be scenario approach to planning investments at the wells. It must be considered future (potential) wellbore interventions at the wells as an integral part of well operation. It is necessary to calculate total investment attractiveness of projects on oil extraction, including the following elements: well construction; operation; in-flow stimulation; water suppression; effects via injection well stock; abandoning. Such approach to planning investments will allow to carry out correct comparative assessment of the existing well operations and repairs technologies with new ones which can push up the cost of separate subprojects, but at the same time enhance its investment attractiveness.

Применение устройств контроля притока в боковых горизонтальных стволах скважин пласта АВ4-5 Самотлорского месторождения

Применение устройств контроля притока в боковых горизонтальных стволах скважин пласта АВ4-5 Самотлорского месторождения

Исследование свойств тампонажных растворов для крепления скважин и боковых стволов с наклонными и горизонтальными участками

Исследование свойств тампонажных растворов для крепления скважин и боковых стволов с наклонными и горизонтальными участками

The Appeal of Mature Fields

What's Ahead - Final column from 2013’s TWA editor-in-chief, Todd Willis. Ask most YPs what they want in their career, and you’re likely to hear descriptors like “cutting-edge,” “major project,” or “new development.” Ask us where we want to work, and locations like Houston, London, or Dubai might come to mind. You probably won’t hear us wanting to tend to 5-B/D stripper wells in the Permian Basin of Texas and New Mexico, or be a field engineer in Baku, Azerbaijan, one of the world’s earliest major energy hubs. Upon initial consideration, these places seem unimportant—not the sexy, cutting-edge future of the oil field. They are where the action was 50 years ago, a relic, interesting to read about in history books, but certainly not to work in. The real technology and capital spending—or so the thinking goes—is in deep water or unconventional gas fields. Indeed, TWA focused this year’s first issue on deepwater plays and the technology required to operate in these areas. On closer inspection, though, the level of ongoing investment into mature assets and their significance to the operations of companies large and small show that this initial impression just doesn’t hold up. Many operators have invested tens and even hundreds of millions of dollars into sustaining or revitalizing older assets. Supervisory Control and Data Acquisition (SCADA) systems and i-Field (intelligent-field) efforts enable an engineer sitting at a desk hundreds of miles away to monitor entire fields single-handedly. Waterfloods, steam floods, polymer floods, infill drilling programs, horizontal side-tracks—all of these enhanced oil recovery (EOR) and improved recovery projects bring tens of millions of dollars of investment capital to these so-called oilfield “relics.” They also bring with them the need for project managers, financial analysts, and talented engineers who can maximize return on investment.

Dynamic Analysis and Vibration of Beam Inside Annulus for Ultra Short-Radius Water Jet Drilling

Conventional water-jet nozzle systems have been developed and partially used in the oil and gas industry to drill horizontal sidetracks. However, this technique still presents a few shortcomings associated with tube buckling and water jet sagging. Due to these problems, the drilled hole deviates from the desired path and does not reach the target reservoir. The issue becomes more complex due to the continuously moving boundaries representing the borehole profile, which is, in turn, governed by the nozzle dynamics. A mathematical model representing the dynamics of water jet drilling confined in a borehole along with drilling mud is developed to predict the sagging phenomenon during the drilling process. The closed form solution of the governing equation is obtained for horizontal drilling in shallow formation layers. The solution shows the strong influence of nozzle vibration and the magnitude of thrust force at the nozzle tip on the profile and the diameter of drilled hole. For sidetrack drilling of greater than 400 m length, the magnitude of sagging is large enough to miss the target reservoir. Furthermore, the dril string buckles at certain magnitudes of thrust forces and penetration lengths.

Cовременные решения для проектирования, оценки и оптимизации горизонтальных скважин и боковых стволов на основе трёхмерных геолого–гидродинамических моделе

Cовременные решения для проектирования, оценки и оптимизации горизонтальных скважин и боковых стволов на основе трёхмерных геолого–гидродинамических моделе

Saudi Arabian Trilateral Oil Well in an Unconsolidated-Sandstone Reservoir

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 120999, ’The First Saudi Arabian Trilateral Oil Well in Unconsolidated-Sandstone Reservoir,’ by Ali S. Raba'a, SPE, and Anthony S. Johnson, SPE, Saudi Aramco, and Keith Parry and Mohammed A. Abduldayem, SPE, Weatherford, prepared for the 2009 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 4-6 August. Multilateral (ML) wells to achieve maximum reservoir contact (MRC) are used widely in new carbonate-field developments in Saudi Arabia, resulting in substantial financial improvement of these assets. A multidisciplinary approach was used to evaluate, plan, and complete the first trilateral well in a heterogeneous unconsolidated-sandstone reservoir in Saudi Arabia. The objectives of the ML well were to maximize reservoir contact to enhance sweep efficiency, to improve well productivity, and to promote ML-well applications in this complex field to extend the field’s production plateau. Introduction The objective of ML-well technology is to improve well productivity, either by maximizing reservoir contact in a single reservoir or by commingling production from two or more producing zones or formations into a single main wellbore. Successes with this well architecture justified extending its use into an oil field in central Arabia. The Permian heterogeneous unconsolidated-sandstone reservoir consists of well-developed eolian sandstones and closely associated interdune and lacustrine deposits. Maintaining wellbore stability while drilling this friable-sandstone reservoir presents a considerable challenge. Wells must be equipped with downhole sand control and electrical-submersible-pump (ESP) artificial-lift systems, which cannot tolerate appreciable solids loading. The candidate well for ML drilling was an idle vertical well that had been shut in because of high water cut (WC) and low productivity. Reservoir characterization and fluid-contact information from adjacent wells were uncertain. Before drilling the laterals, a deviated pilot hole was drilled across the entire reservoir, which provided valuable data that helped optimize placement of the laterals. Re-entry of an existing well to drill and steer three long horizontal open drain holes into the reservoir imposed several constraints and added challenges. The well completion involved installing an expandable sand screen (ESS) in the main bore and standard sand screens in the two laterals to facilitate sand-free commingled production from all three laterals. The lateral completions included a wash-down capability in the high-build-angle laterals and incorporated swell packers positioned just inside the laterals to ensure sand-tight conditions at the Technology Advancement Multilateral (TAML) Level-3 junctions. Horizontal-Well Infill Strategies Several drilling strategies have been applied in the field. Initially, the field was developed with vertical wells at 1-km well spacing and with peripheral water injection. Most wells are equipped with an ESP for oil production. After 5 years of production, a new horizontal-sidetrack infill strategy was implemented to target unswept oil, access low-permeability pay, reduce the WC, and accelerate oil production. Geosteering to intersect the top of the reservoir (shallow horizontal sidetracks) or to follow individual channels was found to be ineffective because of the heterogeneous nature of the reservoir (low vertical conformance) and difficulties in predicting sand presence and continuity. Therefore, the integrated team developed an optimal sidetrack infill strategy of highly deviated wells with minimal geosteering.

A Tool for Liner Running and Cementing Using Electric-Line Coiled Tubing

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 120992, "The Side Exhaust Liner-Running Tool: A Tool for Liner Running and Cementing Using E-Line Coiled Tubing," by Greg Sarber, SPE, and Mark Johnson, SPE, BPXA; Bob Harris, SPE, and Carl Diller, Northern Solutions; and John Milne and Alan Holloway, Baker Hughes, originally prepared for the 2009 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, 31 March-1 April. The paper has not been peer reviewed. A new system for running and cementing liners using electric-line coiled tubing (CT) has been proved on the North Slope of Alaska. The side-exhaust liner-running tool (SELRT) provides the functionality to run and release a liner while using a liner wiper-plug (LWP) system to ensure good cement quality. A jointed-pipe liner is conveyed and cemented with the CT containing an electric umbilical. This innovative equipment has proved to be a substantial health, safety, and environment (HSE) benefit and yields savings in rig time. Introduction There has been a continuous CT-drilling (CTD) campaign on the North Slope of Alaska since 1994. This program re-enters existing vertical wells and drills horizontal sidetracks in the Prudhoe Bay, Kuparuk, Endicott, and Milne Point fields. These sidetracks typically are drilled through 4 1/2-in. production tubing without pulling the tubing or removing the existing production tree. More than 575 new sidetrack wells have been drilled in these fields since 1994. Before 2001, conventional 2 3/8-in.-outside-diameter CT (electric-line-umbilical free) was in use. When a well reached total depth (TD), the typical completion was a solid/cemented liner followed by CT-conveyed perforating guns. The liner-running tool used a ball-drop system to release the liner and a CT dart/LWP system to ensure that uncontaminated cement was placed accurately behind the liner. This system proved quite reliable and robust and accounted for the majority of wells drilled up to 2001. In 2001, a new measurement-while-drilling (MWD) bottomhole assembly (BHA) was tested. To operate, this BHA required an electrical umbilical inside the CT. This drilling system provided higher data-telemetry rates, more real-time downhole information, and better directional control using an electrical downhole orienter instead of a mechanical orienter. This system proved to be especially beneficial in managed-pressure- and underbalanced-drilling (MPD and UBD) applications. The electric orienter minimized shale damage by eliminating the pump cycles needed to operate a mechanical orienter. This new equipment provided sufficient time savings to enable a 30% increase in effective rate of penetration. Unfortunately, some of the productivity gains realized from using the electric-line CT BHA were lost when it came to completing the wells. To run and cement the liner, the CT reel containing the electric line had to be replaced with an electric-line-free reel to use the existing liner-running equipment. Reel swaps are an HSE risk when conducted in the middle of drilling operations, especially when conducted in Arctic winter conditions; the reel exchange consumed some of the time-savings benefits of using the new drilling BHA, additional operating costs were required to inventory two types of CT, and exchanging reels caused a delay from when the well reached TD until the liner was on bottom.

Redevelopment of a Matured Multilayered Carbonate Offshore Field Through High-Technology Horizontal and Multilateral Wells

Summary Oil productivity from Mumbai High field, an offshore multilayered carbonate reservoir, increased significantly through the implementation of a major redevelopment program. Geoscientific information available from approximately 700 exploratory and development wells drilled in the field during nearly 25 years was incorporated during geological and reservoir simulation modeling of the field. High-technology drilling (viz. horizontal/multilaterals for the new development wells) was adopted on field scale to effectively address typical complexity of the layered carbonate reservoirs. Since the commencement of the project in 2000, approximately 140 new wells were drilled, mostly with horizontal and multilateral drainholes. Besides these, more than 70 suboptimal producers were also converted as horizontal sidetracks under brownfield development. The horizontal sidetracks were drilled as long-drift sidetrack (LDST), extended-reach drilling (ERD), LDST-ERD, short-drift sidetrack (SDST), and medium-radius drainhole (MRDH) types of wells through the application of innovative and emerging drilling technologies with nondamaging drilling fluids, whipstocks to kick off sidetrack wells, rotary-steering systems, and expandable tubulars to complete horizontal sidetracks in lower layers. With the implementation of this project, the declining trend was fully arrested and a significant upward trend in production has been established.

High-resolution seismic imaging of a deep gas reservoir from azimuthal offset VSP, Saudi Arabia

ABSTRACT A multi-offset, azimuthal, three-component VSP survey was acquired over a deep Unayzah sandstone gas reservoir in central Saudi Arabia. The objective was to confirm the direction for a proposed horizontal sidetrack to a vertical delineation well. A production test at the vertical well indicated a possible reservoir boundary less than 100 feet away from the well. It was hoped that some of the offset sections might image a small fault, which may represent such a boundary. In addition to the normal zero-offset VSP conducted at the vertical well, two multi-offset VSPs at orthogonal azimuths, and four single-offset VSPs at other azimuths were acquired. Due to excellent cased-hole conditions for the receivers and uniform sandy terrain for the sources, the VSP records were nearly noise-free. The VSP data had virtually twice the dominant frequency of the surface seismic data. The offset VSP sections (both compressional and shear) succeeded in better resolving the reservoir properties of the gas-bearing Unayzah-A sandstone. They showed that its quality deteriorates to the northeast, whereas both its thickness and porosity remain uniform to the northwest, the proposed direction of the horizontal sidetrack. The shorter offset sections in each quadrant surrounding the well showed no clear disruptions that may indicate faulting. This suggests that the boundary detected from the well test may be due to facies change, cementation, or mineralized fractures associated with a major fault bounding the accumulation to the south.

Drilling for Coalbed Methane in the San Juan Basin With Coiled Tubing

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 105874, "Drilling for Coalbed Methane in the San Juan Basin With Coiled Tubing: Results, Learnings, and a World First," by Sam Noynaert, SPE, and Dale Pumphrey, BP plc; and Tony Pink, SPE, Schlumberger; and Tug Eiden, Fred Hartensteiner, SPE, and Chip Nelson, SPE, BP plc, prepared for the 2007 SPE/IADC Drilling Conference, Amsterdam, 20-22 February. In 2006, a coiled-tubing-drilling (CTD) pilot program was initiated in the San Juan basin consisting of seven wells, drilled in order of increasing complexity. The intention was to evaluate the capabilities of CTD and its potential for use in the San Juan basin. The rig used was a new, custom-built, coiled-tubing (CT)/rotary hybrid rig with a single-sized derrick, rotary table, and topdrive. This allowed the rig to drill with jointed pipe, handle and make up bottomhole assemblies (BHAs), and run liners and casing. Introduction The San Juan basin is approximately 9,000 sq miles in northwestern New Mexico and southwestern Colorado. Remaining recoverable gas reserves are estimated to be 12.9 Tcf, with 8.5 Tcf of this coalbed-methane (CBM) reserves. Since the first well was drilled in 1901, thousands of wells have been drilled in the San Juan basin. Most of these wells targeted gas reserves in the Picture Cliffs, Mesa Verde, and Dakota formations. Starting in 1988, wells targeting CBM in the Fruitland Coal began to be drilled. The basin currently contains approximately 30,000 producing wells, the majority of which are producing gas from the Fruitland Coal. Pilot-Program Objectives The drilling program was set up to evaluate the potential of CTD in the San Juan basin. Five major areas of performance were highlighted as key indicators of potential: rate of penetration (ROP), directional capability, rig mobility, re-entry/horizontal-sidetrack performance, and safety performance. Because of the high daily cost or spread rate of a hybrid CTD rig vs. the conventional rotary rigs in the basin, high average ROPs would be the key to enable CTD to compete economically with conventional rigs. Relatively higher average ROPs with CT had been documented in other areas. Along with higher ROPs, overall well-completion time has historically dropped with the use of CT because of CT trip speed and dog-leg-severity capability. The wellbore directional plans included build-and-hold and S-shaped plans and horizontal sidetracks. All of the wells to be drilled except for the sidetracks, both vertical and directional, needed to be drilled with larger hole sizes (8 3/4 and 6 1/4 in.) to accommodate the typical wellbore completions; this necessitated the use of larger, 3 1/2- and 2 7/8-in.-outside-diameter (OD) CT. Although directional work with large-size CT has been completed successfully, smaller-size CT typically is used for directional CTD work. The directional component of the program was complicated further by testing a rotary-steerable system (RSS) for directional control in the wells to be drilled. This was done successfully and was a world first in the industry.

Plasma Channel Miniature Hole Drilling Technology

With growing economic and environmental pressures, oil companies seek ways to increase the oil recovery from every well. Re-entry drilling of horizontal sidetracks from existing wells and multilateral drilling for new wells are techniques which help to achieve that increase. However, new approaches are needed to reduce the cost and to improve efficiency of rotary drilling methods used for these purposes. A new nonrotary plasma channel drilling (PCD) method for drilling of small diameter holes (3.5-15 cm) in oilfields for sidetrack creation and multilateral drilling is described in this paper. The method relies upon the use of the energy of impulse spark discharges which are formed inside the rock formation ahead of the drill position. Repeated formation of the plasma channel results in an effective and controlled drilling action. Plasma channel drills developed at Strathclyde University are able to cut clearly defined circular holes in medium hard sandstone with speeds of up to 16 cm/min using specific energies as low as 400 J/cm/sup 3/. Plasma channel drilling has the potential to increase the lifetime of oil wells and would significantly reduce the cost of exploration drilling and subsurface data acquisition. PCD technology can also be a cost-effective and practical solution for other applications such as mineral mining, water boring and scale removal where micro-hole drilling is essential.

Long-Term Performance of Multilaterals in Commingled Reservoirs

Abstract In this study, a comprehensive transient model was developed for multilateral wells producing from multiple formations separated by impervious streaks. The model is flexible and is capable of simulating the flow with any number of layers, unequal initial layer pressure, non-uniform petrophysical properties for each layer, and unequal layer size. Additionally, each lateral can have non-uniform formation damage and may be selectively completed. We investigated the long-term rate decline and cumulative recovery response of the multilateral wells connecting multiple isolated formations. Total flow rate, cumulative production, and fractional rate for each branch are all compared for several completion scenarios and layer properties. Crossflow between the layers through the wellbore is also evaluated. Introduction There have been many studies on modelling the fluid flow in horizontal wells in single-layer reservoirs or layered reservoirs with interlayer crossflow. In recent years, several studies focused on the productivity of multilaterals in homogeneous formations. To the author's knowledge, the literature provides only one study on the performance of a trilateral well in a three-layer commingled reservoir and one research study on the pressure transient characteristics of multilaterals in layered formations with crossflow. In many field applications, several non-communicating formations may be commingled only through a single undulating horizontal well or several sidetrack laterals emanating from a common pilot hole. The literature lacks a comprehensive investigation of the long-term performance of multilaterals commingling several isolated formations. Background Performance of vertical wells producing from commingled reservoirs has been the subject of many studies in the literature(1–4). However, most of the studies have focused on the transient pressure response of the commingled systems(1–3). Johnston and Lee(4) investigated the flow rate and cumulative production responses of low-permeability layers commingled through a vertical well. Inflow performance of a single horizontal lateral has been examined in detail by many investigators(5–12). Some studies only consider horizontal openholes(5–7). The effects of well completion schemes, such as partial penetration, undulation, perforating, and openhole gravel packing, on horizontal well performance have been discussed in several more recent studies(8–12). In recent years, multibranched wells have been proposed to improve hydrocarbon recovery and to accelerate production. Horizontal well performance with multiple laterals has been considered in several modelling studies(13–18). References (17) - (21) have reported the field applications of the multilaterals. Almost all the previous work on multilaterals addressed the issues related to production from a single formation or layered formations with interlayer crossflow. Among the previous studies, Vo and Madden(17) analyzed the production from a trilateral well commingling three isolated layers in the Dos Cuadras offshore field in California. Inflow Performance Model for Multilaterals in Commingled Reservoirs The physical model considered in this study is shown in Figure 1. The commingled multi-layer system considers an arbitrary number of isolated layers with different petrophysical properties and initial pressure. Impervious layers separate the reservoirs. It is assumed that there is only one lateral in each layer. All the laterals drilled into different layers may emanate from a common pilot hole, as depicted in Figur

Coiled-Tubing Drilling of Horizontal Sidetrack in House Mountain Field, Alberta

Summary In 1995, the first horizontal sidetrack successfully drilled using coiled tubing (CT) was carried out at Shell's House Mountain oilfield. The objective was to drill underbalanced a 378-in. diam by 300-m-long horizontal hole section from an existing vertical, cased oil well. The existing well was re-entered using a conventional drilling rig; a window milled in the casing, and the build section drilled to an inclination of 90°. 238-in. CT was then used to directionally drill the horizontal section underbalanced with nitrified water. The zone of interest was a Devonian-age reef-edge and limestone structure, at a depth of about 2200 m, called the Slave Point. A case history of directionally drilling the horizontal sidetrack using 238-in. OD. CT is provided. Coiled-tubing drilling proved to be a cost-effective alternative to drilling the horizontal sidetrack without using a conventional drilling rig. Shorter trip times, underbalanced drilling, enhanced rates of penetration (ROP), and the ability to maintain weight on bit were all achieved. ROPs increased by up to three-fold while drilling underbalanced.

Screening Criteria to Evaluate the Development Potential of Remaining Oil in Mature Fields

Summary Continuing reservoir management at mature stages often concentrates on delineating pockets of remaining mobile oil. This is becoming a major task for reservoir geologists and petrophysicists. Many old fields are coming up for reactivation as investment opportunities and there is an overall expectation that modern techniques can lead to additional recovery of between 10 and 20%. In this article we will discuss the screening criteria related to reservoir architecture, accumulation condition and production history. The mobile oil remaining can be found in a number of predictable locations in reservoirs depending on their structural style and facies. Attic oil along faults is perhaps the most simple configuration but sizeable volumes of remaining oil can also occur as a function of reservoir stratification and lateral discontinuity. A systematic overview of the different play types has been compiled based on structural or stratigraphic lateral continuity and vertical reservoir connectivity. Screening criteria have been derived on the basis of field examples and models for four play types. The screening criteria specify minimum conditions which may lead to economic re-development with horizontal sidetracks from existing wells. In addition recommendations are given with respect to data gathering to confirm the presence of economically viable targets.