Downhole connections between multiple wellbores have applications in many operations such as extended-reach drilling, multilateral completions, subsurface pipelines, and downhole fluid separation. An R&D project was undertaken to develop and validate an electromagnetic ranging concept for enabling cost-efficient downhole connections—namely, Rotating Magnetic Ranging Services and Single Wire Guidance. After extensive testing that found the ranging technology suitable, an existing offshore well jacket located in Southeast Asia, in 5.1 m of water and 1.3 km from shore, was identified as a good candidate for field validation of the concept. The electromagnetic-ranging technology facilitated the successful intersection of the target well according to plan, including by-pass within specified proximity (< 40 cm) and in the correct sand (+-1.5 m TVD window). This paper discusses some of the many applications of downhole well connections. Furthermore, it explains the Rotating Magnetic Ranging Service and Single Wire Guidance ranging concept, which enables efficient downhole well connections. Introduction Determining the distance and direction to adjacent wellbore(s) is a critical task while drilling relief wells or preventing wellbore collisions. Because of the cumulative and systematic errors inherent in MWD or gyroscopic tools, the measured survey coordinates of a wellbore will have increasing uncertainty with depth, which is referred to as the "cone of uncertainty." For example, a vertical well drilled using a surveying tool with an error cone of 1.5 m/1000m, the radius of uncertainty at a true-vertical depth (TVD) of 10,000 m is 15 m. Hence for blowout intervention, to accurately steer a relief well to a deep intersection by relying on the survey data of the target well alone is practically impossible—that is, without a considerable amount of luck. Instead, the homing-in process must be accomplished by a downhole ranging technique. Although some unique ranging technologies are currently being researched, the most common methods are passive-magnetics or active-electromagnetic ranging, which both depend on steel, such as casing or drillstring, in the target well. Over the last decade feasibility studies, field trials, and implementation of downhole ranging technology have been performed for additional applications. This paper explain examples of applications for downhole well connections and describe the Single-Wire Guidance (SWG) and Rotating Magnetic Ranging Service (RMRS) technology developed and tested for these types of applications. History of Well Connections Downhole well intersections are common for relief wells and have been performed regularly for decades as a last-resort well-intervention method when other surface kill efforts have failed. The original purpose of a relief well was to relieve pressure on a blowing formation by drilling a vertical well and producing the formation at high rates. In 1933 a directionally drilled relief well intersected the flowing reservoir below the surface location of a cratered blowout in Conroe, Texas, marking the first milestone in relief-well development. The first application of electromagnetic ranging to achieve a downhole well intersection was performed on blowout in the Gulf of Mexico in 1980 (Kuckes et al. 1984). Furthermore, in 1982, Kuckes et al. used a modified technique with downhole current injection to demonstrate that casing could be detected in a blowout at a range of at least 200 ft. The technique showed great efficiency in locating blowout tubulars for a direct intersection. Casing detection, along with additional developments in surveying and MWD, provided a technique of triangulating the blowing well, reducing plugging and sidetracks. This again changed the basic strategy for designing relief well trajectories.

Summary In subsea environments, using large-bore/high-rate well designs is often a key contributor to the economic recovery of hydrocarbon resources. Their use is a necessity for accommodating the huge production capacity of the reservoirs they penetrate, with the major benefit of minimizing the number of wells necessary to develop a subsea field. The enthusiasm for using such well designs, however, must also be tempered by a clear understanding of the considerable well control risk they introduce—that risk being an increased level of difficulty in bringing such a well under control if a blowout were to occur. It is common that multiple relief wells, with their inherent complexities and time investment, would be simultaneously required to bring a big-bore blowout under control. The discussion of this fact is, though, not a common topic in industry literature. Instead, capping stacks have been more the focus. Much recent attention has been trained on ensuring that capping stacks are a viable method for quickly responding to a high-rate subsea blowout. This makes sense in light of the simpler, and publicly more palatable, concept of rapidly installing a capping stack on a blown-out subsea well. Still, a capping stack is only as reliable as the wellhead it must connect to. It is because subsea wellheads have such a high chance of being damaged during a blowout that relief wells will always be relied on as the ultimate backstop for ensuring that a subsea blowout can be brought under control. This reliance on relief wells, as they are traditionally envisioned, has limitations though when addressing a high-rate subsea blowout. Any subsea relief well will have inherent limitations resulting from the architecture of choke and kill lines (flow restrictions) and that of the crossover piping at the blowout preventer (BOP; erosion concerns). In the world of high-rate subsea blowouts, these limitations can sometimes translate into multiple relief wells being required to inject fluid at the rates necessary to affect a dynamic kill. However, the simultaneous use of multiple subsea relief wells to dynamically kill a single blowout has only been tried once in the industry's history. As a result, some countries require that stopping a blowout must be possible by drilling only one relief well. In this paper, we describe methods that can be implemented to transcend traditional relief well limitations via using a relief well injection spool (RWIS), with the ultimate goal of dynamically killing a subsea big-bore blowout using a single relief well. The technique varies with water depth. In both shallow-water (826 ft) and deepwater (8,260 ft) environments, the techniques are presented and analyzed that will allow using a single subsea relief well to perform a dynamic kill using 15 lbm/gal drilling fluid injected at 238 bbl/min. This particularly severe scenario, based on a big-bore gas well development in Western Australia, is chosen so that our results will have applicability to most subsea well control events that might arise in the future.

As development of the Barents Sea continues with new plays such as the Castberg, accurate specification of the local magnetic field is important to reliably infer the orientation of the bottomhole assembly (BHA) in horizontal drilling. Since magnetic fields at high latitudes vary spatially and temporally, one requires both spatial models and a way to capture temporal changes. Large temporal changes in the magnetic field can severly distort measured azimuths and therefore must be corrected for. This study, based on a report written for Petroleumstilsynet (Maus et al., 2017), shows that in regions of the Barents Sea within 50 km of a magnetic observatory, either the nearest observatory, interpolated infield referencing (IIFR), or the disturbance function (DF) method may be used for corrections in wellbore surveying to meet accuracy requirements. IIFR and DF will give better error reduction but are slightly more complicated to implement. At distances between 50 km and 250 km, the disturbance field (DF) method best meets accuracy requirements. In remote regions beyond 250 km, a local observatory must be deployed to meet the highest accuracy specifications, but the DF will still far outperform the other interpolated methods at such large distances from an existing observatory. Despite having focused on the Barents Sea region, this comparison of the accuracy of different spatial and temporal magnetic field mitigation methods for wellbore surveying is applicable to high latitude northern and southern regions across the globe.

Post Macondo, industry publications have discussed the equipment, connections, and interfaces needed for capping and containing a blowing subsea well, but they give little insight into developing a well-specific subsea-capping contingency plan. The planning process described here, which has been used successfully on multiple projects and source-control drills, involves assessing the feasibility of deploying a capping stack from a floating vessel, the weight and stability of the capping stack to overcome the force of the blowout jet, and dynamic flow simulations of closing the capping stack outlets without loss of well integrity. This process not only assesses the feasibility, complexity, and risk exposure of the capping operation, but may also justify further planning, studies, or expenditure.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper discusses a field-applicable wellbore hydraulics simulator for modeling cement displacement using SBM (synthetic-based mud) inside casing strings, and calculating ECD (equivalent circulating density) and SPP (standpipe pressure) while drilling with compressible mud. The paper shows how drilling data and model results can be used collaboratively to improve the understanding and solution of well problems. The spreadsheet-based simulator consists of readily available models designed to describe the behavior of SBM under typical conditions encountered in deepwater GOM (Gulf of Mexico) operations. The algorithms account for water depth, pressure, temperature, mud composition, viscosity, wellbore size, and cuttings loading throughout the wellbore.Field tests in straight holes where PWD (pressurewhile-drilling) tools were run show good results. Typical errors between calculated and measured ECD were ~1%. In the casing cementing study, measured cement displacement volume to bump the plug compared favorably with model predictions, after proper considerations of compressibility. Applications to high-angle wells require some adjustments.