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Abstract Reservoir developments that rely on long horizontal wells are common practice. Understanding the inflow distribution from a horizontal well is an ongoing challenge for our industry. The effectiveness of reservoir management decisions are greatly improved with an understanding of the flow distribution across the reservoir interval. While technologies have been developed using tractors or coiled tubing to deploy production logging tools into horizontal wells, it requires a well intervention operation, increases risk exposure and is not always successful. This paper reviews a case study from a multi-lateral well in Alaska where a new style of chemical tracers embedded into the completion equipment was used to derive a quantitative estimate of the inflow distribution in a dual horizontal, multi-lateral well. The chemical tracers, which resemble strips of plastic, are designed to release unique chemical fingerprints when contacted by oil. The tracers are then detected in the oil to concentrations as low as 1 part per trillion. In this case study six locations were selected for placement of oil sensitive tracers. During a shut-in period the strips continue to release their unique chemical tracers causing an increased tracer concentration to develop in the oil immediately surrounding the tracer location. Upon start up, these small volumes of oil, containing the higher concentration of tracer, are displaced to the surface. Samples of the produced oil are analyzed to develop a plot of each tracer’s concentration vs produced volume. The arrival of the oil containing the high tracer concentration is related to the inflow distribution. This paper reviews results from a field deployment in a dual lateral well that contained 3 tracer locations in each lateral. The results from this well indicate that one lateral was producing approximately 30% more than the other lateral. Additionally the data indicates the toe of one of the laterals was a major contributor to the total well flow. This insight into the reservoir performance was obtained with no intervention into the well and only minor modifications to the completion design.
Abstract Drilling several branches into a reservoir from a main wellbore (multi-lateral/multi-branch wells) offers potential benefits in terms of improving drainage, productivity and well economics. This technique has become increasingly popular since the 1990's to the extent that multi-lateral/multi-branch well technology has now become one of the most important innovations within the oil industry. In the paper, the authors review and summarize multi-lateral/multi-branch wells as a development option for oil and gas fields. The process of screening multi-lateral/multi-branch wells applications is discussed, identifying not only the potential benefits of economics and efficient access to reserves, but also the risk associated with both the reservoir application and mechanical systems. Emphasis is placed on providing guidelines for each stage of this evaluation and design processes for these wells, incorporating a multi-disciplinary understanding of the reservoir geology, reservoir dynamics, completion design and operational management of the well. The importance of contingency planning in the process is highlighted, as a means of risk management. Introduction The application of horizontal wells in developing oil and gas fields has dramatically increased and become increasingly important in recent years. The Technology Research Center of Japan National Oil Corporation and The Horizontal Well Technology Unit at Herriot-Watt University initiated in 1993 a collaborative work program for study of horizontal wells. The objectives of this work program were to review and analyze strategically important well technologies, with a view to developing a framework for optimum selection and design progress. The initial phase of work addressed horizontal well issues and their application, resulting in the publication of a Design Guide Book in 1994. An extension of the work was formulated to address multi-lateral/multi-branch wells which have a potentially important role in current, new and existing oilfield developments, and which are rapidly becoming an accepted technology for developing oil and gas reservoirs world wide. They may also promote a reduction in well numbers, and improvements in both productivity and ultimate recovery leading to enhanced economics in both new and mature fields. The rapid evaluation of multi-lateral/multi-branch wells promoted the study which was initiated in 1995 and published in 1996. A database of multi-lateral/multi-branch wells worldwide was compiled and a strategy for the planning and design of multi-lateral/multi-branch wells was encapsulated in tabular and flow chart format in the study. Summary results of this study follow in the remaining sections of this paper. What are Multi-Lateral/Multi-Branch Wells? This chapter examined the definition and the multi-lateral/multi-branch configuration options which are currently available and emphasized the economic and technical benefits which can be derived from their application. P. 135^
Abstract The Troll oil field has been drilled and completed with more than 100 geo-steered extended-reach multi-lateral (MLT) subsea wells having two, three or four branches each to maximize reservoir contact. The Troll team has drilled multi-lateral wells from semi-submersibles for more than 10 years. The wells are equipped with complex intelligent top completion (ITC) systems to optimize production. The oil column of the Troll oil field was initially between 11 and 26m thick, with an overlaying gas cap. The wells are 2-5,000-m-long horizontal multi-lateral branches; many completed with stand-alone sand screens and autonomous inflow control valves (AICD) for the lower completions, with up to 80-90% screen coverage per branch lateral. Production life of MLT wells on Troll is limited by gas break-through and/or high water cut. To increase production life and reservoir meters per well there is a need for flexibility through flow control from the surface. Until recently, the ITC system only allowed for individual control of two-branches by two dedicated inflow control valves (ICVs). For three or more branched wells, the upper-most branch would be individually controlled while flow for the other branches controlled together. If break-through occurs in one of the lower laterals, they would have to be choked/or shut-in together, resulting in lost production and reduced recovery from the other laterals. As a result, there was a need for greater flexibility and inflow control for wells with more than two branches. The operator requested contributions from a supplier for a system based on the existing multi-lateral system, the FlexRite® intelligent completion interface (ICI), which would allow for flow control of all branches. A development project began in 2010, and a new multi-lateral system, multibranch inflow control (MIC), was created in 2011. This system has an increased internal diameter (ID) for installation of the completion string with ICVs and swellable packers through the junction for enhanced well control. In October 2012, the Troll team installed the first multibranch MIC system on the Troll well N-24. This system is believed to be the first TAML Level-5, three-branched well with individual branch control worldwide. With this new and innovative junction and completion system, the operator now has the ability to optimize the oil production from new extended-reach multi-lateral wells. In the future, this innovative multi-lateral solution will enable the operator to increase oil recovery from Troll and other fields, which will help the operator to continue to push the functionality and economic viability of multi-lateral technology worldwide, especially in thin reservoirs. Introduction The Troll field is a large oil- and gas field located 80 km northwest of Bergen in the North Sea. It was discovered in 1979 and consists of three provinces Troll East, Troll West Oil Province (TWOP) and Troll West Gas Province (TWGP). The Troll field contains approximately 40% of the total gas reserves on the Norwegian Continental shelf. Originally, the Troll field was considered strictly a gas field with no commercial oil value. This was due to the thin oil-bearing layers overlaid by a thick gas cap. However, this changed with the advent and evolution of horizontal drilling and later multi-lateral well technology. Three production platforms, Troll A, B, and C, are installed at Troll. Oil is produced and processed on Troll B, a floating platform with concrete hull and Troll C, a floating platform with steel hull. Oil was first produced in the fall of 1995 from Troll B followed by production from Troll C in 1999. Troll A began producing gas in 1996.
Gallivan, J.D. (Heriot-Watt University) | Hewitt, N.R. (Heriot-Watt University) | Olsen, M. (Heriot-Watt University) | Peden, J.M. (Heriot-Watt University) | Tehrani, D. (Heriot-Watt University) | Tweedie, A.A.P. (Heriot-Watt University)
SPE 3044l Abstract Drilling and well completion technology have progressed to make it possible to drain reservoirs with multiple branching wellbores connected into one tubing string - usually known as multi-lateral wells. However, the economic benefit of multi-lateral wells has not been reliably understood up to now because of uncertainties in their cost and performance. This is in part due to technical difficulties in predicting flow performance and drainage efficiency. A number of operating companies in the North Sea have sponsored a research and development project to tackle these difficulties. This paper, based on that project, shows how analytical and reservoir simulation methods have been combined to predict the productivity and sweep efficiency for simple cases in homogeneous reservoirs. The results have then been extended to cover irregular well geometries in realistic heterogeneous reservoirs. The paper concludes with an assessment of the potential and anticipated benefits of applying multi-lateral wells in a range of reservoir types characteristic of the North Sea. The emphasis is on the evaluation processes used. Introduction Horizontal wells added an extra dimension to the industry's ability to drain reservoirs of oil and gas. The advent of multi-lateral wells, with multiple branching wellbores connected into one tubing string, has added a further dimension to that ability. Horizontal wells made it possible to develop fields which were uneconomic using vertical wells and now multi-lateral wells promise to transform the economics of fields which are marginal even when developed using horizontal wells. Fig 1 shows a selection of multilateral well types which are being drilled in various parts of the world. The day is not far off when a small offshore accumulation could be developed using one well in which production and injection are combined. In the early days of horizontal wells, prediction was unreliable due mostly to the increased dependence of performance on reservoir properties near the wellbore. For example, a shale near the wellbore, not evident in the petrophysical data from the well, could have a major effect on well productivity and drainage efficiency. Advances in reservoir description techniques, as well as progress in understanding horizontal well performance, made such predictions more robust. The same progress now needs to be made for multi-lateral wells. Methodology The approach taken in the present work is first to use simple systems in which the bottom hole flowing pressure in each branch and inflow profile along the branch of a multi-lateral well can be solved analytically with good accuracy. The same system is then simulated using a commercial numerical simulator. If required, corrections are made to the well specification data so that the numerical results agree with the analytical predictions. These corrections are made by applying a pseudo-skin as in the recent work of Chen & Tehrani (Ref 3, 1995). For multi-lateral wells in complex, heterogeneous reservoirs the reservoir is "averaged" in such a way that well performance will still be the same while allowing analytical predictions to be made (Ref 4, 1995). Benefits of multi-lateral wells can be evaluated in the same way as conventional wells using production rate, reserves, discounted reserves, cost per barrel and other measures of value. In order to compare different well configurations within one reservoir or between reservoirs both normalised productivity index and discounted barrels/unit cost were considered the most relevant measures of value. Normalised productivity index (NPI) is normalised per 1000 feet of well bore. Discounted barrels/unit cost works well provided a good cost model which gives realistic cost estimates for different well configurations is available. Applications Simple Models. Currently available analytical methods consists of work by Borisov (Ref 1 1954) and Joshi & Raghavan (Ref 2 1990). These methods are limited to symmetrical well configurations in infinite slab reservoirs and have to be extended to cover the geometrical complexity of multi-lateral wells now feasible through advances in drilling technology.