Multilateral Wells in the Castilla Field of Eastern Colombia: A Case History of the Guadalupe Reservoir

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Abstract Castilla field, located 250 km southeast of Bogota, Colombia, was discovered in 1969 by Chevron Oil Company and was originally developed with vertical wells. The 10,300 acre field produces heavy oil from the Guadalupe reservoir (Upper Cretaceous), which has a strong bottom aquifer water drive. Ecopetrol acquired the field in late 2000 and completed the first horizontal well in February 2001. In early 2005, a second drilling campaign was started with directional wells using a 7-well cluster design to increase reservoir exposure and to delay the effect of the aquifer water influx. In 2006, a multidisciplinary team was formed to evaluate the feasibility of advanced well architecture to increase oil sweep efficiency, avoid bypassed oil in the K2 reservoir resulting from coning, and minimize water production. Based on reservoir and drilling analysis, the study recommended drilling three TAML Level 4 multilateral wells to replace nine directional wells originally projected in two different areas of the field. The result has been increased reservoir exposure in K1 and K2, reduced drawdown pressure to produce the K2 reservoir, important reduction in water production (BSW), and higher estimated final oil recovery per well. This paper presents the lessons learned from drilling and completing these three multilateral wells to illustrate the challenges and benefits of using multilateral technology for Castilla field. National Colombian Petroleum Company (Ecopetrol) is evaluating various technologies to increase production and to improve recovery factors in their mature oil and gas fields. As part of that process, a multidisciplinary team evaluated the feasibility of multilateral well technology implementation in some of their mature fields that are currently in the late-development phase. Castilla field, located in the eastern planes of Colombia, was selected as the first option for multilateral technology implementation, based on reservoir features, type of oil, and field antecedents. This paper presents the process used to conceptualize the optimum multilateral well design for Castilla field, integrating all of the geological and engineering disciplines. The disciplines and their areas of focus include the following: Geology - Geological model visualization, target zones definition, pay zones lateral continuity, petrophysical properties, and fluids distribution were evaluated to select the areas to drill with advanced architecture well design.Reservoir - Basic reservoir performance simulation was performed to evaluate productivity with horizontal and multilateral wells, and the difference in final reserves recovery was compared to current conventional directional wells. Water production and coning problems were identified as key factors to define the multilateral well implementation in this field.Drilling - Trajectory design, multilateral junction depth definition and TAML level selection, casing point definition, drilling time, and authority for expenditure (AFE) estimation were the technical aspects evaluated during the planning phase to determine whether or not the technology would be feasible. A comparison with conventional pad design was conducted to validate economic value. Multilateral TAML level 4 system selection flow process is presented applying oil industry best practices.Completion - The optimum lateral completion and production assembly design were main concerns during the planning process. Slotted liners, screens, and open-hole completion options for the horizontal section were evaluated. Intelligent completion designs were analyzed for several multilateral well configurations, and the best alternative was selected to accomplish the production optimization goals. During the operation phase, the geological and geophysical (G&G) and drilling teams worked together to implement a dynamic, real-time optimization process to control positioning of the horizontal wellbores using geosteering techniques. The pay zone completion was based on the quality of rock found while drilling the horizontal sections using real-time information from the logging-while-drilling (LWD) tools. In addition to multilaterals, the introduction of rotary steerable tools and LWD tools were important new technologies for the Castilla field. This paper presents the effect of these tools on the total well cost because rate of penetration (ROP) optimization is yet another important milestone achieved with this project. The results of the three TAML Level 4 multilateral wells are summarized to explain the impressive learning curve achieved in terms of drilling time, drilling and completion cost, effective pay zone drilled, and production results. Based on those results, Ecopetrol is currently drilling several single horizontal wells instead of conventional directional wells where the area permits it, and the savings in drilling time and cost are presented. In general, the results achieved during the implementation of the multilateral well project demonstrate that this technology adds significant value for the Guadalupe reservoir development strategy and that these new techniques applied during the drilling phase provided enormous value in terms of lessons learned.