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Abstract The present work describes aspects related to planning and execution of six multilateral horizontal branches drilled underbalanced (UB) in Carmopolis field, which is located in Sergipe/Alagoas basin, in Brazil's Northeast Region. This field, discovered in 1963, is the country's largest onshore oil accumulation and has its production zones, which consist basically of sandstones and conglomerates, depleted at about 700 m deep (TVD). As the targeted formations are consolidated, UB drilling did not bring any special concern in terms of wellbore collapse. In order to achieve the required bottomhole pressure nitrogen was mixed with a synthetic based mud (SBM) after flowing down through the annular space between the 9 5/8" and 7" casings and passing through a 1" aperture in the 7" casing. After that, the two-phase mixture went up through the annulus between the 7" casing and the jointed pipe drill string. This concentric casing approach for injecting gas made possible the use of conventional MWD, but it brought some concerns, which are addressed and discussed, about the maintenance of the UB condition while operating. The first multilateral well UB drilled in Brazil is an example of the combination of different technologies as multilateral level 2 well design, UB condition and medium radius directional system. In addition, it also involved four different parties where the operating company worked together with two service companies and a drilling contractor to build a team and achieve operational success. Introduction Carmopolis field, which is located in onshore Sergipe/Alagoas basin, in Brazil's Northeast Region (see Fig. 1), is the country's largest onshore oil accumulation at 268 MMm OOIP and a current total oil production at about 2,880 m/d. Discovered in 1963 and promptly brought into primary production, it mainly produces from the sandstone and conglomerate reservoirs of the Carmópolis/Muribeca formation and secondarily from the deeper Barra de Itiuba formation and the fractured methamorfic basement. The Carmopolis/Muribeca formation, which is composed of syntetonic conglomerates and fine clastic sediments, contains four major oil bearing zones, named CPS-1, CPS-2, CPS-3 and CPS-4. As a result, oil quality varies considerably throughout the stratigraphic column, but general reservoir data is given in Table 1. Waterflooding was first implemented in the southern part of the field in 1968. However, after three years of this pioneering implementation, the results were considered inconclusive and the project was abandoned. The combination of adverse fluid mobility ratio, reservoir heterogeneity, and the lack of proper selective injection led to the quick decline of production. Despite those uncertainties, waterflooding was resumed at the main block of the field in 1971 for attempting to revert a 30% production decline. Besides waterflooding, several other technologies have been implemented, as pilot projects, for improving oil recovery. Polymer flooding, steam injection and in-situ combustion have been introduced, tested and evaluated through the years. In summary, the Carmopolis field has been a kind of field laboratory for investigating a wide range of improved oil recovery (IOR) methods. For further details, a comprehensive history of the IOR applications in Carmopolis and the respective results is available in literature.
- South America > Brazil > Sergipe > South Atlantic Ocean (0.84)
- South America > Brazil > Alagoas > South Atlantic Ocean (0.84)
- South America > Brazil > Sergipe > Sergipe-Alagoas Basin > Carmopolis Field (0.99)
- South America > Brazil > Alagoas > South Atlantic Ocean > South Atlantic Ocean > Sergipe-Alagoas Basin (0.99)
- South America > Brazil > Alagoas > Sergipe > South Atlantic Ocean > Sergipe-Alagoas Basin (0.99)
Underbalanced Drilling: Real Time Data Interpretation and Decision Support
Lorentzen, Rolf J. (RF - Rogaland Research) | Fjelde, Kjell Kåre (RF - Rogaland Research) | Frøyen, Johnny (RF - Rogaland Research) | Lage, Antonio C.V.M. (Petrobras) | Nævdal, Geir (RF - Rogaland Research) | Vefring, Erlend H. (RF - Rogaland Research)
Abstract The accurate prediction of the downhole pressures and the returning flow rates in low-head drilling (LHD) and under-balanced drilling operations (UBD) is a major concern in the oil industry. The present work shows an original formulation of a dynamic two-phase flow model based on the classic drift-flux set of conservation equations. However, different from the traditional approach, the closure of the system is obtained by using measured data acquired during the execution of the operation. The innovative concept consists of formulating simple closure relations that are dependent on unknown parameters, which are calculated and updated from time to time to minimize the differences between model predictions and measured data. The potential of this new approach is discussed by presenting some transient examples of application. The current study represents a first step on the development of a methodology for the introduction of a learning while drilling process in the hydraulic design and follow-up of LHD and UBD operations. Introduction A successful UBD or LHD operation requires the control of downhole pressures and the management of the fluids flowing out of the well, which are affected by many factors, as injection of fluids, reservoir inflow performance and operational procedures. In addition, these operative factors are inevitably subject to fluctuations, triggering transient responses to the multiphase system. As a consequence, several parameters like injection rates, bottom hole pressure, choke pressure and outlet rates are usually measured during the operations for helping the management of the process. However, this control task is quite difficult and requires massive efforts for training crews. Besides, the engineering tools and models usually adopted for designing and following up the operations are complex, but not always reliable. In fact, their reliability depends very much on features of the operational scenario, but the knowledge of the operative borders are not completely determined, at least so far. Summarizing, the adoption of a learning while doing philosophy adds real value to the process. It happens because the introduction of a self-improvement element not only remedies some disparities still present in most of the models in current use but also enhances significantly the level of confidence in the process as a whole. In this context, a mathematical methodology is developed for incorporating the measured data into the dynamic model, which introduces the capability of having a continuous enhancement of its performance during the operation. The basic idea consists of estimating parameters in the multiphase model and in the reservoir model to provide a correct interpretation of the conditions in the well. Based on this interpretation, the future state of the underbalanced drilling system can be predicted, helping the management of the flow network in a LHD or UBD operation. In other words, the consequences of a sudden change in the circulation system can be anticipated, providing elements to judge the adequacy of the surface separation equipment for facing the expected situation. Then, proactive actions can then be taken if the predicted transients are unacceptable. The developed methodology is applied to measured data from a 1500 m deep well. Several transient cases are considered, and the ability to predict the state of the circulation system for the different cases is discussed. Dynamic Model A dynamic model for describing the transient behavior of the two-phase flow conditions in LHD and UBD operations can be expressed with basis in the drift-flux formulation of the two-phase flow conservation laws. Due to the complexity of the model, a numerical solution strategy is required.