Girassol Field Research Articles

Well-Performance Monitoring (WPM): Creating Added Value From Raw Data and Application to the Girassol Deepwater-Field Case

Summary Capitalizing on early successes in advanced well control and realtime monitoring, Total Exploration and Production has engaged in a major "digital-field" initiative. Combining both proven and leading-edge technologies, the field-monitoring template is providing a powerful tool for well and facilities performance monitoring and optimization. This paper presents the concept of the WPM module, and the early results of its pilot application whose implementation began in 2009 at the Girassol field located offshore Angola. The WPM module constitutes an integrated real-time monitoring solution for subsea installations, from reservoir inflow to receiving facilities. Proposing advanced features (e.g., a common asset model, a business orchestrator, and a Web-based interface), the tool provides remote access to timely and quality field data, improves communication and collaboration between offshore and onshore, and provides support by specialists from exploration- and-production headquarters. Functional capabilities include data validation, virtual metering, wells and networks modeling, smart alarming, and production optimization. Specific workflows have also been defined to sustain continuous updating of the models to match observed field behavior. This paper illustrates the benefits of the WPM solution in terms of improved production and enhanced well diagnosis. It also reviews the organizational challenges associated with such a project and discusses the key factors ensuring successful implementation and good support from on-site teams. WPM brings forth a new approach for the intelligent surveillance of complex subsea-production systems. Well performance and production and reservoir teams have gained benefit from such a tool. Pertinent information is delivered to the right people in real time, enabling instant diagnosis and minimization of production shortfalls. In addition, the online simulator supports the continuous optimization of the field throughput by real-time integration of changing well behavior or production constraints.

History Matching of Production and 4D Seismic Data: Application to the Girassol Field, Offshore Angola

Time-lapse seismic provides a source of valuable information about the evolution in space and time of the distribution of hydrocarbons inside reservoirs. Seismic monitoring improves our understanding of production mechanisms and makes it possible to optimize the recovery of hydrocarbons. Although 4D seismic data are increasingly used by oil companies, they are often qualitative, due to the lack of suitable interpretation techniques.Recent modeling experiments have shown that the integration of 4D seismic data for updating reservoir flow models is feasible. However, methodologies based on sequential interpretation of 4D seismic data, trial and error processes and fluid flow simulation tests require a great effort from integrated teams. The development of assisted history matching techniques is a significant improvement towards a quantitative use of 4D seismic data in reservoir modeling.This paper proposes an innovative methodology based on advanced history matching solutions to constrain 3D stochastic reservoir models to both production history and 4D seismic attributes. In this approach, geostatistical modeling, upscaling, fluid flow simulation, downscaling and petro-elastic modeling are integrated into the same history matching workflow. Simulated production history and 4D seismic attributes are compared to real data using an objective function, which is minimized with a new optimization algorithm based on response surface fitting. The gradual deformation method is used to constrain the facies realization, globally or locally, which populates the geological model at the fine scale. Moreover, a new method is proposed to update facies proportions during the optimization process according to 4D monitoring information.We present here a successful application to the Girassol field. Girassol is a large, complex and faulted turbidite field, located offshore Angola. First, a detailed geostatistical geological model was built to describe reservoir heterogeneity at the fine scale, while respecting 3D base seismic data. Second, the model was constrained to production data and 4D seismic attributes, applying gradual deformation to facies realizations and varying facies proportions. The integration of 4D seismic data led to better production forecasts and improved predictions confirmed by a new seismic survey shot two years after the history matching period. 4D seismic data also contributed to better characterize the spatial distribution of heterogeneities in the field. As a result, the fine scale geological model was improved consistently with respect to the fluid flow simulation model and the observed data. The Girassol study, already presented in (Roggero et al., 2007, 2008), has been updated with recent information and a more detailed presentation concerning the construction of the geological model based on 3D seismic data.

A Systematic Investigation of Girassol Deepwater-Field Operational Data To Increase Confidence in Multiphase Simulation

Summary After more than 5 years of experience as operator of Girassol, the earliest deepwater field put in production offshore West Africa, Total has recorded a large amount of operational data. The production system includes several conventional subsea loops connected to a floating-production, storage and offloading vessel (FPSO) at 1,350-m water depth, with gas lift injected at the bottom of the risers for activation and flow stabilization. A systematic review of the operating parameters of the subsea production loops over the past years gave the opportunity to extract series of measurements representative of a wide range of flow rates, watercuts, and gas-lift rates, including flow-stability tests performed both on upward- and downward-sloping flow-lines. These data were compared to the results obtained from dynamic simulations performed with the simulation code OLGA, originally used for the design of the subsea production system. The comparison focused on the overall pressure drop between manifolds and topside and on the transition between stable and unstable flow with decreasing gas lift rate. The work was conducted in two steps. First, updating the model of each flowline to implement the details of the as-built geometry, then performing extensive numerical simulations and post-processing of the selected operational cases. Particular attention was paid to the first step to achieve the best compromise between model accuracy and computation speed. The optimum was met when the model, run with the Slug Tracking option, was able to reproduce the transition to unstable flow observed onsite. To investigate future operating conditions of the Girassol field, this methodology will help to establish a confidence level in multiphase simulation. This work can also serve as a reference for other deepwater-field developments.

Turbidity current modelling on geological time scales

A numerical model has been developed to simulate sedimentary architecture resulting from turbidity currents over geological time. The model is based on the cellular automata paradigm. The automata exchange matter and energy and are built in order to reproduce the physical processes which govern turbidity current behavior. The simulated architecture is the result of a given set of geological events. For each of these events a steady state is computed that is assumed to be representative of the average effect of a turbidity current on the construction of the sedimentary architecture. Using model capacities, we reproduce the first sequence of the Lower Pab channel complex formation and a unit of lateral stacked channels of the Angolan deep offshore Girassol field. The model results show that the simulated sedimentary facies distribution is realistic and this may allow a better prediction of the deposits organization in turbiditic systems. Moreover, this model improves stratigraphic modelling resolution and can take over diffusive methods at reservoir scale. The advantages of this numerical approach are a better identification and understanding of deposits heterogeneities and may provide a better representation of the spatial organization, geometry and variability of the geological units that form reservoir architecture in deep-sea clastic systems.

Fiscal system analysis contractual systems

Production sharing contracts are one of the most popular forms of contractual system used in petroleum agreements around the world, but the manner in which the fiscal terms and contract parameters impact system measures is complicated and not well understood. The purpose of this paper is to quantify the influence of private and market uncertainty in contractual fiscal systems. A meta-modelling approach is employed that couples the results of a simulation model with regression analysis to construct numerical functionals that quantify the fiscal regime. Relationships are derived that specify how the present value, rate of return, and take statistics vary as a function of the system parameters. The deepwater Girassol field development in Angola is taken as a case study.

Benefits of a 3DHR survey for Girassol Field appraisal and development, Angola

Can management and partners be convinced to acquire a new 3D high-resolution survey (3DHR) less than three years after acquiring a high quality, conventional 3D? This is what was proposed in 1999 in the deepwater (>1300 m) Girassol Field, offshore Angola block 17—one of TotalFinaElf's largest deepwater projects. The business objective: To make a tangible impact on appraisal and development programs, and ultimately use the new seismic as a baseline survey for 4D monitoring. This article describes the key steps to prepare, acquire, process, and interpret the 3DHR. Preparation included a feasibility study to determine if a new survey was the best economic and scientific route and then to define the optimal acquisition design. CGG was awarded the contract for the 3DHR seismic acquisition and processing. Acquisition required enhanced onboard quality control by CGG and TotalFinaElf, optimal control of acquisition parameters because the source was at a shallow depth, and efficient logistics. Processing included a first pass, 300-km2 fast track volume of four million traces delivered five weeks after the last shot, and final volumes (near and far) with standard poststack time migration after DMO. Special attention was given to preserving the large frequency bandwidth at all stages of processing. Interpretation generated a reservoir model that was more heterogeneous than initially foreseen because the 3DHR nearly doubled spatial and vertical resolution, enabling the interpreters to construct a refined geomodel from inverted impedances and other seismic attributes. Impact: The design of appraisal and development wells was optimized in the field, reducing the total number of wells by 25% compared to field planning with the original 3D seismic. The key ingredients of this success are: (1) solid technical arguments and performance focused on operational and business issues; (2) close interaction between the operator and the geophysical contractor with a detailed QC …

Deepwater Drilling and Testing: Girassol Field

This article is a synopsis of paper SPE 39337, "Experience Acquired During Deepwater Drilling and Testing of Three Exploration/Appraisal Wells in the Girassol Field," by Stephan Crepin, Jean-Luc Ybert, Laurent Foulhoux, Nicolas Payer, and Alain Chassagne, Elf E&P, originally presented at the 1998 IADC/SPE Drilling Conference held in Dallas, 3-6 March.