Jadi, Menayer Al (Kuwait Oil Company, Kuwait) | Kumar, Pranay (IFP Middle East Consulting, Bahrain) | Lislaud, Frederic (Beicip Franlab, France) | Robert, Joël (Beicip Franlab, France) | Alessandroni, Mauro (Beicip Franlab, France) | Lefebvre, Christian (IFP Middle East Consulting, Bahrain) | Groen, Vincent de (Beicip Franlab, France) | Vigier, Louise (Beicip Franlab, France) | Datta, Kalyanbrata (Kuwait Oil Company, Kuwait) | Hafez, Karam (Kuwait Oil Company, Kuwait) | Taneja, Hans (Kuwait Oil Company, Kuwait) | Bhattacharya, Muktibrata (Kuwait Oil Company, Kuwait) | Bond, Deryck (Kuwait Oil Company, Kuwait)
An integrated reservoir study of the Magwa Marrat reservoir has been completed recently. This study was carried out to support the continued development of the reservoir, in particular the planning of a secondary water flood.
The initial part of the study concentrated on reservoir characterization and reservoir performance over a long period, in the order of 30 years, of primary recovery, followed by analysis of a recent pilot water flood. A better understanding of the controls of flow and the role of fracture corridors and diffuse fractures was achieved through and integration of geophysical, petrophysical and dynamic data including tracer tools and in particular through a dynamic model of the water flood pilot. The uncertainties related to structural extension, especially on the flanks of the field and related to aquifer support, were also recognized.
Later on static and dynamic models were built, first around the pilot water flood area and then for the entire reservoir. These models have been used for development planning.
This paper gives an overview of the integrated study but concentrates on the features, detailed below, that were key to better understanding the fluid flow physics and to achieve a satisfactory "history match".
A single porosity model that accounted for matrix permeability, local enhancement to permeability within restricted fracture corridors and the effect of diffuse fractures in "tight" zones was adopted. Matrix permeability values were based on the results of a rock typing study. Static and dynamic pressure, oil production and water movement matching was achieved by making limited and realistic changes to fracture zone permeability, fracture zone extent and some fine tuning of matrix permeability. Well productivities, pressure transient tests, interference tests and production log data were used to guide and validate the history match.
Water-cut match was further improved by making reasonable changes to the structural model in regions where significant structural uncertainty was recognized.
Turkey, Laila (KOC) | Hafez, Karam Mohamed (KOC) | Vigier, Louise (Beicip) | Chimmalgi, Vishvanath Shivappa (Kuwait Oil Company) | Dashti, Hameeda Hussain (Kuwait Oil Company) | Datta, Kalyanbrata (KOC) | Knight, Roger (KOC) | Lefebvre, Christian (Beicip-Franlab) | Bond, Deryck John (Kuwait Oil Company) | Al-qattan, Abrar (KOC) | Al-Jadi, Manayer (Kuwait Oil Company) | De Medeiros, Maitre (Beicip) | Al-Kandari, Ibrahim (Kuwait Oil Company)
A pilot water flood was carried out in the Marrat reservoir in the Magwa Field. The main aim of this pilot was to allow an assessment of the ability to sustain injection, better understand reservoir characteristics. A sector model was built to help with this task.
An evaluation of the injectivity in Magwa Marrat reservoir was performed with particular attention to studying how injectivity varied as injected water quality was changed. This was done using modified Hall Plots, injection logs, flow logs and time lapse temperature logs.
Data acquisition during the course of the pilot was used to better understand reservoir heterogeneity. This included the acquisition of pressure transient and interference data, multiple production and injection logs, temperature logging, monitoring production water chemistry, the use of tracers and a re-evaluation of the log and core data to better understand to role of fractures.
A geological model using detailed reservoir characterization and a 3D discrete fracture network model was constructed. Fracture corridors were derived from fractured lineaments interpreted from different seismic attribute maps:
A sector model of the pilot flood area was then derived and used to integrate the results of the surveillance data. The main output is to develop an understanding of the natural fracture system occurring in the different units of the Marrat reservoir and to characterize their organization and distribution. The lessons learned from this sector modeling work will then be integrated in the Marrat full field study.
The work described here shows how pilot water flood results can be used to reduce risk related to both injectivity and to reservoir heterogeneity in the secondary development of a major reservoir.
The calculation of effective flow properties of naturally fractured reservoir (NFR) has been the purpose of research works for many years. Based on a static characterization of the fracture system (orientations and densities), equivalent flow properties provide continuum representations of discrete systems from which multiphase flows can be simulated using dual-permeability and dual-porosity models. Common flow properties include anisotropic permeability tensors attached to the fracture system itself, and block sizes or shape-factors, which characterize the capability of the fracture and matrix media, to exchange fluids.
Analytical and numerical calculation methods are now proposed by different commercial software tools, or have been the purpose of in-house developments. All methods rely on some conceptual models that are necessarily simplified representations of actual fracture systems, both complex and very partially known. Whether the underlying conceptual models are relevant certainly depends on the particular features of each fracture system. More important is the capability of models to capture features that are consequential for reservoir production. Only then can one expect to build meaningful NFR models likely to be calibrated to match production history data and to perform reliable reservoir forecasting. The CPU-time or memory requirements of implemented methods may also be a concern, as potentially relevant methods or software are unable to get through the calculations when full-field modelling is required.
It follows that the comparison and validation of equivalent flow-property calculation methods and NFR modelling software is anything but an easy task. As a first contribution to this end, we review and compare several equivalent permeability calculation methods available from two commercial software suites and from our own proprietary tool (GoFraK). We first present the numerical and analytical methods that were tested, including the original ones we developed which were expected to show better calculation and speed performances. We then detail the realistic benchmark case studies used to compare the different methods, from the calculation of equivalent flow properties to the multiphase flow simulation of forecast production.
The results are finally presented and discussed. They show that the numerical methods offered by commercial products, based on 3D discrete fracture networks (DFN) to compute equivalent permeability tensors, are generally unable to manage full-field models, and that their simpler analytical methods are to be used with great caution because of important underlying assumptions. These results also validate the approach and methods we developed in GoFraK and demonstrate their robustness and efficiency. Multiphase flow simulations were carried out to evaluate the impact of dual-media models on production forecast. They confirm that permeability tensors are not the only important effective flow properties, block sizes and more generally fracture/matrix transfer functions being also highly consequential. We finally end with preliminary conclusions about the ease of building NFR models and the reliability that can be given to such models.