Application of multi-rate well tests to scale management
- Tore Tjomsland (Statoil ASA) | Bernt Sandoey (Statoil) | Finn Hallstein Fadnes (Statoil Hydro) | Ross Andrew McCartney (Geoscience Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE International Conference on Oilfield Scale, 26-27 May, Aberdeen, UK
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.2 Pipelines, Flowlines and Risers, 1.8 Formation Damage, 5.4.2 Gas Injection Methods, 1.6 Drilling Operations, 4.2.3 Materials and Corrosion, 5.6.5 Tracers, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 5.3.2 Multiphase Flow, 5.5.8 History Matching, 5.7.2 Recovery Factors, 4.1.2 Separation and Treating, 4.3.4 Scale, 2.2.2 Perforating, 1.10 Drilling Equipment, 5.6.4 Drillstem/Well Testing, 3.3.1 Production Logging, 2.4.3 Sand/Solids Control, 5.6.8 Well Performance Monitoring, Inflow Performance, 5.6.1 Open hole/cased hole log analysis, 4.1.5 Processing Equipment, 4.3.1 Hydrates, 3 Production and Well Operations, 4.5 Offshore Facilities and Subsea Systems, 5.2 Reservoir Fluid Dynamics
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Veslefrikk is a mature oil field in the Norwegian sector of the North Sea. It has a layered structure with several pressure-independent layers and three main fluid systems: the Statfjord Formation, Intra Dunlin Group and Brent Group. Each fluid system has distinct formation water compositions but similar oil compositions. Seawater injection has been used for pressure support and many wells have commingled production. The principal scale control challenges are scaling potential and placement of scale inhibitor into zones with different pressure. Although production logging is performed regularly to aid scale squeeze designs and production allocation, this is costly, involves well intervention risks and it cannot always be undertaken when required.
In this study an innovative approach to obtain ‘production logging type' information from wells producing from two zones has been evaluated. It involves undertaking multi-rate well tests where produced water samples are collected at each rate. Depending on the conditions for each test, either qualitative or quantitative integrated analysis of the well test results and produced water compositions can be performed. Information obtained from the tests for each zone includes: Pressure, productivity index, water cut, produced water composition and seawater fraction.
The methodologies adopted for the multi-rate tests and the analysis of their results are described, and the results for four multi-rate tests are presented. The multi-rate tests were undertaken under different conditions and the influence of these conditions on the type and quality of results obtained are discussed, and assumptions and associated uncertainties are identified.
The case studies demonstrate that information useful to scale, well and reservoir management can be obtained from multi-rate tests. In addition, produced water compositions can be obtained from these tests without the need for downhole sampling. However, in each case it is important to assess uncertainties associated with the results.
Veslefrikk is located in block 30/3 of the Norwegian sector of the North Sea. The field has been on production since 1989. It was developed by a 24 slot wellhead platform with drilling facilities in combination with a semi-submersible process platform with a living quarter, Figure 1. The production rate peaked in 1995, and the field is now far into the tail production phase.
Seawater (SW) injection has been the main method of pressure support, but gas injection has also been performed to increase the recovery factor. The first water breakthrough was observed during 1992. The field water cut has now reached 80-85%, and on average the produced water (PW) contains 50-60% seawater. The Veslefrikk reservoir is layered, consisting of several zones with independent pressure regimes (see Figure 2) and to some degree also different fluid systems. Commingled production is extensively used at the field, due to the limited number of well slots and to optimize the production rate.
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