Productivity Impairement From Kaolinite Mobilization: Laboratory & Field Experience, Oseberg Sor
- Niall Fleming (StatoilHydro ASA) | Anne M. Mathisen (StatoilHydro) | Synnove H. Eriksen (StatoilHydro ASA) | Erlend Moldrheim (Hydro Oil & Gas) | Thomas R. Johansen (Hydro Oil & Gas)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- August 2008
- Document Type
- Journal Paper
- 318 - 330
- 2008. Society of Petroleum Engineers
- 5.1.2 Faults and Fracture Characterisation, 1.4.3 Fines Migration, 4.3.4 Scale, 2.2.2 Perforating, 4.5.10 Remotely Operated Vehicles, 1.11 Drilling Fluids and Materials, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.2.1 Phase Behavior and PVT Measurements, 5.6.5 Tracers, 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating, 1.14 Casing and Cementing, 2.7.1 Completion Fluids, 1.8 Formation Damage, 5.1.1 Exploration, Development, Structural Geology, 4.2.3 Materials and Corrosion, 3 Production and Well Operations, 5.6.8 Well Performance Monitoring, Inflow Performance
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The Oseberg Sør field, operated by Hydro Oil & Energy, is situated 130 km west of the Norwegian coast on the eastern flank of the Viking Graben structure. It consists of fault-bounded structural units of varying geological complexity. Within these units, the reservoir intervals are of moderate to poor quality and can exhibit strong contrasts in permeability and formation-water composition. Reservoir-pressure support is provided by combined injection of gas and Utsira aquifer-produced water. The wells are a combination of platform and subsea and include extended-reach horizontals with complex geometry and lesser numbers of vertical wells.
Coreflooding was undertaken with material from the major producing intervals (Ness, Middle and Upper Tarbet, and Upper Jurassic). This coreflooding has been used to assess potential formation damage resulting from application of oil-based mud (OBM) or scale-inhibitor squeeze treatment. In all instances, the major cause of formation damage was the mobilization of kaolinite that can form up to 20 wt% of the bulk rock and that occurs in all producing intervals. Coreflooding demonstrated that even at low flow rates (30 mL/h), permeability was reduced by up to 99% during initial plug saturation and before the onset of treatment. Modification of the coreholder allowed multiport permeability measurements to be made; these measurements gave an indication of the depth of damage.
Field evidence gives only an indirect indication of the effect of kaolinite mobilization on well productivity. For example, a gradual reduction in well productivity was reversed after squeeze treatment. This gradual decline is possibly a result of the migration of kaolinite during well inflow, the consequence of which is a reduction in permeability. Squeezing could have caused the dispersion of kaolinite away from the near wellbore with an increase in well productivity.
Given the adverse results obtained from coreflooding caused by kaolinite mobilization, significant effort has been directed toward identifying methods by which to reduce its impact, including through incorporation of clay stabilizers in scale-inhibitor squeeze treatments and remedial treatments with mud-acid stimulation. Laboratory results of these evaluations will be presented.
Although the occurrence of kaolinite on Oseberg Sør has potentially reduced well inflow performance, it has had a positive influence on scale-inhibitor squeeze lifetimes. A field example will be given to show this.
This paper will demonstrate the approach taken with Oseberg Sør in the identification of the magnitude of kaolinite mobilization from different producing intervals along with the preventative and remedial measures that have been considered and implemented. Mobilization of kaolinite during well production is not a new phenomenon and has been reported from many fields globally (Paveley et al. 2002; Miranda and Underwood 1993; Bishop 1997). The initiation of kaolinite mobilization can result from introduction of a liquid of different salinity to the formation water (salinity shock) or in areas where the critical velocity for fine mobilization has been exceeded. Regardless of the initiation mode, the result is potential productivity impairment caused by pore blockage within the near-wellbore region.
One of the major challenges with kaolinite mobilization is that of recognizing the effect of it in the field. From coreflooding and scanning-electron-microscope (SEM) examination, it is relatively easy to identify the occurrence of mobilized kaolinite and use this to explain reductions in measured permeability. However, for long horizontal wells that are perforated in several intervals and produce from different formations, identifying mobilized kaolinite and the impact it has on well inflow performance is especially difficult. Furthermore, the well-operating conditions that induce mobilization are difficult to determine. For example, on Oseberg Sør it is believed that most mobilization occurs during well production (i.e., the critical flow rate for kaolinite mobilization is exceeded within the near-wellbore region because of drawdown). Because most wells on Oseberg Sør are horizontal, it becomes quite difficult to determine which intervals have been affected by kaolinite mobilization and when this damage occurred. Furthermore, limited core coverage from the various structures and formations that form Oseberg Sør field means that only a general impression is available for the distribution and abundance of kaolinite. Therefore, in the case of the producing wells from Oseberg Sør, it is possible only to infer formation damage that results from kaolinite mobilization.
|File Size||2 MB||Number of Pages||13|
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