A high level screening has been performed of UKCS oil fields to identify the most likely LSWF candidates utilising screening criteria with a focus on kaolinite clay content. The screening results suggest that approximately 57% of the fields have 6 % or higher kaolinite clay content. Of these fields 26 % were water-wet and 74 % were mixed-wet in terms of wettability. This suggests that a significant number of fields would fall within the eligibility for consideration of LSWF EOR although their suitability will depend on field maturity (current recovery factor and facilities constraints). The difficulty in applying LSWF in tertiary mode unlike secondary mode, is in obtaining a reasonable prediction of how the reservoir is likely to respond. The question of core availability and quality has been raised in a number of studies in terms of LSWF and electrical property testing. We propose a methodology which can be applied to compensate for the lack of usable core based on petrophysical log response. The logs can be utilised to determine the clay types present (including fractions) from which the cation exchange capacity can be calculated. Selected compositions from anonymised field data from core was used to provide quality control the log derived values. The most likely recovery mechanism, multi-component ion exchange (MIE), requires the input of key electrical properties into the models (cation exchange capacity, reactive surface area, activation energy and mineral fraction) in order to predict the response of the reservoir to LSWF. In this study the effect of clay content on the reservoir response was modelled indirectly by altering the cation exchange capacity relative to the clay mineral fraction present in the reservoir to determine its effect. Utilising a mechanistic modelling approach, homogeneous Cartesian models were run in the compositional finite difference reservoir simulator GEM to assess the impact on oil recovery. The simulated coreflood tests reveal that under secondary LSWF recovery was 68.4 % compared to 63.6 % for formation water (high salinity). The conservative nature of the relative permeability curves limited the incremental recovery. An analysis of the tertiary recovery utilising a coreflood based on Fjelde et al. (2012) revealed that cation exchange impacts the predicted recovery by up to 2.65 % OOIP for the range of 5 - 30 % clay content. Given that the recovery under tertiary conditions is considered in the literature to be between 6 and 12 %, this is significant and highlights that if idealised data is selected rather than real field data, then significant potential exists to under or over-predict the incremental recovery.

Low salinity waterflooding (LSWF), versus high salinity waterflooding (HSWF) has been the focus of significant research at various centres around the world, yet there is still considerable debate over the exact mechanism that provides incremental oil recovery. The use of the LSWF technique is not widespread in the United Kingdom continental shelf (UKCS). However, it has been announced that the Clair Ridge development will deploy low salinity waterflooding (LSWF) in secondary mode from the start of field life, and a number of companies are currently assessing the applicability of the technique through high level screening and core flooding. Forecasting the potential oil recovery under LSWF is heavily influenced by the simulation technique that is used. Presently the most widely discussed approach is the use of a weighting table with relative permeabilities representing the high and low salinity cases. As the grid block falls below threshold salinity, the simulator utilises the weighting table to assign an interpolated value of salinity. This value of salinity is utilised to represent a change in wettability. While this approach approximates the net effect of LSWF, it does not capture the oil/rock/brine interaction. This study examines the modelling approach to LSWF utilising an in-house generic Forties Palaeocene model in CMG's STARS simulator. The conventional approach of modelling LSWF using high and low salinity relative permeabilities is compared to the latest Multi-component Ion Exchange (MIE) methods by numerical simulation to assess the impact on incremental oil recovery. A sensitivity analysis is then carried out on the effects of specific parameters on incremental oil recovery, utilising published data from fields in the Forties Palaeocene fan system. A discussion is provided. The impact on secondary recovery was accessed with respect to wettability alteration; injection salinity (LSWF versus HSWF); oil viscosity and aquifer influx. The application of LSWF in secondary mode to the Forties Palaeocene Sandstones was found to be favourable for the case of mixed-wet reservoirs.

Horizontal wens have seen a dramatic rise in the range of applications and the number of wens completed during the past decade . However, horizontal wens have been primarily drieled as producers maximising tee benefit from the large reservo ir contact which such boreho les allow. To date there have been only a handful of repo rted applications of horizontal wens as injectors . The potential benefit of horizontal injectors could lie in improving the sweep efficiency and enhancing the degree of pressure maintenance characteristics of reservoirs as they enter an advanced stage of depletion in redevelopment projects .With the above in mind the Horizontal Well Technology Unit in Edinburgh has been conducting a two year research programme looking at the potential for improving hydrocarbon recovery efficiency using horizontal injectors, with the overall aim being to establ ish a sound business case for the utilisation of horizontal injection wells. The investigation has concentrated on botte water and gas injection . The first part of the study use d a box type rese rvoir simulation model, to compare horizontaI and conventional vertical injection wens in different depositional environments .Horizontal water injectors veere found to improve sweep efficiency and achieve production acceleration in certain reservoir environments . These inciucted extreme permeability distributions (fining upwards/downwards in rock properties) and high viscosity oils . Higher NPVs veere achieved in these cases .For gas injection, it w as found [teat, because the high mobility ratio completely dominated tee displacement process, improvements in recove ry veere limited .In the third phase of the project, the focus switched to applying the technology to real North Sea field datasets . The studies have confirmed the conclusion from the Barlier work that horizontal injectors seem to function best in love permeability environments due to the much superior injectivity . In higher permeability environments, viscous driv ing forces can lead to increased recovery in favour of vertical injectors. Introduct i onAt the start of this two year long project (January , 1995), there veere few field developments relying on horizontal injection wens and a pancity of description of their performance in the l i terature . This prompted the study to investigate the reservoir env i ronments/conditions in which horizontally completed injection weíls would perform better than conventional vertical in jectors in terms of ultimate oil recove ry , rate of recovery and resultant net present value (NPV) . The work was undertaken in three p hases : model validation, theoretical sensitivities and study of actual fields . In all cases, where possible, the numerical simulation results veere checkel against analytical calculations .