This paper addresses alkaline sodium silicate (Na-silicate) behavior in porous media. One of the advantages of the Na-silicate system is its water-like injectivity during the placement stage. Mixing Na-silicate with saline water results in metal silicate precipitation as well as immediate gelation. This work demonstrated that low salinity water (LSW, sea water diluted 25 times) could be used as a pre-flush in flooding operations. A water override phenomenon was observed during gel formation which is caused by gravity segregation. Dynamic adsorption tests in the sand-packed tubes showed inconsiderable adsorbed silicon density (about 8.5 × 10 −10 kg/cm 3 for a solution with 33 mg/L silicon content), which is less than the estimated mono-layer adsorption density of 1.4 × 10 −8 kg/cm 3 . Na-silicate enhanced water sweep efficiency after application in a dual-permeability sand-pack system, without leak off into the oil-bearing low permeability (LP) zone. Field-scale numerical sensitivity studies in a layered reservoir demonstrated that higher permeability and viscosity contrasts and lower vertical/horizontal permeability ratio result in lower Na-silicate leakoff into the matrix. The length of the mixing zone between reservoir water and the injected Na-silicate solution, which is formed by low salinity pre-flush, acts as a buffer zone.

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This paper describes how the information from inflow tracer technology was used to optimise the trajectory of a well during the development phase of Dvalin field. The Dvalin field is a high temperature (HT) gas field in the central part of the Norwegian Sea that consists of two separate structures. Each structure has two high perm streaks, the shallower of which was thought to have good reservoir properties whereas there was more uncertainty around the deeper one, the suspicion being that it was of a lower quality. During the exploration phase a DST was performed and it was uncertain if only the upper high permeability streak flowed on the assumption the mud was not optimised for the application. Additionally, the lower high permeability streak was not easily identifiable on the logs, although it was clear from the core. The initial field development concept consisted of drilling four production wells. Due to the uncertainties around the lower reservoir section, it was seen as highly beneficial to obtain information in the early development phase and, due to the challenging environment (HT and subsea), the choice of monitoring technologies was extremely limited. Inflow tracers were therefore chosen for the four planned producers, a technology whereby unique permanent chemical tracers are integrated into polymer rods which are then deployed as part of the lower completion. They remain dormant until encountering a specific target fluid – in this case oil-based mud (OBM). Once activated, they will release into the target fluid for a certain designed life period (in this case for a few months) and flow to surface upon opening the well where they will be sampled and analysed. The analysed data is then interpreted to confirm the zonal clean up and flow contribution. The initial drilling plan consisted of slanted wells penetrating both, the upper and lower high permeability streak. In the event, the inflow tracer from the first well confirmed that the lower reservoir section not only cleaned up effectively but, crucially, demonstrated good productivity the operator could prove they selected the optimal mud and also the presence and contribution of a lower high permeability streak. In addition, a decision was made to change the configuration of the final well from slanted to horizontal in the upper zone, resulting in a 4x increase in well productivity where the tracers played a key role in the decision process. Monitoring well performance at the zonal level is a challenge, especially in HT and subsea wells. In this case inflow tracer technology was successfully used to provide validation of clean-up and flow contribution and thereby helped to optimize the drilling plan and well productivity in the course of the field development thereby increasing the value of the project.