Natural dumpflood injection is used for pressure maintenance in a good channel sand holding considerable reserves. The layer is on depletion drive with very weak aquifer support. Natural dumpflood injection was modeled based on success in a similar layer in an adjacent field. Due to the high mud weight used during drilling, the layer is usually damaged. Dumpflooding experience in the analogue field suggests that injection is initiated only after matrix acid stimulation. Therefore, it was not a surprise when the layer did not take in any water initially. However, once the usual stimulation attempts did not achieve the desired results, possible causes and alternates were evaluated. A comprehensive lab study was designed to assess all the potential problems associated with injection. Fluid-fluid interaction issues like scaling, possible formation of oil-in-water emulsion, fluid-rock interaction such as clay swelling, fine migration related to water incompatibility, all impacting efficiency of water injection on oil mobility and recovery were studied. To simulate every possible field condition all the major water sources were sampled and taken for study. For fluid rock interaction studies, core plugs from the layer was used. Scale tendency was studied using Jar test and predictions at reservoir conditions were made through ChemScale software. The scaling products from Jar test was analyzed with SEM confirming the results. Routine core analysis was performed to measure porosity and permeability in the coreplugs. XRD was done to understand the mineralogy of the layer. After measuring the baseline permeability, the plugs were subjected to flooding with source waters. One set of coreplugs were fully saturated with target water and flooded with source waters. Flooding was repeated on core plugs saturated with oil at irreducible water saturation until it reached residual oil saturation. An investigation of emulsion formation was conducted between oil and source waters. Study results gave an indication of many potential issues like self scaling tendency of source waters and permeability reduction due to fine migration and scale formation. Out of the many factors, the presence of considerable concentrations of sulphate forming cations was identified as the primary issue to focus on. Sulphate reducing chemicals are being evaluated for injection along with the source water. Injection water quality is one of the primary factors to consider for effective injection. This is even more crucial in case of dumpflooding, wherein water is sourced from sub-surface. Due to the wide extent of the field and possible diagenesis effect there could be regional variations in water quality. Due diligence needs to be paid to these regional variations in water quality and choose prudently among alternate source water reservoirs.

Underbalance perforation is one of the best practices to insure less damage to the perforation tunnels. Many papers described the effect of the underbalance perforation either static or dynamic on the cleanup of the perforation tunnel based on the King et al correlation presented in (1986). A complete understanding of the effect of both magnitude and duration of the underbalance during the perforation will help petroleum engineers to design a perforation job and achieve the maximum benefit of the perforation in connecting the well bore to the reservoir. A new approach to control not only the amount of the underbalance, but also the duration of this underbalance, has been applied in one of North Kuwait sandstone reservoirs. The results showed the duration of the underbalance during perforation has a significant effect on clean up the perforation tunnel. Reduction and elimination of the perforating damage (perforating skin) ensures increased well productivity. Previously, the basic technique to clean perforation tunnels in order to decrease perforating damage was static underbalance. The static underbalance has been upgraded to dynamic using a down-hole production valve. The down-hole pressure data was collected by a fast reading down hole pressure sensor with 120,000 reading per second, capable of responding and recording virtual instantaneous pressure changes in the wellbore. A combination between dynamic and static underbalance has been configured to maximize the near well bore clean up around the perforation tunnel. A compressed gas, a packer setting depth and surface release valve were configured to control the duration of the static underbalance. The results show a 50% improvement in well productivity compared with the other wells completed in the same layers. The technique provided optimum volume and duration of the underbalance for all layers with up to 500 psi difference in reservoir pressures. Since this technique was being used for the first time in this reservoir, several perforating simulations were run and evaluated to select the optimum scenario for this well. A deep perforation charge has been loaded in the optimum gun size to maximize the amount of the dynamic underbalance. This paper will present the new technique of underbalance to give a clean perforation tunnel and evaluation of the impact compared to the conventional perforation techniques through pressure data and well modeling.