Improving Sweep Efficiency by Zonal Isolation Using High Expansion Ratio Inflatable Plugs - A Case Study II

Abstract

This abstract is submitted as an addendum to SPE-188853-MS, which deliberate about Improving Sweep Efficiency by Zonal Isolation Using High Expansion Ratio Inflatable Plugs. "M" field contains medium gravity viscous crude (10-20cp) in high permeability sands. Application of EOR technique is considered pivotal in sustaining the plateau production rate and maximizing the ultimate recovery from this field. "M" field is currently under polymer flooding with wells completed in a 5-spot pattern. The high viscosity crude in this field, with an unfavorable mobility-ratio with water, mandated the need to switch from water to polymer flooding. Even though good sweep improvement was observed in most of the patterns, a few pattern producers didn't respond to polymer flood as expected. They exhibited poor sweep efficiency which resulted in bypassed oil and early water/polymer breakthrough. The poor sweep efficiency adversely affects the project economics by reducing the Expected Ultimate Recovery (EUR) and increasing the opex associated with produced water handling. Paper SPE-188853-MS outlined how the installation of "high expansion ratio inflatable plugs" in the pattern producers, improved sweep efficiency. This paper adds further case studies to it, carrying forward the success of these Plugs. Moving onward the process of isolation based on detailed analysis of pattern flood producer wells which were shut-in, due to high water-cut and production handling constraints. Saturation log were carried out to locate the poorly swept sand zones. Also, since most of the wells are sub hydrostatic and exist on artificial lift. N2 assisted PLT were carried out to identify high water cut zones and accordingly zonal isolation of such high water cut zones were planned. Temporary isolation was required to accommodate plans for future ASP (Alkaline Surfactant Polymer) flooding. Both mechanical and chemical isolation methods were explored and accordingly well candidates were identified for each of the methods for isolation. Mechanical isolation methods are discussed in the paper (chemical isolation being discussed in a separate paper). Last paper gave insight about plug passing through a minimum ID of 2.3" and set in a 7" production casing. After this campaign, more candidates with plug setting section of 9-5/8" Casing & 4-1/2" Screens were selected. Plug setting with Coil Tubing & E-line were explored and executed. The jobs were successfully conducted in around 30 producer wells. The isolation resulted in a 3-4-fold increase in the instantaneous oil production with around 40% drop in produced water cut. This demonstrated how the treatments improved the selective drainage of the poorly swept sands by allowing preferential movement of flood front in these sands. To support selective treatment of injector wells for sweep bypassed oil sands, through tubing inflatable straddle packer acidization jobs are being planned to further increase the injection in poorly swept zones.