A West Texas field producing from the naturally fractured Grayburg formation was one of the first waterfloods in the region's carbonate reservoir. The customer identified a significant number of waterflood patterns that suffered from severe communication between injectors and their offset producers. High water production and poor sweep efficiency resulted in greater operating costs and lower oil production.
The estimated incremental oil was 488,000 bbl, resulting in an incremental cost per barrel of $4.68.
Based on the geological information and water flood communication analysis using injection and production data, our TIORCO enhanced oil recovery (EOR) experts recommended a crosslinked polymer gel solution to correct the rapid water channeling through fractures and high permeability streaks. Laboratory analysis was performed and it was determined the MARCIT polymer gel system would be optimal based on reservoir temperature and the injection water total dissolved solids (TDS). The gel is made up of a medium molecular weight partially hydrolyzed polyacrylamide and a crosslinker which are mixed on the surface using specialty equipment and then injected downhole. The reaction rate is sufficiently delayed to allow for placement of the gel in the reservoir.
From 2001 to 2006, 24 injectors were treated in four phases using an average gel volume of 16,550 bbl per well of gel polymer with concentrations from 1,500 to 10,000 ppm. Each injection well had an individual gel volume design based off the estimated thief zone volume between the injector and offset producers. The pumped gel volume and concentrations were changed on-the-fly based on the injection pressure response, which is a good indicator of how effective the gel is filling up the offending reservoir features.
The polymer gel was placed in the high permeability features and fractures responsible for high water production and low sweep efficiency, without damaging low permeability rock matrix. Increasing the MARCIT gel strength allowed the injection pressure to continuously increase throughout the treatment. Oil production increased three months after the first treatment, followed by continual oil rate increases and a significant change in the oil production decline throughout the four phases.
The estimated incremental oil was 488,000 bbl, resulting in an incremental cost per barrel of $4.68, an average payout per phase of 12 months, and an internal rate of return for the customer of 31%.