Casabe Field is a heavy crude mature field with 260 producers, under selective injection of water with 350 injectors, producing close to 14,000 bbl/d of oil and about 80,000 bbl/d of water are being selectively injected under a 5-spot injection model. High water injection rates develop as consequence high flow velocities along its high permeability thinned sands, causing sand jetting over the cement and casing and seriously affecting the integrity of the well and zonal isolation. As typical in a brown field, operational costs are close to the limit, and sand cleaning represents almost 90% of workover operations with an average of 3.4 sand cleaning interventions per year in evaluated wells, which means an inoperability of 40% of time per year. Those events have represented millions of dollars in well interventions, abandonments, and water treatment, for which an aggressive sand management strategy was designed to optimize field operation.
This strategy consists of identifying producing intervals with evidence of sand production in wells with high failure rates, in order to take effective and efficient corrective actions to recover the normal operation of the well with an optimized production. The identification of potential sand-producer intervals has been performed with the combination of last generation of cement evaluation with porosity wireline tools, applying a novel analysis of the acquired data through the processing of a flexural wave to characterize the geometry of the third interface (or open hole). Characterizing the annular geometry with mentioned technologies, has helped identify indications of cavern development behind the casing which also correlates with casing deformation, corrosion, and cement degradation, something expected at sand-jetted intervals. This, of course, means not only production loss but also integrity loss that threatens nearby zonal isolation.
In all the cases where caverns have been detected, cement was strategically and efficiently pumped to cover formation washout. Post-workover and production reports indicate continued production was reached as inoperative time was reduced from 40% to 10%, but also well intervention for sand clean out was reduced from 3.4 to 1.4 per year on evaluated wells. This sand management strategy has been conducted in 10 wells in which more than USD 9 million cost-saving in workover activities have been reported.
The application of new technologies and new ways of data analysis to inspect the physical condition of downhole barriers enabled the operator to save costs and to maintain the control of the integrity of the wells in aggressive environments such as the existing in Casabe Field. The experience gained in the process of identifying caverns behind the casing can be easily passed to other engineering teams facing similar situations, for example in neighboring fields of the Medium Magdalena Valley of Colombia.