Study of Performance with Diverting Agents in Formation Damage and Return of Permeability for Unconsolidated Sandstones using Computed Tomography

The success of matrix acidification depends on the adequate distribution of acids over all the extension to be treated, known as divergence. Acid stimulation of oil and gas reservoirs, with a view to increasing well productivity, has been applied since the late 19th century. Initially applied in carbonate reservoirs, the technique was extended to more complex mineralogies, over a number of years, like unconsolidated sandstones. However, we can say that acid stimulation of wells is the exception rather than the rule. This probably stems from the complex, heterogeneous nature of formation mineral and unpredictability of their response to conventional oilfield acid formulations. With inappropriate acid designs, or poor job procedures, even the best candidate wells can be damaged, sometimes irreversibly. If the interval presents layers with different permeabilities, the acid will tend to penetrate only in more permeable layers, leaving the zones of smaller permeability without treatment. If the reservoir consists in a heterogeneous medium, the treatment could not be uniformly distributed and the lack of good method for acid distribution might result that a great part of the damage will not be removed due to the acid that is only able to penetrate in portion with smaller damage of the interval. In the matrix treatment of extensive intervals (> 10m) it is indispensable the utilization of one method to produce divergence, which can be obtained from particulate materials or more recently with foams, resins, viscoelastics fluids or polymers modified of relatively permeability. The divergent agents can be equally distributed to all extension of the treatment or can be placed in divergent spacers intercalated into the treatment which total volume is subdivided in stages. The aim of this study is to obtain diverting agents that make possible remote operations. In this study, the X-ray computerized tomography (CT) scan was used to evaluate in real-time the performance of diverting agent during rock-fluid interactions. A special aluminum cell (physical simulator) was designed to simulate as closely as possible the same conditions found in "situ" oil wells. For example, pressure, temperature, fluid pressure injection, permeability, porosity and oil and water saturations of studied reservoir. A sequence of tests that was performed in the unconsolidated sandstones that simulate deepwater fields found in Campos Basin, in different formations, confirmed the efficiency of the system, effectiveness and the diverting effect for a lot of zones with different permeabilities.