Abstract
Decommissioning in the oil and gas area is an activity adopted at the end of the productive life of the production facilities, including the wells, whether producers or injectors, in order to safely provide for deactivating the facilities and to be in compliance with specific regulations and technical procedures. This type of activity has been gaining strength in the oil industry given the number of installations which have reached the end of their life cycles. Plugging and abandonment (P&A) operations are performed in relation to the wells, which are based on positioning devices which have properties capable of withstanding the rigors and subsurface requirements, and can establish a durable insulation between the formations to carry fluids under pressure and the surface. The most used material over time has been Portland cement, however other cement materials can also be used. Rice husk ash (RHA) blended with Portland cement is proposed as an alternative material for P&A during an oil well decommissioning. Samples containing RHA and reference samples were cured during seven days at 40 °C, 80 °C and 300 °C according to temperature ranges and methods established by the UK Guidelines. The main samples were formulated with 35% BWOC of RHA in two different densities of 1.78 g/cm3 (RHA-1) and 1.74 g/cm3 (RHA-2), and then compared with a basically composed sample of cement and water (SF0), and a sample with the addition of 35% BWOC of silica flour (SF35), both with a density of 1.87 g/cm3. The performance of the hardened cements was evaluated for compressive strength and permeability, as supported by TGA and XRD analysis. Even though the alternative RHA blend had lower density, it showed improved results in compressive strength under all conditions tested and competitive values of permeability in comparison with the references. The RHA blend showed to be applicable in ordinary and over strength retrogression temperature ranges.
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