Khalifeh, Mahmoud (University of Stavanger) | Hodne, Helge (University of Stavanger) | Korsnes, Reidar I. (University of Stavanger) | Saasen, Arild (Det Norske Oljeselskap and University of Stavanger)
The fundamental of a plug and abandonment operation is to restore cap rock functionality for securing the well-integrity permanently. The current work reviews briefly essential characteristics of plugging materials. Besides, since geopolymers have been suggested as a possible well barrier element, rheological behavior and mechanical properties of a rock-based geopolymer is presented. The consistency and viscosity of different mix designs were investigated to study the placeability of the mixes. Although the slope of the acquired viscosity data may show a Newtonian fluid behavior, a non-Newtonian model (Herschel-Bulkley) simulated the experiments with a lesser deviation than the power-law model. Strength development of the produced geopolymers showed sufficient strength. Confined triaxial compression tests were performed to measure the Bulk modulus, Poisson's ratio, E-modulus and Young's modulus at downhole conditions. Very low Young's modulus (238 Kpsi) and Poisson's ratio (0.01) were measured. The setting time of the mixtures was delayed by using sucrose without compromising the right-angle-set. The use of sucrose as a retarder by 1.9 w% of the total solid phase did not affect the mechanical properties. SEM analysis showed some unreacted aplite particles within the geopolymers. The initial results showed that the rock-based geopolymer has the potential to be utilized as a well barrier element for permanent well plugging and zonal isolation.
Khalifeh, Mahmoud (University of Stavanger) | Saasen, Arild (Det Norske Oljeselskap and University of Stavanger) | Vrålstad, Torbjørn (SINTEF) | Larsen, Helge B. (University of Stavanger) | Hodne, Helge (University of Stavanger)
When a well reaches the end of its life-cycle, it is permanently plugged and abandoned. Since the first discovery in 1966 on the Norwegian Continental Shelf (NCS) till October 2014 nearly 5496 wells have been drilled. Of these wells, 3978 are development and 1518 are exploration wells. Of the development wells, 699 have permanently been abandoned and 279 are in temporary abandonment status. It is estimated that 3279 development wells need to be plugged and abandoned in the future. Besides, the number of wells which will be drilled in future should be added for plug and abandonment.
The costs of these P&A operations will be substantial. Hence, there is a need for technology development that will reduce the costs of all these operations. This development involves both techniques, tools and materials. The current work describes different plugging materials and important characteristics of permanent barriers with respect to long-term integrity. In addition, different roots of failure modes of permanent barriers have been discussed. Geopolymers are suggested as possible permanent plugging materials. Geopolymers are aluminosilicate materials, which solidify. A new geopolymeric material is introduced for the permanent zonal isolation and well plugging; an aplite-based geopolymer. Its placeability was studied by investigating the rheological behavior of the geopolymer slurries. The Bingham and Casson models selected to simulate the slurries' viscosities. Both models were fitted to the measured data. Strength development of the produced geopolymers showed sufficient compressive strength. X-ray powder diffraction was used to characterize the microstructure of the produced geopolymers. X-ray patterns showed formation of an amorphous phase. The measured permeability was in the range of nano Darcy. The initial result shows that the aplite-based geopolymer has the potential to be utilized as a permanent plugging material for well plugging and zonal isolation.
When a well reaches to the end of its life-cycle, it should be permanently plugged and abandoned. Geopolymers have recently attracted abundant attention as alternative materials to cements, and hence, have the potential to be used as permanent barriers. This paper will present an overview showing different types of geopolymers and their chemo-physical properties and how they can be applied to the plug and abandonment (P&A) operation.
To give a better understanding of geopolymers, fly ash-based geopolymers were prepared and examined. Fly ash-based geopolymers were produced by the alkali -activation of class C fly ash with an activator solution (a mixture of NaOH and sodium silicate solution). The NaOH solution was prepared at three concentrations of 6, 8 and 10 mol/L and it was mixed with the sodium silicate solution at a mass ratio of 1 in order to prepare the activator solution. The fly ash-C to liquid mass ratio was 1.9, typically producing final densities in the range of 2.44 s.g. In order to investigate the effect of curing temperature on the mechanical property of the obtained geopolymer, specimens were cured at two different temperatures (87 °C and 125 °C) under a pressure of 5000 psi. This work studies the effect of curing temperature and the NaOH concentration on the mechanical properties of the specimens. Uniaxial compressive strength (UCS) tests and Ultrasonic cement analyzer (UCA) tests were carried out to measure the compressive strength development of the specimens. Scanning Electron Microscope (SEM) images were taken to study the microstructure of the specimens. Measurements of pH of ground specimens was performed and based on the obtained results pH alters during the curing time. These measurements will found a basis for selecting the correct material to the P&A operation.