It is proposed a study for a preliminary investigation aimed to the experimental and numerical characterization of the force that involves the realization of rock perforations by means of an innovative micro-driller device. Numerical simulations are essential to study the Dual Reciprocating Drilling (DRD) system, which is an innovative, bioinspired system of perforation developed in the aerospace field. The extension of the application of the DRD in rock perforations requires the redesign of the system in order to satisfy different specifications. One of the main design variables is the geometry of the penetrator: for its optimization, experimental tests and numerical simulations are necessary. The first step to develop a design campaign is the implementation of a modelling environment able to simulate the mechanical behaviour of the rock: a reference material need to be chosen. The reference material selected is Berea Sandstone, which is commonly used in the field of study. However, a similar but more available material has been chosen for the experimental tests: the Pietra Serena. Berea Sandstone and Pietra Serena have got analogous mechanical properties so it is possible to apply several parameters of the first one in the numerical analyses and use the second one for the experimental tests (necessary to validate the method). The failure criteria used to model the behaviour of the rock are the Mohr-Coulomb and the Drucker-Prager criterion, which give a reliable and efficient representation of the rock behaviour under the investigated state of stress; moreover, they are available on the software Abaqus. An experimental campaign with Pietra Serena has been performed for the calibration and the validation of the numerical models of perforations: the tests, object of the experiments, are the triaxial compression test and the punch penetration test. The triaxial test is used to validate the material model used at different confinement conditions, while the punch penetration test is used to validate the perforation numerical models used in this study. The numerical models have been implemented to estimate the perforation force in quasi-static conditions, at different penetration depths, at different directions of perforation and with different geometries of the indenter. Two different modelling techniques have been applied for the numerical models: the first uses a 3d model and a conversion to SPH particles to better simulate the perforation, while the second considers an axysimmetric model and an Eulerian-Lagrangian adaptive (ALE) mesh algorithm to prevent excessive deformation during the perforation. The results obtained show a perforation force that is too high for the dimensions and for any material selectable for the penetrator, therefore a study on the percussive drilling technique has been also carried out. The percussion breaks the rock creating a mass of small fragments of rock that is called chip. Numerical models have been implemented to simulate the penetration force after the percussion process. The first step of these analyses is the definition of the properties of the chip material, which are different from the ones of the untouched rock. The criterion used to model the behaviour of the chip is the Mohr-Coulomb. The data necessary for the definition of this material have been taken from experimental tests found in literature. All the analyses regarding the percussive drilling use an axysimmetric configuration and an Eulerian-Lagrangian adaptive (ALE) mesh algorithm to prevent excessive distortion. Afterwards different geometries and properties of the chip have been considered to study their influence on the model, as well as the influence of the geometry of the penetrator. The results of the study on the percussive drilling highlight a reduction of one order of magnitude of the force needed for the perforation, with respect to the quasi-static perforation.
Viene presentato uno studio sperimentale e numerico sulla valutazione della forza necessaria per la realizzazione di perforazioni su roccia nell’ambito dell’industria oil and gas. Le simulazioni numeriche sono necessarie per studiare il Dual Reciprocating Drilling (DRD) system, il quale è un sistema innovativo bio-ispirato all’ovopositore dell’insetto Megarhyssa, già sviluppato in ambito aerospaziale. L’estensione in ambito oil and gas necessita la riprogettazione del sistema DRD per soddisfare diverse specifiche. Una di queste variabili di progettazione è la geometria della punta e per la sua ottimizzazione test sperimentali e simulazioni numeriche possono essere utilizzate. Il primo passo per la progettazione del sistema DRD è l’implementazione di un modello numerico in grado di simulare il comportamento meccanico della roccia, scegliendo come materiale di riferimento Berea Sandstone, che è il tipico materiale utilizzato in questo ambito. Per le prove sperimentali è stata utilizzata Pietra Serena, poiché Berea Sandstone non è facilmente reperibile in Italia. I due materiali hanno proprietà meccaniche simili e sono considerati entrambi in questo studio. Il criterio di rottura usato per modellare il comportamento della roccia è il criterio di Mohr-Coulomb, esso rappresenta in maniera veritiera ed efficiente il comportamento della roccia sottoposta allo stato di stress preso in esame, ed è oltretutto presente nel software Abaqus. Una campagna sperimentale, che utilizza Pietra Serena, è stata effettuata per la calibrazione e validazione dei modelli numerici di penetrazione: i test effettuati sono test di compressione triassiale e di penetrazione confinata. I test triassiali sono stati usati per calibrare il modello di materiale quando esso è sottoposto a diversi livelli di confinamento, mentre i test di penetrazione confinata sono stai usati per validare i modelli numerici di penetrazione usati in questo studio. I modelli numerici sono stati implementati per valutare la forza di penetrazione per diverse condizioni di esercizio, quali: la profondità di penetrazione, la direzione di penetrazione e la geometria del penetratore. Due differenti tecniche di modellazione sono state considerate per i modelli numerici: la prima considera l’uso di modelli 3d con la conversione in particelle SPH per ottenere dei risultati delle simulazioni più precisi, mentre la seconda considera modelli assialsimmetrici e un Eulerian-Langrangian (ALE) mesh algorithm per prevenire un’eccessiva deformazione degli elementi del moedllo durante la perforazione. Per ottenere una riduzione della forza di perforazione, la quale è troppo elevata considerando le dimensioni del penetratore e il suo possibile materiale, uno studio sulla perforazione con percussione è stato effettuato. La percussione rompe la roccia creando un insieme di piccoli frammenti di roccia, questo nuovo materiale viene chiamato chip. Dei modelli numerici sono stati implementati per valutare la forza necessaria per la perforazione una volta che è stata effettuata la percussione. Il primo step per l’implementazione di queste analisi è la definizione delle proprietà del chip, le quali sono differenti da quelle della roccia intatta. Il criterio usato per modellare il comportamento del chip è il Mohr-Coulomb. I dati necessari per per definer il chip sono stati ricavati da test sperimentali trovati in letteratura. Tutte le nalisi riguardanti la perforazione con percussione sono state eseguite con modelli assialsimmetrici e con un Eulerian-Lagrangian adaptive (ALE) mesh algorithm per prevenire un’eccessiva deformazione degli elementi del modello. Dopo di che, differenti geometrie e proprietà del chip sono state considerate per valutare la loro influenza sul processo di perforazione. Inoltre anche l’influenza della geometria del penetratore è stata valutata. I risultati dello studio sulla perforazione con percussione evidenziano una diminuzione della forza di perforazione di un ordine di grandezza.
Experimental and numerical simulations of penetration on sandstone
BALOSSI, PAOLO
2016/2017
Abstract
It is proposed a study for a preliminary investigation aimed to the experimental and numerical characterization of the force that involves the realization of rock perforations by means of an innovative micro-driller device. Numerical simulations are essential to study the Dual Reciprocating Drilling (DRD) system, which is an innovative, bioinspired system of perforation developed in the aerospace field. The extension of the application of the DRD in rock perforations requires the redesign of the system in order to satisfy different specifications. One of the main design variables is the geometry of the penetrator: for its optimization, experimental tests and numerical simulations are necessary. The first step to develop a design campaign is the implementation of a modelling environment able to simulate the mechanical behaviour of the rock: a reference material need to be chosen. The reference material selected is Berea Sandstone, which is commonly used in the field of study. However, a similar but more available material has been chosen for the experimental tests: the Pietra Serena. Berea Sandstone and Pietra Serena have got analogous mechanical properties so it is possible to apply several parameters of the first one in the numerical analyses and use the second one for the experimental tests (necessary to validate the method). The failure criteria used to model the behaviour of the rock are the Mohr-Coulomb and the Drucker-Prager criterion, which give a reliable and efficient representation of the rock behaviour under the investigated state of stress; moreover, they are available on the software Abaqus. An experimental campaign with Pietra Serena has been performed for the calibration and the validation of the numerical models of perforations: the tests, object of the experiments, are the triaxial compression test and the punch penetration test. The triaxial test is used to validate the material model used at different confinement conditions, while the punch penetration test is used to validate the perforation numerical models used in this study. The numerical models have been implemented to estimate the perforation force in quasi-static conditions, at different penetration depths, at different directions of perforation and with different geometries of the indenter. Two different modelling techniques have been applied for the numerical models: the first uses a 3d model and a conversion to SPH particles to better simulate the perforation, while the second considers an axysimmetric model and an Eulerian-Lagrangian adaptive (ALE) mesh algorithm to prevent excessive deformation during the perforation. The results obtained show a perforation force that is too high for the dimensions and for any material selectable for the penetrator, therefore a study on the percussive drilling technique has been also carried out. The percussion breaks the rock creating a mass of small fragments of rock that is called chip. Numerical models have been implemented to simulate the penetration force after the percussion process. The first step of these analyses is the definition of the properties of the chip material, which are different from the ones of the untouched rock. The criterion used to model the behaviour of the chip is the Mohr-Coulomb. The data necessary for the definition of this material have been taken from experimental tests found in literature. All the analyses regarding the percussive drilling use an axysimmetric configuration and an Eulerian-Lagrangian adaptive (ALE) mesh algorithm to prevent excessive distortion. Afterwards different geometries and properties of the chip have been considered to study their influence on the model, as well as the influence of the geometry of the penetrator. The results of the study on the percussive drilling highlight a reduction of one order of magnitude of the force needed for the perforation, with respect to the quasi-static perforation.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/135486