The Oil & Gas industry has developed sophisticated technologies to maximize reservoir contact. Hydraulic fracturing (HF) is the most effective stimulation process for tight formations, but there are economic, environmental and operational concerns which constrain its implementation in various contexts, e.g. off-shore conditions or thin reservoirs where fractures may jeopardize cap-rock integrity. Fishbone completion is a newly developed technology that can be considered a cheaper and more reliable alternative to HF. A fishbone completion consists of a sequence of short liners. Each of these houses 3-4 small diameter needles departing in orthogonal directions and contacting the reservoir up to 12 m. Notably, a fishbone completion is usually slightly more expensive than the reference liner completion, this explains why in many brown fields operators implement this stimulation as a trial and error process based on pilot experience. In more challenging environments, where Fishbones can be one of the critical factors that make a project economically feasible, it is necessary to estimate its potential benefits using numerical simulations. In reservoir simulations, wells are modelled according to the so-called Peaceman’s model, which allows to define a well performance indicator. However, this model may not work for Fishbones, because of the complex flow path establishing towards the well in presence of high-density needles. To perform 3D simulations of fishbone completion based field developments, it is necessary to define a proper modelling methodology. In this work, three different modelling approaches for fishbone completion are investigated: High Resolution Grid (HRG), Embedded-Discrete-Fracture-Model (EDFM) and Finite-Element-Method (FEM). The first two methodologies rely on a finite-volume formulation of reservoir conservation equations: the HRG enhances grid resolution to improve accuracy, while in the EDFM needles are treated as fractures and much coarser grid resolution are used. On the contrary, the FEM approach leverages on the possibility to define a mesh conformal to completion geometry. The FEM results are benchmarked with analytical solutions, proving the effectiveness of the specific implementation of the method. The three methodologies are then used to evaluate fishbone benefit on production with respect to a conventional completion through sensitivity analysis for single phase problems. Notably, inconsistencies between HRG results on one side and EDFM/FEM results on the other side together with some specific insights indicated that HRG is not a suitable technique for modelling Fishbones. This provided confidence about using EDFM for a field-like application where it could be possible to show that Fishbones largely anticipate production and give 10% more gas than conventional completions in the whole concession period.
L’industria petrolifera ha sviluppato sofisticate tecnologie per massimizzare l’estrazione di idrocarburi aumentando la comunicazione tra giacimento e pozzo. La fratturazione idraulica (HF) è il processo più efficace per stimolare giacimenti a bassa permeabilità, tuttavia ci sono preoccupazioni dal punto di vista economico, ambientale e operativo che possono limitarne l’applicabilità in vari contesti, come in campo off-shore o in giacimenti sottili dove le fratture possono compromettere l’integrità della roccia di contenimento. Il completamento a Fishbone è una tecnologia di recente sviluppo che può essere considerata un’alternativa più economica e più controllabile rispetto a HF. Un completamento a Fishbones è costituito da una serie di liner, ciascuno di questi ospita 3-4 laterali, di diametro ridotto, uscenti in direzioni ortogonali, contattando il giacimento fino a 12 m. Il completamento a Fishbones è leggermente più costoso di uno convenzionale, ciò spiega perché viene spesso installato in giacimenti maturi come tentativo per prolungarne la vita basandosi su test piloti. In situazioni più complesse, dove questo completamento può essere il fattore chiave che rende redditizio un progetto, è necessario stimarne i benefici tramite simulazioni numeriche. Nelle simulazioni di giacimento, i pozzi sono modellati tramite il modello di Peaceman, che permette di definire un indicatore delle performance di un pozzo. Tuttavia, il modello di Peaceman potrebbe non funzionare per un completamento a Fishbones, visto la complessità del cammino seguito dai fluidi in presenza di laterali ad alta densità. Per svolgere simulazioni 3D di sviluppi di giacimento basati sui Fishbones, è necessario definire un approccio modellistico appropriato. In questo lavoro, tre diverse metodologie per modellare un pozzo a Fishbones sono analizzate: griglia ad alta risoluzione (HRG), Embedded-Discrete-Fracture-Model (EDFM) e metodo agli elementi finiti (FEM). I primi due approcci si basano su una formulazione ai volumi finiti delle equazioni di conservazione dei fluidi in giacimento: l’HRG aumenta la risoluzione della griglia per migliorare l’accuratezza della soluzione, mentre nell’approccio EDFM i laterali sono trattati come fratture e griglie più lasche possono essere usate. L’approccio (FEM), invece, fa leva sulla possibilità di definire una griglia di calcolo conforme alla geometria del pozzo. I risultati FEM sono confrontati con soluzioni analitiche, provando la consistenza dell’approccio implementato. I tre metodi sono poi utilizzati per valutare il beneficio, in termini di produzione, di un completamento a Fishbones rispetto ad uno convenzionale, attraverso analisi di sensitività in sistemi monofase. In particolare, le inconsistenze tra i risultati ottenuti con il metodo HRG e i metodi EDFM/FEM, affiancate a specifici approfondimenti hanno indicato che il metodo HRG non è una tecnica in grado di modellare i Fishbones. Ciò ha supportato la scelta di utilizzare l’EDFM per un'applicazione in un campo reale dove è stato possibile dimostrare come un completamento a Fishbones anticipa notevolmente la produzione, dando il 10% in più di gas rispetto a un completamento convenzionale durante tutta la durata della concessione.
Evaluating performance of Fishbone completions using numerical simulations
ROSA, ANDREA
2017/2018
Abstract
The Oil & Gas industry has developed sophisticated technologies to maximize reservoir contact. Hydraulic fracturing (HF) is the most effective stimulation process for tight formations, but there are economic, environmental and operational concerns which constrain its implementation in various contexts, e.g. off-shore conditions or thin reservoirs where fractures may jeopardize cap-rock integrity. Fishbone completion is a newly developed technology that can be considered a cheaper and more reliable alternative to HF. A fishbone completion consists of a sequence of short liners. Each of these houses 3-4 small diameter needles departing in orthogonal directions and contacting the reservoir up to 12 m. Notably, a fishbone completion is usually slightly more expensive than the reference liner completion, this explains why in many brown fields operators implement this stimulation as a trial and error process based on pilot experience. In more challenging environments, where Fishbones can be one of the critical factors that make a project economically feasible, it is necessary to estimate its potential benefits using numerical simulations. In reservoir simulations, wells are modelled according to the so-called Peaceman’s model, which allows to define a well performance indicator. However, this model may not work for Fishbones, because of the complex flow path establishing towards the well in presence of high-density needles. To perform 3D simulations of fishbone completion based field developments, it is necessary to define a proper modelling methodology. In this work, three different modelling approaches for fishbone completion are investigated: High Resolution Grid (HRG), Embedded-Discrete-Fracture-Model (EDFM) and Finite-Element-Method (FEM). The first two methodologies rely on a finite-volume formulation of reservoir conservation equations: the HRG enhances grid resolution to improve accuracy, while in the EDFM needles are treated as fractures and much coarser grid resolution are used. On the contrary, the FEM approach leverages on the possibility to define a mesh conformal to completion geometry. The FEM results are benchmarked with analytical solutions, proving the effectiveness of the specific implementation of the method. The three methodologies are then used to evaluate fishbone benefit on production with respect to a conventional completion through sensitivity analysis for single phase problems. Notably, inconsistencies between HRG results on one side and EDFM/FEM results on the other side together with some specific insights indicated that HRG is not a suitable technique for modelling Fishbones. This provided confidence about using EDFM for a field-like application where it could be possible to show that Fishbones largely anticipate production and give 10% more gas than conventional completions in the whole concession period.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/144314