## Abstract

Volumetric changes in the active drilling fluid system during drilling operation are commonly termed borehole ballooning or breathing. One of the borehole ballooning contributors is the elastic deformation of an open borehole wall. When the elastic deformation of the open borehole wall occurs, it causes a volumetric change in the active drilling fluid volume in the system; the change in volume will be variable depending on the well in question and occurs frequently.

Prediction of the volumetric change is highly complex, simply because huge number of complicated equations involved. Therefore, the use of the computer is necessary to reduce the process time and improve the prediction accuracy. Hence, Standalone software has been developed (built on Matlab) in order to estimate and quantify the volumetric change of the active drilling fluid system. The main objective of the presented Standalone software is to utilize the existing in situ principal stresses gradients, pore pressure gradient and rock geomechanical properties in order to compute the change in borehole volume for different flow rates. Moreover, it indicates any possible changes might occur to the equivalent circulating density within the referred system. The core of the presented Standalone software are two analytical formulas, which initially

are used to estimate the radial elastic displacement for any point along the open borehole wall, which in turn will be utilized to quantify the volumetric change of the drilling fluid system for the entire open borehole section. The complete governing equations of the developed software are provided

and described in detail. In order to examine the functionality of the software, two case studies have been performed using the developed software, several scenarios were assumed for both cases. The base scenario was defined to use the actual well data without any changes, whereas the changes have been

applied for the other scenarios. The main finding of these studies was that the volumetric change of the open borehole section, due to the elastic deformation of the open borehole wall, is not significant and mainly controlled by the pump flow rate, drilling fluid weight and temperature.

Prediction of the volumetric change is highly complex, simply because huge number of complicated equations involved. Therefore, the use of the computer is necessary to reduce the process time and improve the prediction accuracy. Hence, Standalone software has been developed (built on Matlab) in order to estimate and quantify the volumetric change of the active drilling fluid system. The main objective of the presented Standalone software is to utilize the existing in situ principal stresses gradients, pore pressure gradient and rock geomechanical properties in order to compute the change in borehole volume for different flow rates. Moreover, it indicates any possible changes might occur to the equivalent circulating density within the referred system. The core of the presented Standalone software are two analytical formulas, which initially

are used to estimate the radial elastic displacement for any point along the open borehole wall, which in turn will be utilized to quantify the volumetric change of the drilling fluid system for the entire open borehole section. The complete governing equations of the developed software are provided

and described in detail. In order to examine the functionality of the software, two case studies have been performed using the developed software, several scenarios were assumed for both cases. The base scenario was defined to use the actual well data without any changes, whereas the changes have been

applied for the other scenarios. The main finding of these studies was that the volumetric change of the open borehole section, due to the elastic deformation of the open borehole wall, is not significant and mainly controlled by the pump flow rate, drilling fluid weight and temperature.

Original language | English |
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Publication status | Published - 1 Dec 2016 |

## Keywords

- Elastic Deformation