3D Modeling of Fracture Initiation From Perforated Noncemented Wellbore

Abstract

Summary A 3D numerical model of fracture initiation from a perforated wellbore in linear elastic rock is developed, which allows one to determine the fracture-initiation pressure (FIP) and the location and direction of an initial rupture. The model assumes that the fracture initiates at the point at which the local maximal tensile stress exceeds the rock tensile strength. The 3D boundary-element method (BEM) is used for stress analysis. The model aims to predict the location of initial fractures and the difference in FIP between different perforation intervals in arbitrarily oriented noncemented wellbores. There are many practical applications for this knowledge, but of particular interest for this research is the employment of differently oriented perforations for creating heterogeneity of FIP between wellbore intervals in multistage fracturing treatment. This can enable stimulation of these intervals in a sequential mode and significantly simplify current treatment diversion and completion practices. Comprehensive analysis revealed that the main parameter that can be used for controlling FIP during multistage fracturing treatment is the angle between the direction of the perforation channel and the preferred fracture plane (PFP). The model allows obtaining the range of the angles that is the most suitable for designing and implementation of diversion between the perforated wellbore intervals. The influence of geometrical parameters of perforation (such as length, diameter, and shape) on FIP is substantially less. In addition, we found that against all expectations, increase of perforation diameter can result in higher FIP. It was also discovered that the influence of the intermediate in-situ stress on FIP is comparable with the effect of perforation misalignment, especially in the situation of a horizontal wellbore and properly aligned perforations. On the basis of the model developed, an approximate approach to the evaluation of the effect of wellbore cementation on fracture initiation was suggested. It was discovered that taking into account the state of stress within the cement before well pressurization can result in both an increase and a reduction of FIP, depending on the parameters of perforating and the wellbore orientation. The presented model is a necessary step toward predictable and controllable fracture initiation, which is vital for multistage-fracturing-treatment diversion.

Hydraulic Fracture Initiation and Propagation Model Provides Theoretical Ground for Hybrid-Type Fracturing Schedules in Unconventional Gas Reservoir in the Sultanate of Oman

“…The numerical models traditionally used for simulating hydraulic fracture initiation pressure are based on either linear elastic strength criteria (Hubbert and Willis 1957;Haimson and Fairhust 1967;Hossain et al 2000;Tran et al 2010;Alekseenko et al 2012) or linear elastic fracture mechanics criteria (Weijers 1995;van de Ketterij and de Pater 1999). A few attempts were made to couple elasticity and fluid flow for the case of axial (Garagash and Detournay 1997;Detournay and Carbonell 1997;Bunger et al 2010; Lecampion 2012) and transverse (Lhomme 2005;Lhomme et al 2005; fractures.…”

Impact of Wellbore Orientation on Fracture Initiation Pressure in Maximum Tensile Stress Criterion Model for Tight Gas Field in the Sultanate of Oman

“…Over last 20 years, three different approaches not coupled with the fluid flow have been proposed: an approximated analytical approach using the representation of the perforated wellbore as two noninteracting cylindrical cavities, 3D modeling based on the finiteelement method (FEM), and 3D modeling based on the boundary element method (BEM). More detailed descriptions of each one are provided by Alekseenko et al (2012a). The modeling approach used for the current work falls under the last category listed above (i.e., based on BEM).…”

“…This can be done using the multizone BEM developed by Alekseenko et al (2012b), but constructing the numerical algorithm is more complicated with the multizone BEM, and also computations with this method are too slow for the required volume of stress-state calculations. However, the behavior of cased and open holes is different, and it should be addressed.…”

“…However, the behavior of cased and open holes is different, and it should be addressed. The simplified approach described and verified by Alekseenko et al (2012a) has been used in the current work to calculate the stress state around a cased wellbore using the modified openhole model. …”

Impact of Wellbore Completion Type on Fracture Initiation Pressure in Maximum Tensile Stress Criterion Model for Tight Gas Field in the Sultanate of Oman

“…Details of the models from the former group are provided by Garagash and Detournay (1997), Detournay and Carbonell (1997), Bunger et al (2010), Lecampion (2012), Lhomme (2005), Lhomme et al (2005), and Abbas and Lecampion (2013). An overview of the latter group provided by Alekseenko et al (2012a). The present model is from the group of models not coupled wFith the fluid flow.…”