Thermal-poro elastic stress effect on stress reorientation in production and injection wells
- Ahmed S. Abou-Sayed (Advantek International Corp.) | Zongyu Zhai
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil and Gas Show and Conference, 25-28 September, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.8 Formation Damage, 5.8.1 Tight Gas, 5.2 Reservoir Fluid Dynamics, 1.2.2 Geomechanics, 4.1.2 Separation and Treating, 1.1 Well Planning, 5.8.2 Shale Gas
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Stress reorientation is an important issue for the refracturing design and candidate well design. The long term production/injection causes the stresses to reorient. The temperature differential and pressure differential induced thermal elastic stress and poroelastic stresses are the fundamental reasons for the stress to reorient. A model and numerical scheme are developed to study the effects of thermal differential and pressure differential on stress reorientation. In the model, thermal diffusion and convection is coupled with hydraulic diffusion to obtain the temperature distribution reflecting the cumulative impact. The effective poro-elastic and thermo-elastic stresses are obtained from 1-D displacement equilibrium equation in a radial system. The 3-D in-situ analytical effective stress is superimposed on the 1-D solution. By applying this methodology the 3-D deviated borehole stress model is greatly simplified. The method makes it practical to obtain the stress distribution at any given injection/production time. The thermal stress, poro-elastic stress effects on the stress reorientation are compared and evaluated. Field examples are presented and show that in some cases thermal plays an important role on stress reorientation. The quantified results of the model will give guidance on the fracture treatments and well plan.
Refracturing can prove to be a useful and advantageous tool in the quest to maximize production and recovery from a particular well, field or asset. Refracturing has been widely used specifically in tight gas and shale gas formations to tap into unexploited resources. It is typically thought in such low permeability formations that most of the production and drainage would flow through the fracture system network hence hydrocarbons not connected to this network are unlikely to be produced. By refracturing a secondary fracture is created. The azimuth of this fracture will likely be off the main field maximum horizontal stress azimuth and as much as 90° in some instances. This would allow for new surface areas and even existing natural fracture networks to be exploited and tapped into.
This process has been observed and documented in several fields. Case studies (1), (2), (3), (4), (5), (6), (7), (8), (9), (10) have been aptly documented and published in several papers. Some case studies have gone as far as to document the fracturing events using tiltmeters and were able to map the variations in azimuth. In short field experience has confirmed the existence of this phenomenon.
Modeling of the phenomena has centered along the long term effect caused by the redistribution of the pressure and temperature profiles. The redistribution can be attributed to the production and injection operations that lead to depletion, over pressuring, cooling and heating of the formation at different locations. In the near wellbore region this can lead to stress reorientation as a function of the imposed poro-elastic and thermo-elastic stresses. Several theoretical and numerical models have been put forth to address this type of behavior (11), (12), (13), (14). Weng (15) studied the effect of wellbore deviation on fracture initiation, the potential for multiple fracture initiation and the interaction between these created fractures. Siebrits et al. (16) addressed the conditions under which maximum benefit can be derived from fracture reorientation and delved into the theoretical background. Rewis et al (17) and Chen et al (18) presented a 2D model to evaluate the changes in insitu stresses due to thermal and poro-elastic impact. Hidayati et al (19) looked at understanding the physical nature of the issue and its effects. Soliman et al (20) provided theoretical background for multiple fracturing vertical and horizontal wells. Aghighi et al (21) presented a design methodology for hydraulic fracture treatment in tight gas reservoirs.
|File Size||1 MB||Number of Pages||16|