Thermal-Poro Plastic Stress Effect on Stress Reorientation in Production and Injection Wells
- Zongyu Zhai | Ahmed S. Abou-Sayed (Advantek International Corp.)
- Document ID
- Society of Petroleum Engineers
- Brasil Offshore, 14-17 June, Macaé, Brazil
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.8 Formation Damage, 1.2.2 Geomechanics, 5.2 Reservoir Fluid Dynamics, 3 Production and Well Operations, 1.1 Well Planning, 5.8.2 Shale Gas, 4.1.2 Separation and Treating, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
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Stress reorientation is an important issue for the cuttings injection batching, refracturing design and stimulation candidate well selection. Long term production/injection causes the principal stresses to reorient. Temperature differences and pore pressure differentials induce thermal elastic stress and poroelastic stresses. These induced stresses are the fundamental reasons for the reorientation of the stress field. A model and numerical scheme are developed to study the effects of thermal differentials and pressure differentialss on stress reorientation. The model couples thermal diffusion and convection with hydraulic diffusion to obtain the temperature distribution reflecting the cumulative impact. The effective poro-elastic and thermo-elastic stresses result from the 1-D displacement equilibrium equations in a radial system. The 3-D in-situ analytical effective stress is superimposed on the 1-D solution. Application of this methodology simplifies the modeling of the 3-D stresses in a deviated borehole. The method makes it practical to obtain the stress distribution at any given injection/production time. The thermal stress and poro-elastic stress effects on the stress reorientation are compared and evaluated. Field examples are presented to show that in some cases the thermal stresses play an important role on stress reorientation. The quantified results of the model will give guidance on fracture treatments and well plans during injector or producer construction.
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 since its introduction in the Kuparuk River Unit, Alaska. Recently it has played a role in extending production in tight formations, specifically shale gas plays to tap into unexploited resources. Most of the production and drainage from these formations typically would flow through the fracture network system. Hence, hydrocarbons not connected to this network are unlikely to be produced. Refracturing creates secondary fractures whose azimuths will generally be off the main field maximum horizontal stress azimuth and as much in a perpendicular direction in some instances. This would allow for exploitation from new surface areas and could tap into existing natural fracture networks.
This process has been observed and documented in several fields. Many references (1), (2), (3), (4), (5), (6), (7), (8), (9), (10) have aptly documented and published several case studies. Some treatements documented 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 attributed to the production and injection operations. Depletion, over pressuring, cooling and heating of the formation at different locations results from such operations. 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 addressed 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.
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