Maintaining the Stability of Deviated and Horizontal Wells: Effects of Mechanical, Chemical and Thermal Phenomena on Well Designs

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWellbore instability, particularly in shale formations, is regarded as a major challenge in drilling operations. Many factors, such as rock properties, in-situ stresses, chemical interactions between shale and drilling fluids, and thermal effects, should be considered in well trajectory designs and drilling fluid formulations in order to mitigate wellbore instability related problems.A comprehensive study of wellbore stability in shale formations that takes into account the 3-dimensional earth stresses around the wellbore as well as chemical and thermal effects is presented in this work. The effects of borehole configuration (e.g. inclination and azimuth), rock properties (e.g. strength, Young's modulus, membrane efficiency and permeability), temperature, and drilling fluid properties (e.g. mud density and chemical concentrations) on wellbore stability in shale formations have been investigated.Results from this study indicate that for low permeability shales, chemical interactions between the shale and waterbased fluids play an important role. Not only is the activity of the water important but the diffusion of ions is also a significant factor for saline fluids. Cooling drilling fluids is found to be beneficial in preventing compressive failure. However, decreasing the mud temperature can be detrimental since it reduces the fracturing pressure of the formation, which can result in lost circulation problems. The magnitude of thermal effects depends on shale properties, earth stresses and wellbore orientation and deviation.Conditions are identified when chemical and thermal effects play a significant role in determining the mud-weightwindow when designing drilling programs for horizontal and deviated wells. The results presented in this paper will help in reducing the risks associated with wellbore instability and thereby lowering the overall non-productive times and drilling costs.

Mechanical Characterization of Low Permeable Siltstone under Different Reservoir Saturation Conditions: An Experimental Study

“…Therefore, unconventional natural gas extraction is becoming necessary. Recent advances in the petroleum industry, such as horizontal well drilling and hydro-fracturing, have significantly improved unconventional natural gas production from deep geological formations [5][6][7][8][9][10][11], particularly in countries such as the U.S., China, Canada, and Germany. Of the various reservoir productivityenhancement techniques, hydro-fracturing is dominant and has been widely used.…”

Modelling of Time-Dependent Wellbore Collapse in Hard Brittle Shale Formation under Underbalanced Drilling Condition

“…According to the above analysis, the effects of different parameters on the wellbore collapse are different. Under underbalanced drilling conditions, drilling excavation disturbances cause the original crack extension and new 16 Geofluids microcracks, which causes the shale hydration to expand by the self-water absorption effect of the microcracks. Due to hydration effect, the strength of shale gradually decreases, which is the intrinsic factor that leads to the progressive collapse of the wellbore.…”

“…The free energy thermodynamics model of water molecules negates the effect of differential pressure on water movement in shale and also negates the effects of ion diffusion and ion exchange on shale hydration and does not consider time effects. The third stage is the nonequilibrium thermodynamic method [12][13][14][15][16]. Nonequilibrium thermodynamic method is a comprehensive method to study the chemomechanical coupling of wellbore stability of shale.…”