Shale Failure around Hydraulic Fractures in Water Fracturing of Gas Shale

Abstract

Even though shale has traditionally been considered a hydrocarbon source rock and/or seal rock, some gas bearing shales have been recognized as major reservoir rocks for unconventional hydrocarbon resources. The exploitation of gas shale across North America has generated much activity in the drilling and completion sector of the oil and gas industry, including drilling horizontal wells and multi-stage fracturing with water-based fracturing fluids. During water fracturing, the shale will interact with water and create consequences (hydration, dehydration, fractures etc.) as that happens in drilling. The consequences from this shale/water interaction will not only alter the shale mechanical properties, but also induce stress changes in the shale. These changes may induce favorable or unfavorable fractures in the shale/water interacted zones. This paper first outlines lab observations of the shale/water interactions which generating fractures in gas shale. Then, a stress model is developed with poro-elasticity effect and simulation method for studying stress changes due to shale hydration in near-fracture zones. This paper also describes a sample application of the models to investigate stress changes and potential shale failures in shale around major hydraulic fractures in shale gas. The study presented in this paper that it was mechanically possible to induce multiple secondary fractures around major hydraulic fractures via shale hydration. The modeling in this paper completes the preliminary study and provides a foundation for more complex scenarios in future studies focusing on water fracturing and horizontal well drilling in gas shale. It also provides some new ideas of optimizing hydraulic fracturing in gas shale.

An Investigation of Fluid Leak-off Due to Osmotic and Capillary Effects and Its Impact on Micro-Fracture Generation during Hydraulic Fracturing Stimulation of Gas Shale

“…On one hand, numerical simulation results indicate water intake into the shale matrix would reduce conductivity of main fractures and matrix relative permeability to gas, thus causing formation damage and reducing production performance (Shaoul et al, 2011;Guo and Gao, 2013). On the other, water intake can induce shale failure around hydraulic fracture which greatly increase fracture connectivity, thus leading to a sustained production (Dehghanpour et al, 2013;Ji and Geehan, 2013). The later has been studied extensively in the context of swelling of clay minerals in shales and gas entrapment which result in wellbore instability (Chenevert, 1970;Yew et al, 1990;Schmitt et al, 1994).…”

Wellbore instability in shale gas wells drilled by oil-based fluids

“…Unfortunately, oil phase trapping induced by white oil and kerosene may be more fatal than water phase trapping because white oil or kerosene is prone to be adsorbed by organic matter of shale, the main place storing adsorbed shale gas. The white oil or kerosene adsorbed by organic matter can prevent multi-scale gas mass transfer, including gas desorption, diffusion and seepage from organic pores to a fracture network, and affect gas production, while the invaded water in shale may be helpful to shale gas production [23]. At present, environmental friendly high performance water based fluids are developed [7].…”

Experimental Investigation on the Crack Evolution of Marine Shale with Different Soaking Fluids

“…Most researchers focused on revealing hydration mechanism (CHENEVERT ME, 1970;DARLEY HCH, 1969;Dokhani et al, 2015;Roshan et al, 2015;Wen et al, 2015;Liang et al, 2015;Kang et al, 2017) and developing effective anti-hydration drilling fluids to guarantee wellbore stability (Deville et al, 2011;Riley et al, 2012;An et al, 2015;Zhong et al, 2016;Barati et al, 2017). However, in the view of reservoir stimulation, it might be a positive effect on improving recovery ratio in shale gas reservoir (Dehghanpour et al, 2013;Ji and Geehan, 2013;Morsy and Sheng, 2014), because hydration induced fractures could enhance the formation permeability.…”