The Unconventional Unconventionals: Tectonically Influenced Regions, Stress States and Casing Failures

Abstract

Not all unconventional plays are created equal, in a substantial number of regions around the world the tectonic environment is quite different from the typically relaxed and more passive states found widely in most, if not all, of the US unconventional plays. This is merely a function of the relative proximity of such plays to distinct geological features characterized by active tectonic plates and with dynamic margins and recent activity. The Nazca plate associated with the Andes, the Arabian plate linked with the Al-Hajar mountains and the Indian plate connected with the Himalayan mountain range are just a few examples of tectonically influenced regions, where potential hydrocarbon traps are subject to complex states of stress generated by convergent plates, subduction zones and associated faulting. This scenario often translates into severe strike-slip and reverse fault stress states. Additionally, the presence of both multi-layered and laminated formation geology as well as the presence of overpressure and pressure differentials, typical of tight gas and shale gas, can exacerbate this situation even further. This situation can result in an extremely challenging environment for the successful execution of hydraulic fracturing and the associated development of unconventional resources. This paper will demonstrate, that such complex stress-states will directly affect well completions and hydraulic fracturing in a multitude of ways, but that some of the most impactful consequences are often severe casing failures, production-liner restrictions and complex fracture initiation scenarios. Casing failures are responsible for increased intervention costs as well as higher costs for the upgraded and strengthened wells. Equally, such issues can severely impair efficient execution of the completion plan and create a bottle-neck to subsequent well production. Horizontal, complex and pancake fractures will typically develop in strike-slip / reverse fault stress states, often resulting in fracture conductivity and connectivity loss that will greatly impair the eventual well performance. Layer interface slippage and natural fault re-activation are dominant mechanisms for hydraulic fracture induced casing failures. Examples of micro-fracs, micro-seismic and other diagnostics will be presented aiming to document the practical difficulties encountered while completing wells in these complex environments. This paper will demonstrate that unconventional development in such environments requires a renewed focus on all aspects of well design and construction, from directional drilling and lateral placement to casing selection and lower completion design. All these considerations are made with the goal of enabling the competent delivery of a highly effective and conductive fracture network, to efficiently access and produce the hydrocarbon resource.

Strength analysis of perforated casing in ultra-deep horizontal shale wells during sublevel acidizing and hydraulic fracturing process

“…11–13 Moreover, in acidizing fracturing conditions, activation and slip of faults caused by fluid entering the formation can also seriously affect casing integrity. 14–23…”

Multi-criteria material selection for casing pipe in shale gas wells application

“…Although the API standards guidelines such as API Spec 5CT, API Spec 5C2 and 5C3 have proved to be adequate reference materials for casing materials in conventional oil and gas wells but inadequate for unconventional wells such as shale gas wells (Hay and Belczewski 2003). The challenges however posed by unconventional wells are numerous and entirely different from conventional wells (Casero and Rylance 2020;Mohammed et al 2020). The study of Gouveia et al (2020) on the current search for oil and gas shows that the casing is being increasingly exposed to unconventional reservoirs, i.e.…”

Identifying Casing Failures with Signature Fracturing Treatment Pressure Behavior

“…A literature search conducted in OnePetro's online technical literature library using the keywords "casing deformation" or "casing failure" and "unconventional" and "fracturing" showed 124 results, where the first relevant publication was presented eight years ago (Sugden 2012). Over the past five years, several publications have covered overviews and case histories regarding this topic (Daneshy 2015;King and Valencia 2016;Adams et al 2017;Barreda et al 2018;Yu et al 2019;Casero and Rylance 2020). Other authors focused on technologies used to detect and quantify casing failures (Hamilton and Pattillo 2019;McCarthy et al 2020;Robertson et al 2020).…”