Developing an Evaluation Method for Casing Connections used in Hydraulically Fractured Wells
Authors: Hamilton Kirk , Pattillo P. David 
Published: January 2019

Hydraulic fracturing as a means to stimulate production has become an effective way to extract oil and gas from low-porosity, low-permeability, hydrocarbon-bearing formations. The technology used in support of hydraulic fracturing is evolving at a fast rate, which has enabled operators worldwide to achieve improved recovery in increasingly complex well environments.

The well designs and completion strategies associated with hydraulic fracturing come with a unique set of challenges. During well construction, the long lateral sections of extended-reach wells may require the production (or intermediate) casing to be rotated and pushed through build sections of relatively high curvature (greater than 10° per 100 feet or 30 meters); furthermore, some operators rotate the casing during cementing to improve cement quality. This rotation can subject the casing connections in the build section to a high number of rotating-bending load cycles. This cyclic loading can result in high stresses in the thread roots of the casing connections, which may lead to localized yielding of the material and potential structural failure. The hydraulic fracturing process itself subjects the production casing to rapid increases in internal pressure to high magnitudes, which will result in cyclic pressure loading for wells with multiple stages. Given these considerations, casing connections that are used in hydraulically fractured wells can be subjected to significant cyclic loading before the well is produced, and this loading may have an impact on the overall casing connection sealing and structural capacity in subsequent well operations.

In 2015 the American Petroleum Institute (API) published the first edition of Recommended Practice 100-1, Hydraulic Fracturing – Well Integrity and Fracture Containment, to provide the industry with guidelines and considerations for hydraulically fractured well designs, including recommendations on casing string design. This document does not include specific criteria for how to assess the performance of equipment. Since current connection evaluation protocols such as API RP 5C5 and ISO/PAS 12835 do not target the types of loading that are commonly observed in hydraulically fractured wells, connections that are evaluated under these protocols may not be suitable for hydraulic fracturing. Due to the critical role that casing connections play in well integrity, various industry stakeholders (operators and connection manufacturers) discussed the concept of creating an application-specific method to evaluate casing connection performance in hydraulically fractured wells.

In 2016 the API established a committee of industry experts under Work Item (WI) 3081 to develop this new evaluation protocol for casing connections used in hydraulically fractured wells. This protocol will provide users with a means to evaluate casing connection performance under a consistent method of discrete test program elements developed to replicate the cyclic rotating-bending loads of well construction and the pressure cycling of multi-stage hydraulic fracturing. Unlike its predecessors, this protocol will not follow the traditional prescriptive approach but rather allow the end user to customize a test program made up of the various elements that are representative of their application. Once published, this protocol will be referred to as API Technical Report (TR) 5SF, Guidelines for Evaluation Casing Connection Performance in Multi-Fractured Horizontal Wells.

This paper will summarize the development of API TR 5SF, the various test program elements that have been created to replicate the unique loads of hydraulically fractured wells, and provide examples of customized test programs that can be derived from the various test program elements.