Casing Leak Repair Allows Continued Hydraulic Fracturing
Authors: Carpenter Chris 
Published: July 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212933, “Casing Leak Repair To Continue Hydraulic Fracture Stimulation,” by Gaston Oscar Ciminari, Gonzalo Cabo, SPE, and German Rimondi, Pluspetrol, et al. The paper has not been peer reviewed.

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The authors introduce a successful alternative for repairing casing failures on an unconventional well that allows hydraulic fracture continuity to accomplish the original fracturing plan, considering well-integrity conditions throughout the entirety of well production life as the main intervention objective. The resulting well production was higher than the expected estimated ultimate recovery (EUR) for the landing zone.

Introduction

In December 2020, during the execution of hydraulic fracturing on a three-well pad in the Vaca Muerta unconventional shale reservoir, an annular communication suddenly occurred in one of the wells. This event took place during the execution of the ninth fracturing stage of 33 planned.

After a thorough pressure analysis of this event and verification that all pressure barriers were correct and in place, it was decided to stop fracturing treatments in this well and complete pending fracturing stages in the other two wells of the pad until the problem was well understood and a solution was found.

Diagnostics

The initial good condition of the well barrier was verified by a positive casing-integrity test (CIT) at 13,000 psi before the first fracturing pump. Maximum treatment pressure was kept under the CIT pressure, with an acceptable safety factor margin maintaining the well with annular communication, and was continuously pressure monitored.

Once the fracturing fleet finished the intervention and left the pad, the engineering focus of the completion was oriented to determine the location and geometric characteristics of the casing leak. It was decided to start from the simplest to most-complex diagnostics interventions.

The diagnostics interventions, and their results, are detailed in the complete paper. A bullheading pumping test was executed, and an increase in Section B pressure was observed. This showed clear communication between both sections. During circulation tests, it was observed that, by reducing pressure in Section B, Section A pressure response followed the pressure trend; opposite pressure changes in Section A, however, did not reflect on Section B pressure changes.

Based on flow-test behavior, it was believed that a casing mechanical failure with a flow area of 0.044 in.2, equivalent to a 0.23-in. orifice, was the reason for the annular communication.

With the aid of a coiled tubing (CT) unit and a bottomhole assembly (BHA) principally conformed with a multiple-set mechanical packer, it was possible to apply testing pressure below and above the packer seals at different depths to confirm the casing-leak position. A unique failure was located in the zone between 998 and 1002 m. A casing joint was located at 999.5 m; thus, it was assumed that a mechanical problem existed on this casing-joint connection.

A wireline BHA composed of an injection-logging tool and a temperature sensor was used to reduce the zone of uncertainty. As a result of this log, the failure zone was located between 999.4 and 1000.4 m. The failure evidently was near the joint but not in it.

Immediately after well-fluid changeout, the real-time downhole camera was run on wireline and showed what appeared to be a small hole 1 ft over the casing joint.