Crosswell Strain and Production-Interference Testing Integrated in the Permian Basin
Authors: Carpenter Chris 
Published: March 2024

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 212336, “How and Where Wells Talk: Integrating Crosswell Strain and Production-Profile-Interference Testing,” by Matthew Lawrence, SPE, Ziebel; Janel Andersen, SPE, PDC Energy; and Yuanshan Zhang, Ziebel. The paper has not been peer reviewed.

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In Permian Basin fracturing operations, azimuths and intensities recorded by single-use distributed fiber optics in two wells are integrated and compared with post-flowback production-allocation and interference testing acquired with intervention fiber optics to identify areas of hydraulically conductive fractures and communication between offset wells. The production-allocation/interference testing method appears to reveal hydraulically connected fractures even in the absence of strain data.

Introduction
Intervention-based fiber optics have proved a valuable and cost-effective tool in understanding during-fracturing and post-flowback well and section performance. During-fracturing diagnostics, such as crosswell strain measurements from an offset monitor well, describe where fractures intersect the monitor well and reveal details such as azimuth, fracture-propagation velocity, and activation and reactivation statistics. These critical data points help inform cluster, stage, and well-spacing decision-making. While the absence of observed strain activity does not indicate the absence of created fractures, the existence of a strain activity indicating a fracture does not guarantee hydraulic functionality.
The hydraulically functional fracture network can be understood with post-flowback production profiling. Particularly when combined with interference testing, fiber-optic production profiling identifies and differentiates productive and unproductive sections of unconventional laterals. Combination of during-fracturing and post-flowback technologies reveals the clearest picture of the functional fracture network.
On an eight-well pad in the Permian Basin, the operator acquired fiber-optic crosswell strain data on two wells using single-use fiber, revealing details about the created fracture network. Sixty days after the wells went on production, a combination production-allocation and interference sensing program was executed with intervention fiber optics on two of the wells.

Designing a Diagnostic Project in the Delaware Basin
The operator completed an eight-well pad in the Delaware Basin on the western slope of the Permian. The wells were landed in three rows across the upper and lower Wolfcamp, which had a formation thickness of approximately 600 ft true vertical depth. Four of the laterals were completed from south to north (Wells 11N, 14N, 21N, and 31N), and five of the laterals were completed north to south (Wells 12S, 13S, 22S, 23S, and 31S). Two of the north-to-south wells, one in the middle (23S) and one in the lower bench (31S), were designated as monitor wells for during-fracturing diagnostic data acquisition (Fig. 1).
Zipper operations were conducted in three groups, with the laterals on the outside edges of the pad fractured first (11N, 14N, and 21N) in a south-to-north order, followed by the inner laterals in the second zipper group (12S, 13S, and 22S) in a north-to-south order.