Frac-n-Flow Testing to Screen Brittle Fracture Stages in Wolfcamp Formation, Permian Basin, USA

Zhengwen Zeng

doi:10.3390/en14175450

Abstract

A new technique, fracturing-and-flowing (frac-n-flow) testing, is introduced for horizontal drilling and multistage hydraulic fracturing (HDMHF) practitioners to check if the next stage would be a brittle fracture using the instantaneous shut-in pressure (ISIP) from the current stage. It was developed to reduce the number of not-flowing clusters in HDMHF treatments due to stress shadows in the development of tight oil reserves in Wolfcamp, Permian Basin, USA, and other similar fields. Preliminary frac-n-flow testing results show that a medium (200–1000 psi) increase in confining pressure under representative field in-situ stresses can transfer Indiana limestone from brittle fracturing to semi-ductile failing. Consequently, folds of increase (FOI) of matrix permeability vary from +13 (i.e., increase by 1300%) to −0.39 (i.e., decrease by 39%). Limestone is one of the major lithological components in Wolfcamp formation. Field ISIP data of two HDMHF wells in Wolfcamp formation show that the maximum stress shadows are +1297 psi and +1716 psi, respectively. These stress shadows might have transferred the fracturing process from brittle to semi-ductile, converting the corresponding stages from being stimulated and conductive (fracturing-n-flowing) to being damaged and not-flowing (failing-n-not-flowing). Field completion reports of the two wells confirmed that screen-out and other interruptions of operation occurred in these high stress shadowed stages.

Highlights

During the energy crisis in the 1970s, the US Department of Energy (DOE) initiated financial support for research and development (R&D) efforts in the exploration and production of unconventional oil and gas resources [1,2]
Advanced well completion technology of combining horizontal drilling with multistage hydraulic fracturing is the dominant technology used in producing tight oil from Wolfcamp formation
Production log data indicated that many clusters are not-flowing; and many Hydraulic fracturing (HF) stages are performing below the nominal average production rate

Summary

Introduction

During the energy crisis in the 1970s, the US Department of Energy (DOE) initiated financial support for research and development (R&D) efforts in the exploration and production of unconventional oil and gas resources [1,2]. Using new completion technologies of combining horizontal drilling and multistage hydraulic fracturing, these unconventional oil and gas resources are technically producible [6,7]. In 1960, Griggs and Handin [45] classified rock failure under room temperature and different combinations of axial and radial stresses into brittle and ductile. They correlated each failure mode based on the stress-strain curves and their ultimate strains. Rocks can undergo a range of failures, from brittle splitting at an ultimate strain below 1% to ductile flowing/swelling at an ultimate strain larger than 10%

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