Abstract

Various completion designs have been employed throughout the 10+ year life of the Fayetteville Shale. Designs have changed from geometrically-spaced completion stages to a design of variable completion spacing segregating intervals of similar rock type. Because of stratigraphic and structural variations along a horizontal well, wellbores often include sections of more ductile/clay-rich rock types in addition to desirable sections dominated by more brittle/quartz-rich target rock types. Ductile rocks are challenging to break down and fracturing screen outs often occur. As a result, geosteering interpretations are used to place stages in similar rock types. The geosteer interpretation transforms the geologic position along the lateral back to a nearby vertical pilot hole. While testing geosteer/engineered completion design, conventional engineered completion designs were also tested. This utilized cased or open hole logs in the lateral to design stages minimizing the differences in rock break-down stress between clusters. Obtaining logs for the conventional designs presents operational challenges and risks which can increase costs. This led to investigating an alternative way to characterize the rock along the lateral.

The purpose of a Cost-Effective Engineered Completion Design is to increase well performance utilizing existing pilot hole data. Sonic and density logs in the pilot hole are used to calculate rock mechanical properties in the vertical section. These properties are then interpolated along a nearby lateral using the geosteer interpretation to identify the rock properties along the lateral. Additionally, XRD analysis of drill cuttings along with drilling metrics are used to validate lateral characterization. In turn, this is used to optimally place each completion stage in similar rock types, thereby maximizing the rock that is stimulated. Analyzing the drill cuttings and correlating with drilling metrics helps reduce costs and risks compared to running additional logs for rock characterization.

This Cost-Effective Engineered Completion Design has been found to be a low risk method of minimizing the differences in rock break-down stress between clusters. One indication of the success of this method is that brittle/quartz-rich stages treated with lower pressures compared to ductile/clay-rich stages. Testing is ongoing.

Introduction

The Fayetteville Shale team has employed various completion designs throughout its 10+ year life. Designs have evolved from geometrically-spaced completion designs to engineered completion designs. Engineered completions have been designed using geosteering interpretation and logs for the purpose of minimizing the differences in rock break-down stress between clusters. The Cost-Effective Engineered Completion Design has been found to be a low risk method of accomplishing this goal. The objective of this method is equal and successful fracture propagation in every cluster of each stage to improve productivity.

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