Abstract

In 2019-2020, a modeling study was undertaken to characterize past refrac performance and to provide screening criteria and design improvements for future refracs. In the subsequent years, refrac design changes, informed by modeling, were successfully tested and evaluated in the field.

Two historical wells were selected for the basis of the two-phase study. Well A and Well F were originally completed with 100- and 67-foot cluster spacing, respectively. Each well was refractured after three years of primary production. In Phase One, a model of each well was constructed. Each model was calibrated to the primary production period of the respective well and refrac prediction blind tested against actual refrac performance. In Phase Two, the calibrated models were used to evaluate screening criteria and design changes. Refrac opportunities were screened based on primary cluster spacing and stimulation intensity (proppant/fluid loading). Design changes evaluated included: timing of refrac (delay after start of primary production), cluster spacing, and stimulation intensity.

Modeling of refrac performance demonstrates high production performance predictivity for both wells tested, in line with the significant EUR gains observed in the field.

Model screening and optimization of refracs demonstrated:

○ The uplift from refracs is largest with sparsest primary completion cluster spacing, and smallest with tightest primary cluster spacing.

○ Increased production with higher refrac proppant/fluid volumes with diminishing returns

○ When frac and refrac designs held constant, 30-year EUR was similar whether wells were refrac’ed 1, 3, or 5 years after initial completion.

○ For equivalent proppant/fluid volumes, reduced cluster spacing increases short-term productivity but reduces long-term productivity.

Screening criteria and optimization informed future refrac implementation.

This study demonstrates a workflow for characterizing past refrac performance and optimizing future refrac selection and design.

Introduction

In March 2019, Chesapeake Energy acquired substantial acreage rights (∼420,000 net acres) in Austin Chalk and Eaglebine reservoirs, located in central Texas. The acreage acquired is in a geographic area called the Brazos River Valley (BRV). Most of the acreage acquired is in Lee, Burleson, Brazos, Madison, Grimes, Robertson, and Washington counties, located some 85 miles East of Austin, Texas. This study focuses on the development of refracture opportunities on existing wells drilled by previous operators in the Eaglebine reservoir.