Abstract

In the past few years, the Boonsville Bend Conglomerate gas field has been fractured utilizing a foamed (70 - 75% nitrogen) organometallic crosslinked fluid. Recent studies illustrate that organometallic crosslinked foamed fluids damage the proppant pack permeability greater than 60% with breaker at 140F. Damage of this extent greatly reduces the outcome of the stimulation treatment. A guar based fluid utilizing a new, organically complexed borate crosslinking system and nitrogen mixed at 60 - 65% was selected. This fluid shows superior rheology properties and excellent clean break characteristics. An independent consortium has confirmed greater than 85% retained permeability with breaker at 140F. Stability of the system is such that increases in sand concentrations from three pounds per gallon up to five pounds per gallon have been incorporated into the designs. This redesign has lowered overall fluid volumes, even thought the quality of the foam is ten to fifteen percent less.

Introduction

Recently, wells fractured with an organometallic crosslinked foam showed low fluid recovery, poor production performance, and post frac sand production in the bend conglomerate formation in the Wise and Jack county areas of North Central Texas. The test wells used in this discussion were all in the Atoka group of the Boonsville field area of North-Central Texas. This group consists of five systems: the Boonsville fluvial-deltaic, the Smithwick pro-delta/basin-fill, the Grant deltaic, the "Pregnant" pro-delta/basin-fill, and the Brazos fluvial-deltaic. The "Conglomerates" of the Boonsville system are the primary reservoir for the field. They consist of fine to coarse grained sandstone and grade more commonly to fine to medium-grained poorly sorted, subrounded conglomerates and occasional thin, widespread limestone. The main constituents of the "conglomerates" are quartz with chert and feldspar, and commonly gluconite, especially in the lower part of the Atoka.

FRACTURE FLUID HISTORY

The use of a nitrogen foamed CMHPG polymer based fluid, utilizing titanium and zirconium as the delayed crosslinker was initiated due to several benefits of the fluid. The main advantages were good thermal stability and reduced tubular friction pressures. However, current research indicates that up to 80% of the proppant pack permeability can be damaged using a transitional metal crosslinker.

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