Stimulation of Gas Storage Fields To Restore Deliverability
Authors: Fogler H.S. , Crain E.R. 
Published: December 2007

Deliverability of a number of gas storage fields in the Michigan stray sandshas been decreasing steadily in recent years. This paper describes thedevelopment of a successful stimulation procedure through mathematicalmodeling, laboratory core flood experiments, and field observations. Theprocedure was applied to a number of wells in the Michigan stray sands andprocedure was applied to a number of wells in the Michigan stray sands andachieved deliverability increases of up to 426%.

Introduction
The deliverability of a number of gas storage wells in the Michigan straysands has been declining steadily over the years. In the Austin storage field, the loss of deliverability had averaged 4.8% per year for the last few years.One of the major reasons for this loss of deliverability is damage to theformation in the immediate vicinity of the wellbore. This damage can resultfrom a number of causes, such as salt precipitation, shale fillup, finesmigration, and oil precipitation, shale fillup, fines migration, and oilresidue. One method for increasing or restoring the productivity of oil and gassandstone reservoirs is productivity of oil and gas sandstone reservoirs ismatrix acidization. While acid stimulation has been extremely successful inincreasing or restoring the productivity of oil and gas producing reservoirs, it productivity of oil and gas producing reservoirs, it previously has not beenvery successful in stimulating previously has not been very successful instimulating the gas storage reservoirs of central Michigan. This paperdescribes the procedure and results for the paper describes the procedure andresults for the successful acid stimulation of wells in gas storage that havedeteriorated greatly. The Michigan stray sandstone formations are of the lateMississippian age and have a mineralogical composition of approximately 86%quartz, 3% feldspars, 4% chlorite, 2% kaolinite, 2% illite, 2% calcite, and 1%siderite and pyrite. Historically the stray sand reservoirs were completedopenhole and, depending on the era, some type of absolute open flow or gaugeflow during drilling-in was obtained. Upon conversion to the use of storage, along-term deterioration of flow potential was noted. This deterioration was notonly from the reported original potential but also from the more accuratepotential but also from the more accurate backpressure tests run earlier duringthe storage operation. The need for corrective procedures was apparent. Earlystimulation attempts for the stray sandstone were designed to increase porosityby solution of the silicates and calcite with HF and HCl, respectively. Theseattempts did not increase the deliverability significantly. A review of thetreatment reports and discussion with field engineers indicate that it wasdifficult to inject the acid and, when it was able to be injected, it wasfracturing into undesirable zones rather than flowing uniformly into theopenhole formation. Two conclusions from this earlier work were a relativelyhigh increase in cost per thousand cubic feet and a reaffirmation of thedifficulty of liquid injection into the Michigan stray sands.

Theory
During the past 5 years, significant advances have been made in modelingflow and reaction in porous media.
JPT
P. 1612