Estimation of Effective-Fracture Volume Using Water-Flowback and Production Data for Shale-Gas Wells

Abstract

Summary Primarily, gas-production data are the main tool used to analyze shale-gas reservoirs. Water production is not usually included in the analysis. In this paper, post-fracturing water flowback and long-term water production are added to the analysis. The water data are usually available but are analyzed separately and not combined with long-term gas-production data. In this paper, procedures and examples are presented, including water-flowback and water-production data, in the analysis of shale-gas wells using rate transient analysis. A number of simulation cases were run. Various physical assumptions were used for the saturations and properties that exist in the fracture/matrix system after hydraulic fracturing. Water flowback and long-term production periods were then simulated. The results of these simulations were compared with data from actual wells by use of diagnostic and specialized plots. These comparisons led to certain conclusions which describe well/reservoir conditions after hydraulic fracturing and during production. This paper shows the benefits of a new method for combining water-flowback and long-term water-production data in shale-gas analysis. Water-production analysis can provide effective-fracture volume which was confirmed by the cumulative produced water. This can help when evaluating fracture-stimulation jobs. It also shows some pitfalls of ignoring flowback data. In some cases, the time shift on diagnostic plots changes the apparent flow-regime identification of the early gas-production data as well as water production data. This leads to different models of the fracture/ matrix system. The presented work shows the importance of including water-flowback data in the long-term production analysis.