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

Abstract

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 waterproduction 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. IntroductionWater production is usually ignored when analyzing and forecasting shale-gas-well performance. The process involves pumping thousands of barrels of water with proppant and additives into the rock at high pressure. Numerous operators along with Wattenbarger and Alkouh (2013) have indicated that the percent of injected fluid recovered (load recovery) in shale-gas wells ranges from 10 to 40%. Flowback is the early data (water/gas rate and pressure) gathered after fracture stimulation of the well, which might be followed by a shut-in. The flow sequence of the usual shale well is presented in Fig. 1 where there is a shut-in period between flowback and production because delays in the pipeline connection. Most operators ignore flowback data and do not combine it with production data.The paper has four main parts: (1) a review of the literature related to flow-regime identification and the diffusivity equation, (2) verification of the new method with a simulated model, (3)

The Effect of Temperature on Flowback Data Analysis in Shale Gas Reservoirs: A Simulation-Based Study

“…In this subsection, we qualitatively investigate the effect of temperature on flowback data analysis. As described in Appendix B, we applied Alkouh et al's [15] method of flowback data analysis to estimate effective fracture volume for Scenarios-1, -2, and -3 (refer to Section 4.1). Figure 17 shows the cartesian plot of rate-normalized pressure (RNP) versus material balance time (MBT) (refer to Equations (A1) and (A2) in Appendix B).…”

“…After the fracturing treatment, shale gas wells often go through a period of shut-in days to prepare production equipment at surface [13][14][15][16][17]. This shut-in period may last from several days to months [16,18,19].…”

“…Recent studies suggested that the rate and pressure data recorded during flowback can provide a very early opportunity to characterize fracture network after the fracturing treatment [31][32][33]. Several analytical models have been developed to describe the production behaviors during the flowback period [15,[34][35][36][37][38]. These studies have demonstrated that applying these models on field flowback data can estimate fracture length, fracture volume, and fracture conductivity.…”

Required Understanding for the Development of Shale Reservoirs in the Middle East in Light of Developments in North America

“…Many factors can affect the flowback after fracturing job, such as pumping schedule, fluid type and the fracturing fluid chemistry (polymer loading, cross linkers and breakers). Flowback rates and characteristics can be used to estimate some of the fracture properties (Crafton 2010;Williams-Kovacs and Clarckson 2013;Alkouh et al 2013).…”

Flowback Fracture Closure: A Key Factor for Estimating Effective Pore-Volume

“…This can lead to misleading history-match and erroneous forecast when applied to field data. Alkouh et al (2014) went a step further by an alternate semi-analytical approach based on observations from a number of simulation cases mimicking the flowback process. They compared the results of the simulation studies with actual field production data using diagnostic and specialized plots.…”