New Advances in Shale Gas Reservoir Analysis Using Water Flowback Data
Abstract
Shale gas reservoirs with multistage hydraulic fractures are commonly
characterized by analyzing long-term gas production data, but water flowback data is
usually not included in the analysis. However, this work shows there can be benefits to
including post-frac water flowback and long-term water production data in well analysis.
In addition, field data indicate that only 10-40% of the frac water is recovered after the
flowback. This work addresses two main question: Where is the rest of the injected frac
fluid that is not recovered and what is the mechanism that is trapping it? And how can the
water flowback data be used in estimating effective fracture volume using production data
analysis tools?
A number of simulation cases were run for single and two phase (gas/water) for
modeling flowback and long-term production periods. Various physical assumptions were
investigated for the saturations and properties that exist in the fracture/matrix system after
hydraulic fracturing. The results of these simulations were compared with analytical
solutions and data from actual wells using diagnostic and specialized plots. The results of
these comparisons led to certain conclusions and procedures describing possible reservoir
conditions after hydraulic fracturing and during production.
Past publications have suggested that the lost frac water is trapped in the natural
fracture or imbibed into the rock matrix near the fracture face. Natural fracture spacing
could be a possible explanation of the lost frac water. These concepts are tested and the
challenge of simulating a natural fracture with trapped water without imbibition is solved using a new hybrid relative permeability jail. This concept was tested for the period of
flowback, shut-in and production.
This work presents 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 will help when evaluating fracture-stimulation jobs. It also shows the benefits of
combining flowback and long-term water production data in the analysis of shale gas
wells. In some cases, the time shift on diagnostic plots changes the apparent flow regime
identification of early gas production data. This leads to different models of the
fracture/matrix system. The presented work shows the importance of collecting and
including water flowback data in long-term production data.
Citation
Alkouh, Ahmad (2014). New Advances in Shale Gas Reservoir Analysis Using Water Flowback Data. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /152548.