Phoenix Reservoir Engineering Consulting
Operator has a number of wells producing from a multilayer, low-permeability gas reservoir. Wells are completed with 10 to 20 frac stages, over a 7,000 foot gross interval. Because of the range of depths, the operator has used a variety of different proppant types. To optimize future frac treatments in this area, the operator began a study of the effect of proppant type on fracture treatment effectiveness.
Our role in this study was to estimate effective fracture half-length, in-situ permeability, and drainage area for each frac stage by history matching production and production log data. Each well had from one to three years of daily production, and from two to five production log runs.
We also performed statistical analysis of frac half-length results to determine whether differences in frac length for different proppant types were statistically meaningful.
The standard oilfield correlations for estimating brine density, formation volume factor, and solution gas-water ratio cover only a limited range of pressures and temperatures. Most of these correlations were developed decades ago and are based on limited experimental data. There are a lot of experimental data on brine density and solubility in the general literature that had never been incorporated into correlations for the properties of interest in the petroleum industry prior to this study.
Using a comprehensive database of brine PVT data compiled from the general literature, we developed new correlations for brine density, specific volume, coefficient of isothermal compressibility, and methane solubility. The new correlations fit the available experimental data within measurement accuracy over the range of pressures from 0 to 200 MPa (0 to 29,000 psi), temperatures from 0 to 300oC (32 to 572oF), and NaCl content from 0 to 5.7 moles/kg H2O (0 to 25 weight% NaCl).
We also developed equations for calculating standard oilfield PVT properties for brines with dissolved methane, including brine density, water formation volume factor, solution gas-water ratio, and coefficient of isothermal compressibility from the new correlations.
To make the correlations useful to the client, we implemented the new correlations in a C++ class library.
Gas storage wells often experience a decline in productivity and injectivity over time. The causes of this decline are not well understood. Does the damage accumulate gradually over time? Or can the onset of damage be correlated with specific events, such as switchover from withdrawal to injection operations?
We developed a module for processing high frequency electronic flow measurement (EFM) data from gas storage wells to identify shutin periods, resulting from normal storage operations, that might be analyzed as pressure transient tests.
We also developed a module to analyze pressure transient test data quickly and easily, and to graph the results in a variety of ways to assist the operator in understanding how damage accumulates over time.
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Last updated October 01, 2009.