Pressure Transient Analysis – PTA

The interpreted pressure transient test is a primary source of dynamic reservoir data. Tests on oil and gas wells are performed at various stages of drilling, completion, and production. The test objectives at any stage range from simple measurement of reservoir pressure to complex characterization of reservoir features. Most pressure transient tests can be classified as either single-well productivity tests or descriptive reservoir tests.

Applications of pressure transient tests

Productivity tests are conducted to:

  • Determine well deliverability
  • Characterize formation damage and other sources of skin effect
  • Identify produced fluids and determine their respective volume ratios
  • Measure reservoir pressure and temperature
  • Obtain representative fluid samples suitable for PVT analysis
  • Evaluate completion efficiency
  • Evaluate workover or stimulation treatments.

Descriptive reservoir tests are conducted to:

  • Assess reservoir extent and geometry
  • Determine hydraulic communication between wells
  • Characterize reservoir heterogeneities
  • Evaluate reservoir parameters.

Pressure Transient Analysis, or PTA, is, in most cases, about analyzing high frequency, high resolution shut-in data. The data are captured during dedicated well test operations such as DSTs or production tests or during routine operational shut-ins by Permanent Downhole Gauges (PDG). The pressure response from these shut-ins can be used to provide information about the reservoir within the radius of investigation for radial flow or the area of investigation for more complex geometries. The diagnostic plot of choice is the loglog plot where the pressure and the Bourdet derivative allow the identification of reservoir geometry and properties, these are then matched with models. Specific operations require specific processing, such as multirate gas tests, interference tests, multilayer tests, etc. The development of deconvolution allows us to combine several of these shut-ins in time to provide information much deeper into the reservoir than would normally be feasible by a shut-in alone.

Saphir NL is the industry standard PTA software, used by nearly all major IOC’s, NOC’s, Independents and Service Companies. Its simple user interface and workflow allows for fast training and self-learning for occasional users. For the advanced user, it offers a unique combination of analysis tools, analytical models and numerical models which can connect to other dynamic data application such as Topaze NL for Rate Transient Analysis and Rubis for fullfield history matching.