Types and Purposes of Well Tests

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Types and Purposes of Well Tests

• Pressure transient tests
• We generate and measure pressure changes with
  time
• Deliverability tests
• Well controlled production
• (Production Analysis)
• Use of production data for goals usually achieved
  by well testing

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Goals of pressure transient tests (PTA)

• to quantify important reservoir rock, and fluid
  properties
• permeability, porosity and average reservoir
  pressure
• to locate and identify reservoir heterogeneities
• sealing faults, natural fractures, and layers
• to characterize near wellbore and wellbore
  conditions
• affected by drilling and completion operations

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Production data analysis

• Reservoir properties (permeability, skin factor,
  fracture half-length, etc).
• Reservoir pore volume (estimated using long-term
  production performance).
• Estimated ultimate recovery (EUR)movable fluid
  volumes.

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PTA Single-Well Tests

• one well in which the pressure response is
  measured following a rate change.
• pressure buildup test
• shut in after controlled production
• drawdown or flow test
• (specific drawdown tests are called reservoir
  limits tests)
• pressure falloff test
• similar to a pressure buildup test, except it is,
  conducted on an injection well
• injectivity test
• Inject into the well at measured rate and measure
  pressure as it increases with time
• analogous to pressure drawdown testing.

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PTA Multiwell Tests

• Flow rate is changed in one well
• Pressure response is measured in one or more
  other wells
• Directional variations of reservoir properties
  (orientation of natural fractures)
• Presence or lack of communication between two
  points in the reservoir
• Ratio of the porosity-compressibility products of
  the matrix and fracture systems

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Multiwell tests

• Interference tests
• The active well is produced at a measured,
  constant rate throughout the test
• (Other wells in the field must be shut in so that
  any observed pressure response can be attributed
  to the active well only.)
• Pulse tests
• The active well produces and then, is shut in,
  returned to production and shut in again
• Repeated but with production or shut-in periods
  rarely exceeding more than a few hours
• Produces a pressure response in the observation
  wells which usually can be interpreted
  unambiguously (even when other wells in the field
  continue to produce)

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Deliverability tests (DT)

• production capabilities of a well under specific
  reservoir conditions
• primarily for gas wells
• absolute openflow (AOF) potential
• inflow performance relationship (IPR) or gas
  backpressure curve

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DT Flow-After-Flow Tests

• (referred to as gas backpressure or four-point
  tests)
• producing the well at a series of different
  stabilized flow rates
• measuring the stabilized bottomhole flowing
  pressure at the sandface
• typically, with a sequence of increasing flow
  rates

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DT Single-Point Tests

• low-permeability formations
• flowing the well at a single rate until the
  bottomhole flowing pressure is stabilized
• required by many regulatory agencies
• requires prior knowledge of the well's
  deliverability behavior
• (from previous testing or from correlations with
  other wells producing in the same field under
  similar conditions)

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DT Isochronal Tests

• Specifically, the isochronal test is a series of
  single-point tests developed to estimate
  stabilized deliverability characteristics without
  actually flowing the well for the time required
  to achieve stabilized conditions
• The isochronal test is conducted by alternately
  producing the well, then shutting in the well and
  allowing it to build up to the average reservoir
  pressure prior to the beginning of the next
  production period.

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General Test Design Considerations

• If properly designed and implemented, a well test
  can provide much useful information about both
  individual wells and the reservoir
• In general, the goals of a well test are not only
  to obtain sufficient. data to meet the stated
  objectives, but also to accomplish these tasks in
  a timely and inexpensive manner

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Issues

• Development Wells vs. Exploration Wells
• Producing Wells vs. Injection Wells
• Shallow Wells vs. Deep Wells
• Stimulated Wells vs. Unstimulated Wells
• Effects of Reservoir Properties
• Low Permeability vs. High Permeability Formations
• Single Zones vs. Multiple Zones
• Safety and Environmental Considerations
• Sweet Gas vs. Sour and Corrosive Gases
• Other environmental Concerns 

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Production data analysis

• Reservoir properties (permeability, skin factor,
  fracture half-length, etc).
• Reservoir pore volume (estimated using long-term
  production performance).
• Estimated ultimate recovery (EUR)movable fluid
  volumes.