Page 241 - Introduction to Petroleum Engineering

228 TRANSIENT WELL TESTING
the vicinity of the well. Flow capacity and formation damage measurements indicate
the quality of a completion. Some pressure transient tests provide fluid samples that
are suitable for measuring fluid properties.
The integration of information from PTT with data from other sources can be used
to help characterize the reservoir. For example, flow rate changes at one well can lead
to pressure changes that can be observed at another well if the reservoir does not have
an impermeable barrier between the two wells. This gives an idea about the conti-
nuity of the flow path between the two wells. Another example of integrating data is
the combination of PTT flow capacity with formation thickness. In this case, an
estimate of formation permeability in the region of the well investigated by the
pressure transient test is estimated by dividing flow capacity from the pressure
transient test by the net thickness of the formation from a well log.

12.1.1 Flow Regimes

Figure 12.1 displays different flow regimes at the well resulting from a rate change.
The circle on the well pressure axis is initial pressure p . The early time response is
i
dominated by wellbore and near‐wellbore effects. Wellbore effects are associated
with the volume of the wellbore, while near‐wellbore effects are associated with the
quality of the borehole wall. The wellbore volume is known as wellbore storage, and
the quality of the borehole wall is quantified by a variable known as skin.
The transition region is the period of time between wellbore‐dominated flow and
the infinite‐acting region. The infinite‐acting region is the period of time when the
pressure response behaves as if it is not affected by either the wellbore (inner
boundary) or outer boundary. A departure from the trend set during the infinite‐ acting
region indicates that the pressure transient is being affected by the reservoir boundary.

12.1.2 Types of Pressure Transient Tests

Well flow rate can be either increased or decreased in both production wells and
injection wells. Consequently, the four possible types of pressure transient tests

Early time response

Well pressure Transition region Infinite-acting region Boundary effects

Time
FIGURE 12.1 Flow regimes.