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4.7 Verification of Treatment Success 197
4.7
Verification of Treatment Success

4.7.1
General

The evaluations techniques that are commonly used to assess the success of
a particular stimulation measure can be grouped into two main classes: those
techniques whose significance is restricted to the borehole wall or its immediate
vicinity, and those that are capable of gauging the extension of induced fractures
into the reservoir and obtain estimates on reservoir volume and fracture properties.
The former are the classical wire line measurements, the latter primarily the
evaluation of standard well test, flow-back test, or inter-well tests, in case tracers
were applied during the injection.

4.7.1.1 Wireline Based Evaluation
The most basic and cost-effective way of assessing stimulation success will be
achieved, besides an evaluation of caliper logs, via a combined temperature and
spinner survey. The temperature can be used to quantify the height of the induced
fracture since the formation is cooled down, where it takes injected fluid during
the course of the stimulation. Spinner surveys allow to quantitatively assess the
actual flow into the well, coming from fractured intervals. In case radioactive
tracers were admixed to the stimulation fluid or, if applicable, to the proppants,
gamma ray logging can be used to identify those zones, which predominantly took
fluid or proppants during the course of the stimulation. Wire line–based electric
or acoustic imaging surveys have turned out, analog to a prestimulation fracture
evaluation, to be a very meaningful way of evaluating the fracture inventory created
during the stimulation.

4.7.1.2 Hydraulic Well Tests
Many different types of well tests can be performed, and the choice depends wholly
on the information that is being sought. Being clear about the objectives of the test
is paramount when deciding the type of test to carry out. The general objectives are
as follows:

• Evaluate existing fracture systems
• Assess fractures induced by hydraulic stimulation
• Investigate matrix transport properties
• Determine reservoir boundaries
• Assess reservoir compartmentalization.

A Pressure drawdown survey, in which the flowing bottomhole pressure is
measured while the well is flowing, is a primary method of measuring productivity
index (PI). Establishing a stable rate over a long period can be difficult, creating
some uncertainty in the analysis.