Page 236 - Intelligent Digital Oil And Gas Fields

186 Intelligent Digital Oil and Gas Fields

for optimizing well operations during the construction of an automated
production workflow.
Diagnostic actions use the best average surface production and pressure
data (from the well test data described in Section 5.4), transform the surface
pressure to down-hole data, and then estimate the well productivity index
relationship (IPR). The IPR curve is the main tool that a PE uses to evaluate
well deliverability. Next, the PE must understand liquid lift performance;
the choke setting, GOR, tubing size, depth of end of tubing, and frequency
are the preliminary data needed to build the multiphase flow equation and
finally the VLP curve. The diagnostic and troubleshooting can be classified
depending on if the well is operating under natural flow or the artificial lift
method used such as GL, ESP, or PCP.

5.6.1 Natural Flow
Input: The essential data for natural flow diagnostics are THP, choke size,
and water, oil, and gas meters. In the absence of an MPFM, VFM val-
idated periodically with well tests are required to evaluate the diagnostic
in natural flow wells.
Constraints: Minimum allowable f BHP , pressure drop, maximum velocity
to avoid early water breakthrough or sand screen out, maximum rate to
avoid conning or cresting, and maximum f BHP to avoid fracture pressure.
KPI: Typical KPIs used for diagnostic are: downtime production, differ-
ence with maximum allowable.
Output: Productivity index values (IPR), skin factor, AOF, k*h, and
estimation of reservoir pressure.
Control: Choke size.
Typical diagnostic:
• Pressure drop increasing due to fast reservoir depletion or additional
skin generated by solids production.
• Well flowing under slugging state due to flow regime changing to
critical condition.
• Oil rate drops due to early water breakthrough.

5.6.2 ESP and PCP Systems
A modern ESP system is equipped with panel control and a variable speed
drive (VSD), which is connected down-hole to the well through electrical
cables with sensors capable of reading discharge pressure (PDP),