KAPPA DDA Book v5.12

110 / 743

Dynamic Data Analysis – v5.12.01 - © KAPPA 1988-2017 Chapte p110/743
3.H Quality Assurance and Quality Control
3.H.1 Introduction
During the early 1980’s the oil industry, especially in Northern Europe, went through a totally
justifiable drive to increase the quality and efficiency of work carried out in most of the
commonly related services involved in the production of oil and gas.
Quality control manuals and procedures had to be presented to prove that every effort was
fulfilled by the involved parties to assure that work, equipment and preparation procedures
were documented and followed. These documents had to be approved by a ‘controlling body’
before the company was qualified as an approved contractor. The QA/QC manuals described
and identified the procedures to follow, backed up by checklists, tests, inspections and
certification by approved inspectorates.
This drive was mainly directed towards offshore construction and sub-sea technology to
optimize equipment performance and the quality of engineering works, including the safety of
oil and gas installations and oil field operations.
Service companies were no exception, but QA/QC was limited to planned and regular
calibration of mechanical and electronic measuring devices. As service companies claim no
responsibility for any loss or damage due to faulty measurements and interpretations, there
was no procedure to validate measured data before analysis.
However methods were developed in the early 1990’s. They allow quality control of downhole
pressure and temperature measurements, and they ensure that the data is valid and usable by
the engineer for further analysis. Such validation increases the confidence in the results of the
analysis and eliminates, to a large degree, errors that could lead to major mistakes in the
decision process of optimum development and production of petroleum reserves.
3.H.2 Background
The introduction of the Bourdet derivative revolutionized the approach to PTA. It gave us
deeper sensitivity and multiplied our analysis ability. It also complicated the diagnostics by
revealing phenomena unseen and not understood until this time.
This sensitivity had a price: as both reservoir response and operational problems affect the
same pressure response, too often the Bourdet derivative response to fluid movements in the
wellbore, phase segregation and temperature anomalies would wrongly be associated to a
reservoir feature and interpreted as such.
It was necessary to enable the engineer to differentiate between the representative data of the
reservoir response and the part caused as a result of a signal from other phenomena.
The techniques described in this chapter were developed as a result of severe interpretation
problems encountered in many fields and led to the introduction of the concept of Differential
Pressure Analysis.
It will be shown how the use of pressure differentials measured between pressure gauges
placed at different levels in the test string can help the interpreter to identify the pressure data
that is valid for interpretation, and enable him to save time by eliminating useless data caused
by anomalies and wellbore phenomena. The method brings ‘Quality Control’ one step further,
and should be an integral part in the overall QA/QC programs of any company dealing with
downhole measurements of pressure and temperature.