The last few years has seen an increase in the usage of gauge comparison techniques to qualify electronic pressure recorder responses and to distinguish between reservoir and non-reservoir pressure effects. The pressure difference and primary pressure difference curve are examples. Such evaluations are focused on identifying poor quality data to exclude or discount from the interpretation data set. Consequently, data validation tends to be macroscopic in nature and does not address the idiosyncrasies that are unique to electronic pressure gauges.
In this paper, pressure gauge responses are reviewed with the use of pressure and temperature plots and pressure and temperature difference plots to specifically identify limitations in the pressure representation by the gauge. Pressure and temperature calibration errors, dynamic pressure and temperature response time and electronic noise are some of the phenomena discussed and illustrated.
Understanding how these effects manifest themselves in a pressure transient data set allows the analyst to identify and qualify gauge response errors. Specific gauges types can be recommended or test designs altered to minimize gauge error.
The 1980's saw integration of electronic pressure transducers into the mainstream of pressure data acquisition. These gauges were capable of better quality pressure data made available to the analyst in a more timely manner than the existing bourdon tube, plate and scribe type of system. Electronic gauges were also able to record time dependent temperature data, adding an additional dimension to the previous maximum temperature reading. Resolution, accuracy and quality were definitely improved.
The electronic nature of these gauges provided discretisation detail of time and pressure data previously unheard of with the bourdon tube equipment This allowed for a more detailed pressure-time description of the drawdown or buildup under investigation.
Coincident with the increased use of electronic pressure recorders was the evolution of computer assisted pressure transient analysis. In retrospect these two independent developments (both significant in themselves) collectively had the most significant influence in pressure transient analysis since the development of the derivative curve.
The evolution of computer aided interpretation enabled the pressure transient analyst to incorporate multiple reservoir models and boundaries into the same pressure profile marking a shift in the fundamental methodology in which data was used in analysis. Prediction of pressure responses from a given flow rate and duration was possible for any hypothetical reservoir model and boundary influence. This prediction was used as the basis for comparison with the actual data set.
The non uniqueness of the well test analysis solution led to the matching of multiple reservoir model hypotheses, all with a reasonable fit, to the acquired data. To resolve the uniqueness issue, the analyst was required to ascertain the probability of occurrence for the model proposed and scrutinize the fit between the simulated and acquired data in more detail. Unknowingly, this change in evaluation technique from comparison of absolute pressure value to the variability between acquired and simulated pressure points initiated the scrutiny of gauge response data.
This ability to both model and record the pressure responses of a well test analysis in a very detailed manner soon identified inconsistencies between the two information sets.
