Data Collection Instrumentation and Interpretation for Geopressured Aquifer Well Tests
Authors: Rose Robert Eugene , Doherty Mark G. 
Published: December 2007

The Wells of Opportunity program funded by the Department of Energy, sought to determine the amount of natural gas and thermal energy entrained in geopressured, geothermal aquifers of the Texas and Louisiana Gulf Coast fairways. This determination was made by bringing representative wells onto production for periods long enough to ascertain such characteristics as temperature, gas/brine ratio, reservoir boundaries and permeabilities. During testing, amounts of produced gas and brine were carefully monitored through a computer controlled instrumentation station, which provided reliable and precise indications of the amounts of recoverable gas being produced from the reservoir.

A data collection system was designed to be integrated into the surface test equipment to provide real-time control and data compilation during the well tests. Pressure transmitters continuously monitored the wellhead tubing and annulus, separator, and disposal wellhead pressures. Differential pressure transmitters (DPTs) provided continuous readings across the flare line orifice plate and downstream brine filters. Temperature transmitters relayed wellhead brine, flare line gas, and disposal brine temperatures. Turbine meters upstream of the choke and after the separator measured the brine flow. Signals from an acoustic sand detector located after the choke and upstream of the separator were monitored to provide data on solids production.

All sensors sent outputs to an analog to digital converter that was monitored by a microcomputer, which converted the outputs to standard units. The computer scanned each channel every five seconds and appropriately averaged the measurements over an interval selected by the operator. Data was recorded on magnetic cassette tapes by date and time. In addition, a separate thermal printer displayed a list of the recorded values. The microcomputer's internal printer displayed calculated flow rates for the two-phase flow at the wellhead and for the brine after the separator.

Strip chart records provided real-time control information during the test. All pressures, both differential pressures, brine and gas temperatures, and sand detector signals were displayed, and the physical records were maintained for interpretation of well performance.

The data collection system coupled with the interpretation software permitted gas/brine ratio to be determined with accuracy of five percent for values as low as 0.02 MCF/STB. In addition, graphical representation of well performance, brine flow rates, gas production, pressure histories, etc., could be made as the test progressed.

Data system reliability was very high. Downtime was minimal even under relatively harsh environmental conditions for electronic equipment. A backup power supply functioned properly during power failures without interrupting data collection. This data collection system, while designed initially for geopressured aquifers, is adaptable to the automated collection of scientific and engineering information for the interpretation of well tests of other petroleum resources.