Surface pressure data recorders can be a valuable #welltesting tool. Validity of the technique is demonstrated by two illustrations. This example flow and buildup #welltest was conducted on a 350 m low density sweet gas well with both subsurface and surface electronic pressure recorders installed. The first pressure derivative plot is from the subsurface data, the second from the surface data. Quantitative analytical results from the two methods (kh, s’, qs, pr) were virtually identical.
Electronic surface pressure recorders have proliferated over recent years. Manufacturers offer a variety of units ranging from single channel stainless steel strain-gauges to multi-channel quartz-crystal transducers. Ambient temperature compensation algorithms have been incorporated successfully into most electronic gauges.
The only practical difference for evaluating surface data vs. subsurface data is an algorithm, such as Cullender & Smith, to convert surface measurements to sandface values.
Unfortunately, after decades of accepting surface tests for Initial Pressure Gas requirements for shallow, low deliverability wells, the Alberta Energy Regulator (#AER) issued Directive 2010-38 demanding subsurface data.