Isochronal, modified isochronal, and LIT testing are used routinely as a basisto forecast deliverability of gas reservoirs. This paper shows an applicationof this technique to the naturally fractured Palm Valley gas field in central Australia. Results are corroborated with the use of a dual-porosity numericalsimulator.
The initial isochronal tests of 4 wells are presented together with thedeliverability equations. This is followed by a comparison with 40 months ofproduction history. The data show that values of "e" in the Rawlins and Schellhardt equation have been declining continuously for all 4 wellsthroughout the 40 months of production history.
The conclusion is reached that conventional isochronal test analysis is notreliable to forecast deliverability References and illustrations at the end ofpaper of gas wells in naturally fractured reservoirs. Use of this approach caneasily lead to optimistic forecasts.
The Palm valley Gas Field is situated in the central-northern Amadeus Basin, Northern Territory, Australia (Fig.1) approximately 120 km. southwest of Alice Springs. The structure is an arcuate anticline mapped from surface expressionand seismic data (Fig.2). The western and eastern plunges are poorly defined, however, the anticline axis can be traced for over 40 km.
Production from the field commenced in August 1983 with the completion of an 8"pipeline to Alice springs. Natural gas has been used as a replacement forliquid fuels in electricity generation. Gas production from the field hasincreased steadily currently averaging 141,000 standard m3/d (5MMSCFD) to Alice Springs.
In September 1986 a fourteen inch trunk pipeline was completed connecting thefield to the city of Darwin, 1300 km to the norch, and to several major townsen-route. Production for this pipeline has reached 622,000 standardm3/d (19 MMSCFD) and again has been used as a liquid fuelreplacement in electric power generation.
Development of the field has followed the definition of reserves and during thepast 24 years, estimation of the gas reserves has been the subject of manystudies. The most significant being by Strobel et al.' in 1976; areservoir simulation study by van poollen and Associates in 1985 and a recentreserves study by servipetrol Ltd. in 1990. These studies quantified reservesof 1.08 × 109 standard m3 (3B.2 × 109 SCF),9.2 × 109, m3 (325 × 109 SCF), and 19.25 x109 m3 (680 × 109 SCF), respectively andreflect the increasing contribution of production history and technologicaladvances. To July 1991, 1.20 × 109 standard m3 (42.3 x109 SCF) has been produced from the field over its 24 year life andthis now provides valuable history for reserve studies.
A recent paper by these authors2 presented drawdown and buildupanalysis of the Palm Valley field using type curves for dual-porosity systems,3 pressure derivatives, specialized semilogarithmic crossplots, anda numerical simulator for dual-porosity systems. The results of the analysiswere highly satisfactory. Another publication by these authors presented thenumerical simulation of Palm valley_ 4
