Tunu is a multilayered gas field operated by Total EP Indonesie in the Kutei basin, which has produced 8Tcf since 1993. It consists of thousands of gas-bearing sandstone reservoirs, spread over up to 2000m of vertical gross thickness, developed using tubingless completions (more than 700 wells to date). Perforations are performed by light electric unit swamp barges, following a progressive bottom-up strategy.
Perforation techniques applied in the field typically involve perforating in static under-balanced pressure conditions with conventional guns and charges (underbalance value and gun design may vary). However, more than 40 reservoirs were perforated using Dynamic Underbalance technologies between 2005 and 2011.
This paper presents an in-depth comparative survey of the performance of these 2 perforation techniques, and compares the productivity obtained from these jobs to an extensive benchmark of documented conventional perforations.
Methodologically, all reservoir and perforation parameters influencing perforation performance are reviewed, to search for, and correct, any possible statistical bias in the comparison of different groups of reservoirs. Using methods classically used in epidemiological statistics, the aim is to get a statistically sound comparative survey on the productivity provided by these two techniques of perforation.
Based on two independent methods, this paper shows that the Dynamic Underbalance technique provides reservoir productivities significantly better than conventional perforations in gas reservoirs. The robust statistical confidence associated to this productivity increase will be explicitly discussed and presented in this paper.