RIASSUNTO
Abstract
Donggi Structure is one of the gas field prospected in Banggai Basin, Central Sulawesi. Donggi-1 (DNG-1), which is the first well drill in this field, was drilled in August 14, 2001 and was reached TD at 2498.5 m. The drilling in this well has been successfully done without any major problem and it is ± 2 day finished ahead of drilling prediction/program.
Donggi gas field is commonly composed of Carbonate reef (limestone). The lithology of this field sequence from surface down to basement is : Celebes Molase, followed by POH formation (clay with sandstone), Mentawa member (reef of limestone), Minahaki formation (limestone) and Tomori formation (limestone).
To prove the gas prone seeing from logging evaluation after drilling, TCP gun was run by using ""Extreme Underbalance Perforation"" technique to perforate the well completed with the DST assembly. The gun system is a mechanical release that secures the guns firmly during perforation and avoiding the risk of fishing the tool after the operation. The well is flowing immediately after the perforation which will allow immediate well clean up. Therefore, the well productivity will increase and formation damage will be minimized. In EUB perforation, it is created more than 1000's psi drawdown instead of less than 100's psi in classical perforation.
The EUB application in this well has been successfully flown the gas and condensate during the test and reduced the skin effect and increase the reservoir productivity. It can be seen from the DST-4 and DST-5 analysis result that the skin factor is negative.
The isochronal and pressure build up analysis result in zone-4 is Pr = 2560 Psia, AOFP = 25.1 MMSCFD, skin factor is -1.88 and the radius of investigation is 206 m, and in zone-5 is : Pr = 2540 Psia, skin factor is - 4.42, and the radius of investigation is 1593 m.
Introduction
Donggi well # 1 (DNG-1) is the first exploration well in Donggi field. This well was drilled in the centre of the Donggi closure. Donggi field is located 50 km westward of Senoro-1 discovered well in Banggai province, Central Sulawesi.
The well is spuded in on 14 August 2001 and reaches depth at 2498.5 mss on 4 September 2001. Five interval of perforation then tested by running DST. DST-1,2,3 is dry and the last two intervals have tested as a proven gas formation.
Extreme Underbalance Perforation
Nowadays underbalance perforation has been most widely accepted / applied in oil / gas wells completion, especially in development wells. Several experiments have been performed in order to optimize perforation result. In general, there are four key aspects to perforating that play an important role in determining the productivity : perforation dimensions (length and diameter), shot density, phasing and perforation damage1.
Single shot perforating / flow experiment has provided a basic understanding of perforation damage and underbalance cleanup. Although turbulent flow does occur at very early times with low viscosity fluids, it is not considered the dominant factor affecting cleanup. Two forces are considered : The first is the pressure differential across a particle during gradient. The second is the subsequent transient, weakly compressible radial flow (laminar or turbulent)2.