Gas fields in the Mahakam Delta are the most prolific in Indonesia. TOTAL E&P Indonesia operates Tunu, Tambora, Handil, Peciko, Bekapai and Sisi Nubi fields. To meet the increased production requirements while enhancing economic development, the operator is reducing drilling costs as much as possible. Slim hole well is the optimal gas well configuration being applied in Tunu and Tambora fields. The slim hole design diminishes the size and number of casing strings to produce the low pressure gas reserves economically.
The latest well design, known as the light slim hole well, reduces the number of casing strings from previously four, to become three strings: conductor, surface, and production tubingless. In light slim hole well, the 24-in. conductor casing is hammered to 130 m depth, similar to the previous design. The 9 5/8-in. surface casing is set at 1,300 m TVD. The well then is completed with 4 ½-in. production tubing, which is set at around 4,000 m TVD.
Like all gas wells, light slimhole requires adequate zonal isolation along the production section. Cement sheath failure will result in sustained casing pressure and, in the worst case, loss of the well. A long open hole section has to be cemented from bottom across the production zones to 300 m above surface casing shoe. Placing a nearly 3,000 meters column of cement slurry along production casing is therefore one of the most challenging operations done on the well.
The long cement column translates into large temperature differences between the bottom hole and the top of cement and high circulating pressure during slurry placement. In this case, the temperature difference can reach 90 degC [162 degF]. Design and selection of the cement slurry requires specific and tailored approach to ensure the cement sets uniformly along the long column, ensuring proper zonal isolation. By using advance software resources, the temperature of the cement particle is analyzed precisely during the cement placement. This paper outlines cement design approach for this long section hole, describes the overall cementing process, and shows field results of light slim hole wells in the Mahakam Delta.
For several years, TOTAL E&P Indonesia had been optimizing their well architecture by reducing the size of slim hole wells in order to cut the overall drilling cost. These efforts between 2005 and 2007 led to reducing the drilling time of these slim wells toabout 22 to 26 days.
The drilling phase has three sections which are shown in Fig.1, while the conductor pipe construction was not included in drilling time as it was hammered before rig arrival on well site.
The new light well design has two drilling phase as shown in Fig.1and is identified as light slim hole well. The design had gone through comprehensive study to meet Geology-Geosciences requirement as well as economic value. The main characteristics of the light slim hole well design are:
• Two drilling phases i.e.:
12 ¼-in. OH cased by 9 5/8-in. surface casing
8 ½-in. OH cased by 4 ½-in. production tubingless.
Well profile has J shape.
Maximum well inclination is 30 degree.