RIASSUNTO
Abstract
Japan Petroleum Exploration Co., Ltd (JAPEX) and Mitsubishi Gas Chemical Company Inc. (MGC) operate the Higashi Niigata Oil & Gas Field in Niigata, Japan. One of the wells, NS-6, a gas producer, had produced a large amount of formation sand, which filled up the surface production facility and production tubing resulting in production being shut-in at the end of 2002.
This paper will discuss a workover performed on this well, which was conducted in an effort to extend well life. Due to the depleted nature of the reservoir, a through-tubing gravel pack was chosen as the means to re-complete the well. The through-tubing gravel pack service was supplied by a local service company working in co-operation with a specialist through-tubing service provider who also provided onsite installation supervision. This method of through-tubing remediation was the first time this type of installation was used in Japan.
The local service company personnel with support from their Malaysia sand-control team worked with the customer and the specialist through-tubing service provider to design the job, and as a result of their expertise, the job was successfully performed. This case history will discuss 1) the planning and successful execution of the job, 2) its cost efficiency and safety, 3) its capability to meet majority of JAPEX's and MGC's goals, and 4) the valuable experience it provided for planning future remedial activities that may be required in this field.
Introduction
Japex and Mitsubishi Gas jointly developed the Higashi Niigata field, located in the Niigata prefecture in Japan. This field, which was discovered in early 1960, is located approximately 260 km north-northwest of Tokyo (Fig.1). The main producing horizon, the 2900m B+B1 reservoir, is approximately 2620m true vertical depth (TVD) and is a sequence of two sand packages that are 30.5m gross and 10m net thick. Field development commenced in 1965, and 8 wells were completed to drain this reservoir by 1996 (Table 1). This is a major producing field for Japex as gas production from this reservoir makes up some 50% of Higashi Niigata field production and 14% of all of Japex Nagaoka-area production.
Well NS-6 in this field was spudded in April of 1966 and was the 2nd developmental well drilled. After appraising deeper horizons, which were found to be water bearing, the well was completed in the 2900m B+B1 reservoir in Sept. 1966 as a single zone, cased and perforated completion inside 5-1/2-in casing with 2-3/8-in. 4.7# completion tubing. Fig. 2 shows the original well configuration. Gas production from NS-6 commenced in Oct. 1966 at an initial rate of around 50,000 m3/day of gas, 20 kl/day of condensate, and 0.2 kl/day of water. In 1974, a tubing leak was discovered in NS-6 and rectified, after which NS-6 was used as a swing producer for the field.
In mid-1980, gas/water ratio (GWR) in this well started to change as a result of increased water production, and by late 1990, GWR was less than 10,000 m3/kl. Sand production did not occur with the increased water production, as gas production was controlled to maintain drawdown at approximately 5% of the reservoir pressure.
In March 2002, NS-6 was shut-in to rectify a flow line problem. In the course of resuming production, the high drawdown caused a massive sand influx, which filled up the production tubing, surface line, and separator. The well remained shut-in till it was recompleted with a through-tubing gravel pack in September of 2004. Production from the 2900m B+B1 reservoir prior to the shut-in was 23,910 m3/day gas, 6.9 kl/day condensate and 3.3 kl/day water at a wellhead pressure (WHP) of 13 MPa.