Modified Offshore Drilling Operation - Serban Well (Nunukan Block)

Abstract

Abstract Serban is an offshore drilling project located in Nunukan Block, Indonesia, approximately 3 km northwest of Bunyu Island, an offshore area with very shallow water depth, from below 1 (one) meter at low tide to more than 3 (three) meters at high tide. The most suitable drilling rig unit for such conditions is a swamp barge rig, but availability is very limited due to demand. As a result, inspired by the tender- assisted drilling rig, the option to modify an onshore drilling rig for an offshore drilling operation was chosen to overcome the aforementioned lack of availability. Onshore rig equipment was laid out on an offshore drilling platform and flat top coal cargo barges. An offshore platform size 23 m × 28 m, was built to accommodate rig substructure, mast and well control equipment. The other rig equipment and supporting facilities, such as mud tanks, mud pumps, SCR system, cementing unit, pipe racking area, drilling material area, on site port camps, etc, were located on the existing three (3) flat top coal barges size 288 ft × 80 ft. Serban-3 offshore well proved to drill safely using this modified system. An initial expense for drilling platform construction was required, but the daily operation rig costs using this system was almost 70% less than when using the swamp barge rig and 50% less than when using the tender-assisted drilling rig. This is of course a significant cost saving, especially for long term drilling projects. Although some improvements are still required, this system is a promising alternative to overcome the limited availability of rigs for very shallow offshore areas. Introduction Serban-3 delineation well is located in Nunukan Block, East Kalimantan province, Indonesia (see Fig.1), an offshore area with very shallow water depth. The reference wells, Serban-1 and Serban-2, were drilled in the 1980's using a swamp barge drilling rig unit. The limited availability of swamp barge rig units in the market was the main trigger for the idea to evaluate the use of an onshore rig unit for offshore drilling operation. The existing rig type in the market, the tender-assisted drilling rig, inspired this idea. An offshore platform was built to position the substructure and mast, and supported by flat top coal barges to position other rig equipment. The first step in applying this modified system was to choose a rig candidate, in particular observing the procedures of rigging up and rigging down. Rigging up and rigging down is the most critical operational step, because it is conducted under two different conditions: the lower mast part will be stationed on the platform (static condition) while the upper mast will be positioned on a floating barge (dynamic condition). An onshore 1000 HP rig with cantilever mast - sling short rig floor elevator type, was chosen as the rig candidate and observed during the drilling operation in Senoro-4 well, Central Sulawesi. The second step was to determine the platform size based on the requirements for the existing rig candidate and on the number of wells planned. Finally, the third step was to lay out the rig equipment to determine the size and number of supporting barges required. Platform (See fig 2 and fig 3) The platform is 23 × 28 m and designed for two (2) wells with 750 ton capacity (excluding 250 ton weight of the platform) to accommodate the heaviest load during the drilling operation. The platform consists of two decks, top deck and lower deck. Top deck was functioned to position substructure, mast, and well control equipment. Lower deck was functioned as working area for wellhead and BOP (blow out prevention) handling. The platform is a fixed platform type with floating over installation method. The first step for platform installation was pile preparation. Four (4) piles of 42" supporting pipe were piled (38 m depth) before platform installation. Steps of pile installation:Survey team to locate and mark piles positionDeploy piling template and place guide beams on top of templateSurvey team to mark the exact pile position on guide beams by theodolite from two different locationsWeld pile guide on the guide beamPosition crane barge to lift 1st section of pile then insert to the pile guideSurvey to check the pile vertically from two different pointsLift pile hammer and insert to pile end. Start piling until pile end is 1 m above the platform.Dismantle diesel hammerCut deformed pile endRepeat the same procedure for the other pilesFor the last, cut pile end to cut off elevation