Offshore Dubai is a maturing oil province and to access outlying, isolated hydrocarbon reserves it is necessary to expose several unstable sections of troublesome shale during drilling operations. Historically during the drilling of these wells, wellbore time-based instability issues have been experienced in the Aruma and Laffan shales on offset wells with shorter buildup sections. It is therefore necessary to drill these sections as efficiently as possible, minimizing the time these shales are exposed.
Dubai Petroleum looked at a combination of new technologies available in the market that could help both to optimize the drilling of these sections and to meet the directional objectives. To control the shales a high-performance water-based mud (HPWBM) system with triple inhibition was proposed to Dubai Petroleum after a series of tests and field experience in the region.
To achieve the directional objectives and minimize the time to drill the section, a performance drilling system (rotary steerable tool in combination with a modular motor) and drilling dynamics sub were suggested. The section was drilled safely in a single run with all drilling objectives achieved and breaking all previous 24-hr ROP drilling records for an offshore Dubai Petroleum well. No shale instability issues were experienced, including the longest Aruma shale section ever drilled by Dubai Petroleum.
The combination of new technologies and detailed planning applied offshore Dubai for the first time allowed a step change in the Dubai Petroleum offshore drilling and enable previously inaccessible hydrocarbon reserves to be reached and produced.
Introduction
Geological and geophysical subsurface studies had indicated the potential of isolated, unrecovered hydrocarbon reserves offshore Dubai which could not be accessed by standard sidetrack operation. In the past decade mostly sidetracks of exisiting wells had been drilled to enhance production, prior to the drilling of a horizontal section within the reservoir. Typically a build section was drilled and the well landed in the top of the main carbonate reservoir of the Ilam and Mishrif, with the build section then cased off and a horizontal section then drilled, completed, stimulated and produced.
To develop the above-mentioned isolated reserves a cost comparison between a "new drill" versus a "semi-extended reach well" was carried out. This comparison concluded that a semi-extended reach well would be more viable and less costly than a new drill.
To meet the given target requirements it was necessary to drill a build section in excess of 6,800-ft (2,073-m) with approximately 4,000 ft (1,219 m) of Aruma shale and 340 ft (104 m) of Laffan shales at 76-degree inclination. Historically during the drilling offset wells, they exhibited time-dependent wellbore instability issues.
Dubai Petroleum looked at new technologies available in the market that could be used to help both optimize the drilling of these sections and also to meet the directional objectives. For controlling the shales a high-performance water-based mud (HPWBM) system with triple inhibition was introduced to Dubai Petroleum. To achieve the directional objectives and minimize the time to drill the section, a performance drilling system (rotary steerable tool in combination with a modular motor) and drilling dynamics sub were utilised.
