Gyro While Drilling Technology – Solution for Directional Top Hole Drilling
A new borehole surveying technology, gyro while drilling (GWD), provided benefits for Sakhalin Energy Investment Company Ltd. (Sakhalin Energy) when used on two multiwell offshore platforms with only 2.5 to 3 m spacing between well slots. Such narrow slot spacing makes it impossible to get good MWD surveys while drilling top hole because nearby casing magnetic interference results in extremely high collision risk. Conventionally, this risk is mitigated by using wireline single-shot gyro and drop gyro, but both of these methods have drawbacks, such as extra personnel involved in wireline operations, additional rig time, and higher risk of stuck pipe. GWD was used to survey 30-in. conductors, already driven in place at the start of the campaign, and to survey 17.5- to 24-in. tophole sections. To date, 15 top holes have been successfully drilled and surveyed with this technology, with significant savings in rig time and reduced personnel on board (POB) due to the lower number of personnel needed in comparison with conventional wireline gyro surveys.
This paper intends to raise the awareness of the oil and gas industry about the new GWD borehole surveying technology, which has been proven to be reliable and which requires much less rig time and fewer POB for the job.
The overall results after 15 top holes drilled are: 12.6 rig days saved due to reduction of surveying time, reduced HSE exposure by eliminating wireline operations, improved platform POB while drilling top holes, and increased precision of the BHA steering by bringing the direction and inclination (D&I) package closer to the bit.
In this project, GWD technology has proven its ability to reduce rig time while providing close-to-the-bit and accurate D&I measurements, which is essential for drilling directional top holes in offshore environments. A full field data analysis details the significant rig time reduction and reduced POB when using GWD technology versus conventional wireline single shot and drop gyros.
GWD technology can be applied as a solution to any offshore project where using gyro surveys is inevitable because of a crowded well setting that makes the use of conventional MWD tools impossible.
Sakhalin Energy began drilling Phase 2 development wells as part of Sakhalin-2 project, offshore Sakhalin Island, Russia, in the summer of 2007. There are two out of three offshore platforms drilling simultaneously. To date, 15 top holes have been successfully drilled and surveyed with GWD technology. GWD technology service was deployed for the first time in May 2008 for drilling 24-, 22-, and 17 ½×20-in. tophole sections and surveying 30-in. conductors on both offshore platforms.
Sakhalin-2 was conceived as a project to produce oil and gas from the Piltun-Astokhskoye (PA) and Lunskoye fields in the Sea of Okhotsk, offshore Sakhalin Island, and sell it into the rapidly growing Asia-Pacific market. An operating company—Sakhalin Energy Investment Company Ltd.—was established in 1994 to meet these objectives. Today, the company’s shareholders are Gazprom (50% plus 1 share), Royal Dutch Shell (27.5% minus one share), Mitsui (12.5%), and Mitsubishi (10%). The two fields are located some 15 km offshore north-east Sakhalin in water depths of 30 to 50 m. Sakhalin Energy adopted a phased approach to the project implementation.