South-Tambeyskoye gas-condensate field, located in the north-east of the Yamal Peninsula was discovered in 1974. Project, which started in late 2013, is currently operated by JSC "YAMAL LNG". The field consists of 5 shallow gas reservoirs and 37 deep gas-condensate reservoirs with the depth variations from 900 m to 2850 m TVD. The proved and probable reserves of the South-Tambeyskoye field are estimated at 926 billion cubic meters of natural gas. The field development plan stipulates drilling of 208 directional production wells with horizontal completion and length of horizontal sections exceeding 700 meters from 19 well pads until 2021. Liquefied Natural Gas (LNG) plant will start production in 2017 and reach its full capacity in 3 stages. LNG will be exported through the seaport facility. Specially designed for the project, 15 LNG icebreaker tanker, each of which has a capacity of 170,000 cubic meters, will ship the LNG to international markets.[1] Located far above the Arctic Circle, the region is ice-bound for seven to nine months during the year and isolated from the oil and gas infrastructure. Due to stringent deadlines, extreme weather conditions and lack of existing infrastructure only reliable companies with the leading technologies and expertise were involved in the drilling campaign. Detailed planning, well-coordinated interaction among the participants, and new technologies guaranteed a successful start of the project and provided accident-free implementation of drilling plans. By a joint effort of field operator, drilling contractor and oilfield service company a new Drilling System was designed, which included a full range of engineering solutions and technologies for efficient and failure-free construction process. The system allowed implementing best practices of directional drilling, bits, drilling fluids, as well as effective utilization of geomechanics and geosteering. Rotary steerable systems (RSS), oil-based mud (OBM) and advanced logging while drilling (LWD) technologies combined with continuous drilling optimization process allowed to significantly reduce well construction time. LWD tools eliminated the number of wireline runs providing equal log quality to G&G department. Application of geosteering in conjunction with formation boundaries detecting tool provided vital information while drilling and ensured maximum contact of the wellbore with the reservoir. Real-time geomechanics and trajectory optimization process joined with the best drilling and tripping practices significantly reduced risks associated with drilling process. Special attention was paid to the well construction time: apart from the aiming for the fastest rate of penetration (ROP), flat time was also reduced by optimizing full operational process: the number and frequency of wiper trips was revised, unproductive time due to the failures was minimized. Currently, drilling of each section is performed in one run. Further optimization plans include application of invert emulsion mud with the ability to change the type of emulsion for completion purposes. This approach will ensure better drill-in quality and increase productivity of the wells. In order to reduce well position uncertainties associated with the azimuth errors while drilling at high latitudes, geomagnetic referencing service will be provided [2]. The service includes development of precise 3-D magnetic model for the field and constant monitoring of the earth’s magnetic field variations by the magnetic observatory. Advanced wellbore surveying will minimize geological uncertainties and well-to-well collision risks.

Drilling in Russia's Far East has always been associated with industry-defining ultra-extended-reach drilling. With the emergence of more powerful drilling rigs and advances in measurement- and logging-while-drilling (MWD and LWD) tools, these wellbores can be designed to reach farther. Therefore, accurately penetrating and exploiting distant reservoirs have resulted in critical dependence on high-accuracy surveying techniques. Successful target penetration and meeting anticollision requirements without the need for shutting production in nearby wells are key proponents for a geomagnetic referencing service (GRS). Geomagnetic referencing is the technique to minimize the lateral position uncertainties when using MWD. This is particularly important for wellbores that extend the boundary of the drilling envelope with stepouts greater than 13 km. The wellbore azimuth accuracy is highly dependent on the quality of the magnetic data used to produce the geomagnetic reference model. This model characterizes the absolute magnitude and vector direction of the natural magnetic field for every point along the wellbore. Representation of the local crustal magnetic contribution is key to the process since it constitutes a significant error in the lateral wellbore position. Since 2011, a new, highly accurate geomagnetic referencing methodology has been used in Russia's Far East. Global contributions are accounted for by a high-definition geomagnetic model (HDGM). In addition, the local crustal magnetic anomaly is represented by 3D ellipsoidal harmonic functions tracking the shape and depth of the Earth, thereby providing seamless integration with HDGM and avoiding distortions faced by conventional plane-Earth approximations. A comparison with the previous industry standard shows improvements of 0.5° in azimuth determination. This high-degree geomagnetic technique will serve well for a number of upcoming developments in Russia's Far East, continuing to push the drilling envelope and providing essential, accurate wellbore positioning, while offering significant time and cost savings.

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