Borehole survey is a very crucial element in drilling a well. The data will be utilized during all phases of drilling campaign – planning, execution, and post drilling. During planning, borehole survey data are critical to avoid well collision with nearby well. It is done through correct survey of offset data and correct toolcode assigned to the survey program together with database QAQC. While actual drilling itself, the survey will be closely monitored to ensure that the well is clear from any collision risk. The survey will guide the directional driller to steer to the geological objectives and hit the geological target with high confidence. Finally, once drilling has been completed, the survey data will be tied in to geological and reservoir models and to be used for planning of future campaign. Since the last forty years, measurement while drilling (MWD) surveys have been the backbone for the borehole surveying. MWD surveys are in fact a measurement/surveying while static condition not during online drilling itself. Industry has experienced multiple evolution of MWD surveys, but none of the evolutions lead to the survey in dynamic conditions. Realizing the true potentials of getting the survey data in dynamic condition, it will help the rigsite operation to minimize the risk associated with longer stationary time. With this definitive dynamic survey while drilling can accurately be taken while drilling, moving, rotating and sliding, it had proven to eliminate the survey-related rig time per survey and reduced associated drilling risks, therefore improves the overall drilling efficiency. The service incorporates the new telemetry innovations that enables up to 20bps and the advance drilling dynamics design includes three-axis shock and vibration and turbine power. Additionally, geological accuracy is refined using gamma ray and electromagnetic resistivity in combination with continuous six-axis direction and inclination sensors. The deployment of this dynamic-survey-while drilling service had enable the operator to acquire precise BHA location data at a higher frequency during drilling for improved decision making, eleiminating up to 15 min of survey-related rig time per survey. This also eliminated the need for additional pump cycles along with their associated washouts, stuck pipe risks and other directional drilling difficulties. The ultimate yield is definitive dynamic surveys, delivering real-time borehole conditions that reduce time to TD. This paper also covers the advance procedure of taking definitive non-static survey. The challenge is to ensure the non-static data to be sent continuously and meet survey acceptance criteria. Hence, the continuous survey data can be qualified as definitive survey and assigned a proper toolcode. To validate this continuous survey measurements, the author analyses the survey comparison with conventional static survey and gyroscopic survey results in the field test runs. The author will then present the conclusions, further work recommendations in which this wellbore surveying advancement can transform the well construction process with great impact in drilling efficiency, as well as minimizing the stuck pipe risk and wellbore uncertainty.

In 2012, a redevelopment infill drilling campaign took place in a brown field, offshore Malaysia. Accurate wellbore positioning was critical to place a well within a path that navigates 2200 ft through an antithetic faults panel, separated approximately 900 ft, and with a 120 ft general throw; and to intersect the five target reservoirs of the well. The complex well path also faced the challenges of infill drilling in a brown field, such as collision avoidance in a crowded field, the location of the target reservoirs relative to the available drilling slots; as well as trajectory restrictions due to completions design. This paper presents the well design solutions that include a rigorous anti-collision analysis and a comprehensive survey programme. The survey programme consists of gyro while drilling (GWD) on the upper section of the well until the path is clear of magnetic interference from neighboring wells and the application of in-field referencing (IFR) correction for conventional measurement while drilling (MWD) magnetic survey based on accelerometers and magnetometers. IFR improves survey accuracy with a multi-station analysis that corrects the survey error with the localised crustal effects in the magnetic field of the earth. It was used for well positioning in between faults and for target intersection. It enabled drilling the well with higher confidence while intersecting the target reservoirs. A reduction of 60% on survey uncertainty was observed. The more accurate wellbore survey also optimises collision analysis for future well plans and it gives more reliable control points to update the subsurface static model. The benefits were obtained without compromising the drilling performance given that no extra operational time is required for the survey correction. Introduction Context The well is located in a brown field, offshore Malaysia. Three infill drilling campaigns have been executed since a decade ago to increase oil recovery. To maximise the use of existing assets and to optimise cost, infill drilling has been performed from existing drilling facilities by either accommodating new drilling slots or side-tracking idle wells. The well was planned to target several reservoirs located in crestal position in the southern block of a rollover anticline formed by growth faulting. In the study area, faults show a general east-west trending direction. The reservoirs are entirely related to sealing against faults while within reservoirs the seals are marine flooding surfaces. Well design considerations The well design process consisted of identifying the available surface location -a well with high water cut, idle since 2007- and selecting the subsurface targets. Once drilling targets were identified and preliminary well trajectories were built, an integrated team approach was used to optimise the well paths, usually requiring a compromise between the desired and the practical approach.

Over the last decade, new technologies and economic strategies have enabled operators to give new life to mature fields and old platforms. Production and economic optimization are main goals of reentry campaigns. With time, the industry has seen growing opportunities for reentry wells as mature fields and platforms are becoming older and less productive. Fully utilizing reentry technological capabilities and achieving successful operations require effective well planning and execution. Cutting and pulling of old completions and casings, wellbore cleanouts, plug and abandonment operations, section milling, mud systems, well integrity, cased-hole and open hole sidetracks, whip stocks, cutting/swarf handling, surveying tools, well collisions, and existing rig capabilities on platforms are the major challenges to the growth of reentry business. However, development of rotary steerable systems, logging while drilling, modern surveying tools, and under-reaming technologies have given impetus to the reentry well drilling market. From the concept phase of plug and abandonment to well delivery and production, seamless planning and communication is required among all the stakeholders. Modern surveying tools such as continuous north-seeking gyros and gyro while drilling have revolutionized the surveying industry in high magnetic interference environments, giving ease to planning sidetracks and accurate wellbore positioning in high well-density environments. Drilling close to the motherbores is becoming a common and attractive way of exploiting the reserves as no detailed logging and characterization is required. This has resulted in complexities of directional drilling and well collision risks. Risk of well collisions with producing wells is one of the biggest challenge in reentry wells.

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