No abstract

Accurate wellbore geometric placement is fundamental to achieve the objective of maximizing hydrocarbon production and recovery. It is especially essential in real time to drill complex 3D well trajectories that penetrate multiple thin geological targets. Accurate placement is also critical to avoid catastrophic subsurface collision of nearby offset wells. This is critical in particular in this gigantic field with over 800 wells drilled by two different operators with several hundreds more wells to follow. Almost all Bottom Hole Assemblies (BHA) run in this field include a Measurement-While-Drilling (MWD) survey tool to survey the wellbore while drilling. The MWD is a magnetic survey tool that is subject to errors that limit the magnetic survey accuracy. One of the main sources of error is the variation in the local magnetic field due to the crustal anomalies in this field. The magnetic surveys can provide an accurate geometric well placement by incorporating the knowledge of the local magnetic field disturbance to the main geomagnetic field model and by compensating for the drill-string magnetic interference. The Geomagnetic Referencing Service (GRS) technique based on magnetic surveys was introduced in this field. This technique utilizes the local magnetic data that is measured over the field by acquiring a high-definition airborne gravity and magnetic survey. The accuracy of the geometric well trajectory of the first oil producer well is compared between the MWD, cased gyroscopic and GRS surveys and the advantage of the GRS is presented. The benefits of applying GRS in real-time while drilling is paramount, where it provides an accurate well position in real time when corrections to the well trajectory are still possible. It prevents the costly sidetracks if the post drilling gyroscopic survey shows the well has missed its target. In most cases, GRS is an alternative to the gyroscopic surveys where it provides magnetic survey accuracy that is comparable to the casing gyroscopic survey tools. Hence, it saves the cost and risk of running gyroscopic survey tool as well as the cost of the extra rig time required to run a gyroscopic tool after drilling.