Combining Best-in-Class Surveying Measurements to Provide the Most Accurate Wellbore Position

A survey program is designed for every well drilled to meet the well objective of penetrating the target reservoir and avoiding colliding with other offset wells. The selection of the wellbore survey tools within the survey program is limited in number and accuracy by the current surveying technologies available in the industry. This article demonstrates how a higher level of accuracy can be achieved to meet challenging well objectives when the accuracy of the most accurate wellbore surveying technology individually is not sufficient. This highest level of wellbore positioning accuracy to date is achieved by combing two wellbore positions of the same wellbore trajectory. The first wellbore position is calculated using the latest technology of magnetic Measurement-While-Drilling (MWD) Definitive Dynamic Surveys (DDS). The accuracy of the MWD DDS has been enhanced by correcting potential error sources such as misalignment of the survey package from the borehole, drill-string magnetic interference and limited global geomagnetic reference and accelerometer sensor accuracy. Further, the MWD DDS inclination accuracy is improved using an independent inclination measurement from the Rotary Steerable System (RSS). Hence the first position is derived from magnetic MWD DDS after applying In-Field Referencing (IFR), Multi-Station Analysis (MSA), Bottom Hole Assembly (BHA) sag correction (SAG), and Dual-Inclination (DI) corrections. A Second wellbore position is calculated using the latest technology in Gyro-measurement-While-Drilling (GWD). The results and comparisons of multiple runs are presented. The highest accuracy of wellbore positioning had been proven in successful case studies by penetrating a very small reservoir target on an extended reach well that was unfeasible using either the most accurate enhanced MWD DDS or the latest GWD technology. The presented case study shows how the wellbore objectives of penetrating the tight target reservoir had been confirmed by Logging-While-Drilling (LWD) images and interpretation of the subsurface team. This gave the highest accuracy of the wellbore position accuracy to date while drilling assured placing the well with higher confidence to maximize reservoir production without colliding with nearby offset wells. In reservoir sections, the wellbore survey accuracy limits boreholes' lateral and true vertical depth spacing, constraining reservoir production. In the top and intermediate sections, wellbore survey accuracy limits how close the well can be drilled in the proximity of other offset wells. This directly impacts the complexity of the directional work and the cost per drilled foot. This technique unlocks the potential to improve the wellbore positioning accuracy significantly. It demonstrates the highest wellbore positioning accuracy achieved to date when compared to the latest magnetic MWD surveys after correcting all known errors compared to the GWD.