Case Studies of Active Resistivity Ranging in Near-Parallel Wells by Means of Ultradeep Azimuthal Resistivity Tool While Drilling

As the number of new wells is continuously increasing across oil fields to maintain and enhance hydrocarbon production, there is an ever-growing challenge to safely drill near existing wellbores, given their downhole location inaccuracy caused by well surveys with an ellipse of uncertainties up to hundreds of feet. An emerging well ranging solution, known as active resistivity ranging and built from the measurements of the ultradeep azimuthal resistivity (UDAR) tool, can be the key technology to accurately determine the relative distance and direction of adjacent wells to avoid the risk of potential collisions during drilling operations. According to Chen et al. (2022), the electromagnetic measurements of the UDAR tool have high sensitivity to a close, near-parallel well that exhibits a high-resistivity contrast with the surrounding formations. Therefore, a novel workflow was developed to determine in real time the distance to the target well using a simulated tool response table, while the measured angles of UDAR’s second harmonics can derive the azimuthal orientation of such a wellbore. Motivated by the successful initial results, this ranging technology was then applied to distinct scenarios with the objective of evaluating its performance when the wells are close to vertical and in a more complex case of high-angle wells. In the vertical scenario, the formation layers are nearly perpendicular to the wells, leading to the formation effect being primarily due to inhomogeneity and thus a relatively moderate impact in the UDAR measurements. Consequently, the ranging workflow can accurately determine the distance to the target cased well. However, in the case of high-angle wells, the measurements are very sensitive to both casing and formation layers. Besides the formation effect caused by resistivity anisotropy, other subsurface features can also interfere in the UDAR measurements, such as bed boundaries proximity, high structural dip, and formation discontinuities. Thus, an additional step is applied to first remove the formation-only response from the measured data, which substantially improves the ranging results in terms of relative distance accuracy. The respective case studies provide technical support to this innovative ranging to be capable of deploying at any well inclination, from vertical all the way to horizontal, under near-parallel scenarios. By effectively detecting nearby wells while drilling, such an application can largely increase the safety in the drilling operations and thus potentially enable well construction even within the zones that are nowadays not permitted due to the collision risks. Additionally, it can be applied beyond the anti-collision solution, such as well twinning and borehole interception.