Strategic Well Landing and Risk Mitigation in Heterogeneous Formation With Deterministic Automated Inversion and Remote Monitoring

Abstract

Abstract The K-W horizontal well was drilled to produce gas reserves from A sand and oil reserves from B sand. Accurate landing of the well in the target B sand is critical for the placement of the 6 1/8" lateral section within the reservoir. The main objective of reservoir navigation in the 8 ½" build section is to detect and map the reservoir top as early as possible to smoothly place the well 10ft TVD below the top of the B sand with an inclination of 85 degrees. Several operational risks have been identified during pre-well feasibility study, including reservoir resistivity and thickness variation, presence of intra-shale, presence of faults, and depth uncertainty from old seismic data. To mitigate the risks, extra-deep azimuthal resistivity technology was included in the bottom hole assembly. The real-time reservoir navigation was carried out remotely with frequent updates on real-time log analysis and observations provided to the client via a 24/7 virtual meeting. The service provider implemented a newly introduced centralized reservoir navigation system, which provides quicker data handling and seamless job handover. Multiple deterministic inversion workflows with constrained parameters were set-up to process the real-time extra-deep resistivity measurement, maximizing reservoir detection and mapping capability. As a result, the 8 ½" hole section of K-W well has been landed within the target formation. After the last marker, log signatures indicated good correlation with offset well data, extra-deep resistivity detected the presence of sand from a distance of approximately 34ft TVD. However, the automated inversion multi-layer mapping indicated possible reservoir pinch-out. A decision was made by the operator to further drop inclination and cut down through the entire formation. When the well crossed the expected reservoir top, extra-deep resistivity quickly decreased and log signatures indicated the presence of a thin sand before entering the basal shale formation, which was accurately mapped by inversions. In the post-well phase, deterministic uncertainty and the new statistical uncertainty analysis were run to evaluate the position of the main boundaries defined by extra-deep reading measurements. 1) deterministic approach is instantaneous and based on the linearized dependency between measurements and model parameters; 2) statistical quantification is based on the analysis of set of intermediate inversion models and includes industry-standard P50 visualization. This paper presents a case history of implementing extra-deep resistivity technology to overcome geological uncertainties during well landing in a complex environment. The novel approach of utilizing multiple deterministic inversion workflows maximized detection capability and accurate mapping of the reservoir structure, allowing early risk mitigation even before entering the target reservoir.