ACCESSING MULTIPLE FAULT BLOCKS WITH A HORIZONTAL WELL USING UDAR TECHNOLOGY IMPROVES ECONOMICS AND REDUCES FOOTPRINT OF INFILL WELLS: A GOA CASE STUDY

Drilling sub-vertical infill wells in mature, compartmentalized fields is an economically challenging task because the resource volumes in individual fault blocks may not justify capital expenditures. In contrast, a single horizontal well can access multiple fault blocks, which may simultaneously facilitate favorable well economics and reduce overall environmental impact. In this paper, we will describe the complexities of well planning and execution of a horizontal well through several fault blocks in a deep-water turbiditic-sandstone reservoir. Key planning and operational challenges included narrow drilling margins, risk of losses due to faults and damaged zones through differentially depleted sands, risk of wellbore stability issues, and uncertainty of lateral fault placement and dip separation. During well planning, uncertainties of the geological model were reduced based on all available seismic data (Elastic Full Waveform Inversion (eFWI), Kirchoff, Reverse Time Migration (RTM), offset well data, and nearby cored reservoir. During operations the use of high resolution Ultra Deep Azimuthal Resistivity (UDAR) tools proved critical in the seismic depth calibration and in adding complexity to the geologic model. UDAR tools were utilized for geosteering in both landing and horizontal sections. During the well execution phase, the team utilized a real-time collaboration and decision room, staffed 24/7 by a multi-disciplinary subsurface team from operator and service provider. The collaboration room facilitated quick, optimized geosteering decisions based on UDAR data integrated with seismic, LWD logs and imaging, and formation pressures. We will discuss the novel application of UDAR technology in a structurally complex 3D environment, due to non-orthogonal faults, through the landing and lateral drilled sections. We will describe the challenges and highlights of the 2-year long pre-drill study, real-time execution, interpretation, decision making, and post-drill analysis associated with the UDAR application. Although UDAR tools have been in service for several years, the application has been mostly in 1D environments with subtle structural relief and minimal stratigraphic changes often utilizing pilot wells. Due to uncertainties and artifacts of UDAR 1D inversion images in 3D environments and drilling without a pilot well, an LWD OBM imaging tool and formation pressure tool were also incorporated to identify the faults, fault blocks, and reservoir features to assist with real-time geosteering decisions. We present examples of real-time geomapping through a structurally complex reservoir compared to 1D and 2D inversions from memory data and show the operational decision impacts. We discuss the benefits and challenges of using UDAR technology in a 3D environment, with large structural changes due to the presence of multiple non-orthogonal faults. We document artifacts seen by 1D inversion in a 3D environment and highlight areas of improvement in forward modeling and inversion needed for this technology in future applications. We illustrate how a collaboration of a multi-discipline team during well planning and the execution phase and integration of UDAR data with other formation evaluation tools led to a reduction in uncertainty from UDAR results and streamlined the geosteering decision making-process. The paper describes the best practices and lessons learned for UDAR pre-job modeling and interpretation of real-time inversion in landing and reservoir sections.