The process of drilling a successful extended-reach well often involves addressing many geological challenges. Some of these challenges are due to uncertainty in the structure model along the horizontal section as well as the lateral changes in the reservoir properties, from heel to toe of the well. This uncertainty may affect the borehole tortuosity as well as reduce the reservoir contact. It is clearly observed that approaching the less-porous boundaries causes undesired borehole azimuth swings. Often, the need to drill complex or challenging ERD wells efficiently,contrasts with geological aspects of data requirement and transmittal, reactive geosteering response times and accuracy of well placement. This may often require non-unique approaches in Middle East carbonate reservoirs when considering stacked sequences of reservoirs with different properties / net pay thickness; different top- and bottom-seal lithological units, and zones with limited markers requiring stringent well placement. The objective of this paper is to illustrate that by assessing the details of reservoir geology and key operational markers relevant for best practices, drilling approaches can be customized for each reservoir or scenario: for example, defining drilling ROP windows on a per-target layer basis. A well-placement methodology and workflow were developed and integrated with the calculated mechanical specific energy (MSE). The MSE is calculated using both surface drilling parameters and downhole drilling dynamics data from the drilling downhole optimization collar. The methodology also includes an optimized bottom hole assembly (BHA) design with azimuthal density image and a point-the-bit rotary steerable system (RSS) to geosteer the well within a thin target layer. This occurs while maintaining the planned target trajectory with a minimum borehole tortuosity using real-time drilling optimization. The understanding of the target layers with the analysis of the historic offset horizontal wells resulted in the delivery of engineered solutions to mitigate the uncertainty in the geological challenges.The MSE along with the downhole drilling dynamics data from the drilling downhole optimization collar has shown good correlation with real-time logging-while-drilling data and can help in making quick real-time geosteering decisions.It was reliable in determining the change in the stratigraphic movement of the well trajectory along the horizontal section. In addition, using the drilling downhole optimization collar effectively can assist in anticipating any approach to different porosity boundaries that help to reduce or eliminate the undesired borehole azimuth swings. As a result, the downhole vibrations are also mitigated and constantly remain within the allowed limits using downhole measurements for torque at bit and weight on bit.This study has shown outstanding and promising results for the potential value added when using the MSE along with the downhole drilling dynamics data in a proactive geosteering technique for a geosteering/geostopping portfolio. The uniqueness of the integration of the MSE and real-time geosteering geological model lies in its ability to address the geological challenges, enhance the drilling process, and maximize the asset value in the reservoir field of this study.Further study is needed to include different reservoirs to validate the concept.

ADNOC's limestone reservoirs suffer from the phenomena of injection water traveling preferentially at the top of the reservoir placing injection water above oil held there by capillary forces. Horizontal wells placed below areas of water override, cause the water above to slump unpredictably, increasing water cut and eventually killing the horizontal. Ultra Deep Directional Electromagnetic (EM) Logging While Drilling (LWD) tools provide the measurements to identify and map these water zones, improving reservoir management and design optimal well placement. 1D & 2D EM inversion modeling was conducted on two of ADNOC's largest oil producing reservoirs to evaluate the ability of an Ultra Deep Directional EM LWD Resistivity tool to identify water slumping in the presence of formation bed resistivity contrasts and predict depths of reliable detection (DOD) under various well trajectory scenarios. The inversion was run using depth of inversions up to 150 ft, the maximum expected vertical distance of tool to injection water. Modeling provided an optimized tool configuration (frequency, transmitter-receiver spacing's) to meet objectives. The inversion results further provided guidance for Geosteering, Geomapping and Geostopping decisions. The inversion results in these reservoirs indicated that the Ultra Deep resistivity tool has a DOD of 50-150 ft to pick reservoir tops and water slumping or non-uniform waterfront boundaries. The real-time inversion will optimize landing and drilling long horizontal section to increase net pay for production and even through sub-seismic faults, measuring changes in the reservoir fluid distribution, reduce drilling risk and exceed well production life. This information will aid in updating static model with water flood areas, reservoir tops, faults and structure, designing better infill well spacing and trajectories within bypass oil regions, designing proactive and not reactive smart well completions to delay or reduce water production and ultimately extended plateau and improve ultimate recovery factor. Furthermore, it will aid resistivity mapping of underlying or overlying reservoirs for future development plans. The encouraging results of this study confirmed to move forward with a field trial in these challenging reservoirs for better reservoir and fluid characterization and its management.

The value of the continuing integration of logging-while-drilling (LWD) and directional drilling processes has been more prominent in the current economic environment in terms of optimizing field development costs by means of precise well placement, as well as improved reservoir characterization and drilling performance in real time. A successful horizontal drain was drilled in an undeveloped Reservoir A for the first time in an offshore carbonate sequence, using advanced LWD acoustic and high-resolution microresistivity sensors. The well plan required maximizing the exposure of the most porous body in a thinner sublayer. This sublayer lies directly over a large, developed carbonate reservoir as part of the Upper Jurassic Carbonate sequence located offshore Abu Dhabi. The flow test results during the drillstem test (DST) operation for the first appraisal well in the target reservoir produced at a rate that was greater than expected. Production log data were acquired and integrated with the LWD microresistivity image interpretation. In addition, in this environment, the inferred Rt and Rxo measurements from the LWD azimuthal focused resistivity tool were shown to be more reliable than conventional electromagnetic wave resistivity measurements, which are prone to exhibiting significant polarization, anisotropy, and bed boundary effects. Lessons learned from the first appraisal well in Reservoir A for reservoir characterization and flow unit identification were used and implemented in the planning and successful delivery of the future horizontal wells. Unlike the other reservoir subunits that are deposited within the same sequence, the field development strategy for these undeveloped reservoirs has been under review based on the recent data. The field development strategy used enhancements in well placement, formation evaluation, and production technologies, including extended reach horizontal wells, with maximized reservoir exposure in the sweetest zones, to compensate for the poor petrophysical character and low oil mobility. This case study presents insights into the advanced geosteering and multidisciplinary reservoir characterization processes along these successful horizontal drains drilled in undeveloped Reservoir A and the future horizontal wells. It also demonstrates the integration between the geological and petrophysical interpretation and the use of acoustic measurements and high-resolution microresistivity imaging. This combination has enhanced the understanding of Reservoir A in terms of the unexpected production performance and helped optimize efforts for the future field development plan.

This paper present the successful deployment of the ultra-deep EM tool in a mature carbonate reservoirs to reduce the uncertainty associated with fluid movement for horizontal/ MRC well-placement optimization and enable precise geosteering to maintain distance from fluid boundaries and mapping of nearby reservoirs for future reservoir development. In addition, the EM tool can facilitate to optimise lower completion design liner (blank pipe length, PPL, ICD and swellable packer depth). The high heterogeneity of reservoir qualities increase uncertainty in fluid distribution and make drilling long horizontal, oil producer wells in offshore mature giant carbonate fields very challenging. The usual plan is to drill a pilot hole crossing the reservoir sections, evaluate log saturation, and then re-optimize horizontal sections accordingly. To study the possibility of eliminating pilot holes, an ultra-deep electromagnetic (EM) tool was deployed. The first objective was to detect reservoir boundaries and predict resistivity of the target before penetrating it (Geostopping). The second objective was to optimize the horizontal drain (Geosteering), and map resistivity of adjacent reservoirs for well completion and future well optimisation (Geomapping). Pre-well inversion modeling was conducted to optimize the spacing and firing frequency selection in order to facilitate early real-time geosteering and geostopping decisions. The plan was to run the ultra-deep resistivity tool in conjunction with shallow propagation resistivity and density-neutron porosity while drilling the 8½ in landing section. The objective was to be able to detect the lithology boundary early and predict the resistivity of the reservoir before penetrating, facilitating geostopping decisions. This would allow optimization of the horizontal section to geosteer the well in an oil-saturated layer 4-6 feet from top boundary while geomapping the surrounding reservoirs’ resistivity. The EM tool delivered accurate mapping of thin reservoir layers while drilling the 8½ in section, as well as enhanced mapping of low resistivity zones up to 85 feet true vertical thickness in a challenging low-resistivity environment. Comparison to recorded open-hole logs for validation showed good results, enabling identification of the optimal geostopping point in the 8½ in. section. The EM tool is able to save up to five rig days in the future by eliminating pilot holes. The 6 inch horizontal section was successfully geosteered and placed 4-6 feet from top boundary. The EM tool was able to map reservoir resistivity 30 feet TVD below the wellbore and the completion design was designed accordingly. Additionally, the EM inversion for the nearby reservoirs helped to modify the plans for nearby future wells.

An Ultra-Deep Directional Electromagnetic LWD Resistivity (UDDE) tool was deployed in a mature Lower Cretaceous carbonate reservoir to map injection water movement. These thick carbonate reservoirs experience injection water preferentially travelling laterally at the top of the reservoir. The water held above oil by negative capillary forces slumps quickly, leading to increasing water cut, eventually killing the natural lift horizontal producing well. Real time 3D and 1D inversions provided important accurate mapping of the non-uniform water fronts and reservoir boundaries, providing insights into reservoir architecture and water movement. The candidate well is located in an area of significant uncertainty regarding fluid distribution and structural elements like sub-seismic faults etc. Pre-well 1D inversion results indicated that the water slumping front away from wellbore can be mapped within a vertical radius of 60-100 ft TVD. However, 1D inversion is not accurate where steeply dipping or discontinuous formations exist due to the presence of faults and is expected to impact well placement, mapping water fronts / formation boundaries and long-term oil recovery. Therefore in the real time, full 3D and 1D inversions of the Ultra-Deep EM data were run to provide high quality reservoir imaging in this complex geometrical setting and deliver improved reservoir fluid distribution and structure mapping. The pre-well inversion modeling optimized the frequency and transmitter-receiver spacing of the UDDE tool. The bottom hole assembly (BHA) configuration also included conventional LWD tools such as Neutron-Density, propagation Resistivity and Gamma Ray. Multiple 3D inversion datasets were processed in real-time using different depths of inversion ranging from 50 ft up to 120 ft depth. The 3D inversion results during the real-time drilling operation detected the non-uniform waterfront boundaries and water slumping up to 80 ft TVD above the wellbore using a slimhole (4¾″) tool. An interpreted sub-seismic down-thrown fault was mapped which controlled the non-uniform slumping fluid distribution, causing the water front to approach closest to the wellbore in this location. This suggests that the fault zone is open and provides a degree of increased permeability around the plane of the fault. The real-time 3D inversion, 1D shallow and 1D deep inversion results showed comparable structural imaging despite being inverted independently of each other. These results permitted updates to the static / dynamic reservoir models and an optimization of the completion design, to delay the water influx and thereby sustain oil production for a longer period of time. Field wide implementation of the UDDE tool and its advanced technology with improved 1D and 3D inversion results will enhance the quality of realtime geosteering, mapping and updating of reservoir models which have challenging water slumping fronts and structural variations. This will enable improvment in well locations, their spacing and finally allowing the proactive design of smart completions for enhanced oil production and improved recovery factors.