This paper presents a method for integrating information obtained from ultradeep azimuthal electromagnetic (EM) technology, and processed during geosteering activity, to update a 3D reservoir model. The latest developments in logging-while-drilling (LWD) technology, unimaginable until a few years ago, dramatically improve understanding reservoir structure far away from the wellbore. Ultradeep azimuthal EM technology provided a step change in remote detection capabilities by mapping resistivity contrasts up to tens of meters away from the wellbore. This innovation helps identify unexpected pay zones while drilling, improves subsurface understanding, and leads to well placement optimization in real time. In addition, the multiboundary reservoir mapping, provided by inversion of the ultradeep azimuthal EM measurements, allows for improvement in 3D reservoir model updates when addressing field development optimization. The method presented integrates field geological knowledge, wellbore-centric LWD data (logs and images), EM reservoir mapping information, and interpreted seismic data to refine a 3D reservoir model in the neighborhood of the well. The ultimate goal is to include the data acquired in horizontal wells in a live reservoir model update across the entire cycle of the well placement workflow. The process includes a feasibility study for technology and strategy selection, real-time geosteering execution and data integration to update the 3D reservoir model in near real time. Collaborative cross-disciplinary teams, composed of both operator and service company specialists, are focusing more and more of their attention on integrating this information into optimal field development strategy. Nowadays, it is possible for operators to handle multiboundary reservoir mapping data directly within dedicated geological modeling platforms. Advanced software solutions, designed to improve data accessibility, are the base for new integrated workflows for accurate 3D reservoir models using a multiscale dataset.

Structural estimation capability ahead of the bit is evolving with innovative combination while drilling of borehole and surface data in real time. A pioneering workflow has been developed to recalibrate the reservoir structure via integration of surface seismic with synthetic seismic, derived from logging-while-drilling (LWD) measurements. Modern LWD services have nowadays reached a significant depth of investigation capability, expanding the horizons of geosteering applications. The most recent ultradeep azimuthal electromagnetic (EM) technology provides real time information on a cylinder of rock around the wellbore, up to 200 feet of diameter. This technology enables a new opportunity to update the pre-drill 3D geo-model with the measured local volume of information. Synthetic seismic, derived from EM measurements, is compared with real seismic data, using non-rigid matching to quantify the depth mismatch. The estimated displacement is then applied to the real seismic and to the pre-drill 3D geo-model repository (i.e. identified reservoir horizons, faults, and geobodies) to predict the structural setting of the reservoir ahead of the bit. It is possible to iterate through these steps using an automated process while geosteering. The workflow was tested on post-drill data acquired on an Eni well, recently geosteered within an oil reservoir consisting of fluvial and deltaic deposits of Triassic age. The automated interpretation tools, integrated on the seismic interpretation software, allowed building a pre-drill model in two-week time. The model provided a base for the creation of the geosteering roadmap considering the structural features potentially present along the planned trajectory. The real time simulation lasted two days in a play back mode, focusing on the assessment and validation of the workflow. Each process iteration took few minutes to provide results, validated in parallel with LWD available data. The calibration provided a robust dip and structure estimation and additionally the confirmation of fluid contact position, as identified in the pre-drill model. The workflow unlocked extra look ahead possibilities for optimal geosteering, and proved to be able to provide robust information 150m, on average, ahead of the bit. The presence of structural discontinuities was successfully validated within 30 m measured depth from the predicted position. This novel approach is a step further toward the possibility of providing accurate reservoir updates ahead of the bit, and so forth to improve well placement operations while updating 3D geo-models in real time.

No abstract

The transgressive sandstones of the Badenian 16.TH reservoir have been on production for over 65 years. As part of a recent field re-development project the oil production has been accelerated with high-angle/horizontal wells. Targeting drainage areas to access attic oil with the accurate placement of these boreholes was deemed business critical. Previous mapping efforts did not capture the undulating structural nature of the top of the first sand layer. Since the "sweet spot" of the reservoir was assumed to have a gross thickness of 1 to 2 meters, the application of proactive geosteering with the latest Logging-While-Drilling (LWD) technology was viewed as essential. This paper describes the placement of two wells, which benefited from active geosteering based on the data transmitted and interpreted in real-time. A multilayer bed boundary detection service was the primary source of information to place the boreholes close to the target formation top and to map the presence of fluid transition zones. Deep azimuthal electromagnetic measurements enabled continuous real-time, 360 degree, mapping of the direction and distance to resistivity changes in the formation. Conventional LWD logs (gamma ray, nuclear, and resistivity measurements) provided formation evaluation and saturation estimation while drilling. The rotary steerable system completed the drill string and ensured directional control. Proactive decision-making used real-time inversions to optimize the landing and improve well placement, since critical data - distance to boundary, geometry of the remote reservoir top and fluid changes in transition zones - were available in real time. In all wells the trajectory was maintained within the zone of interest by taking the proactive, real-time decisions while drilling. The integration of multilayer inversion results with recorded borehole images enabled a comprehensive interpretation and detailed 3D structural modeling in the post-job phase. Sub-seismic faulting and local dip changes were revealed that were not predicted in the pre-drill geological model. Finally, structural information, formation evaluation results, and oil-water transition zone mapping were used to optimize completion design to delay the increase in water production. The production results confirmed the anticipated volumes, proving the advantages of the innovative LWD applications and their capability for optimized placement of such production wells. The use of the directional multilayer detection service aided structural interpretation, definition of the reservoir geometry and the position of the current fluid transition zones. This in turn led to improved accuracy in the description and understanding of the reservoir.

Nikaitchuq is an oil field on the North Slope of Alaska that has been developed with more than 60 extended-reach wells having 6,000-ft to 18,000-ft-long horizontal sections. The main reservoir interval in Nikaitchuq corresponds to a shelfal lobe composed of two main sand bodies, encased in structural depressions. The development scheme consists of waterflood line drive with horizontal producers and water injection wells located side by side. The majority of the development wells were designed with a single horizontal trajectory undulating between the two main sands bodies in counter phase with the related water injectors. To be successful, such challenging well design requires accurate geological modeling, effective geosteering capabilities, and sensible well data acquisition. The objective of the approach here described is to correctly reconstruct the reservoir geometry by integrating numerous data and information coming from such long horizontal wells. However, data and information that have originated from different sources have different levels of accuracy. A thorough data quality assessment is a mandatory step in any data integration exercise. Hence, all information available in each horizontalwell section was reviewed in detail and cross-examined. Bed boundary mapping data interpretation via different inversion processes and log and image interpretations (such as gamma ray, neutron density, resistivity, density images, deep azimuthal electromagnetic data) were compared, validated, and integrated in the 3D geological model to perform a very precise reconstruction of reservoir internal geometry. Such accuracy in modeling was not only aimed at enhancing the precision of volumes in place and resource estimates, but it was also a prerequisite for the successful drilling of the subsequent wells during the field development. The novelty of the approach consisted in the integration of density image logs, bed boundary mapping data, and resistivity modeling results to derive accurate information on the reservoir geometry at a scale useful for 3D modeling. This use of data goes beyond common practices.