The Middle Cretaceous Burgan reservoir in Minagish Field exhibits variable depositional clastic settings ranging from "Fluvial", "Fluvio-tidaT to "tidal wave sands". The sand bodies of Upper Burgan reservoir are highly heterogeneous in terms of the stratigraphic architecture implying extensive lateral facies variations, stacked sand bodies and varying petrophysical properties. Modeling the target sand channels and optimizing subsurface well trajectory with maximum reservoir contact requires "high resolution" geological and seismic data integration in order to minimize uncertainties related to correlations of timeline surfaces, channels geometries and sub-seismic fault network. Since traditional logs could not capture the textural differences characterizing the reservoir zones, Real-time formation evaluation and geosteering challenges addressed to ensure the successful drilling and completion of level-4 "Multi-lateral" producers. A combination of the latest advanced geo-steering technology used in this well including Rotary Steerable, Distance to Boundary and Sourceless petrophysical evaluation while drilling. The uncertainties in the geostatistical models were further reduced while drilling the first lateral section (LAT-0) by deploying extra deep azimuthal resistivity measurements. It has a higher precision and accuracy to consistently mapping the rise in OWC due to production operations with depth of detection up to 100 feet TVD above and below the well path and maintaining a standoff from the top of onset transgression undulating surface with poor sand facies. The resultant mapping window provided accurate guides to update the geo-models. The formation evaluation along with borehole imaging and geo-correlation assisted in identifying a fault having a great impact on well positioning of the upper lateral due to a high amount of throw fault with significant formation dip changes. This is in turn eliminating risks of geosteering in such a complex heterogeneous reservoir. The integrated approach utilizing geological, seismic, petrophysical and geosteering data provided better understanding for well positioning while drilling and achieving the MRC without exiting the sweet zones of targeted upper and lower Burgan sandstone in Minagish field and enhanced water free oil production.
The objective of this paper is to describe a comprehensive approach integrating static and dynamic well characterization to optimize well completion and subsequent improving oil production in thin sand reservoirs.The following procedure was used to estimate and optimize the production potential of 3 feet sand reservoir located in Limoncocha Field:• Accurate well logging program to identify thin sands. (Vertical Resolution, Static Data) • Open Hole Mini DST program to estimate permeability, skin effect, and reservoir pressure and productivity index. (Dynamic Data) • Anchored guns with 800 psi of static underbalance to avoid control fluid invasion. • Well completion done with drilling rig; No well test is required using this methodology. • PVT sample taken in cased hole for further characterization and continuous improvement.
Summary A significant oil resource exists within the Schrader Bluff and stratigraphic equivalent West Sak reservoirs located on the central North Slope of Alaska. The Schrader Bluff resource is under development in the Kuparuk River Unit, Milne Point, and within the Prudhoe Bay Unit. These areas have developed reservoirs with oil viscosities up to 200 cp under waterflood and viscosity-reducing miscible gas injection. A grass roots penta-lateral gas-lifted producer was drilled and completed to unlock untapped oil in the northern portion of the Polaris S-Pad Schrader Bluff viscous oil reservoir in Prudhoe Bay, Alaska. This producer was the first multilateral well drilled in the Orion and Polaris Schrader Bluff reservoirs in ≈8 years. The team worked to unlock surface and subsurface opportunities, delivering a substantially lower cost of access than planned. Production rate from Schrader Bluff reservoir wells has a positive correlation with contacted net sandstone. Optimal well placement in each of the five laterals was key to the delivery of a successful project. A novel approach to geosteering was used to maximize net sandstone exposure, utilizing deep azimuthal resistivity and real-time user-guided multilayered inversion modeling.
A unique challenge for ongoing Schrader Bluff development is to increase field production with the drilling of a high-angle, multilateral producer. To address the challenge, a project was initiated with the primary goal to safely drill five laterals with a key emphasis on maximizing net sand exposure while balancing the short- and long-term value associated with selecting the appropriate technology. This paper focuses on the technical aspects of the proactive geosteering with azimuthal resistivity measurements and multilayered user-guided inversion used in this project. The prewell study based on multiple offset wells is discussed in detail, followed by presenting the highlights of the real-time drilling/geosteering operations, and concluded with the comprehensive post-well analysis study after all five laterals were drilled. The key effort before the drilling was thorough simulation of various scenarios for several target formations. It allowed the selection of the proper geosteering service level (tools and data inversion methods), providing required resolution capabilities but not exceeding the project budget. Value of inversion on real-time data is demonstrated with several examples accompanied by uncertainty analysis of inversion results. Post-well processing included quantification of the main fault amplitude, in-depth uncertainty analysis, and 3D visualization, as well as geological interpretation using an advanced 3D modeling application. The final position and orientation of the major fault were supported with the results of 2D inversion performed in the vicinity of the fault. The integration between advanced geosteering tools and an active team effort helped achieve this complex penta-lateral well, drilling all legs with excellent directional control with numerous steering adjustments and a final net pay of 20,455 ft out of 28,886 ft drilled, which exceeded the operator’s expectations.
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