fax 01-972-952-9435. AbstractProductivity potential evaluation in viscous reservoirs has been difficult in the past due to difficulties in native fluid sampling and in-situ dynamic formation testing evaluations. This is the result of the high oil viscosity and the unconsolidated sands in which they are usually deposited, which create limitations to natural flowing and smooth well testing / production.There is no unique answer to the main question "how do we sample heavy oils in unconsolidated sands". However, from the experience Schlumberger has acquired during years, several modifications have been done to the wireline formation testers (WFT) 1 , such as the Modular Formation Tester (MDT*), and new modules have been developed which, linked to new best practices, have allowed high viscous oil sampling and in-situ formation testing. Some of the new modules and practices include, the extra large diameter (XLD) probe, dual packer with customized gravel pack screens, extra high-pressure displacement unit pump for low flow rates, advanced down hole flow analysis monitoring (DFA*) and special sampling techniques.In this paper, we present a methodology, which integrates formation tester pressure and water-cut measurements with detailed reservoir characterization from logs to better understand the viscous oil dynamics in sandstones reservoirs in order to optimize fluid sampling. _________________________ * Mark of SchlumbergerA commercial reservoir simulator ECLIPSE* in fully implicit, black oil mode is used to simulate the multiphase flow during WFT pumping. Around the wellbore very fine grids are used, which, linked to a multi-segmented wellbore option, allows to model the clean out (contamination level versus time curve) and fluid drainage for different scenarios of oil viscosity, reservoir anisotropy, drilling fluid invasion, flow rate and WFT position relative to the top boundary.The modeling results were validated using WFT field data with different rock and fluid properties. Some correlations were developed for field use that estimates filtrate contamination as a function of clean out time for several WFT modules.A good understanding of the limitations and benefits of each tool under each scenario contributes to a better collaboration in the design and optimization of sampling jobs (best practice and calibration of available analytical planners for field use).

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOver 100 horizontal laterals averaging 4,600 feet in length have been drilled in a shallow, heavy oil reservoir in Eastern Venezuela. Measurement While Drilling (MWD) continuous directional measurements and Logging While Drilling (LWD) azimuthal measurements are used to steer the wells through the reservoir, along a specific well path chosen from vertical stratigraphic wells for each pad and 3 Dimensional (3D) seismic which covers the field area. Experience from drilling the horizontal wells has shown that this reservoir is laterally discontinuous between the vertical stratigraphic wells and that this discontinuity is not always predicted from the surface seismic. However, the LWD azimuthal measurements, presented in the form of a 3D image is able to give the orientation of the wellbore relative to the geometry of the channels. Another use of the azimuthal images is to identify the numerous shale stringers that are only a few inches thick. These stringers are not detectable on the vertical stratigraphic wells due to the limited bed resolution of the wireline logging tools run in these wells. These stringers in the laterals greatly reduce the non-azimuthal resistivity measurements and give a false indication of an approaching reservoir bed boundary.

More than 50 horizontal laterals averaging 4600 feet in length have been drilled in a shallow, heavy oil reservoir in eastern Venezuela. Precise navigation through the formations was necessary to optimize placement of the lateral drainholes and maximize the percentage of reservoir sand exposed. To meet this requirement, an optimized bottom hole assembly (BHA) design and logging while drilling (LWD) interpretation technique were developed based on field experience. Measurement while drilling (MWD) continuous directional measurements were used to steer the well through the reservoir, along a specific well path chosen from three-dimensional (3D) seismic that covers the field area. The LWD azimuthal and bit electrode measurements were integrated with the 3D seismic to allow an interactive interpretation of the stratal boundaries present within the reservoir which resulted in continual refinements to the planned well path. Using the information derived from the LWD azimuthal and bit electrode measurements, the location of shale stringers, bed boundaries, and pay sand relative to the BHA could be determined and the well then steered in the appropriate direction to maintain an optimum position within the oil reservoir. As a result, the number of sidetracks was reduced and the percent sand encountered increased. The longest horizontal lateral in Venezuela was also drilled and completed as part of this project.

Modeling initial water saturation in transition zones in Carbonate has been a long lasting challenge particularly in heterogeneous reservoirs. The variation of water saturation has a considerable impact on initial volumes estimation, oil recovery prediction as well as the design of field development plans.Log-derived saturation can suffer from interpretation uncertainties particularly in the transition zone associated with the lack of knowledge of Archie exponents and especially n variability related to wettability. Moreover in the transition zone True Formation Resistivity ("Rt") evaluation presents a wide range of uncertainties as Laterolog and Induction Log domains overlap. Therefore there is a strong need for an independent source of water saturation profile.Mercury Injection Capillary Pressure (MICP), Porous Plate and Oil-Displacing-Brine Capillary Pressure measurements on core samples, at reservoir conditions, are used for building a reliable saturation profile for different rock types. In this paper the reconciliation process of water saturation from revised log analysis, laboratory measurements and Water Oil Contact takes into account the uncertainties on each source of data acquisition.The proposed methodology has been applied to a giant carbonate reservoir in Abu Dhabi and has improved the robustness of the water saturation evaluation in the transition zone. Production data are in a good agreement which supports the consistency of the methodology.

This paper describes an integrated and rigorous approach for viscous and middle oil reservoir productivity evaluation using petrophysical models calibrated with permeability derived from mini tests (Dual Packer) and Vertical Interference Tests (VIT) from open hole wire line testers (MDT *). It describes the process from Dual Packer Test and VIT pre-job design, evaluation via analytical and inverse simulation modeling, calibration and up scaling of petrophysical data into a numerical model, history matching of Dual Packer Tests and VIT with numerical simulation modeling. Finally, after developing a dynamic calibrated model, we perform productivity forecasts of different well configurations (vertical, horizontal and multilateral wells) for several deep offshore oil reservoirs in order to support well testing activities and future development strategies. The objective was to characterize formation static and dynamic properties early in the field development process to optimize well testing design, extended well test (EWT) and support the development strategies in deep offshore viscous oil reservoirs. This type of oil has limitations to flow naturally to surface and special lifting equipment is required for smooth optimum well testing / production. The integrated analysis gave a good overall picture of the formation, including permeability anisotropy and fluid dynamics. Subsequent analysis of different well configurations and lifting schemes allows maximizing formation productivity. The simulation and calibration results are compared to measured well test data. Results from this work shows that if the various petrophysical and fluid properties sources are integrated properly an accurate well productivity model can be achieved. If done early in the field development program, this time / knowledge gain could reduce the risk and maximize the development profitability of new blocks (value of the information1).