The Jurassic Marrat reservoir in Umm Roos field of West Kuwait (WK) is a low-permeability carbonate reservoir with heterogeneous petrophysical character that limited the predictability of reservoir properties and highly deviated development wells are preferred to maximize the exposure of the reservoir. However, there is an environmental risk and high operational cost when running radioactive-based porosity logging tools in such complex well profiles. To avoid that risk, Nuclear Magnetic Resonance (NMR) with conventional resistivity and gamma ray in a logging while drilling (LWD) program is proposed to achieve real-time formation evaluation and efficiently support well placement to maximize the reservoir contact. This paper presents the application of LWD-NMR as an alternative solution to evaluate reservoir properties as well as to land the highly deviated well successfully in the best reservoir sweet spots to achieve the maximum outcome for production.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents the results and methodology of the openhole stability analysis under production scenarios of one horizontal wellbore drilled and two horizontal wellbores planned in Jurassic carbonate reservoirs of West Kuwait. The main objective of the analysis was to investigate the stability of these horizontal wellbores under multiple drawdown conditions and different reservoir depletion scenarios in order to select a suitable completion strategy which guarantees borehole stability during the productive life of the reservoirs.The stability study includes the mechanical property characterization of the formations and the in-situ stress tensor description of the oil field. The static mechanical properties were obtained from the log responses and petrophysical analysis of several wells around the field by using a micromechanical approach. This approach is based on a constitutive model describing the microscopic processes occurring in a rock sample during tri-axial loading. A postprocessing analytical program for borehole-wall failure prediction and in-situ stress estimation/calibration was used in the open-hole stability analysis. The open-hole stability analysis consisted of predicting the shear failure zone around the borehole wall under production scenarios. When the shear failure zone covers the full extent of the borehole wall, the risk of borehole collapse becomes imminent. Therefore, the maximum drawdown which maintains borehole stability was obtained for each horizontal wellbore as a function of reservoir pressure depletion.The open-hole stability analyses were also done with multiple compressive strength degradation scenarios in order to address the effect of grain-cement disintegration after acid stimulations. The results of these analyses were found to be useful in evaluating and deciding optimal well completion (open-hole, cased and cemented or slotted/expandable liners) for these wells.

Whole cores provide important and high-quality information about mineralogy, rock fabric and texture, porosity, saturations, geomechanical properties, facies stacking patterns, depositional environment, and fracture networks that often cannot be discerned with much certainty using other subsurface data sets. Here we present results from the detailed digital sedimentologic descriptions of three whole cores in West Kuwait that capture portions of the Middle/Upper Jurassic Najmah Formation, an important source rock and unconventional reservoir. The integration of detailed digital core descriptions with high-resolution XRF scanning of the cores, high-density routine core analysis and petrographic (thin section, epifluorescent, fracture-focused, and SEM) data, and a combination of XRD mineralogy and organic petrology provide the opportunity to evaluate multiple reservoir quality indicators across several depositional and diagenetic facies. Linking diagnostic indicators to specific facies (and providing constraints on the likely variation within) rather than simply associating these properties with broader stratigraphic intervals should enhance our ability to predict naturally inherent variations in the formation which will improve lateral well placement and completions strategies. It is anticipated that the data gathered, and the interpretations made from it will be used to design and alter the development and completion strategies across the asset to increase production and reduce risk.

Hydrocarbon exploration and production in unconventional reservoir is under-developed in Middle East. Therefore, the understanding about this subject is still scanty which leads to conspicuous uncertainties in comprehensive reservoir evaluation and development. It plays a critical role to minimize the cost of exploration, drilling and operations. Detail plan for core acquisition and study is crucial to provide accurate and sufficient information to unlock the potential of Jurassic unconventional reservoirs in West Kuwait (WK). Hydraulic fracturing has proven to be a successful technique for increasing the productivity of unconventional reservoirs. However, before reaching that step, many factors should be intensively evaluated to minimize the risks. A potential area to place a MSF well should satisfy several criteria: high TOC, hydrocarbon maturity (oil, wet gas, or gas), less bitumen, proper containment to hold the vertical extension of fractures beyond the upper/lower boundary, etc…This paper aims to describe the integrated process of reservoir characterization to identify Najmah Kerogen sweet spots in order to facilitate the first Multistage Hydraulic Fracturing (MSF) well in West Kuwait (WK) unconventional reservoir. The study showed that Najmah Kerogen reservoir in WK fields has world-class quality of hydrocarbon potential: average TOC is 10-13%, Kerogen type II/III, mostly in the oil window except some fields have high potential of wet gas/condensate. Thermal maturity increases basin-wards from South-East to North-West. The reservoir is organic-rich mudstone that comprises mainly calcite, dolomite, quartz, kaolinite, and pyrite. In general, the middle unit has lower organic content and higher brittleness compared to the upper and lower one. The reservoir characteristic of the middle unit is favorable for landing the MSF well. The upper unit contains high bitumen amount, so it should be voided in the plan of MSF. Fracture analysis shows the majority of natural fractures are following NNE-SSW direction that in line with regional tectonic understanding and results the favorable drilling direction in NW-SE to ensure the wellbore stability and maximize the efficiency of hydraulic fracturing job. As a result, Field-H was identified as the best candidate to drill the first MSF well in Najmah Kerogen (middle and lower unit) from the outcome of the study. The comprehensive understanding of Najmah Kerogen was crucial to develop unconventional reservoirs in WK fields, especially when the development of unconventional reservoirs is still in the early phase.

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