TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNatures of Nahr Umr shale instability problems in Zakum field are studied in Geomechanical and chemical views. Literatures, past drilling data, wireline logging and well test data, and analysis of cuttings and cores are studied to define the cause of the problem and find the way to fix it.By using the record of past drilling troubles, problems are likely in the highly deviated well, and relationship between drilling direction and trouble occurrence is not clear. It has obvious relationship with mud weight and chemicals, however the causality is not clear.The Geomechanical model was set for the formation from the analyzed data, available literatures and measured data in the recently drilled well. Also, mechanical and chemical characteristics of the shale are examined with cuttings recovered from wells, and cores from past wells. Mineralogical test are mechanical strength measurements are performed for the samples. Observation and testing of the samples unveil the fact that the shale has severe anisotropic feature of the mechanical strength and physical feature such as permeability.By integrating the facts and findings, the authors determine the failure mode as bedding plane failure caused by its anisotropic feature and pressure penetration. Counter measures are proposed based on the numerical studies of poro-elastic and discontinuous modeling.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA laminated and fissured formation around a horizontal borehole is modeled as a combination of intact rock blocks and permeable fractures with a DEM code. The model is used for understanding the mechanism of rock failure problems observed in a shale formation of an offshore field. Different mud weights and stress conditions are applied to the model to simulate the rock failure around deviated holes in laminated and fissured shale.The numerical simulation shows that shear failure along the bedding planes is the predominant mode of collapse of the hole when mud under pressures penetrate into bedding planes on which shear stress is applied. The severity of wellbore instability varies with stress states and wall conditions. The effect of a plugging agent in mud is verified by comparison between permeable and impermeable wellbore models.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractOperation availability, environmental safety, and storage capacity of the slurrified cuttings re-injection into a shallow, permeable formation off-shore Abu Dhabi was evaluated using a computer simulator for hydraulic fracturing.For the study, Umm Er Radhuma formation of Z field is chosen as the disposal formation, meanwhile Rus formation is regarded as the cap rock over the formation for isolating injected fluid and solid from propagating to seabed. A Geomechanical model of the formations which includes stress regime, formation pressure, rock mass properties, and leak-off characteristic was established with available data from literatures, wire line logging, and water disposal history in the same formation.The numerical model, which is developed by the authors , provides the estimation of injection pressure, fracture geometry and size, and storage volume of the slurry with a modeled injection schedules. The effect of solid particle concentration which may reduce pressure near fracture tip and cause screen off is taken into account for the fluid flow analysis and the determinatin of the fractrue geometry.