Good geomechanical modeling can provide valuable information for the efficient design and drilling of wellbores. Incorporating real-time wellbore stability monitoring during drilling can reduce the associated risks, especially for deepwater extended-reach wells. This paper presents the preparation, delivery, and outcome of the field trial for a real-time wellbore stability monitoring service delivered at Shell Exploration and Production Company's office in New Orleans. Three key objectives were set for the field trial:to develop the processes to incorporate real-time wellbore stability into the current operations center monitoring provision,to provide frequent updates of the wellbore stability model using a geomechanical modeling technique that was independent of the operator's own methods, andto monitor and verify the geomechanical model based upon the drilling experience enabling proactive decision making during drilling. For the operator's asset team, the main objective was to reduce trouble time and make execution of the well successful. Ram Powell VK 913 A-9 well was chosen as a candidate for the field trial. The Ram Powell tension-leg platform is located in 3200 feet of water in the Eastern Gulf of Mexico. A-9 was planned as an extended-reach exploration and would have the highest angle at the shallowest depth in the field. A geomechanical model for the prospect had already been created using the operator's own well-established methodology. This pre-drill model was transferred into the service company's software, and the real-time model was calibrated to generate as close to the same output as possible. After verifying the real-time model using the drilling experience on the closest offset wells, the 24 hr realtime stability monitoring commenced. The real-time geomechanical monitoring encompassed pore pressure prediction, rock property calculations from formation evaluation tools, wellbore trajectory updates, and the use of surface and downhole drilling data to verify the geomechanical model. Integration of the real-time wellbore stability monitoring contributed to the successful drilling and casing of this deepwater extended-reach well. The trial resulted in a greater understanding of the geomechanics of the field. The trial also resulted in a better understanding of procedures for maximizing the value of real-time data and of associated monitoring services, services that will be incorporated in future Shell E&P wells. Introduction Shell Exploration and Production Company, in co-operation with Halliburton Sperry-Sun, established a real-time Operations Center (OC) within the operator's office in New Orleans.1 The operations center is regarded as enabling a multidisciplinary workspace that seamlessly integrates all aspects of the company's well construction activities. Halliburton Sperry-Sun and GeoMechanics International (GMI) had cooperatively developed a real-time enabled version of new geomechanical analysis software, and approached the operations center with a proposal to complement and enhance the existing well construction process. The proposal was accepted, and a trial was initiated to establish the feasibility of real-time wellbore stability monitoring within the operations center environment. An extended-reach (ERD) well design was chosen that would become the shallowest ERD well attempted on the prospect. Field Trial Outline The ultimate goal of the trial was to enable the real-time update of the geomechanical model output using measurements from the actual conditions encountered during drilling and, crucially, to provide the updates within a time frame and in a format that allowed proactive decision-making while drilling. To meet this goal, the trial had three central objectives. The first was to develop the processes that would allow the incorporation of real-time wellbore stability monitoring into the existing operations center well-construction structure. The second was to provide frequent updates of the wellbore stability model, which in this instance would use techniques that were independent of the operator's own methods. The third was to monitor and verify the geomechanical model based upon the drilling experience to enable proactive decision-making during drilling.
An understanding of geomechanics can save millions of dollars in drilling costs by reducing the likelihood of poor borehole conditions, stuck pipe and lost circulation. Basic wellbore stability modeling has been successful in the past, but may prove inadequate in some cases because the mechanism of borehole failure and characterization of fracturing is not sufficiently addressed. In these cases, a more complex geomechanical model is required. We describe an example where a complex geomechanical model was applied to address anisotropic wellbore failure due to weakly bedded rocks, and lost circulation due to equivalent annular mud weights in excess of near and far field stresses. This same model was then used to predict mud weights that should mitigate problems in future wellbores. Introduction Drilling operations in the Gulf of Mexico often experience a challenging drilling environment. The combination of high overpressures and weak rocks can quickly narrow the range of downhole operating mud weights. In many cases, basic geomechanical modeling can help to mitigate these challenges by helping to understand pressures at which boreholes fail and/or pressures at which fractures propagate away from the wellbore. Unfortunately in some cases, these basic models are not adequate in fully describing the earth model and therefore have shortcomings when determining operating mud weight ranges. The Shenzi Field in Green Canyon blocks 653 and 654 (figure 1) is an instance where understanding parameters outside of the general geomechanical failure model has allowed for improved drilling operations. Early exploration and appraisal drilling in the deepwater (+3000 ft water depth) subsalt field resulted in significant wellbore instabilities and lost circulation in the subsalt formations. After the first wellbores were drilled, it was believed the instabilities could be accounted for by the uncertainty in the pre-drill models. Adjustments were made to key parameters such as pore pressure, rock strength and stress magnitudes, however additional drilling problems continued to occur in subsequent wells. It was quickly realize the problem extended beyond the uncertainty in the current geomechanical model and that there were other considerations that needed to be made before future wells were drilled. While drilling the first wells, it was observed that the borehole instabilities were more severe when drilling down dip at low angles-of-attack to bedding, but almost non-existent when drilling up dip at angles nearly perpendicular to the bedding planes. Operations also experienced significant lost circulation when raising the mud weight to compensate for the instabilities in the down dip wellbores. The high mud weights required to limit borehole collapse only increased the risk of losses in naturally depleted sands. The narrow mud window was also constraining the casing design, which resulted in severe cost overruns. A greater understanding of the mechanism for instabilities and lost circulation needed to be gained to prevent these cost overruns in future wells. Theory and Geomechanical Modeling Despite sometimes being under-utilized, basic geomechanical modeling has been a part of the industry for quite some time. It is the modeling of the earth's mechanical properties coupled with the regional in-situ earth effective stresses[1,2]. The complexity of this model is determined by how many of the mechanical properties can accurately be quantified, how robust the calibration of the stress magnitudes and directions has been, and how these properties vary across the reservoir. When applied correctly, the model can be used to understand how the earth will react when subjected to a drilling scenario[3]. These "reactions" are generally things we would like to avoid when drilling wells. They include, but are not limited to, wellbore cavings, lost circulation, wellbore ballooning events[4], and reaction with the mud[5]. To mitigate all of these potential problems, the geomechanical model should be as robust as possible. Unfortunately, often the lack of proper data available does not allow for robust models.
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