A detailed visualization of borehole size and shape, both while drilling and prior to running casing, completions, or wireline logging equipment, is an essential requirement to minimize non-productive time (NPT) associated with poor borehole quality or wellbore stability issues. The required visualization is made possible using logging-while-drilling (LWD) high-resolution ultrasonic imaging technology, suitable for both water-based mud (WBM) and oil-based mud (OBM) systems. This paper provides borehole size and shape assessment from field deployments of a 4¾-in. ultrasonic calliper and imaging tool, illustrating the impact on borehole quality of various bottom-hole assembly (BHA) designs, including positive displacement mud motors (PDMs) and rotary steerable systems (RSS). The visualization of borehole quality enables features such as borehole spiralling and enlargement to be assessed and used as input into optimizing completions planning and formation-evaluation programs. In addition, the combination of high-resolution travel-time and reflection-amplitude images enables artefacts induced by drilling equipment, including RSS, to be identified and understood. High-resolution travel-time and reflection-amplitude images and 3D borehole profile plots are presented from multiple wells, showing how different drilling systems and logging parameters, including drillstring rotation and logging speeds, impact borehole quality. The relationship between the angular bend in the PDM and the impact it has on borehole spiralling is discussed. The LWD logs presented illustrate the factors that influence borehole quality and the methodology used to ensure that high-resolution images are available in both vertical and high-inclination wellbores, leading to the ability to reduce the NPT associated with wellbore stability issues. The observation and assessment of drilling artefacts and irregular borehole size and shape act as inputs into optimizing completion and logging programs, evaluating the optimal placement of packers and other completion equipment, and the design of the drill bit and BHA. The ability to collect high-resolution travel-time and reflection-amplitude ultrasonic images in both WBM and OBM, in wellbores ranging from 5¾ to 7¼-in., leads to significant improvements in the understanding of wellbore quality. Borehole size and shape can now be visualized in real time in either water or oil-based drilling fluids at a resolution capable of identifying all significant drilling-induced geometric artifacts. This allows the adjustment of drilling parameters to minimize NPT associated with common drilling hazards, the optimization of completion programs and wireline logging programs.
A gas field is producing condensate with higher density than typical due to its higher napthene and aromatic content. Several future gas fields to be developed also have condensate with similar properties as this single field. The changes in future condensate properties and increasing amount of this atypical condensate will have major impact on existing refinery. It was necessary to create an integrated reservoir and surface facilities model and characterised fluids that can produce prediction of future feedstock including these aromatic condensate to the refinery. The model also produced the usual outputs such as gas quality and condensate quantities forecast over the life of the gas fields. A compositional network model consists of fluid modelling, reservoir, well, topside facilities and pipeline modelling through to the onshore terminal process modelling were developed in order to model the export gas and condensate network. Steady state models were developed and validated against operating condition for each system and an integrator was utilized in order to integrate the subsurface and process simulator together. For the fluid modelling, a compositional model suitable to produce assays was used instead of black oil model in order to predict the quality of both the gas and condensate delivered. The fluid models for fields with aromatic condensate used True Boiling Point (TBP) assay instead of a standard gas chromatograph composition from a Pressure, Volume and Temperature (PVT) laboratory test report. Several characterisation methods were developed and tested in order to obtain representative and relevant properties for refinery design. Other gas fields which had a more common chemical characteristic of paraffinic dominant condensate used standard characterisation method. The model enables representative prediction of condensate properties relevant for refinery design and evaluate options to develop the fields. The work will show that an integrated sub-surface-surface network model is essential in order to define the impact for a development throughout the value chain, specifically the changes to the products and downstream facilities. It will also provide an insight on the impact of fluid characterization methods of different types of condensate.
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