The production of hazardous gases such as CO2 and H2S impose high risks to offshore operations, with lethal impacts on personnel, along with special equipment required and environmental challenges. Hydrocarbon productions require that part of this gas could disperse on the atmosphere, so a comprehensive risk analysis is necessary to evaluate the gas disposal event. Computational Fluid Dynamic (CFD) can be used to effective study how the wind and environment can interfere with the gas dissipation in the air. In this work, a specific analysis was necessary to produce a gas well with up to 80% CO2 fluid composition. A CFD Gas Dispersion Analysis evaluated the turbulent airflow over and offshore drilling vessel perimeter to map the flammability levels and hazardous gases concentration zones, depending on winds speeds, wind directions, and well gas flowrates. Parallel processing was applied in order to reduce the computing time for simulation of 52 cases on gas release on burner booms and relief lines, and 56 cases for leak analysis on the process plant. The results permitted defining using 3D maps the concentration levels of hazardous gases on the rig expected on each scenario condition, as well as the coverage area outside the vessel affected by the gas release.
Well testing is a proven method for reservoir characterization, which is important for well-completion design, future development strategies, stimulation needs, and determining the commercial feasibility of the reservoir. This paper presents a surface data-acquisition system and its applications for rigless well-testing operations. Drill-stem testing (DST), which is classified as a temporary completion of a well, typically involves a large and complex operation. A key activity during DSTs is collecting downhole pressure and temperature data using gauges at the bottom of the well that monitor pressure changes throughout the operation. Particularly crucial are the shut-in and initial build up, which provide insight into major reservoir properties. While shutting in the well at the bottom reduces the effects of wellbore storage, providing the most accurate downhole measurements, it also requires a rig and numerous personnel to prepare the well and run in hole (RIH) the test string. A rigless DST operation using a surface closure and surface data-acquisition system has been used in several wells to optimize data acquisition recovery as a non-invasive alternative to running downhole pressure gauges for pressure-transient well testing. The effectiveness of the data-acquisition system provides advantages and accountability by avoiding the cost and risk of running equipment downhole and monitoring tests in real-time at surface. The surface gauges acquire high-resolution pressure data at the wellhead during flowing and shut-in, which are then converted to bottomhole conditions using proprietary models. Because this technique is nonintrusive, it can be used to test wells in which downhole gauges are impractical or cost prohibitive, such as highly deviated, horizontal wells with tubing restrictions, sour-gas, high-pressure wells with high bottomhole temperatures, and low-cost evaluations. For mediumto high-permeability formations, a three-day test is typically sufficient to calculate basic near-bore and reservoir properties, including skin, permeability, and initial pressure. Longer tests that track pressure changes to reservoir boundaries can also be used to calculate the reservoir size. The data-acquisition system has proven its efficacy after enabling a low-noise response and low-pressure changes resulting from temperature effects. Based on data provided by the data-acquisition system, the operator designed a well-testing campaign and achieved results typical of those expected using a conventional approach.
Solids production has been an issue in the oil and gas industry for years. Several materials and configurations have been tested under different conditions to determine how to produce fluids more efficiently when abrasive solids are present. This paper discusses well-testing operations involving formations with the potential for solids production. The discussion focuses on the choke manifold, which is a crucial piece of equipment used during testing operations. The choke manifold facilitates dual-flow paths that control the well flow at surface from the upstream control equipment to the downstream process equipment and allows the operator to perform choke changes without interference to operations or test objectives. It is responsible for controlling the flow rate, upstream choke pressure, downstream choke pressure, and for maintaining critical flow. These tasks are easily achieved using a single choke when no solids are produced. However, when solids are present during the flow through the choke manifold, erosion can occur in the choke body and beans. When these parts are damaged, the well should be shut-in and all operations suspended to repair the damaged equipment. Previous experience shows that the use of chokes in series combined with a high-resistance material (tungsten carbide) improved the choke manifold capacity to work with abrasive solids with less erosion issues. Such capability relies on the lower velocity and pressure changes provided by chokes in series. The choke configuration was tested in the field with a high abrasive flow (gas with solids) and resisted, as expected. Computational fluid dynamics (CFD) simulations were used to analyze the flow-velocity profiles in the flow path of the choke manifold. This study presents a comparison of these results with actual field data (pressure upstream and downstream of the choke manifold during different flows) to demonstrate how the three-choke system can provide safer operations with abrasive flows.
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