Carbonate reservoirs are often characterized by high pressure and high content of H2S and CO2. For these reasons, drilling the reservoir is the most challenging activity of such fields and long-term zonal isolation across the reservoir section is one of the primary requirements. In the example well considered for this study, the production liner is set at a depth of approximately 4,500 meters and the mud density is 16.2 lb/gal (1.95 g/cc). After a production liner is cemented, the well undergoes several operations such as fluid displacement, casing/liner pressure tests, stimulations, production, and injection; these operations create load on the cement sheath. Carbonation of neat Portland cement systems in CO2 environments is well known in the industry. The carbonation is of significant concern if the CO2 can enter the cemented annulus. The surface area of the cement sheath that contacts CO2 should be minimized to help prevent carbonation. This can be achieved by reducing the permeability, preventing the formation of cracks and micro-annulus, and reducing the components in the cement sheath prone to attack from CO2. To assure long-term sealing properties of the cement sheath during the life of the well, a cement formulation has been developed to be mechanically durable and chemically resistant to aggressive environments. The cement system discussed in this paper was designed to withstand the stresses imposed by changes of pressure regime during the well life by improving elasticity and thus helping prevent damage to the cement sheath. In addition, the potential for carbonation was limited by reducing the components in the slurry formulation that could react with CO2. Mechanical properties and resistance to CO2 environments of the cement system were tested in the laboratory. The cement system was successfully evaluated in the yard test. Cement sheath analysis, slurry design and testing are discussed. The results presented in this work should help in the design and implementation of solutions to contain reservoir fluid and injected fluids, including in the presence of H2S and CO2. Introduction The main objectives for cementing are to:support the casing.protect the casing from shock loads (tubular collapse).provide a pressure-tight seal between zones containing either different pressure regimes or fluid content for the entire well life.protect the casing from corrosion.seal off zones of lost-circulation or thief zones. To meet these objectives, the properties required in the cement slurry and the set cement sheath includes the following:Stable at the given density—no free water and no settling.Easily mixed and pumped.Provide adequate thickening time, fluid loss, and gel strength.Meet the optimum rheological properties required for mud removal.Impermeable to annular fluids while curing.Develop strength quickly after placement in the annulus.Develop mechanical properties to help ensure well integrity for well life.Bond to casing and formation.Have low permeability to resist reservoir fluid migration and attack.Stable under downhole conditions of temperature, pressure, and chemical exposure.
The development of heavy oil reservoirs is one the future targets of the major oil companies worldwide. Most of the heavy oil fields are produced through cold production methods leaving behind significant amounts of unproduced reserves. Today several EOR (Enhanced Oil Recovery) techniques and, in particular, thermal methods are available to achieve higher recovery factors.However, some technologies, like the downhole electrical heating have been recently improved, allowing enhancement of production, therefore, improvement of the recovery factor with relatively low investment cost with respect to the high costs involved in the implementation of the thermal technologies.In order to increase the production of a heavy oil reservoir in the offshore Congo, a study of down hole electrical heating application have been carried out showing encouraging results.The aim of the study was to evaluate the benefit associated to the application of this technology through the reservoir modeling. Significant results were achieved in terms of increasing of the recovery factor.The use of heat to increase the reservoir temperature showed good results in terms of heavy oil viscosity reduction starting from 1,000 cP at reservoir conditions (34°C) down to much lower values throughout the production time resulting in increased production rate and consequently, higher recovery factor from this reservoir.The first application of this technology has been performed in a long horizontal well section of about 500 meters length completed with production sand screen. The electrical heating mineral insulated three phase cables were deployed throughout the horizontal well section by means of a dedicated completion tail pipe.Several design challenges have been faced to properly centralize the heating cables and clamp the same around the completion tail pipe due to the well design constraints. This paper will describe the results of the reservoir modelling analysis, the completion planning activities and the lessons learned during the operations.
Drilling exploration wells may be challenging due to uncertainties related to several factors like well downhole pressure, pore and fracture pressures, etc. As a result, a well may fail to reach its target depth.Managed Pressure Drilling (MPD) is a useful technique in challenging conditions. It allows pore and fracture pressures to be accurately calculated while drilling, and the mud weight adjusted accordingly. Besides, it reduces the chance of human errors as it is an automatic device managed by specific software.Eni's distinctive MPD system is the e-nbd™ (Eni Near Balance Drilling). This system consists of an innovative drilling process that maintains constant bottom hole annular pressure at all times. The system does not require that mud circulation be stopped and compensated with a back up pressure.The e-nbd™ is assisted by a proprietary system for continuous circulation that is called e-cd™ (Eni Circulating Device). The e-cd™ system is composed of special subs that are positioned on top of each drilling stand. The number of required subs is defined by the length of the open hole section that is to be drilled with continuous circulation. The system is completed by a dedicated manifold that is positioned on the rig floor that automatically diverts mud flow from the Stand Pipe Manifold to the subs.e-nbd™ through the e-cd™ System ensures a continuous MPD process, without any "transient" time. This paper presents this innovative system and the achieved results. It reports a summary of the applications performed to date, including some offshore applications from floaters, as well as the major benefits of the system.
Chemical tracers have recently been used to identify oil and water production along different intervals in open hole slotted liner completion, compartmentalized with swellable packers. The reservoir is a fractured carbonate brown field containing several sub-areas producing asphaltene and clasts in which chemical inflow tracers have provided greater understanding of characterizing the reservoir and its' well performance in deviated wells. The permanent downhole tracer systems have been successfully applied in two onshore wells in Italy. The principle of this technology is to place a number of unique chemical tracer systems in different compartments along the length of the lower completion with only minor modifications for clean-up and production monitoring. The system releases tracer into the well stream when wetted by the target fluid, oil or water. When wetted by the opposite phase they will remain dormant, meaning no tracers will be released. The application of permanent oil and water tracer systems placed at pre-defined intervals along the production zones of the wells. Upon well start up, oil samples were taken at the surface and were analyzed to identify which zones were effectively contributing to oil and water production. Permanent water tracer systems were installed aiming at detecting the onset of early water breakthrough. After water break-through has occurred, a regular sampling program is performed and samples analyzed to identify the location of water production to understand the water profile evolution over time. Swellable packers have been used to segment the horizontal sections for the purpose of selective zonal stimulation and to optimize future water shut off intervention by treating the offending zones based on tracer detection. This paper will discuss an innovative wireless approach using chemical inflow tracers as the technology enabler with field proven case studies for clean-up verification, identifying where water and oil is flowing, assess stimulation job effectiveness and estimate relative flow contribution between intervals. Lessons learned for future installations will also be discussed. TX 75083-3836, U.S.A., fax +1-972-952-9435
In a global context aiming to unlock a low carbon future by industry decarbonization, developing the infrastructure for capturing and storing CO2 emissions is a key target of countries, energy companies and regulatory bodies. Injection for geological storage in suitable reservoirs is an advantageous option which presents challenges related to the completion accessories and string exposed to the injected fluid and the thermodynamical loads during injection and the well life. The purpose of this work is to simulate by numerical analysis and full-scale test, the behavior of a gas-tight Metal-to-Metal OCTG premium dope-free connection when subjected to low temperatures and loads generated by the effect of a sudden CO2 high pressure drop during injection in depleted reservoirs. Extreme temperature drop down caused by the Joule-Thompson (J-T) effect between injection conditions (P-T) inside the tubular and those in the annulus, may expose tubing connections to a thermal shock reaching a temperature near the theoretical figure of -78.5°C. This temperature drop assumed as worst-case scenario is also explored. The analysis is performed considering estimated loads for a CO2 injection case study. The numerical analysis and full-scale test performed confirm the structural and sealability performance of the connection is not affected by the exposure to such low temperatures. Additionally, transient thermal loads, with a drop of approximately 100°C, appears to be not critical for the metal-to-metal dope-free seal integrity and also not affecting the structural integrity of the connection. The challenges setting up of a prototype testing frame, simulating the cooling by thermal shock, lead to a methodology for assessing CCS projects premium connection able to define a robust testing protocol for cryogenic temperatures. The numerical and full-scale results collected on the tested connection size, together with the ones previously tested, allow extrapolation to near sizes of the same premium thread family. The results achieved by testing a premium connection which has been subjected to a thermal shock approaching -78.5°C represent a forefront in the industry, demonstrating the reliability of the product not only in operative conditions during CO2 injection, but also after an extreme event, assessing performance for the CCUS storage projects.
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