Subsea Environments Research Articles

Performance Characteristics for an Interstitially Insulated Coaxial Pipe Using Wire-Screen Mesh for Deepwater Applications

Summary The petroleum industry has endeavored to meet the high demand for crude-oil products with exploration and production into ever deeper ocean waters. Under these subsea environments, pipeline insulation is essential to prevent pipeline blockage that results from the solidification of paraffin waxes that are present in the crude oil. To maintain proper crude-oil temperatures above the paraffin-solidification point, new insulation techniques with enhanced thermal-insulation performances are essential in minimizing pipeline heat loss. A new insulation concept that involves an interstitial wire-screen mesh has been developed and with its thermal performance has been investigated, which was initially quantified with test coupons under simulated environmental conditions. These results correlated very well with comparable values from a test of a subsequent prototype-pipe section. Furthermore, an analytical model has been developed that compared very favorably with the experimental results for the coupon-test runs. Ultimately, this study has confirmed the feasibility and performance characteristics of the insulation concept, and it has also demonstrated the thermal competitiveness of the interstitially insulated coaxial technology.

Environment classification using Kohonen self‐organizing maps

Abstract: This paper describes a new method for classifying three‐dimensional environments in real time using Kohonen self‐organizing maps (SOMs). The method has been developed to enable autonomous underwater vehicles (AUVs) to navigate without human intervention in previously unexplored subsea environments, but can be generalized to unmanned aircraft equipped with appropriate sensors flying over unchartered terrains, or spacecraft exploring remote planets, subject to appropriate pre‐mission training. The method involves a fuzzy comparison between a SOM created in real time using accumulated sensor data and a class atlas of SOMs derived from previously trained and manually classified environments. This enables mission‐ and environment‐appropriate AUV navigation strategies to be selected in real time. Simulation results using real‐world, three‐dimensional environment data acquired from digital elevation maps are presented, which demonstrate the potential of the method.

A Real-Time Subsea Environment Visualisation Framework for Simulation of Vision Based UUV Control Architectures

The simulation requirements of UUV visual-based technology points toward a readily available candidate solution in the form of modern 3D graphics rendering technology, which has the capability to generate photorealistic representations of synthetic subsea environments in real-time. This paper describes the ongoing development of a simulation platform for synthetic seafloor terrain generation and visualization. Originally designed as an operator aiding-tool to provide improved situation awareness through visual immersion in the mission scenario, it is intended to use the augmented reality display representing the onboard camera to support the continued appraisal of a real-time vision-based UUV navigation system currently under development within the Research Centre.

Technology Update: Moving Toward High-Flow-Rate Intelligent Wells

New developments in analysis, modeling, and testing are playing a major role in advancing intelligent-completion technology toward the goal of withstanding sustained high flow rates. Completions that can deliver sustained high flow rates are crucial to helping operators meet the long-term challenges of developing reserves in subsea and deepwater environments. High well costs, particularly in subsea and deepwater development projects, pose a continuous challenge to operators to "do more with less" to achieve the most efficient means of drilling and completing wells. The pressure is on to target more reservoirs and increase recoverables with fewer wells. Drilling-technology advances now enable well teams to reach deeper sands with more contact areas or reach multiple pockets in "designer" wellbores. To make these designer wellbores viable long-term producers, completion designs must be able to withstand sustained high production or injection rates for the wells' long life spans. Intelligent-well technology, which allows for independent control of multiple reservoirs without the need for intervention, has contributed significantly to enhancing the functionality of designer wellbores in challenging environments. Increasingly, however, the question is, How can maximum functionality of an intelligent well be achieved in conjunction with high deliverability rates that are expected to be sustained for the next 10 to 20 years? With no industry data available, accurate modeling and validation testing are critical to advancing intelligent-well technology to its next logical application. Extensive efforts have been undertaken by Baker Oil Tools to predict accurately how high flow rates with the possibility of solids will affect the functionality and longevity of intelligent completions, with the primary focus being on the remotely operated valve. Predicting Erosion Erosion can affect the life of high-flow-rate completions significantly. Completion designs may include 10- to 20-year life expectancies with flow rates of 30,000 to 60,000 B/D. These rates are applicable for both production and injection wells. Tubing and casing sizes, pressure ratings, and flow areas are among criteria considered in all completion designs—with a goal of determining how much fluid can be produced from or injected into the well, as the case may be. In each instance, predictions of well deliverability must take into account subsequent velocity of the media that could include solids within the flow stream. How can these wells last 10 to 20 years at this constant rate? There are many different models and methods available within the industry to predict erosion. The challenge is in applying these models to relatively new intelligent-well technologies. Studies use nodal analysis to predict deliverability, constraints, and pressure and velocity profiles of the individual wellbore. Computational-fluid-dynamics (CFD) software enables evaluation at the component level. How does one know that this CFD model is correct? Nodal-analysis models used by the industry have proved to be reliable. The characteristics of suppliers' equipment are the unknown. How do specific design features affect flow rates into or from a wellbore? How do high flow rates with the possibility of solids affect the functionality and longevity of the completion?

Horizontal Drilling and Openhole Gravel Packing with Oil-Based Fluids-An Industry Milestone

Summary An increasing number of horizontal wells requiring sand control are being gravel packed, particularly in deepwater and/or subsea environments in which completion reliability is paramount because of the prohibitively high cost of remediation. Tophole sections in many of these wells are being drilled with oil-based (OB) fluids, with the common practice of switching to water-based fluids when the reservoir drilling starts. In the last several years, some operators started using OB drilling fluids in the reservoir section as well and gravel packed them with water-based fluids. In some cases, these practices required running predrilled liners in OB fluids and subsequently displacing to water-based fluids before running in hole with the sandface screens and gravel packing. In other instances, screens could be run in hole with OB fluids in the wellbore, and gravel packing could be performed with water-based fluids. In both cases, the presence of reactive shales and/or water-sensitive productive zones can introduce serious concern, in the event that carrier-fluid losses occur into the formation during gravel packing. Although a base-oil or diesel can be used as a carrier fluid, low density of the base oil limits such applications to low-pressure/depleted wells. In this paper, we present a case history of the first successful application of drilling and completing in an all-oil environment, using a reversible OB reservoir-drilling fluid (RDF) (the filter cake of which reverses wettability from oil to water when exposed to an acidic fluid) and an OB gravel-packing fluid. The carrier fluid used in this application included a filter-cake cleanup solution in the aqueous internal phase of the OB carrier fluid, extending the application of simultaneous gravel-packing and cake-cleanup processes that have been successfully practiced in water-based-fluid environments to OB systems. The subject application was in a high-rate gas field located offshore Trinidad, with anticipated production rates in excess of 150 MM scf/D per well. Presented in the paper is the drilling and completion selection methodology based on extensive laboratory and yard testing, along with the details of the completion and recommendations for future applications based on lessons learned. A direct comparison of the all-oil drilling and completion process to water-based drilling and completion is also presented based on a case history from the same field.

Development of an aluminium/sea water battery for sub-sea applications

There are two modes of operation for an aluminium/water battery: use of hydrogen-evolving or oxygen-reduction cathodes. In the first case, the current density is ≈10 mA cm −2 at 0.5 V. This leads to significant increase of pH and deposition of Ca/Mg(OH) 2 at the cathode, leading to sharp decrease in battery performance. On the other hand, in the oxygen-reduction mode, the current density is ≈0.1 mA cm −2 at 1.4 V, because of the low concentration of O 2 in sea-water. Long-term tests of an Al/water battery using Teflon-bonded CO 3O 4/C oxygen reduction cathodes in Brightlingsea Harbour, Essex, over a test period of 70 days have shown that the performance of this battery is stable and that it is possible to increase its performance by means of multi-cathodes on either side of the anode. A conceptual design shows that such a battery has an energy density of 1008 Wh kg −1 over an operating period of one year, significantly higher than all the conventional primary batteries considered for use in sub-sea environments.