Offshore Campaign Research Articles

Do gravity data justify a rifted “Liguro-Provençal Basin”?

The geodynamic evolution of the Liguro-Provençal Basin and its crust and upper mantle structure remain debated, especially regarding the role of rifting in continental break-up and seafloor spreading. Our study incorporates updated datasets, including new gravity maps from the AlpArray Gravity Working Group (complete Bouguer, free air, and isostatic anomalies) for 3D modeling and gravity field analysis, seismic data from Lobster offshore campaigns for direct comparison, and geodynamic models, supplemented by seismic profiles from previous French and Italian campaigns to constrain the interpretation. We used GFZ’s IGMAS + software for interactive 3D modeling, creating a density model extending to 300 km depth that includes crustal and upper mantle inhomogeneities based on prior geodynamic models. This hybrid approach, with polygonal structures for the crust and voxels for the upper mantle, clarifies individual contributions to the gravity field. Extending initial gravity modeling from the SPP MB4D project INTEGRATE, our work provides a consistent 3D density model for the Alps and Ligurian Basin. The constrained 3D modeling and numerical analyses (terracing, clustering, filtering, curvature), along with vertical stress and gravitational potential energy calculations, suggest that rifting has significantly influenced the basin’s geological evolution.

Alignment calibration and correction for offshore wind measurements using scanning lidars

Long range scanning lidars offer great potential to measure wind characteristics for a variety of application in offshore wind energy. In order to derive accurate wind measurements it is critical to thoroughly calibrate the beam alignment. In offshore environments, the pitch and roll angle of a scanning lidar can be determined from sea surface levelling (SSL). This paper compares two methods to perform SSL, a method based on PPI scans and a novel method using RHI scans. Moreover, a previously described method to identify the distance at which the laser beam enters the water is extended to be applicable to larger measurement distances. Based on data from an offshore campaign in the North Sea, the differences between the RHI and PPI methods and their sensitivity to the selected elevation angles (PPI) and distances (RHI) are analysed. It is shown that both SSL methods prove to be robust for determining pitch and roll for all examined settings. The average results of the two methods show only minor differences. The standard deviation across all settings and both methods is 0.010° for pitch and 0.024° for roll. Compared to typically observed platform movements introduced by thrust on the wind turbine, the differences between different SSL settings are small. Comparison of the platform movements measured by the high sensitivity inclinometer and SSL shows that even slight differences in pitch and roll can be detected by SSL. This indicates a high level of accuracy for both methods investigated.

Alignment of scanning lidars in offshore wind farms

Abstract. Long-range Doppler wind lidars are applied more and more for high-resolution areal measurements in and around wind farms. Proper alignment, or at least knowledge on how the systems are aligned, is of great relevance here. The paper describes in detail two methods that allow a very accurate alignment of a long-range scanning lidar without the use of extra equipment or sensors. The well-known so-called hard targeting allows a very precise positioning and north alignment of the lidar using the known positions of the surrounding obstacles, e.g. wind turbine towers. Considering multiple hard targets instead of only one with a given position in an optimization algorithm allows us to increase the position information of the lidar device and minimizes the consequences of using erroneous input data. The method, referred to as sea surface levelling, determines the levelling of the device during offshore campaigns in terms of roll and pitch angles based on distance measurements to the water surface. This is particularly well-suited during the installation of the systems to minimize alignment error from the start, but it can also be used remotely during the measurement campaign for verification purposes. We applied and validated these methods to data of an offshore measurement campaign, where a commercial long-range scanning lidar was installed on the transition piece platform of a wind turbine. In addition, we present a model that estimates the quasi-static inclination of the device due to the thrust loading of the wind turbine at different operating conditions. The results show reliable outcomes with a very high accuracy in the range of 0.02∘ in determining the levelling. The importance of the exact alignment and the possible applications are discussed in this paper. In conclusion, these methods are useful tools that can be applied without extra effort and contribute significantly to the quality of successful measurement campaigns.

Full-Field Optimization of Offshore Squeeze Campaigns in Total Gulf of Guinea Fields

SummaryScale inhibitor (SI) squeeze treatments are one of the most common techniques to prevent downhole scale formation. In this paper, we present the optimization of treatment design for multiple wells included in offshore campaigns. Two offshore fields with 8 and 12 production wells in west Africa were considered that are separately treated via yearly squeeze campaigns. The wells included in each campaign are treated in a single trip of the supply vessel. Based on the storage capacity of the vessel, the available volume of SI onboard should be optimally allocated to each of the wells (having different properties and water production rates), so that they are all protected from scaling for 1 year until the next campaign is carried out. A hybrid optimization methodology was applied to optimize the squeeze campaign design.The gradient descent (GD) algorithm was first applied to derive the squeeze “isolifetime proxies” related to each well. Each proxy includes all the possible squeeze designs that result in 365 days of squeeze lifetime in the well. Using these proxies, any combination of wells’ squeeze designs could be nominated as the campaign design, because that would result in treating all wells until the next campaign. The multiobjective particle swarm optimization (MOPSO) technique was implemented to optimize the campaign design by simultaneously minimizing the total SI volume and the total injection time for the whole campaign. Minimizing the total pumping time would consequently minimize the deferred oil volume and the total cost of squeezes in the field.Finally, the Pareto Front was identified for each field, showing the most optimum campaign designs. The Pareto Front was shown to be a valuable tool for the operator to make a trade-off between the size of the vessel and the injection time; that is, to use a bigger vessel to transport more inhibitor to the wells or to use a smaller one but for a longer time to inject more water during the squeeze treatments in the field. A cost analysis was performed to identify the most optimum deployment plan providing the most optimum inhibitor allocation strategy, including the optimum inhibitor volume and the optimum injection time for each campaign.

New trenching results along the \u0130znik segment of the central strand of the North Anatolian Fault (Turkey): an integration with preexisting data

This paper provides a new contribution to the construction of the complex and fragmentary mosaic of the Late Holocene earthquakes history of the İznik segment of the central strand of the North Anatolian Fault (CNAF) in Turkey. The CNAF clearly displays lower dextral slip rates with respect to the northern strand however, surface rupturing and large damaging earthquakes (M > 7) occurred in the past, leaving clear signatures in the built and natural environments. The association of these historical events to specific earthquake sources (e.g., Gemlik, İznik, or Geyve fault segments) is still a matter of debate. We excavated two trenches across the İznik fault trace near Mustafali, a village about 10 km WSW of İznik where the morphological fault scarp was visible although modified by agricultural activities. Radiocarbon and TL dating on samples collected from the trenches show that the displaced deposits are very recent and span the past 2 millennia at most. Evidence for four surface faulting events was found in the Mustafali trenches. The integration of these results with historical data and previous paleoseismological data yields an updated Late Holocene history of surface-rupturing earthquakes along the İznik Fault in 1855, 740 (715), 362, and 121 CE. Evidence for the large M7 + historical earthquake dated 1419 CE generally attributed to this fault, was not found at any trench site along the İznik fault nor in the subaqueous record. This unfit between paleoseismological, stratigraphic, and historical data highlights one more time the urge for extensive paleoseismological trenching and offshore campaigns because of the high potential to solve the uncertainties on the seismogenic history (age, earthquake location, extent of the rupture and size) of this portion of NAFZ and especially on the attribution of historical earthquakes to the causative fault.

Case study: successful disconnection of a traditional floating production storage and off-loading unit

Decommissioning a producing asset within a low oil-price market scenario with a possibility of resuming production at a later stage is becoming a frequent task. The main objective of the offshore campaign is to release the floating production storage and off-loading unit (FPSO) at the earliest time by disconnecting all production risers, umbilical and mooring chains, and ensuring integrity of the subsea assets for future use. The entire project for the disconnection of this FPSO was managed in four phases. The first two phases were related to shutdown of production and FPSO clean-up. The FPSO readiness for disconnection was required before the final two phases: disconnection of risers and mooring lines. Detailed engineering was carried out in consultation with various stakeholders involved in the project: the regulator, the company, the FPSO owner and the installation contractor. Through feasibility studies, the best option was selected, which included innovative solutions to reduce overall offshore duration and project costs. The project was successfully completed by meeting the key objective of early departure of the FPSO without lost time injury or any significant environmental incidents.

Lidar-based wake tracking for closed-loop wind farm control

Abstract. This work presents two advancements towards closed-loop wake redirection of a wind turbine. First, a model-based wake-tracking approach is presented, which uses a nacelle-based lidar system facing downwind to obtain information about the wake. The method uses a reduced-order wake model to track the wake. The wake tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a simulation with the Simulator fOr Wind Farm Applications (SOWFA). Second, a controller for closed-loop wake steering is presented. It uses the wake-tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, the two approaches enable a closed-loop wake redirection.

A review of the LATEX project: mesoscale to submesoscale processes in a coastal environment

The main objective of the LAgrangian Transport EXperiment (LATEX) project was to study the influence of coastal mesoscale and submesoscale physical processes on circulation dynamics, cross-shelf exchanges and biogeochemistry in the western continental shelf of the Gulf of Lion, Northwestern Mediterranean Sea. LATEX was a five-year multidisciplinary project based on the combined analysis of numerical model simulations and multi-platform field experiments. The model component included a ten-year realistic 3D numerical simulation, with a 1 km horizontal resolution over the gulf, nested in a coarser 3 km resolution model. The in situ component involved four cruises, including a large-scale multidisciplinary campaign with two research vessels in 2010. This review concentrates on the physics results of LATEX, addressing three main subjects: 1) the investigation of the mesoscale to submesoscale processes. The eddies are elliptic, baroclinic and anticyclonic; the strong thermal and saline front is density-compensated. Their generation processes are studied; 2) the development of sampling strategies for their direct observations. LATEX has implemented an adaptive strategy Lagrangian tool, with a reference software available on the web, to perform offshore campaigns in a Lagrangian framework; 3) the quantification of horizontal mixing and cross-shelf exchanges. Lateral diffusivity coefficients, calculated in various ways including a novel technique, are in the range classically encountered for their associated scales. Cross-shelf fluxes have been calculated, after retrieving the near-inertial oscillation contribution. Further perspectives are discussed, especially for the ongoing challenge of studying submesoscale features remotely and from in situ data.

Lidar-based wake tracking for closed-loop wind farm control

This work presents two advancements towards closed-loop wake redirecting of a wind turbine. First, a model-based estimation approach is presented which uses a nacelle-based lidar system facing downwind to obtain information about the wake. A reduced order wake model is described which is then used in the estimation to track the wake. The tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a SOWFA simulation. Second, a controller for closed-loop wake steering is presented. It uses the wake tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, this paper aims to present the concept of closed-loop wake redirecting and gives a possible solution to it.

Startup of Pazflor Giant Offshore Angola Tackles Challenges From Two Reservoirs

This article, written by Editorial Manager Adam Wilson, contains highlights of paper OTC 23176, ’Startup of a Giant,’ by Arnaud Constant and Lionel Ramat, Total E&P Angola, prepared for the 2012 Offshore Technology Conference, Houston, 30 April- 3 May. The paper has not been peer reviewed. The Pazflor development includes four reservoirs in Block 17 deep offshore Angola, which produce to a floating production, storage, and offloading (FPSO) unit through one Oligocene subsea loop and three Miocene lines connected to subsea separation units (SSUs) and subsea pumps, with associated-gas and water-injection facilities (Fig. 1). The startup of the Pazflor field required a response to three simultaneous challenges—startup of a large complex facility; flow assurance for two different reservoirs and oil qualities, an Oligocene field with light oil and Miocene fields with heavy viscous oil; and operating innovative Miocene subsea facilities with gas/liquid separation on the seabed. Startup Preparation Manning and Training. Although most of the production personnel were already experienced with FPSO operations, specific attention was given to training and a local training center at the Total E&P Angola offices was maximized. One of Pazflor’s innovations was the design and use of an immersive training simulator (Fig. 2). This simulator was generated from construction of a 3D model and represents all the topside facilities with realistic rendering. In this 3D environment, operators move virtually through a simple interface, allowing for familiarization with their future facilities. Because all equipment is tagged, the operator can easily link his work documents, such as process flow diagrams and piping and instrumentation diagrams, to the actual FPSO environment before its completion or without actually being there. This simulator also can be used to simulate procedures execution, either individually or in a group, thanks to preloaded scenarios. Startup Milestones and Initial Planning. The precommissioning, commissioning, and startup activities were structured according to milestones defined in the early project stage by field operations teams and included in relevant project-packages contracts. This breakdown by startup milestones was taken into account by the commissioning team from the early onshore commissioning stage and was later used to prioritize offshore construction, commissioning, and startup activities during the offshore campaign. Eighteen startup milestones were considered initially, focusing on utilities, oil production, water injection, gas injection, and export systems and covering prestartup, startup, and normal- operations phases. The facilities were split into systems and subsystems, with a total of 669 subsystems, each linked to a specific startup milestone.

The Prestige Wreck Fuel-Recovery Project

This article, written by Technology Editor Dennis Denney, contains highlights of paper OTC 17534, "The Prestige Wreck Fuel-Recovery Project," by R. Hernan, A. del Corral, C. Berenguer, SPE, R. Paez, J. Sparrowe, and J. Moro, Repsol YPF, originally prepared for the 2005 Offshore Technology Conference, Houston, 2-5 May. This article is an overview of the recovery project to extract the hydrocarbons remaining in the wreck of the Prestige tanker. The ship, carrying approximately 77 000 tonnes of heavy fuel oil, broke up and sank in 3850-m-deep water in November 2002, 240 km off the northwestern coast of Spain. During the sinking, and for a period of several months afterward, a large amount of fuel was spilled, ending up mainly on the shores of Galicia. Repsol YPF, though in no way connected to the vessel or its cargo, was appointed by the Spanish government to recover the fuel remaining inside the wreck. Extraction of the remaining fuel was carried out in 2004 by use of large-volume aluminum shuttles. An innovative core-flow technique was used to extract this extremely viscous fuel (500 kPa·s at the shuttle offloading conditions) from the shuttles and offload it into a floating storage and offloading (FSO) vessel. Finally, bioremediation was used to accelerate the biodegradation of the remaining immobile fuel. Project Summary On 19 November 2002, the oil tanker Prestige broke up and sank in two parts. Approximately 37 000 tonnes of heavy fuel was believed to remain in the wreck, which continued leaking. The Spanish government commissioned a permanent solution for stabilizing the wreck and neutralizing its cargo. Potential solutions included the use of shuttle tanks to transport oil from the wreck to a surface container, pumping the oil to the surface by use of a riser system, and enclosing the whole wreck in a sarcophagus. Fuel viscosity at the wreck conditions was extreme (3 to 4×106 kPa·s), which, at this depth, precluded the use of conventional techniques. Repsol YPF (with technical assistance from BP, Eni, Petrobras, Statoil, and Total) outlined an action plan to be completed in 2003. The plan approved by the Spanish government consisted of the following. - Develop work-class remotely operated vehicles (ROVs) to operate at 4000 m water depth. - Seal all remaining leaks. - Carry out data acquisition on the wreck and its fuel composition and mobility, as well as on the environment and the marine soil, to assist future interventions. - Test a batch-extraction scheme that used shuttle bags. - Perform basic engineering studies of confinement solutions as an alternative if the above scheme did not work. Sonsub was hired as the main contractor, and, in the spring and summer of 2003, it carried out an offshore campaign for the above program to establish the basis for the actual fuel recovery planned for 2004.

California Offshore Geology and Exploration: ABSTRACT

During the years 1948 to 1961 the oil industry spent more than $150,000,000 exploring the submerged oil potential of offshore California. Seven oil or gas accumulations were discovered, but none appears to be of sufficient size to yield a significant profit to the operator. Prior to 1948 four giant California offshore oil fields (Elwood, Rincon, Wilmington, and Huntington Beach) had been developed with total estimated ultimate reserves exceeding 1,500,000,000 barrels. Published reports had outlined unexplored offshore basins with vast volumes of sediments. Producing fields onshore but close to the ocean are estimated to yield ultimate recoveries ranging from 150,000 to 550,000 barrels per acre. Hypothetical offshore extensions of these producing trends led to enthusiastic multi-million-barrel estimates of the offshore potential. In 1953 the Tide and Submerged Land Act triggered a hectic exploration campaign. Sophisticated, costly tools were developed. Estimates indicate that 40,000 miles of seismic lines were shot. Several hundred coreholes were drilled. Bonus bids at State offshore sales reached new highs in 1958 when approximately $55,000,000 was paid for five parcels of land at prices ranging up to $6,175 per acre. Drilling during the following year resulted in four discoveries. From the oil finders' view, 1959 was a very successful year in California exploration history but from the economic viewpoint the results do not appear impressive. Many major companies continue the offshore campaign with improved methods and tools, yet the California offshore potential remains largely unexplored. Economic development of this oil to serve our companies and the exploding West Coast population requires re-assessment of exploration methods, more advancements in technology, less expensive drilling and completion techniques, a better understanding of offshore economics, and more realistic appraisals of individual prospects. End_of_Article - Last_Page 260------------

Outline of Weather and Wave Forecasting Techniques

Introduction Oil operators engaged in drilling on the Continental Shelf of Louisiana andTexas are in agreement that adverse weather and wave action are two of thegreatest hazards to the safety and efficiency of their work. It was anticipatedwhen the offshore operations commenced that such would be the case, andexperience to date has verified this assumption. Because atmospheric conditionsand wave action involve tremendous amounts of energy it is highly unlikely thatit will be possible to control any but the most localized weather and wavephenomena within the foreseeable future. Thus, as long as the offshoreoperations involve the movement of small craft and barges over exposed waters, and the transfer of personnel and heavy equipment from these craft to eitherfixed structures or larger craft at close quarters, the weather and waveproblem will remain. Taking into consideration the persistence of the wave and weather problemand the improbability of achieving a direct solution, the Humble Oil & Refining Company, in planning its offshore campaign investigated thepossibility of forecasting wave and weather conditions in order to providewarnings of dangerous conditions and increase efficiency in day-to-day planningof work. It was recognized that predictions of wave and weather conditionsbased on meteorology and oceanography, both geophysical sciences, are not 100per cent accurate and application of forecasts in the offshore work wasdependent on whether they provided information which was sufficiently greaterin accuracy than the layman's guess to be worth the expenditure involved. During World War II, meteorology and oceanography were used with success inreducing danger resulting from environmental conditions and increasingefficiency of operations exposed to the elements. This success was partiallythe result of improvement in the scientific techniques involved and theprocurement and distribution of observational data, and partially due to thelarge scope of the military operations which meant that a reduction of lossesof a relatively small percentage of the total cost amounted to a large figureexpressed in terms of dollars. Since the offshore drilling involves anextremely large financial investment, it was considered that the experience ofthe Armed Services in successfully employing meteorology and oceanography mightbe duplicated in the oil industry. In addition, the oil industry's successfulexperience in utilizing seismology, geology, and terrestrial magnetism; allgeophysical sciences, indicated that meteorology and oceanography, also of thefamily of geophysical sciences and sharing their scientific assets andliabilities, might be profitably put to use. T.P. 2546