The Vega subsea field in Norway has been producing successfully using a continuous Mono Ethylene Glycol (MEG) injection, topped up with corrosion inhibition means. A topside reclamation process allows reuse of MEG, however, limits the possibilities to produce saline water. In order to manage wells producing saline formation water and to increase ultimate recovery, a new flow assurance and integrity philosophy without continuous MEG injection is considered. This paper describes the options on hydrate as well as integrity management and the modifications both on the subsea and topside facilities required to enable an operational philosophy change. This change of the operational philosophy appears feasible, using either timely depressurization or Low Dosage Hydrate Inhibitors (LDHI) as well as a film building corrosion inhibitor in the system.
The well discussed in this paper has a history of sand production and has exhibit long cyclic slugging behavior with a frequency of several days and reduced average production. The lower completion has a 2000-ft gap between the mule shoe and the packer that is exposed to the larger diameter of 7-in. liner. It is not fully understood whether the slugging is caused by the gap at the lower completion or by sand transportation or both.
Dynamic wellbore modelling with sand particle transport is essential to model the abovementioned complex slugging behavior. A stepwise approach was adopted to allow systematic evaluation of this complex slugging phenomenon. Initially, a lumped inflow with no sand transportation was assumed. In the next stage, sand transportation was included with zonal inflow details added. Several sensitivities on sand particle sizes, particle density, zonal productivity index, etc. were carried out, all of which were aimed at reproducing the long cyclic slugging behavior observed in the field.
Transient simulations successfully produced the slugging behavior observed in the field. Cyclic slugging was seen to be caused by the flow dynamics generated by particles of small to medium size. Some of the key findings were complete blockage by porous sand stationary bed at the lower completion gap (with subsequent pressure buildup), transition from stationary bed to moving bed, rate-dependent velocity of a slow-moving particle bed (eventually producing to surface), and fresh sand particle production from the reservoir at increased drawdown. Measured data from the sand detector confirmed the production of sand, particularly around the same period as predicted by simulation.
Potential slug mitigation solutions were established that should help to achieve higher and stable production. One solution was to achieve higher flow velocity and therefore enable sand transportation as a continuous moving bed (i.e., no blockage), such as reducing the gap size at the lower completion section together with either tubing size reduction or electric submersible pump (ESP) installation. The other solution was to implement an appropriate sand control/sand consolidation method.
Sand production is a common flow assurance issue and sometimes can result in unstable flow behavior causing reduced production. This work is the first attempt to implement particle transport modelling in transient multiphase flow simulation to successfully address a slugging issue in a real well. The analysis helped in understanding the mechanism causing the slugging and arriving at a potential mitigation solution. Further, it provides a step-by-step workflow and a template to address such problems.
The FPSO Kaombo Norte came on stream on July 27 2018, offshore Angola. When both its FPSOs will be at plateau, the biggest deep offshore project in Angola will account for 10% of the country's production. Kaombo reserves are spread over an 800-square-kilometer area. The development stands out for its subsea network size with more than 270 kilometers of pipeline on the seabed between 1500-2000m water depth, including subsea production wells more than 25km away from the production facility.
During the project phase, measures have been taken in order to standardize the subsea design overall including the thermal requirements. By necessity the insulation design of the subsea component is driven by the most stringent part of the development which is then applied throughout the complete system on Kaombo. This inevitably infers that certain parts of the system operate with a built-in margin regarding thermal performance. With an overall objective to optimize the OPEX the use of this margin on some assets generates added-value in the operational phase by reducing production shortfalls through reducing the number of preservations undertaken during life of field.
In order to improve the overall preservation sequence, crude abilities to delay hydrates formation and/or to transport hydrates have been studied on the coldest fields. It was found that studied crudes present interesting properties to delay hydrates formation. These tests have been performed with crude samples in lab conditions in order to assess the temperature and pressure when hydrates start to form. The results indicate that it is possible to extend the waiting period (i.e. time before launching preservation) well inside the hydrate thermodynamic zone and operating "safety" zones have been defined depending of the actual temperature and pressure.
An optimized preservation sequence postponing the decision point to restart or preserve was finally implemented thanks to:
An accurate knowledge of the full system thermal performance especially including the weak links The study of crude properties for the most penalizing fields vs. hydrates plug risk
An accurate knowledge of the full system thermal performance especially including the weak links
The study of crude properties for the most penalizing fields vs. hydrates plug risk
The methodology implemented is today already field proven and application of the extended waiting period was performed allowing reduction of shortfalls and smooth restart. A significant impact is expected for the full life of the field.
Lloyds Register Senior Flow Assurance Engineer Oche Ameh explains what flow assurance is and the importance of this field in oil and gas extraction. The Nigerian National Petroleum Corporation announced a three-point smart strategy aimed at ending gas flaring in Nigeria’s oil and gas industry in 2 years.
If you've taken a career break and are now looking to return to the workforce, would you consider taking an internship? Career reentry expert Carol Fishman Cohen thinks you should. Lloyds Register Senior Flow Assurance Engineer Oche Ameh explains what flow assurance is and the importance of this field in oil and gas extraction. While a résumé matters for getting a data science job, having a portfolio of public evidence of your data science skills can do wonders for your job prospects. Data story consumers are focused on summarized results and highlights instead of details of the analysis.
When the underlying cause of flow-related issues on offshore projects is unknown, an expert said an investigation of fluid flow behavior based on an understanding of the first principles of flow assurance is necessary. This paper focuses on a numerical-modeling analysis of the acid-gas-injection (AGI) scenario in carbonate HP/HT reservoirs, and presents the way in which AGI impacts asphaltene-precipitation behavior. A presentation from the 2016 Gulf of Mexico Deepwater Technical Symposium examines a testing strategy to determine the effectiveness of paraffin inhibitors.
A former technical manager with Petrobras discusses the development of the company’s flow assurance philosophies and strategies. This paper illustrates a numerical approach to estimate the deposition profile of precipitated wax crystals and its effect on flow-related parameters in pipelines. Options for avoiding these issues are also explored. Systematic experimental and modeling approaches to designing a safe operating strategy for a 5-km deepwater-subsea-flowline case study are presented to address unplanned shutdown and restart events for waxy-crude production.
As operators rely on longer subsea tiebacks, an upward trend in the number of plugs caused by paraffins and hydrates has been seen. New prevention and remediation methods are discussed to help solve these challenges. A former technical manager with Petrobras discusses the development of the company’s flow assurance philosophies and strategies.
Cold finger tests are a standard method for testing paraffin inhibitors, but there is no standard testing protocol, and sometimes different labs can see inconsistent results. Shell and BHGE studied the root causes of these issues. As operators rely on longer subsea tiebacks, an upward trend in the number of plugs caused by paraffins and hydrates has been seen. New prevention and remediation methods are discussed to help solve these challenges. A test method is being developed to screen paraffin chemistries in the presence of brine, closer resembling dynamic field conditions.