From measurement collection to remaining useful life estimation : defining a diagnostic-prognostic frame for optimal maintenance scheduling of choke valves undergoing erosion
Condition Based Maintenance (CBM) aims at regulating maintenance scheduling based on data analyses and system condition monitoring. Clear advantages of optimizing maintenance scheduling include relevant cost savings and improved safety and plant availability. A critical aspect is the integration of CBM strategies with condition monitoring technologies for handling a wide range of information sources and eventually making optimal decisions on when and what to repair. In this work, a practical case study concerning maintenance of choke valves in offshore oil platforms has been investigated. Choke valves used in offshore oil platforms undergo erosion caused by the sand grains transported by the oil-water-gas mixture extracted from the well. Erosion is a critical problem which can affect the correct functioning of the valves, result in revenue losses and cause environmental hazards. In this respect, this work proposes a diagnostic-prognostic scheme for assessing the actual health state of a choke va lv and eventually estimating its Remaining Useful Life (RUL). In particular, the focus has been on th e identification of those parameters which contribute to the actual erosion of the choke valve, the development of a model-based approach for calculating a reliable indicator of the choke valve health state, the actual estimation of the choke RU L based on that indicator using statistical approache s and, finally, the investigation of methods to reduc e the uncertainty of the RUL estimation by adding highly meaningful knowledge on the erosion state of the choke valve .
Condition assessment, remaining useful life prediction and life extension decision making for offshore oil and gas assets
Offshore oil and gas assets are highly complex structures comprising of several components, designed to have a lifecycle of about 20 to 30 years of working under harsh operational and environmental conditions. These assets, during their operational lifetime, are subjected to various degradation mechanisms such as corrosion, erosion, wear, creep and fatigue cracks. In order to improve economic viability and increase profitability, many operators are looking at extending the lifespan of their assets beyond the original design life, thereby making life extension (LE) an increasingly critical and highly-discussed topic in the offshore oil and gas industry. In order to manage asset aging and meet the LE requirements, offshore oil and gas operators have adopted various approaches such as following maintenance procedures as advised by the original equipment manufacturer (OEM), or using the experience and expertise of engineers and inspectors. However, performing these activities often provides very limited value addition to operators during the LE period of operation. This paper aims to propose a systematic framework to help operators meet LE requirements while optimizing their cost structure. This framework establishes an integration between three individual life assessment modules, namely: condition assessment, remaining useful life (RUL) prediction and LE decision-making. The benefits of the proposed framework are illustrated through a case study involving a three-phase separator system on a platform which was constructed in the mid-1970s in West Africa. The results of this study affirm the effectiveness of this framework in minimizing catastrophic failures during the LE phase of operations, whilst ensuring compliance to regulatory requirements.
Production enhancement from sand management philosophy. A Case Study from Statfjord and Gullfaks
Statfjord and Gullfaks are "Brown" fields operated by Statoil in the Tampen area of the North Sea. The production from these fields is characterized by large volumes of water and increasing sanding tendencies. The operator has for many years followed a strategy whereby sand produced with the wellstreams has been handled topsides prior to on-site disposal. The adoption of a sand management strategy has been crucial for prolonging economic reservoir development during tail production. By choosing to deal with sand topsides the operator has been able to pursue low cost slot replacement drilling where wells are completed without sand control equipment. The cased-hole functionality has facilitated multitarget drilling and is suited to selective production of each sand member through cheap plug/perf interventions. Significant gains in production (acceleration) and reserves (IOR) have resulted from the pursuance of sand management in these fields. Examples of wells showing productivity improvements as a direct result of allowing intervals to produce sand are presented. In addition, production gains achieved from replacing choked back "sand free" production with "maximum acceptable sand rate" production are presented. Increased sand tolerance has also led to reserve increases in some wells as unproductive intervals that were previously sanded up have cleaned up and started to flow. It will be argued that this strategy negates many concerns with formation damage during well work because such damage is produced out with the sand and the wells clean up naturally. The transient nature of sand production is discussed and the production gains observed in each field is presented. Such a strategy requires that the sand production is managed in a safe and controlled manner where the negative consequences of sand production are manageable and predictable. This paper will also discuss the improvements made in sand detection and on-line erosion mapping required to improve the sand tolerance of these facilities.