This paper presents the various challenges faced by a 10-km waxy crude oil pipeline at Field 23, as the pipeline has not been able to be pigged for almost one year due to recurring pigging issues such as broken/damaged pigs, vibrations and high pressures that were close to trip settings. The implemented pigging frequency as per operating philosophy is every two weeks. However, the frequency has been extended based on field experience. Due to these issues, Operation team immediate action is to devise a pigging program that works and to avoid recurring issues. Flow Assurance (FA) engineers working together with Operation team devised a plan that incorporates lab analysis and conducted desktop studies which include field data analysis and application of various FA simulation tools. The main challenge is to develop a robust FA model that is reliable enough to use for detailed analysis, be able to reproduce field data and use it to develop the most suitable pigging program. Additionally, it is worth noting that the pipeline has gone through rigorous wax chemical optimization that potentially contribute towards wax incremental issues in the pipeline. It was also observed that the fluid has changed tremendously from initial design basis due to fluid blending from non-associated gas (NAG) and oil zone and production header temperature mixing effects. Therefore, the initial operating envelope was found to be no longer suitable for this pipeline. From extensive lab analysis, fluid modelling update, metocean data calibration and wax deposition tuning, the FA models were able to match the field conditions within < 10 % variance. A field tuned baseline model was developed. Several options have been proposed and analyzed such as varying pig types, pigging and chemical methods where extensive FA modeling were performed to evaluate the suitability of each method/application to develop a more suitable pigging program. A detailed workflow on the chosen program was then produced based on a progressive pigging method utilizing multiple pig types at a reduced flowrate with chemical application. Although wax dissolution effects from wax dissolver chemical was not modeled, this model-based approach was a success in that we were able to reduce pig stuck risk during actual field implementation. The success of the waxy crude oil pipeline pigging campaign has sparked an immediate interest among the Production/Operation engineers especially on the application of a robust FA models, in which when it is well calibrated, enable effective and immediate troubleshooting of issues at site. This work has set a benchmark for FA engineers to update/develop a well-calibrated FA model during operation phase to facilitate optimization and troubleshooting programs.
A gas field is producing condensate with higher density than typical due to its higher napthene and aromatic content. Several future gas fields to be developed also have condensate with similar properties as this single field. The changes in future condensate properties and increasing amount of this atypical condensate will have major impact on existing refinery. It was necessary to create an integrated reservoir and surface facilities model and characterised fluids that can produce prediction of future feedstock including these aromatic condensate to the refinery. The model also produced the usual outputs such as gas quality and condensate quantities forecast over the life of the gas fields. A compositional network model consists of fluid modelling, reservoir, well, topside facilities and pipeline modelling through to the onshore terminal process modelling were developed in order to model the export gas and condensate network. Steady state models were developed and validated against operating condition for each system and an integrator was utilized in order to integrate the subsurface and process simulator together. For the fluid modelling, a compositional model suitable to produce assays was used instead of black oil model in order to predict the quality of both the gas and condensate delivered. The fluid models for fields with aromatic condensate used True Boiling Point (TBP) assay instead of a standard gas chromatograph composition from a Pressure, Volume and Temperature (PVT) laboratory test report. Several characterisation methods were developed and tested in order to obtain representative and relevant properties for refinery design. Other gas fields which had a more common chemical characteristic of paraffinic dominant condensate used standard characterisation method. The model enables representative prediction of condensate properties relevant for refinery design and evaluate options to develop the fields. The work will show that an integrated sub-surface-surface network model is essential in order to define the impact for a development throughout the value chain, specifically the changes to the products and downstream facilities. It will also provide an insight on the impact of fluid characterization methods of different types of condensate.
Cyclonic devices are ubiquitous in industrial processes and have been used for particle separation for decades. However, designing a highly efficient, compact cyclone for erratic flow conditions and particles of varying types, sizes and density remains a challenge. This paper aims to present the challenges, lessons learnt and recent development in cyclone technology for solid separation. Primarily, a discussion on typical cyclonic desander geometries is conducted. Failures and sub-optimal operation of cyclonic wellhead desanders within the company are analysed, and subsequently the failure mechanisms and factors leading to inefficiencies are identified. Computational Fluid Dynamics (CFD) simulations and flow loop testing are further performed to verify the particle separation efficiency and quantify the erosion risks of the typical cyclone geometries. The typical cyclonic geometries are considerably less efficient in multiphase-flows compared to the gas-solid or liquid-solid flows. As a result, the overflow section of the cyclone often contains particles larger than the design specification. Changing operating envelope over time, for example, reducing production and changing flow regime affects cyclone efficiency over time. Based on a systematic analysis of the desander failures in the fields, a few design improvements have been proposed to overcome these limitations, resulting in a novel technology. This new cyclonic technology with multiple barrier system can successfully maintain the 98% target removal of 10microns particle under erratic multiphase-flows conditions. Furthermore, it can be designed to handle various types of particles e.g., sands, HgS and other solids. The versatility of this system provides promising technology for ageing fields with excessive solids production.
Typically, for a high volume, low condensate-gas ratio offshore gas production field having high content of carbon dioxide (CO2), hydrogen sulphide (H2S), mercury and solid particulates having to meet Liquified Natural Gas (LNG) inlet specification would require an enormous facility exceeding the largest available floatover vessel capacity. Aside from an enormous and complex processing facility, it would also require a large emergency disposal system and sour service pipeline material to cater for start-up and process excursion scenarios. In order to obtain a commercially attractive solution while meeting technical integrity and designing for operational excellence in mind, several innovative design approaches were implemented. The scope of this paper will cover major optimization implemented at gas treatment system, emergency blowdown system, export gas pipeline, and venting system at receiving platform.
Wax deposition is one of the major risks that causes a serious threat to pipeline transportation during operation, if not prevented. The remediation actions are usually costly; hence mitigation methods are in place to completely avoid the issues from happening. The wax deposition modelling technique has been accepted as a tool to design and continuously optimize the wax management strategy. Non-Newtonian oil-wax viscosity is an important parameter affecting wax deposition in pipelines. The present and widely used viscosity model assumes exponential behaviour as observed in the emulsion system. In this paper, it is demonstrated that this assumption may not be suitable for Malaysian waxy crude oil applications due to instantaneous change of viscosity below WAT and PPT. This paper focuses on the application of the Pedersen and Ronningsen viscosity model available in the commercial fluid and flow simulators namely PVTsim ®, Multiflash ® and OLGA ® which are widely used by the flow assurance fraternities, and how it will impact wax deposition prediction accuracy specifically when applied to Malaysian waxy crude oils. ABSTRAK: Pemendapan lilin adalah salah satu risiko utama yang menyebabkan ancaman serius kepada pengangkutan saluran paip semasa operasi jika tidak dicegah. Proses membaiki biasanya memerlukan kos yang tinggi; oleh itu kaedah mitigasi disediakan bagi mengelakkan isu ini daripada berlaku. Teknik model pemendapan lilin telah diterima sebagai alat bagi mereka bentuk dan merupakan strategi optimum pengurusan lilin secara berterusan. Kelikatan minyak-lilin bukan Newton adalah salah satu parameter penting yang mempengaruhi pemendapan lilin dalam saluran paip. Anggaran model kelikatan semasa yang digunakan secara meluas menjangkakan tingkah laku eksponen seperti yang diperhatikan dalam sistem emulsi. Kajian ini menunjukkan bahawa kaedah anggaran mungkin tidak sesuai bagi aplikasi minyak mentah berlilin Malaysia disebabkan oleh perubahan kelikatan serta-merta di bawah WAT dan PPT. Kertas kerja ini memberi tumpuan kepada aplikasi model kelikatan Pedersen dan Ronningsen yang terdapat dalam cecair komersial dan simulator aliran iaitu PVTsim ®, Multiflash ® dan OLGA ® yang digunakan secara meluas oleh persatuan jaminan aliran, dan keberkesanan pada ketepatan anggaran pemendapan lilin khususnya apabila digunakan pada minyak mentah berlilin Malaysia.
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