In this paper, we will highlight some of the impactful collaborative efforts completed within DeepStar Phase XII of the X200 Flow Assurance committees leading to the development, integration and deployment of novel technologies. This project aims to establish in what cases asphaltene deposition in reservoirs is a real problem. Flow reduction can occur in deepwater wells, which manifests as effective "skin" or high pressure drawdown required for fluid flow to be maintained. It is typically concluded, without additional evidence, that such problems are the result of asphaltene deposition. Some models for asphaltene deposition were developed between 1990 and 2005. However, the principal obstruction to validation of these models has been a credible core flow test to show increased flow restriction with depositing asphaltenes. At present, operators are unable to estimate the risk of development due to asphaltene deposition in reservoirs and the perceived flow impairment. To best assess the treatment frequency and effectiveness that is required for project development and execution, there is a need to be able to correctly predict the rate of formation damage in reservoirs from asphaltene deposition and develop effective remediation treatments. A successful project will provide test protocol, results, and analysis tools that can be applied to risk management evaluation for asphaltene fouling in reservoirs. Asphaltene precipitation and deposition in the production tubing and surface facilities is a well- documented issue and different methods are available to manage this problem. However, the problems that asphaltenes may cause in the reservoir, especially in the near-wellbore region, are much less understood. There is a lack of experimental capability to properly identify this problem and evaluate the corresponding potential strategies for prevention and/or remediation if/when needed. In addition, the available modeling tools to account for this problem have limited capabilities. Within this project, we aim to develop experimental procedures and modeling methods to establish whether impairment caused by asphaltene deposition in reservoirs is a real problem or not, and to develop an understanding of the mechanisms by which asphaltene precipitate, alter wettability and potentially deposit in the formation obstructing flow. A new experimental setup for Saturates, Aromatics, Resins, and Asphaltenes (SARA) characterization was designed and implemented in the lab to perform faster and more reliable analyses. Core flood experiments have been designed and successfully executed to induce the precipitation of asphaltenes inside the core upon addition of an asphaltene precipitant (e.g., n-pentane or n-heptane), which is crucial to obtain more meaningful and more representative experimental conditions. It has been observed that when n-pentane is used to precipitate asphaltenes, even though asphaltene aggregates are present in the system, the core flood test results do not show apparent damage to permeability. However, when asphaltenes are precipitated upon addition of n-heptane, aggregates have a more solid-like structure, which in turn have more tendency to block the pore throats. A microfluidic device was developed and used to visualize asphaltene deposition in porous media, at ambient pressure and different temperatures, flow rates, and driving force of asphaltene precipitation. The test results obtained from microfluidic device are in good agreement with the test results from the core flood experiments. A Computational Fluid Dynamic model based on Lattice-Boltzmann theory was developed to simulate asphaltene deposition inside porous media and is being validated for the capability to scale up lab results to field conditions.
Gas hydrates can form in subsea oil and gas flowlines, where the depths of seawater and ocean conditions provide the thermodynamic environment for hydrate stability. Hydrates present a major flow assurance problem due to the relatively fast timescales at which they can form, grow/agglomerate, and plug a flowline. The common strategy for preventing hydrate formation uses thermodynamic inhibitors (THIs). However, THIs can be cost prohibitive or impractical as the water content in the flowline and its seawater depth increases. Therefore, there is growing interest in the use of alternative hydrate management strategies, such as the injection of low dosage hydrate inhibitors (LDHIs), which are active at considerably lower concentrations than THIs (e.g. 2 vol.% of LDHI versus 50 vol.% of THI). Anti-agglomerants (AAs) are a type of LDHI that prevent agglomeration and allow hydrates to flow as a slurry in oil and gas subsea flowlines. Before field deployment, AAs are screened and selected using laboratory set-ups, mimicking field conditions, in order to evaluate their performance and determine the effective dosage. Current hydrate agglomeration characterization methods implemented in the industry are non-uniform and qualitative, which can lead to conservative recommendations. In this work, the possibility of quantifying hydrate agglomeration in the presence of AAs is investigated, along with studies of the mechanisms via which AAs may operate. One mineral oil and two crude oils were used with a commercial AA in a high pressure stirred autoclave, equipped with particle imaging probes. Motor current input at a fixed RPM was monitored throughout the experiments and serves as an indicator of relative viscosity of the hydrate slurry. This investigation enabled the development of a comprehensive AA performance evaluation. Hydrate agglomeration was detected and quantified by simultaneous increases in the relative motor current and chord length distribution.
In this work, the effects of an anti-agglomerant (AA) and salt (sodium chloride, NaCl) on water-in-oil (w/o) emulsion stability with and without the presence of gas hydrates is presented. The characteristics of gas hydrate formation and the hydrate slurry transportability were determined using a high pressure autoclave cell, with continuous mixing. The stability of the emulsions was independently measured by performing bottle tests, where the stability of the emulsion was determined by observing any evidence phase coalescence for a period of one week after emulsification. In addition, the stability of the emulsion with hydrate formation and dissociation was tested using high pressure differential scanning calorimetry (DSC). From high pressure autoclave studies, it was observed that the formation of a stable emulsion was shown to with the subject oils led to transportable hydrate slurries. Note however, it was observed that for this specific oil at 75 vol.% water cut and the addition of both AA and salt, a highly viscous mousse with viscosity of ~100 000 cP formed when the emulsion was saturated with methane gas at 950 psia and 20 °C. Even without the presence of hydrate, the formation of a highly viscous mousse may not be desirable in the field production system since it could render the system inoperable (effectively plugged). Interestingly, it was observed that the highly viscous mousse produced dispersed slurry of hydrates upon hydrate formation. Based on the autoclave studies, the absolute motor current (which indicates the relative viscosity of the system) at maximum amount of hydrate is 2 times lower of its original viscosity.
DeepStar® is an operator-funded Research & Development joint industry consortium including members of the oil community such as oil & gas companies, vendors, regulators, and academic/research institutes working in multidisciplinary technology areas. The DeepStar Project has been in continuous operation since its inception in 1991 and has focused on issues and technologies required to successfully tackle future development and production challenges identified by its members.1 The focus of this manuscript and extension, the presentation, will be on the numerous projects that were the baseline for current industry standards. The DeepStar program is split into six technical areas of focus from subsurface and drilling to topside and autonomous operations and everything in between. The manuscript will be written focusing on those technical areas and the supporting projects in which final documents are used within the standards. The emphasis will be on three strategic areas of interest for our DeepStar members; first Integrity Management and the integration of our guidelines into the 1) API RP 2SIM Structural Integrity Management of Fixed Offshore Structures2, 2) API RP 2RIM Integrity Management of Risers from Floating Production Systems3 and 3) API RP 2 MIM Mooring Integrity Management.4 The second topic is DeepStar work on AUV interface standards5 and the integration of our work into API RP 17H6 and into the SWIG JIP.7 The final topic highlighted within the session on Standards is DeepStar’ continuous work on Subsea Chemical Storage and Distribution Systems Subsea8 to which DeepStar has developed the business case, background requirements, field case studies, and funding commercialization development on this topic since 2010.9 This manuscript outlines DeepStar’ strategies, projects, and accomplishments through a collaborative effort amongst operators, engineering firms, manufactories, academic intuitions, and government regulators. Through this joint effort, members have been able to minimize the cost and risk of industry-wide engagement and technology development, while at the same time making the most of the organization's particular technology achievements. This aligns with DeepStar’ vision for the development of deepwater technology, which is closely tied to the development and qualification of advanced technologies and gaining acceptance within the oil & gas community. DeepStar has continuously confronted industry-wide issues and provided a forum for discussion and technology acceleration.
This work shares some of the impactful collaborative efforts completed within DeepStar® Global Deepwater Technology Development Program as part of Phase XII projects in X500 Drilling & Completions committees. It will lead to gap identification and provide a current baseline of shearing technologies. The goal of this research was to survey the BOP industry and gather information about the current state-of-the-art of shearing systems as well as future shearing technologies. The work includes: development of a survey form/table, data collection, and reporting. A survey table has been developed as part of the present project. The survey table includes: equipment specification (description/type, rated pressure, rams type, etc.), equipment capabilities (water depth rating, compatibility with H2S environment, working temperature range, etc.), equipment options to improve performance (customizable options to enhance shearing performance ram capabilities and/or options for specific applications such as sour service), and testing (repeatability of shearing and durability performance, tested pipe sizes, wall thicknesses, material grades, evidence of testing, etc.). The desired outcome of the present work includes DeepStar® operators members being allowed access to performance information regarding current state-of-the-art shearing systems summarized in one report. The report will facilitate discussion about the available shearing capabilities as well as future technologies. This document can also be helpful in selecting BOP providers (and/or future technology providers that will be able to operate in 20 ksi pressure conditions).
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