Flow Assurance: A challenging path to well completions and productivity
Authors: Joshi Nikhil B. , Muhammad Moin , Creek Jefferson Louis , McFadden Jim 
Published: October 2008

Flow assurance issues such as asphaltene deposition are one of the important areas being studied today due to the high cost of deepwater E&P. Thus, effective measurements to understand asphaltene phase behavior in the reservoir fluid are required. The present text discusses the effects of sample handling as well as oil-bassed mud contamination on the results for asphaltene precipitation.

Introduction

The invigorating interest of the E&P industry in deepwater has enabled the discipline of flow assurance to come to the forefront. With an increase in number of deepwater wells, it is imperative to minimize risks caused by solids deposition due to the high costs and difficult accessibility. To achieve this goal, early identification of possible tribulations and development mitigation strategies plays a key role in a successful completion and operation of a well. These are accomplished through an effective sampling and analysis program that gives insight into the tentative flow assurance issues. This paper discusses the impact of appropriate representative fluid sampling, sample handling and flow assurance analysis to the bottom line. A case study of the effect of fluid sampling on the flow assurance results is presented.

The flow assurance issues in deepwater are primarily due to the deposition of solids in the production path. The tentative areas of solids deposition, amongst others, can be as follows:Near wellbore region,Production tubing,Subsea wellhead,Subsea flow lines, andSeparators. Solids deposits can be classified into four major species:asphaltenes,waxes,hydrates, andscaling, or combination of any of the above. In the present text, primary focus is on asphaltenes. It is necessary to understand the behavior of asphaltenes in the reservoir fluid, to devise strategies to mitigate risks of their deposition. Their behavior can be studied by following an effective and well-planned sampling and analysis program. The program can be structured by taking into account the fundamental knowledge of these species and their behavioral history. Typical behavior of asphaltenes is discussed briefly in the following text.

Asphaltenes are defined by their solubility characteristics. They are soluble in aromatic solvents such as toluene but precipitate upon addition of n-alkanes such as n-heptane. During production, asphaltenes are also known to precipitate as a result of change in pressure, temperature and or composition of the fluid. Asphaltenes are usually the heaviest fractions of the crude oil. From literature and past history, it is known that asphaltene precipitation is more likely to occur in an under-saturated, light reservoir fluid than a heavy hydrocarbon system. It is also noteworthy that problems due to asphaltenes occur in a two-step process:precipitation from the reservoir fluid, anddeposition of the precipitated asphaltene particles, which causes plugging.

Presently, methods to understand asphaltene precipitation are used to understand their behavior. New techniques are being developed to measure asphaltene deposition but are not in common use in the industry.