Abstract

A high ratio of success has been seen in removing formation damage from older heavy oil wells using an asphaltene suspending agent in conjunction with a selective stimulation tool. Treatment involves spotting the agent at the formation face and in the immediate well bore region, allowing it to soak for a minimum of 16 hours, and then over flushing with a high volume of light crude at sub fracturing pressure. Results are shown from a number of wells from three different fields. Incremental production has been as high as 8X and has been sustained for as long as 18 months.

Introduction

Determining whether or not a well is producing to its maximum potential and, if not, how to remedy the situation is never a simple task. Notwithstanding, there are certain factors which can make a given problem within a given field more likely to occur than others. An excellent example is asphaltene problems in heavy oil wells. Asphaltenes are highly aromatic compounds containing small amounts of sulfur, nitrogen, and oxygen which give rise to a molecule with a partially positive charge. The resulting structure is held together through π - π, hydrogen and acid base bonding whose molecular weight has been reported to be a function of its environment: environments that favor dissociation of the individual units, such as higher temperatures and higher degrees of solvent aromaticity, result in lower molecular weights and thereby result in suspension; conversely, environments that favor association, such as lower temperatures and less aromatic solvents, result in higher molecular weights and thereby result in flocculation and precipitation.1 Typical Lloydminster heavy crude contains between 12% and 15% asphaltenes by weight, although it can contain as much as 22% in some fields. Essentially insoluble in oil by themselves, asphaltenes are held in suspension in oil by natural surfactants called resins. However, the bond holding the resins to the asphaltene is rather weak; resins can be stripped from the asphaltene through contact with light end alkenes as well as through variations in temperature and pressure.2 Thus, asphaltene precipitation can occur through the production process itself (due to decreased temperature) or can be induced through the use of loading fluids containing high amounts of light end alkenes. When asphaltenes do precipitate, it is likely that they will crystallize on a negatively charged solid, such as sand or clay. If the crystal is produced along with the sand, this precipitation does not represent a production problem (although it may cause a subsequent treatment problem). If, on the other hand, the sand / asphaltene conglomerate is not produced and enough sand is held together by this asphaltene type ‘cement’, the wellbore can eventually clog. Producing heavy oil through this blockage would be similar to filtering cold molasses through a high mesh filter.

Methods used to correct inflow problems due to asphaltenes have typically involved re-perforating or the use of solvents, either alone or in a "blend" with oil. Historically, re-perforating heavy oil wells gives a short term increase in production.

This content is only available via PDF.
You can access this article if you purchase or spend a download.