Abstract
Asphaltene is a naturally occurring constituent of crude oil consisting of high molecular weight components which in most cases are in equilibrium within the liquid phase at initial reservoir conditions. As crude oil is produced and the energy of the reservoir depletes, the equilibrium is distressed and asphaltene can precipitate out of the liquid phase. Precipitation of asphaltenes is a condition for asphaltenes deposition, but precipitation will not always result in deposition. Deposition of asphaltene has the potential to negatively impact productivity of oil wells up to the point of completely shutting in production if the problem is not identified on time and mitigated and/or treated properly. The objective of this work is to present a systematic process for data acquisition and data analysis to identify the region in the well production system where asphaltene deposition is occurring leading to a properly designed operating strategy for production and interventions.
In order to identify and mitigate (or treat) the organic damage caused by asphaltene deposition near the wellbore, a methodical surveillance plan has been developed to acquire and interpret the required information at the right stage of the oil field development. The methodology consists of combining two different approaches: 1) Laboratory analysis of reservoir fluid samples using near infrared (NIR), high pressure microscope (HPM), and particle size analysis (PSA); and 2) Pressure transient analysis and multi-rate testing.
This procedure has allowed us to determine when skin develops and where in the well production system between the perforations and the downhole gauge asphaltene deposition is occurring. Specifically, we have been able to integrate results of asphaltene onset pressure (AOP) with quantification of total damage and the evolution of Darcy versus non-Darcy skin to identify if damage is worsening in the formation rock or anywhere below the permanently installed downhole pressure gauge. This paper presents an innovative approach as the integration of reservoir fluid characterization; pressure transient analysis and multi-rate testing have been combined to fully assess the damage mechanism, location of the damage, and the evolution of damage as a function of cumulative production. As a result of this methodology we have been able to properly design and schedule treatments to enhance well productivity and extend the longevity of the wells without exorbitant operating expenses and unnecessary downtime. Individually, these interventions have generated economic value and greatly increased the worth of deepwater oil fields in the Gulf of Mexico through sustainable delivery.
