Physicochemical Characterization of Crudes and Solid Deposits as a Guideline to Optimize Oil Production

Abstract

A comprehensive analysis scheme devised in order to cope with solid precipitation during oil production is being currently followed in many Venezuelan production units. Three goals from the scheme are: 1. Identification of remedial actions based on deposits characterization, 2. Selection of the most efficient dispersant additive, 3. Choice of the proper solvent mixtures for cleaning production strings, when organic types were assessed to be the main components of the deposit. This paper addresses these aspects with examples taken from a field located in eastern Venezuela. Introduction Solid precipitation has been experienced in many Venezuelan production units since the past decade1–3. A preventive and corrective global approach to handle the problem has been proposed1,4,5, based on the historical production records and physicochemical characterization of fluids and available solid deposits. For operationally unstable crude oils (production records showed solids precipitation), one of the key issues is the identification of chemical dispersants able to prevent solids adhesion to pipe walls. One way to find the proper additive(s) is to titrate a sample of the dead crude with an alkane precipitant, including a certain dosage of a commercial inhibitor. This titration is commonly carried out at ambient conditions, following published methodologies6,7. However, recent findings suggest that this procedure when done at high temperature improve the detection limits and the reproducibility of this determination8. When field workovers made available solid deposits, expanded possibilities are then open through their analysis in order to get to understand the origin of the problem and, to improve the remedial and preventive actions to be taken for each particular case. The deposit analysis scheme has been described previously3,9,10 and a picture of the general causes for precipitation can be achieved by correlating deposits compositional information got from wells drilled into the same reservoir. Another benefit derived from deposit characterization is the identification of the proper solvent mixtures to effect their redissolution, when organic types were the main components of the solid. Ultrasonic, accelerated extraction and simple redissolution experiments were carried out to this end. Simple redissolution experiments proved to be the best trade-off. Some results in this regard have been published10, and more details are to be found within the discussion from this paper. Examples from a field study located in eastern Venezuela illustrate the application and benefits derived from the titration, characterization and dissolution protocols, which will be also covered by themselves within this paper. Crudes and deposits were sampled during the past 2 years from the field identified during the ensuing discussion like "Field PST".

Ultrahigh-Resolution Magnetic Resonance Mass Spectrometry Characterization of Crude Oil Fractions Obtained Using n-Pentane

“…As the asphaltene deposit builds up, permeability decreases, causing a reduction in oil production rates . In extreme cases, oil production can stop and removal of the deposit is the only solution …”

“…2 In extreme cases, oil production can stop and removal of the deposit is the only solution. 3 Among the causes that induce asphaltene deposition, changes in composition can play a significant role when recovery methods, such as vapor extraction (VAPEX), expanding solvent steamassisted gravity drainage (ES-SAGD), and N-solv, are attempted to produce heavy oils. 4 These methods employ hydrocarbon solvents, such as propane, butane, pentane, and hexane, to reduce the viscosity of the crude oil and ease production.…”