Asphaltene-Prevention Work Flow Enhances Oil Production in High-Temperature Fractured Carbonate Reservoirs

Abstract

Summary Asphaltene precipitation is a common phenomenon in mature reservoirs that seriously impairs oil production. In high-temperature (HT) fractured carbonate reservoirs, the situation becomes critical when asphaltene precipitates at reservoir conditions, blocking the production channels and starting a cycle of production decline in which additional pressure drop increases the precipitation of the asphaltene fraction. Therefore, it is essential to make an early diagnosis of the problem and deliver an optimal solution to avoid further production decrease. A proper diagnosis regarding the point of precipitation along the production path requires a complete analysis of the well's production behavior and reservoir characteristics. To avoid asphaltene precipitation inside the rock matrix, different methods can be applied: maintaining reservoir pressure above the asphaltene-onset pressure, avoiding coproduction of incompatible reservoir fluids, adjusting artificial-lift conditions, or injecting solvents with inhibitors or dispersants. In two mature fields in southern Mexico that have been producing since 1995, an operator needed to determine where the asphaltene precipitation was occurring. An integrated diagnosis work flow was instrumented that included the creation and analysis of the asphaltene-phase envelope plus an asphaltene-onset screening test by use of a solids-detection system (SDS). After coupling screening results with a pressure/temperature flowing survey, it was identified that asphaltene precipitation occurred inside the reservoir when the bottomhole flowing pressure dropped below a critical level. To address the organic deposits and unstable pressure behavior successfully, asphaltene-precipitation characterization was essential. In some cases, a decrease in oil production after executing unsuccessful matrix-cleanup treatments with solvents results from a misdiagnosis of organic precipitation or a lack of knowledge about flocculation and precipitation causes. To avoid this problem, a new methodology for the inhibition-treatment design was added to the diagnosis work flow; this methodology includes a new adsorption-type asphaltene inhibitor as part of the matrix-cleanup treatment. As a result of this diagnostic-solution work flow, an optimum bullheaded inhibition treatment was determined and applied to the candidate wells. In all study cases, the time lapse between inhibition treatments was extended by 60 days on average, resulting in steadier oil flow rates plus significant reduction in well intervention and deferred production costs. In addition, the post-treatment results showed that, in 50% of the documented interventions, the inhibitor treatment improved overall production performance by at least 10%. The systematic engineering work flow presented in this paper includes the diagnostic procedure, data from laboratory testing, chemical selection, and treatment application. Subsequent treatment results enhanced the field operator's understanding of asphaltene precipitation in the formation matrix and provided more insight into maximizing oil production with specialized technology solutions that used a novel adsorption-type asphaltene inhibitor.

Phase Behavior and Reversibility Mechanisms of Asphaltene Precipitation for High-Pressure High-Temperature CO2–Oil Systems

“…Asphaltenes are identified as polydisperse fractions, polar, brown to black, and considered as a solubility class insoluble in n -pentane or n -heptane but soluble in toluene, benzene, or xylene . Researchers know them as the most complex components of crude oil, having the heaviest molecular weight, no melting point, and no unique chemical structure. , They can be found as a dispersed fraction in the fluid phase, an agglomerated-colloidal-viscous liquid phase, or stacked chunks of solid particles. The asphaltene particles have no specific shape, and their complex-vary molecular structure is classified into the island and archipelago groups.…”