Equations to predict precipitation onset and bubblepoint pressures of asphaltenic reservoir fluids

Abstract

A set of algebraic equations to predict upper onset-of-precipitation and bubble-point pressures of asphaltene-containing reservoir fluids in wide temperature ranges are proposed. In developing the equations, laboratory data of 11 Mexican and 12 more live oils have been analyzed, and a correlation of these data with temperature has been found. A modified least-squares regression method has been used to develop two versions of the proposed equations. In one version, a single pressure/temperature data point is required to predict the entire onset/bubble-point curves at any temperature. For oils with no experimental precipitation data available at all, a second version of the proposed expressions employs standard chromatographic data of the reservoir fluid to provide a reasonable prediction. The average absolute deviations in calculated onset and bubble-point pressures by the proposed equations are 2.53 and 0.45MPa by the one-point correlations, respectively, and 3.96 and 1.62 MPa by the compositionally-based correlations, respectively. The developed expressions are simple and can be used to provide reasonable predictions of upper onset and bubble-point pressures of asphaltenic live oils in cases where laboratory data are scarce.

Estimation of the SARA Composition of Crude Oils from Bubblepoint Pressure Data

“…Step 1: The type of crude oil (light, medium, or heavy), the light-end composition, and the bubblepoint data set are input as the data set to a problem. As an example (see Table ), data of “well-3” of ref were taken.…”

“…In a previous work, del Rio et al plotted the bubblepoint pressure ( P bp ) as a function of temperature ( T ) for a series of Mexican crude oils. For the range of temperatures studied, it was found that a correlation of P bp ( T ) can be described by a family of parallel straight lines, where, for each crude oil, where B bp is a constant independent of the crude oil and f bp ( C bp ) is an independent term of the straight line.…”

“…For the range of temperatures studied, it was found that a correlation of P bp ( T ) can be described by a family of parallel straight lines, where, for each crude oil, where B bp is a constant independent of the crude oil and f bp ( C bp ) is an independent term of the straight line. In the study by del Rio et al, it was proposed that f bp ( C bp ) depends on composition of the oil in the following form: where x H 2 S , x N 2 , and x CO 2 are the molar fractions of H 2 S, N 2 , and CO 2 ; t Sa , t Ar , t Re , and t As are the values of the SARA compositions in weight percent (wt %); and f H 2 S , f N 2 , f CO 2 , f Sa , f Ar , f Re , and f As are constants. The procedure to calculate all constant terms in eqs and is the following.…”

“…Table shows some features of our database. The set includes SARA analyses reported in 108 public papers found in open and private literature. ,− …”

“…SARA analyses provide further compositional information on the resin/asphaltene content of a producing fluid. For a flow-assurance study, of a given production asset, the SARA separations require extensive time and laboratory resources, and reproducibility issues have been a constant challenge. − To avoid this difficulty, a few calculation approaches for estimating the SARA composition of asphaltenic fluids have been reported in open literature.…”