Patent Document ID: 9416647
Application ID: 13754549
Patent Flag: 1

Claim One:
1. A method for characterizing petroleum fluid in a reservoir traversed by at least one wellbore, the method comprising: (a) at a plurality of measurements stations within the at least one wellbore, acquiring via a borehole tool at least one fluid sample at the respective measurement station and performing via a data processing system of the borehole tool downhole fluid analysis of the fluid sample to measure properties of the fluid sample, the properties including concentration of a plurality of high molecular weight components; (b) for each given one of a plurality of class-types corresponding to different subsets of a predetermined set of high molecular weight components, using a model of the a data processing system that predicts concentration of the high molecular weight components of the given class-type for said plurality of measurement stations; (c) comparing via the data processing system the predicted concentrations of the high molecular weight components for the plurality of class-types as derived in (b) with corresponding concentrations measured by the downhole fluid analysis in (a) for said plurality of measurement stations to identify the best matching class-type; (d) in the event that the best-matching class type identified in (c) corresponds to at least one predetermined asphaltene component, evaluating via the data processing system asphaltene stability in the petroleum fluid of the reservoir at a given depth in the reservoir using equilibrium criteria involving an oil rich phase and an asphaltene rich phase of respective components of the petroleum fluid at the given depth, wherein the equilibrium criteria of (d) are defined by a relationship of the form 
 x i oil γ i oil =x i asph γ i asph , where the subscript i corresponds to the respective component of the petroleum fluid of the reservoir at the given depth, superscripts oil and asph correspond to the oil rich phase and the asphaltene rich phase, respectively, of component i at the given depth, x i oil is the mole fraction of the oil rich phase of component i of the petroleum fluid of the reservoir at the given depth, γ i oil is the activity coefficient of the oil rich phase of component i of the petroleum fluid of the reservoir at the given depth, x i asph is the mole fraction of the asphaltene rich phase of component i of the petroleum fluid of the reservoir at the given depth, and γ i asph is the activity coefficient of the asphaltene rich phase of component i of the petroleum fluid of the reservoir at the given depth, and wherein the equilibrium criteria of (d) are further defined by a relationship of the form: ∑ i = 1 N ⁢ ⁢ x i asph - ∑ i = 1 N ⁢ ⁢ x i oil = ∑ i = 1 N ⁢ ⁢ ( K i - 1 ) ( L + ( 1 - L ) ⁢ K i ) ⁢ z i = 0 where K i =x i asph / x i oil =γ i oil / γ i asph , K i is an equilibrium constant of component i, L is mole fraction of the oil rich phase of all N components of the petroleum fluid of the reservoir at the given depth, and z i , is the mole fraction of the mixture of the oil rich phase and asphaltene rich phase of component i at the given depth; and (e) using the results of (d) for reservoir analysis.