A method of determination of fluid characteristics in a well, wherein said method is implemented by a computer and comprises: /a/ receiving mass ratios provided by a Downhole Fluid Analysis measurement, each mass ratio being associated with a set of hydrocarbon cuts, and receiving a molecular ratio provided by a Gas While Drilling measurement, said received molecular ratio being associated with a set of hydrocarbon cuts; /b/ converting received mass ratios into molecular ratios based on predetermined molecular weights, each predetermined molecular weight being associated with a set of hydrocarbon cuts; /c/ normalizing converted molecular ratios with the received molecular ratio; /d/ determining parameters ( α, β) of a sequence defined by x n = α 1 − β n x n − 1, x n being a molecular fraction of the hydrocarbon cut of rank n, n being an integer, each parameter ( α, β) being comprised between 0 and 1, each normalized molecular ratio being associated with a member of the sequence or a sum of members of the sequence, at least a difference between said normalized molecular ratio and the associated member or the associated sum of members being minimized; /e/ computing an estimated molecular weight of hydrocarbon cuts comprising molecules having k or more carbons ( Mw k +) function of k + 1 1 − α Δ M, where k being an integer and Δ M being a predetermined value representing a molecular weight increment between two hydrocarbon cuts; /f/ if a stabilization criteria is not met, the steps /b/ to /f/ are iterated with the estimated molecular weight as one of the predetermined molecular weights in step /b/, wherein the stabilization criteria of step /f/ comprises at least one following condition: - an absolute difference of a value of α between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - an absolute difference of a value of the estimated molecular weight between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - a number of iteration of steps /b/-/f/ exceeds a predetermined value; /g/ outputting the values of the parameters determined in step /d/. /a/ receiving mass ratios provided by a Downhole Fluid Analysis measurement, each mass ratio being associated with a set of hydrocarbon cuts, and receiving a molecular ratio provided by a Gas While Drilling measurement, said received molecular ratio being associated with a set of hydrocarbon cuts; /b/ converting received mass ratios into molecular ratios based on predetermined molecular weights, each predetermined molecular weight being associated with a set of hydrocarbon cuts; /c/ normalizing converted molecular ratios with the received molecular ratio; /d/ determining parameters ( α, β) of a sequence defined by x n = α 1 − β n x n − 1, x n being a molecular fraction of the hydrocarbon cut of rank n, n being an integer, each parameter ( α, β) being comprised between 0 and 1, each normalized molecular ratio being associated with a member of the sequence or a sum of members of the sequence, at least a difference between said normalized molecular ratio and the associated member or the associated sum of members being minimized; /e/ computing an estimated molecular weight of hydrocarbon cuts comprising molecules having k or more carbons ( Mw k +) function of k + 1 1 − α Δ M, where k being an integer and Δ M being a predetermined value representing a molecular weight increment between two hydrocarbon cuts; /f/ if a stabilization criteria is not met, the steps /b/ to /f/ are iterated with the estimated molecular weight as one of the predetermined molecular weights in step /b/, wherein the stabilization criteria of step /f/ comprises at least one following condition: - an absolute difference of a value of α between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - an absolute difference of a value of the estimated molecular weight between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - a number of iteration of steps /b/-/f/ exceeds a predetermined value; - an absolute difference of a value of α between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - an absolute difference of a value of the estimated molecular weight between two iterations of steps /b/-/f/ is lower than a predetermined threshold; - a number of iteration of steps /b/-/f/ exceeds a predetermined value; /g/ outputting the values of the parameters determined in step /d/.