A method to estimate well flowing gas-oil ratio and composition using pressure and temperature measurements across a production choke, a seed composition of oil and gas, and a thermodynamic simulator

TL;DR

This paper presents a thermodynamic simulation-based method to estimate well flowing gas-oil ratio and composition from pressure and temperature measurements across a choke, useful when direct composition measurements are unavailable.

Contribution

The method combines a seed composition with a thermodynamic simulator to accurately estimate wellstream properties without direct sampling, improving field management.

Findings

Predicts gas-oil ratio with up to 12% error

Estimates compositions with a maximum 21% error

Requires a temperature drop measurement accuracy of 0.01°C

Abstract

In this work we propose and demonstrate a method to estimate the flowing gas-oil ratio and composition of a hydrocarbon well stream using measurements of pressure and temperature across a production choke. The method consists of using a numerical solver on a thermodynamic simulator to recombine a seed oil and gas until the simulated temperature drop across the choke is equal to the measured value. This method is meant for cases where it is not possible to measure periodically individual well composition. A study case and reference solution were generated using the reservoir model presented in the SPE (Society of Petroleum Engineers) comparative case Nr. 5 linked with a process simulator. Time profiles of well producing gas-oil ratio, wellstream compositions, compositions of surface conditions oil and gas, and temperature drop across the choke were generated with the models. The method proposed was then employed to estimate the flowing gas-oil ratio of the reference solution. Results show that the proposed method predicts with reasonable accuracy (maximum 12% percent error) the well gas-oil ratio and compositions during the life of the field when using compositions of surface oil and gas from initial time. When using compositions of surface oil and gas from later times, the prediction accuracy of the gas-oil ratio improves at those times but worsens for times before and after. A measurement error for the temperature drop across the choke of at least 0.01 {\deg}C is required to achieve convergence of the method. The mean percent error between the predicted and real mole fractions has an upper bound in time of 21% when using initial surface oil and gas as seed compositions.