THERMODYNAMICALLY CONSISTENT ESTIMATION OF HYDROCARBON COMPOSITION FROM NUCLEAR AND MAGNETIC RESONANCE MEASUREMENTS

摘要

Accurate assessment of hydrocarbon compositionsis critical for optimizing oil and gas production.However, in-situ assessment of hydrocarbonproperties is difficult because of environmentalconditions and fluid sample quality. Fluid samplescan be acquired using wireline formation testers(WFT) for laboratory analysis, but the number ofsamples is limited to discrete depths. Reservoirfluid samples tested in the laboratory may notexhibit the same properties as in-situ samplesbecause the phase behavior of hydrocarbons variessignificantly with temperature and pressure.Thermodynamically consistent fluid interpretationsare crucial for obtaining accurate estimates of insituhydrocarbon properties and composition.We introduce a new method to quantify in-situhydrocarbon properties from borehole nuclearmeasurements. These measurements are influencedby rock fluid and matrix. After separating matrix,water, and hydrocarbon effects on borehole nuclearmeasurements, we use the hydrocarbon-dependentportion of the nuclear response to assesscomposition. Application of the new hydrocarboncomposition method to two field examples,including one in a gas-oil transition zone, yieldedreliable and verifiable results. Oil-viscosity valuesderived from NMR T_2 distributions and WFTpressure data confirmed the estimated hydrocarboncomposition. Our estimation method allowscontinuous assessment of compositional gradientsat in-situ conditions and providesthermodynamically consistent interpretations ofreservoir fluids that depend greatly on phasebehavior. Combining nuclear and NMRmeasurements identifies variations withinhydrocarbon columns, diagnoses reservoirconnectivity, and facilitates optimized hydrocarbonproduction.