Method and system for determining vapor pressure or composition of hydrocarbon liquids

A method for determining the composition of a mixture of crude oil and natural gas liquids at a given temperature comprising the steps of:

• providing data comprising the vapor pressures of respective predetermined mixtures of crude oil and natural gas liquids at selected temperatures;
• causing the liquid mixture in question to flow through eductor means while measuring the total pressure of said liquid mixture at a location in said eductor means which comprises the minimum pressure point of fluid flows in said eductor means for a plurality of selected pressure differentials measured across said eductor means;
• determining when the slope of a curve represented by the locus of the total pressure at said minimum pressure point in said eductor means as a function of the selected pressure differential across said eductor means which produces said total pressure, respectively, is substantially zero;
• and
• comparing the total pressure value when said curve slope is substantially zero with said data representing the vapor pressures of said respective predetermined mixtures to determine the composition of the liquid being measured.

A method for determining the vapor pressure of a liquid composition such as crude oil and natural gas liquids at a given temperature comprising the steps of:

• causing the liquid composition to flow through eductor means while measuring the total pressure at a fluid suction port in said eductor means for a plurality of selected pressure differentials measured across said eductor means;
• determining the slope of a curve represented by the locus of the total pressure of the fluid at said suction port as a function of the selected pressure differential across said eductor means which produces said total pressure, respectively, by the equation:
• P.sub.s =A.sub.e.sup.-B.DELTA.P
• wherein P.sub.s =total pressure at said suction port, A is a constant, B is the slope of said curve, e is the base of natural logarithms and .DELTA.P is said selected pressure differential;
• and
• determining the intercept of said curve with a curve representing the relationship of total pressure at said suction port in said eductor means versus the pressure differential across said eductor means for a degassed liquid composition, which intercept is related to the bubble point pressure of said liquid composition.

A system for determining the vapor pressure of a liquid composition comprising crude oil and relatively low molecular weight hydrocarbon liquids comprising:

• conduit means for withdrawing a sample of said liquid composition from a flowstream;
• pump means connected to said conduit means;
• a plurality of eductors connected to receive liquid from said pump means and having a construction whereby liquid flowing through said eductors reaches a minimum pressure at a predetermined point in said eductors, respectively;
• said plurality of eductors being arranged in parallel for receiving liquid flowing from said pump means and including flow control means interposed between said eductors and said pump means for varying the flow rate of liquid through said eductors, respectively;
• pressure sensing means for sensing the total pressure at said minimum pressure point in said eductors, respectively;
• and
• pressure sensing means for measuring the pressure differential across said eductors for liquid compositions flowing through said eductors, respectively.

A system for determining the vapor pressure of a liquid composition comprising crude oil and lower molecular weight hydrocarbon liquids comprising:

• conduit means for conducting a sample of said liquid composition;
• pump means connected to said conduit means;
• eductor means connected for receiving liquid from said pump means and having a construction whereby liquid flowing through said eductor means reaches a minimum pressure at a predetermined point in said eductor means;
• said conduit means comprising a plurality of conduits arranged in parallel for receiving liquid flowing from said pump means and including flow control regulating means interposed in said conduits between said eductor means and said pump means for varying the flow rate of liquid through said eductor means;
• pressure sensing means for sensing the total pressure at said minimum pressure point in said eductor means, respectively;
• and
• pressure sensing means for measuring the pressure differential across said eductor means for respective flow rate of said liquid composition flowing through said eductor means, respectively.