SPE 164334 Well Test Rate Conversion to Compositional Wellstream
Mohammad Faizul Hoda, SPE, Petrostreamz AS | Curtis Hays Whitson, SPE, NTNU, Petrostreamz AS
SPE Middle East Oil and Gas Show and Exhibition, Manama, Bahrain, 10–13 March 2013
Well test rates are measured with test separators operating at varying pressure and temperature during initial production tests for a new well and during periodic tests used to monitor well performance and allocate multi-well production separator rates.
Converting test separator gas and oil volumetric rates to a common (fixed) set of surface separator conditions is useful to ensure consistent history matching and rate allocation, development of valid inflow performance relations, and correlating well performance changes over time. This paper provides a method to convert reported test rates to a molar compositional wellstream rate. This compositional wellstream will exactly reproduce the reported test rates at the separator conditions prevailing when rates were measured. The compositional wellstream rate can then be re-processed through a fixed set of separator conditions to provide total surface gas and stock-tank oil rates.
The requirements for converting test rates to a compositional wellstream include: (1) an appropriate EOS model, (2) an estimate of the wellstream composition – the “seed feed”, (3) test separator volumetric rates, and (4) test separator conditions of pressure and temperature. The seed feed is usually the previously-determined wellstream composition from an earlier test. The seed feed is flashed at test separator pressure and temperature, resulting in equilibrium gas and equilibrium oil compositions. These equilibrium compositions are recombined in a ratio that yields exactly the test separator gas-oil ratio with the EOS model, thereby yielding wellstream composition. Properties of the separator phases are used to convert separator volumes to moles and thereby wellstream molar rate.
Sometimes a similar conversion is needed for volumetric gas and oil rates resulting from a multi-stage separation process. An important example is conversion of black-oil rates to compositional wellstreams, where the black-oil PVT tables have been generated from a multi-stage separation process.
Finally, we discuss the processing of compositional wellstreams through a higher-level (group, field, or asset) process facility that takes into account the total feed composition of the process facility, and how to back-allocate well contributions of total product rates.
Copyright 2013, Society of Petroleum Engine