Data Accuracy from Well Test Operations

Abstract

This master thesis presents a study on data accuracy from well test operations. All data measuring methods, except bottomhole and surface PVT sampling, is investigated for the accuracy related to procedure and equipment used. The objectives with this study is to highlight potential weaknesses in the procedures or equipment so that Expro can improve the quality of their data acquisition. The main research area is the measurement methods, but also the impact of the type of fluids produced has been studied. Oil, gas or gas/condensate may have different inaccuracies for different methods. Results from this study shows that some of the measurements should be improved. The most critical measurement is the oil flow rate, where no procedure for executing meter correction factor is given. Oil flow rate is one of the most important surface parameters the client want obtain with a well test and should therefor be as accurate as possible. Another weakness is an Excel spreadsheets that is used for various calculations for oil is not protected and formulas has been manipulated. This may again give wrong output values. Another factor is the lack of knowledge among offshore personnell about phase changes due to changes in pressure and temperature. This may have impact on all the measurements that include gas and oil. Since this is something they can not expect offshore personnell to be experts on, should the procedures be updated to cover all scenarios for measurements of various phases. The conclusion from this study is that measurements regarding oil and gas parameter are the most inaccurate and an update of procedures is necessary to improve the data accuracy. Most of the calculations today is done by computer softwares, but correct input values is necessary to get correct output values. Knowledge about what formulas the software contain is important to know to be able to make necessary measurement and data collection for input variables to the software. This should be taken into account if procedure is to updated.