Pressure Drop In Wells Producing Gas And Condensate

Abstract

Abstract Actual field pressure drop – flow rate data from 102 wells producing gas-condensate mixtures at gas-liquid ratios ranging from 3900 to 1,170,000 sef per barrel are presented and analyzed in detail. The phase conditions in the well bore are determined by standard flash calculations. Pressure-gradient data for flow under single-phase conditions are compared with conventional predictions and found generally to confirm them. For the tests in which two-phase conditions arc prediction throughout the well bore, tile field data are compared with several wholly empirical prediction methods with a previously proposed method and with a new method partly based on the mechanics of flow. The new prediction method incorporates an empirical estimate of the distribution of tile liquid phase between that flowing as a film on the wall and that entrained in the gas core. It employs separate momentum equations for the gas-liquid mixture in the core and for the total contents of the pipe. The empirical method, which treats the total well effluent as a single-phase gas of well-effluent properties, and the new empirical-mechanistic method give predictions of comparable accuracy, with average deviations in the pressure gradient of −0.4 and + 0.1 lb/ ft and root-mean-square deviations of 1.9 and 2.1 lb / ft respectively. Where two-phase conditions are predicted in part of the well bore, with single-phase conditions in the remainder, treating well effluent as a single-phase mixture gives predictions in good agreement with the data. The new empirical-mechanistic method predicts the pressure gradient with comparable accuracy. INTRODUCTION AZIZ. GOVIER AND FOGARASI (1973) recently reviewed methods of predicting pressure drop in wells producing oil and gas at gas-oil ratios generally below 30,000 scf/ bbl and mostly in the range of 150 to 1600 scf/ bbl. They compared actual field data on 48 wells with n variety of empirical prediction methods and a proposed method based on the mechanism of flow, The proposed method gave results with an accuracy equal to the best of the empirical methods. The flow patterns encountered in the well tests were identified using the flow-pattern map of Govier and Aziz (1972). Most of the test data showed that single-phase (liquid), bubble and slug flow were encountered respectively in the lower, middle and upper reaches of the pipe. The present paper is concerned with the analysis of pressure-drop data in wells producing gas at high gas-liquid ratios, showing a comparison of the actual pressure drop with predictions from various empirical and mechanistically based methods and the development of a modified method based on the mechanics of flow. The various empirical and other pressure-drop relationships are reviewed in detail in Govier and Aziz. Pressure-Drop Equations Govier and Aziz give the mechanical energy equation for vertical flow of a single- or multi-phase mixture written for a small elevation change, dz, as follows: (Equation in full paper) Ros gives graphical relationships for the prediction of EG and fn. Details are" also available in Govier and Aziz.