A Novel Approach to Estimate Severity of Paraffin Deposition Inside Production Tubing for Vertical Lift Performance Matching in Well Models

Abstract

The vertical-lift performance curves are often generated with the aid of computer software for creating well models of producing oil and gas wells. These models are used as tools for optimizing fluid production, generation of production forecast and well problem diagnosis. The well models are further used to plan for future requirement of artificial lift assistance. One of the important components for development of representative well models is the Vertical Lift performance and Inflow Performance curve matching. The vertical lift performance curve is generated separately using well test data using various correlations and the best matching correlation to actual well pressure gradient is selected for VLP-IPR matching. The VLP depends on various factors such as tubing size, gas-liquid ratio, wellhead pressure, etc. The producing oil wells having higher paraffin content tend to deposit paraffin wax inside the production tubing reducing the flow area and increasing the pressure drop. The deposition generally occurs near the surface and at greater depths the tubing is free from deposition due to higher temperature because of the geothermal gradient. Due to this an error is induced as the effective inside diameter of tubing is less than the actual diameter entered by the user, this leads to variation in the actual and calculated pressure drop ultimately leading to deviation by more than 10% in many cases. This paper describes implementation of method to enter the severity of paraffin deposition in a particular length of tubing and dividing the total length of tubing into sections having different internal diameters. The estimation of deposition can be done by carrying out mechanical scraping operation in which the wax is cut mechanically using paraffin cutters of various sizes starting with the smallest and gradually increasing to higher sizes of cutters. The restriction due to wax is evident at the surface by monitoring the weight loss in the wireline weight indicator. By using this method an accurate well model can be created which will represent the actual behavior of the producing well thereby increasing the accuracy of any further predictions.