Enhanced-Gel-Strength Concept Optimizes Chemical Use in Pipeline for Waxy Crude
Authors: Wilson Adam 
Published: October 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 186295, “Application of Enhanced-Gel-Strength Concept for PPD Chemical Optimization in Banyu Urip Export Pipeline,” by Alinda Dwitawidi, ExxonMobil, prepared for the 2017 SPE/IATMI Asia Pacific Oil and Gas Conference and Exhibition, Bali, Indonesia, 17–19 October. The paper has not been peer reviewed.

Banyu Urip crude contains 26% wax, which can lead to flow-assurance challenges in a crude pipeline exposed to lower temperatures. Injection of pour-point-depressant (PPD) chemicals has been considered an effective method to ensure flow of moderate waxy crude. For the Banyu Urip field, PPD injection was compared with other methods and found to be the best option. Nevertheless, it still contributes to approximately 20% of the operating costs. Optimization of this chemical use can bring benefits through lowering operating costs.

Introduction

The Banyu Urip Field is in East Java, Indonesia. The facilities process a stabilized crude, which is then transported through a 20-in. export pipeline to a floating storage and offloading vessel. The export pipeline is divided into two sections, a 72-km onshore section and a 23-km off-shore section.

High wax content is a key characteristic of Banyu Urip crude. The stabilized crude’s wax appearance temperature is 46°C, and its pour point is 33°C (±3°C). With a lowest ambient temperature of 27°C for the onshore section and 24°C for the offshore section, a risk exists of the crude temperature dropping below the pour-point temperature during a no-flow condition, which may cause gelling in the pipeline (Fig. 1).

Several options were considered for a flow-assurance strategy, including continuous PPD injection, pipeline displacement, and electrical heating along the pipeline. Continuous PPD injection was seen as the best option from cost and operability perspectives. Consequently, chemical-injection facilities were installed in all the well pads for continuous PPD injection. To maintain pour point at 24°C, initial calculations required approximately 500-ppm PPD injection. At current production rates, this equates to approximately 20% of the Banyu Urip operational expenditures.

Description of Processes

Continuous PPD injection with a 24°C pour-point target is an inherently conservative approach to keeping the crude pour point lower than the lowest expected ambient temperature. Furthermore, the PPD is not required in normal flowing conditions; rather, it is only required when the pipeline is shut in for a long period, which can cause the crude to cool to ambient temperatures.

In normal operation at design rates, crude enters the export pipeline at approximately 75°C and reaches the storage vessel at approximately 70°C. The export pipeline is insulated, which helps maintain heat in the crude for several days before reaching its pour point, even in no-flow conditions.

When the crude has reached pour point and starts forming a gel, the weak gel (within a certain gel strength threshold) is still breakable by application of export pump pressure within the pipeline maximum allowable working pressure (MAWP).

With a 20-in. pipeline, a radial temperature profile exists in which the center of the pipeline usually will have a higher temperature, making it easier to break the center with pressure.