Prevention of Emulsion Formation During Matrix Acid Stimulation Jobs Using A Multi-Node Injection System and a pH Buffering Complex
Authors: Marcano K. , Subero D. , Holder G.M. 
Published: December 2007

Prevention of Emulsion Formation During Matrix Acid Stimulation Jobs Using A Multi-Node Injection System and a pH Buffering Complex.

A perennial problem during matrix acid stimulation jobs is the prevention of emulsion formation during pumping of the acid treatment downhole and during flowback of the spent acid returns up the wellbore and through the production facilities to the storage tanks. The presence of emulsion commingled with crude oil in the storage tanks decreases the volume of the crude oil available for sale and also affects the logistics of storage tank volume available for incoming crude oil. During normal non-acid production periods, various chemicals are routinely injected both at the production platform and the fluid collection, separation and storage terminal. However, during the flowback of spent acid returns from matrix stimulation jobs, the tendency of emulsion formation from the wellbore to the terminal is extremely enhanced and very sensitive to certain system parameters. If the system parameters are not fully understood and controlled, the result of emulsion formation is invariably catastrophic.

This paper presents the results of three years of study into the subject of emulsion prevention and control during matrix acid stimulation jobs in the Teak, Poui and Samaan fields, offshore Trinidad. The salient system parameters from the wellbore to the terminal which affect emulsion formation are presented. A unique Multi-Node Fluid Injection System, developed and utilized in Trinidad for the total control of the system parameters is also presented. Another aspect of this paper is the discovery, by the authors, of the application of a pH Buffering Complex to provide the ultimate method (to date) to control the formation of emulsion along the production system. The combination of the Multi-Node Fluid Injection System. and the pH Buffering Complex offers the best solution to date for the prevention and control of emulsion formation during matrix acid stimulation jobs.

Introduction

The Teak A, Poui A and Sarun A production platforms are approximately 40 km, 19 km and 45 km respectively off the South East coast of Trinidad. The Teak A production platform processes oil produced from five (5) platforms in the field. The Samaan A platform processes oil from three (3) platforms and the Poui A facilities from two (2) platforms.

After acid stimulation jobs, severe emulsion problems can occur at the production facilities, both offshore and at the tank farm, Galeota Point, Trinidad. Offshore, the difficulty in fluid separation resulted in extreme work scheduling on the production pumps and in some cases, environmental concerns with the dumping of water overboard. At the Galeota Point base operations, the problem could result in thousands of barrels of oil being "tied-up" in the form of emulsions in the storage tanks, which affects crude oil sales and shipment.

Test samples taken from the production system showed that in some cases emulsions were being produced from the well. in some cases, the degree of emulsion decreased upon neutralization. In other cases, the quantity of emulsion increased or actually developed upon neutralizing. In all cases, spent acid returns were neutralize using Soda Ash or Caustic Soda solution. Typical spent acid returns consisted of o to 3 percent HCl acid.

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