Novel Filtration Process Eliminates System Upset Following Acid Stimulation Treatment
Authors: Hebert P.B. , Khatib Z.I. , Norman W.D. , Acock A. , Johnson M. 
Published: December 2007

Recent changes in the environmental compliance rules and regulations regarding the overboard discharge of produced water have altered the way well stimulation fluid returns are processed. The flow back of treatment fluids, formerly handled under exception rules, was handled in a manner which normally minimized facility processing upsets. With the introduction of the new regulations, processing stimulation returns caused system upsets and has even halted production until the flow back treatment has been completely accomplished.

The application of a filtration process used to avoid these problems in several acid flow back situations is presented. The filtration process equipment is described as well as operational considerations that may help eliminate facility upsets while maintaining environmental compliance. Discussion of the additive packages tested for pre-job oil emulsion and water oil and grease screening is included. Fluid analysis of the flow streams into and out of the filtration process and cost for four case histories are summarized.

Introduction

The use of acid systems to stimulate or to improve oil and gas production has been around since 1932. As the understanding of the acidizing process has been better defined the acid systems have become more and more chemically complicated. These chemical packages added to the live acid system improve not only the removal of damage but also the clean-up and flow back of spent acid, not to mention the enhancement of hydrocarbon production.

Accompanying this practice comes the task of processing well stimulation fluid returns without causing severe upsets in the surface treating facilities. Recently, with the new EPA overboard discharge requirements, processing the aqueous phase has proven to be much more difficult. Bansal, Durham, Houchin, Picou, and others evaluated the reduction or elimination of acid additives and found that this kind of optimization could be taken to only a minimum threshold concentration before sacrificing the chances of achieving successful add stimulations. All of the additives used in add systems are, by design, water soluble or at least water dispersible. This characteristic maximizes the efficiency of the add. This same characteristic causes the return fluid stream to have unacceptable levels of these same chemicals, along with their crude oil extractable counterparts. These chemicals show up in the water phase of the separation system. Rather than attempting to reduce or eliminate key component additives in the stimulation package and sacrificing the effectiveness of the treatment, some other methods of achieving appropriate water quality were investigated.

This paper discusses the necessity of treating the stimulation flow back fluid through separate handling facilities. In this paper,the impact of add additives on oil and grease content in overboard water discharges is quantified,the causes of upsets in production facilities are discussed,the various options for processing acid returns are summarized, anda novel filtration process for removing both dispersed and soluble hydrocarbon in water is presented.

The performance of this filtration process is demonstrated through four field case histories and the cost for each is summarized.

Returns Processing from Acid-Stimulated Wells

Acid stimulation to improve and maintain productivity of impaired wells is a profitable activity, thus a common practice for Shell Offshore Inc. However, reduction of well stimulation cycle time and minimization of associated production downtime are important economic value drivers.

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