Abstract
With the increasing need for highly cost-effective well production enhancement applications, acid stimulation is becoming increasingly popular. To be successful, acidizing procedures require distribution of stimulation fluids across and within the desired treatment interval. Historically, this has been approached with mechanical placement or chemical diversion of treatment fluids. Method selection can be crucial to treatment success – and an increasing number of options exist – each with its own set of limitations and uncertainties. Preferences and success vary for matrix and fracture acidizing – in vertical and deviated wellbores, in sandstones and carbonates and in cased and perforated, gravel packed, and openhole completions. Method selection and implementation can be daunting but greatly rewarding – calling for creativity and field experimentation.
This paper focuses on the important role of acid placement and diversion, and the types, purposes, benefits and pitfalls of the methods currently in practice. The importance of treatment placement was evident and recognized in the earliest acid treatments conducted in the late 19th century. Although this need has been recognized since the dawn of acidizing, at no point in its history has a diversion method found universal reliability and acceptance. Insufficient interval coverage is perhaps still the most common reason why acid jobs often fail to meet expectations. A well-conceived treatment in all other aspects of design (damage assessment, selection of fluids and additives, and volumes) can count for nothing if the treatment does not enter or cover those portions of the interval with the greatest need of stimulation.
Since the first commercial acid treatments in the 1930s, mechanical placement has evolved from crude rubber "packers" to advanced coiled tubing technologies. Chemical and particulate diverters have evolved from chicken feed to specialized chemical systems, including self-diverting fluids. With chemical diversion, different methods have come into and fallen out of favor – replaced by new ideas, or those forgotten and subsequently revived.
Within its historical perspective, this paper discusses present-day acid placement and diversion methods, their best applications and their limitations – with a view and emphasis on industry needs and direction for the future.
