Overflush and Fracturing: Playing Poker with your Completion

Abstract

Since the inception of hydraulic fracturing, the industry has wrestled with the concept of over/under- flushing, and has always pitched this as a binary philosophy, attempting to determine/define that this is either a fundamentally good or a bad approach. This schism simply grew with the extensive development of unconventionals; the use of overflush being an inherent and fundamental requirement for an effective and economic unconventional completion sequence. This paper will demonstrate that the true answer, as any engineer would expect, is that a detailed assessment is what is required and on a case-by-case basis. The paper will describe and reference several fracturing case histories, in both the Conventional and Unconventional environments, where the application of an overflush, an underflush or an engineered approach have been assessed or applied. Rather than taking an easy headline grabbing route to perpetuate the myth that the process is a major paradigm, or simply either a good or a bad thing. This paper will discuss some of the key aspects that impact the suitability of one approach over another; and how engineering the implementation can lead to a broader range of applicability/suitability for the most economically effective outcome. This includes an appreciation of the production/economic profile and exposure to risk, which is hugely different in say an ultra-deep-water five well offshore development vs. a field development with some 100s – 1,000s of wells in a lower-cost onshore environment. The paper will describe and demonstrate some of the fundamental variables that need to be considered; attempting to elaborate on a few of the key parameters which can influence the effective outcome. The paper will also indicate that there are several different scenarios whereby any form of overflush can result in a detrimental impact on the production rate and EUR, and that these must be fully appreciated. Subtleties, related to reservoir characteristics and fracture geometry; should be examined and appreciated. Additional aspects such as how the production, drawdown and pore-pressure will be managed can also have an impact. All these considerations, and more, will be discussed, described, and referenced. While there is no doubt that the overflush debate will continue unabated, the intent of this paper is to reduce the damage (or uncertainty), one way or the other, that will result. It is an attempt, at a minimum, to ensure that the debate becomes solely a technical one related to the approaches to be taken rather than a black and white one of right or wrong. Ultimately, the paper will advise, and inform, that the approach should be fully considered, engineered in detail and tailored to each and every application and that as a result is no longer simply considered a binary question.