Abstract

Proper fluid and proppant placement are crucial to successful propped fracture stimulation. Numerous completion diagnostic technologies are available to characterize the placement of the treatment. Until recently, characterization of fracturing fluid cleanup could only be simulated in the laboratory and anecdotally monitored in the field. A technique utilizing a family of unique, environmentally friendly, fracturing fluid compatible, chemical tracers has now been developed for quantifying segment-by-segment recovery for individual fracturing treatments and stage-by-stage recovery for multi-stage fracturing treatments. Case histories demonstrate that individual, chemically-differentiated and/or proppant-differentiated, fracturing treatment segments and/or individual fracturing treatment stages are often not being effectively recovered. It has also been demonstrated that the chemical make-up and/or the proppant scheduling of these individual fracturing fluid segments may not only be detrimentally affecting their incremental cleanup but ultimately the production contribution from the corresponding portions of the fractured reservoir. The validation of improvements in fracturing fluid cleanup and production enhancement resulting at least in part from changes in the chemistry of the fracturing fluids and/or changes in proppant scheduling are demonstrated using the tracer technology.

Introduction
Chemical Frac Tracers

In an effort to bolster the level of understanding regarding the dynamics of hydraulic fracture placement and subsequent fluid flowback/cleanup, the technology of chemical frac tracers (CFT's) was born. Borrowing from many years of experience with interwell tracing, several families of non-radioactive chemical compounds were identified that could potentially be placed in segmented portions of the frac fluid so as to more directly measure the flowback efficiency of each fluid segment. Armed with this flowback profile data together with the net pressure history of the frac treatment, it was believed that much could potentially be learned both about the dynamics of segmented fluid placement as well as segmented fluid flowback/cleanup. Given the established formation/fracture damage potential for conventional proppant transport fluids, those fluid segments not adequately recovered following the treatment could, in principle, detrimentally affect the effective flow capacity of the fractured interval.

Chemical frac tracers were designed to be placed in chemically-differentiated and/or proppant-differentiated fluid segments of the fracturing fluid so as to assess the cleanup of the fracture as a function of segment fluid chemistry and/or fracture geometry. In so doing, it was believed that the sufficiency or insufficiency of addition rates for key frac fluid additives such as polymers, breakers and gel stabilizers could be assessed. It was also believed that the relative cleanup of individual frac treatment stages in a multiple stage completion procedure could be monitored. It was further hoped that inferences could be made from these data regarding lateral placement effectiveness of proppants and vertical communication between zones.

Background

The detrimental effects of fracture conductivity reduction resulting from incomplete fracturing fluid flowback/cleanup are well documented. Most of these studies have focused on the effects of flowback procedures on postfrac well performance.1–4 Some of the detrimental effects associated with improper flowback procedures include proppant flowback, proppant crushing, and fracture plugging. Despite its inherent effects on well performance, frac fluid flowback/cleanup has been overshadowed in recent years by a preoccupation with proppant flowback and methodologies for preventing flowback.

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