Monitoring Fracturing Fluid Flowback and Optimizing Fracturing Fluid Cleanup Using Chemical Frac Tracers

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.

Understanding Flowback as a Transient 2-Phase Displacement Process: An Extension of the Linear Dual-Porosity Model

“…Among existing flowback chemical analysis models (Asadi et al, 2008;Sullivan et al, 2004;Willberg et al, 1998;Woodroof et al, 2003), Gdanski et al (2007) was on of the first to incorporate a chemistry layer to a 2-D numerical simulator. This simulator was used to history-match the composition of flowback fluid.…”

“…This calls for a model that captures the transient 2-phase (gas/oil + water) flow in HF, and can be used for history matching rate and pressure data measured during flowback operations. Flowback chemical (tracer) analysis (Asadi et al, 2008;Sullivan et al, 2004;Willberg et al, 1998;Woodroof et al, 2003) could provide (1) an efficient means of differentiating formation water from flowback water (fracturing fluid + formation water) and (2) an optimal fracture clean-up or load recovery workflow.Developing an appropriate model for analysing rate/pressure measured during flowback operation requires a proper review of the static framework and flow physics of existing unconventional reservoir models. This paper extends the existing linear dual-porosity model (DPM) and develops a flowback analysis model (FAM) which accounts for transient multiphase flow in HF.…”

“…This model assumes that water-saturation drop with time causes a corresponding non-linear increase in hydrocarbon relative-permeability in HF. The application and drawbacks of these methods are discussed below.Among existing flowback chemical analysis models (Asadi et al, 2008;Sullivan et al, 2004;Willberg et al, 1998;Woodroof et al, 2003), Gdanski et al (2007) was on of the first to incorporate a chemistry layer to a 2-D numerical simulator. Fifteen tight oil, tight gas and shale gas wells completed in the Bluesky, Cardium, Evie, Muskwa and Otter-Park Formations were used for this study.…”

Optimizing Fracturing Fluid Cleanup in the Bossier Sand Using Chemical Frac Tracers and Aggressive Gel Breaker Deployment

“…The "hybrid" water-frac treatment design has been used successfully in the study area for a number of years [12][13] . The hybrid water-frac design, as outlined in Table 1, incorporates a substantial volume of treated water prepad pumped at a high rate, followed by a relatively large crosslinked gel pad, and moderate volumes of 40/70, 20/40 and/or 30/50 proppants also pumped at a high rate.…”

Quantitative investigation on the characteristics of ions transport into water in gas shale: Marine and continental shale as comparative study

“…Zolfaghari et al (2015) established a model to evaluate the complexity of networks based on salinity profile. Woodroof et al (2003) established the post-fracturing flowback analysis model that depends on monitoring the salinity profile and optimizing the flow-back regime.…”