A New Shear-Tolerant High-Temperature Fracturing Fluid

Abstract

The extent of crosslinking a polymeric fracturing gel can significantly contribute to the success or failure of a hydraulic fracturing treatment. In certain cases, excessive crosslinking while the fluid is in the tubulars can result in friction pressures that are too high, and may prohibit the treatment from achieving the design goals. With titanium (Ti) or zirconium (Zr) crosslinked gels, which are known to be prone to irreversible shear degradation, early crosslinking in the tubulars can substantially reduce the final gel strength, even to the degree that near wellbore proppant transport is compromised, and the treatment may screenout. On the other hand, a Ti or Zr crosslinked gel which crosslinks substantially after exiting the perforations may not have sufficient proppant transport capability to complete the treatment successfully. Varying treatment conditions such as mixwater composition and temperature, tubular shear rate and transit time, and reservoir temperature pose difficult challenges to routinely achieving the optimal crosslinking state. Conditions such as offshore wellbore temperature profiles and viscous heating in smaller diameter tubing can further complicate the task. Various chemical means have been employed to tune the crosslinking temperature for specific treating conditions. These methods involve addition of chemicals to control the crosslinking kinetics, such as pH buffers, crosslinker concentration, and competing ligands to temporarily bind the metal crosslinker. Blended crosslinkers containing a single Group 4 (Ti, Zr) metal with different organic ligands with different binding strengths have been employed to achieve crosslinking at two temperature ranges so that early viscosity for proppant transport can be developed. Mixed metal crosslinkers, such as aluminum and Zr have also been formulated for this same purpose. This paper examines the disadvantages of these strategies, and describes the development and deployment of a high-temperature fracturing fluid system that has shown to overcome those issues. Introduction Achieving the design fluid viscosity at in-situ conditions is critical for a number of reasons. Fracture initiation, propagation, and resulting dimensions are strongly influenced by the viscosity. Proppant transport, also determined by fluid properties, is necessary for fracture areal coverage and helps determine well performance. Overcoming the various demands on a gel formed from a single organometallic crosslinker are difficult to achieve (Fig. 1). Ideally, the crosslinking could be triggered instantaneously just after the fluid exits the perforations, avoiding high friction pressure and degradation resulting from shear in the tubulars and perforations. Crosslink the fluid too early and the friction in the tubulars will rise significantly and, as it will be shown later, a significantly crosslinked fluid cannot be sheared without permanent damage to the polymer molecular weight, and therefore to the fluid viscosity. Low initial viscosity from crosslinking too late may result in a narrow, near-wellbore fracture, impeding proppant transport. Either crosslinking a single organometallic system too early or too late risks premature screenout. (Nolte 1988, Walser 1988, Almond 1984) Gelling at varying temperatures can be achieved by delivering a crosslinker that has two (or more) organometallic complexes: one that could yield limited crosslinking at a lower temperature for initial proppant transport, and the second complex for higher temperatures experienced in the fracture. This approach would manage friction pressures. However, the gel would still suffer irreversible degradation due to the strong metal bonds existing during high shear in the tubulars.

Development of the Gemini Gel-Forming Surfactant with Ultra-High Temperature Resistance to 200 °C

“…Shear recovery is one of the important indexes to evaluate fracturing fluid field application performance [ 47 ]. The viscoelastic surfactant gel solution in this work belonged to pseudoplastic non-Newtonian fluid.…”

New Polymer Fluid for Hydraulic Fracturing in Russia

“…After high shear, fluids crosslinked with borates are known to recover their viscosity (Parris et al 2009), unlike titanium or zirconium crosslinked fluids, which undergo irreversible degradation. However, the rate of shear recovery and the temperatures at which fluids should be tested for shear recovery are still not well understood.…”

A Novel Approach to Crosslink Delay of Low-pH Fracturing Fluid

“…al 1989;Mirakyan 2009). Chemical methods of delaying crosslinking with CMC, CMG, CMHEC or CMHPG for fracturing applications at low pH are often not effective because the delaying compounds lose their ability to chelate due to protonation of anionic binding sites at low pH; this facilitates early release of the zirconium cation for crosslinking.…”