Benefits of the Novel Fiber-Laden Low-Viscosity Fluid System in Fracturing Low-Permeability Tight Gas Formations

Abstract

Abstract Most of the low-permeability tight gas market that is treated by low-viscosity slickwater fracturing treatments results in ineffective propped fractures due to rapid proppant settling. Currently hybrid fracturing and ultra-lightweight proppants are employed for improving performance of slickwater treatments. The hybrid fracturing methodology uses a combination of linear and crosslinked gels to improve proppant placement. The disadvantages of existing lightweight proppants are their high cost and applicability only to reservoirs characterized by low closure stresses. Novel fiber-laden low-viscosity fluid technology has been developed to improve proppant transport for hydraulic fracturing in low-temperature tight gas formations. Such a system creates a fiber-based network within the fracturing fluid that decouples proppant settling from fluid viscosity. This network entangles proppant, dramatically reduces proppant settling, and provides a mechanical means to transport and place the proppant at greater distances from the wellbore. An additional advantage of the new system lies in fiber degradability, which leads to a nondamaged fracture conductivity with time. Fluid rheology of fiber-laden fluids was measured over a 150-230 °F temperature range under various fiber loadings. Studies showed that under bottomhole temperature and fluid pH fiber decompose and form a water-soluble species. During fiber degradation, the permeability of the fiber-laden system approaches the value of permeability for the baseline system without fiber. Compatibility study of the degradation byproducts with formation water showed no precipitate formation in high salinity environments. The results demonstrate that the new fiber technology ensures uniform proppant placement within a long fracture, provides permeability equal to pure proppant pack values, and offers higher production rates in comparison with conventional fracturing treatments. Introduction Tight-gas formations are characterized by very low permeability values, usually in the range of micro- or nanodarcies. Long effective fracture half-lengths are required to optimize production rates and ultimate recovery in these formations. Good proppant placement throughout the payzone is very important, and minimizing height growth into unproductive adjacent layers significantly improves the economics of the fracturing treatment. Due to the high flow velocities in the propped hydraulic fracture in tight gas formations, there is an additional requirement to minimize non-Darcy flow effects and multiphase flow effects-commonly addressed using round, spherical proppants strong enough to withstand the effective stress in the fracture. All these requirements could be fulfilled by fracturing with low viscosity fluids if it were not for rapid proppant settling. Proppant settling, or even worse proppant settling out of the payzone, severely limits the effective fracture length1. Inability of low viscosity fluid to carry proppant for extended periods at bottomhole temperature leads to a full proppant settling before the fracture closes. Poor carrying properties of such fluids result in poor vertical coverage of the fracture with proppant and therefore non-optimal fracture conductivity. Summarizing the aforementioned, the following general requirements for fracturing tight-gas formations could be defined:Create maximal effective fracture half-lengthContain fracture height within pay zoneMaximize fracture conductivity using correct proppant and clean fluidsEnsure both good vertical coverage and deep placement of the proppant within the fracture. One of the existing ways to minimize particle settling during hydraulic fracturing is to use high concentration polymer crosslinked fluids having excellent proppant transport characteristics. However, being highly viscous, the crosslinked fluids can break out of zone. Furthermore, the high polymer concentration may cause irreparable damage to fracture conductivity. These two factors make this methodology inefficient in formations with extremely low permeability (microdarcies or less).