Abstract
To economically produce gas from tight reservoirs poses challenges resulting from high bottomhole temperature, low permeability, and high Young’s modulus and rock compressive strength. Hydraulic fracturing, which is necessary to exploit the tight reservoirs, faces constraints such as high fracture initiation and treating pressures, risk of premature screenout, and conductivity degradation. A conventional fracturing treatment in such challenging environment necessitates increased polymer concentration in fracturing fluids and using smaller-size proppant at low concentrations. This results in shorter effective fracture half-length and low fracture conductivity. Additionally, high polymer concentration is not easily cleaned up and may create further damage to the proppant pack. These challenges are compounded where the reservoir is relatively tight and often cannot supply enough energy to clean up the injected fracturing fluids.
To overcome these challenges, channel fracturing was introduced in which proppants are added in pulses to the fracturing fluids, creating stacks of pillar-like structures inside the fracture. These pillars hold the fracture open, and the voids surrounding them form stable channels along the entire geometry of the fracture thereby providing an open pathway with near-infinite conductivity. The technology reduces amount of proppant pumped compared to a conventional treatment, and most of the standard expensive high-strength proppant, required for fracturing in high-stress environment, can be substituted by intermediateand low-strength proppants or even natural sand. The hydrocarbons will flow through the open channels and not through the pack. Additionally, pulsation of proppant during pumping virtually eliminates the risk of a screenout.
Extensive laboratory tests have been conducted to verify the concept of using nonstandard proppant with channel fracturing in high-stress formations. The results of these tests were positive, and trial treatments have been pumped. To date, more than 50 channel fracturing treatments have been conducted in the clastic reservoirs. Some of them have been performed with nonstandard proppant as a part of the treatment. No screenouts were observed even in the formations that were tight with narrow pressure margin between the in-situ stress and completion integrity limitations. Production results after channel fracturing treatments are more consistent compared to conventional proppant fracturing and are not related to the type of propping material used.
