Exploit low-permeability oil- and gas-bearing clastic sandstones

PetroChina Chang Qing needed to unlock the reservoir potential of and exploit low-permeability oil- and gas-bearing clastic sandstones. The Chang-6 formation usually has a thin barrier between the sandstone layers, and the wells drilled in the formation usually require two fracturing stages performed in the upper and lower layers.

The reservoir’s high heterogeneity quality and limited pressure drive often impacted the hydraulic fracturing performance by reducing the effective hydraulic fracture half-length and fracture conductivity due to partial cleanup. Likewise, the limited reservoir pressure restricted the amount of pressure drawdown that can be created during production operations.

Improve reservoir inflow performance

The HiWAY flow-channel fracturing technique was initiated in the first three vertical and S-shaped wells, which were selected based on the initial well assessment and their proximity to surrounding wells to allow for the proper production comparison.

The successful application of the HiWAY technique within the different oil blocks enabled the final phase of the field trial to be attempted in the gas block. Initially, two vertical and S-shaped wells were selected to evaluate the technology—one with four fracturing stages and the other with three stages. The number of stages was based on the geology and reservoir quality, which included the He-8, Shan-1, Shan-2, Taiyuan, and Benxi formations.

Within the tight gas reservoirs, most of the net pay zones are very thin without a strong barrier that would allow for proper fracture confinement. In some cases, depending on the fracture propagation, there can be fracture confinement issues resulting in higher-than-expected near-wellbore height. When several techniques are compared with the simulated hydraulic fracture geometry using the actual well model, conventional crosslinked gel fracture treatments could result in more height growth in the near-wellbore vicinity and less overall fracture length.

A hybrid design could result in less height growth due to a low-viscosity fluid pumped in the pad stage, whereas the HiWAY technique would enable an increase in the effectiveness of the fracture geometry half-length and reduce the potential screenout due to high leakoff or creation of pinch points. In both load simulation scenarios, the volume of proppant for the conventional and flowchannel fracturing technique was the same, but the hybrid treatment required an increment in fluid volumes.

Reduced proppant by 70% and fluid requirement by 47%

The 180-day cumulative production showed that wells stimulated with the HiWAY technique performed better than 85% of offset wells that were completed with the conventional fracturing treatment. The wells completed with the HiWAY technique performed similarly to horizontal wells, yet the average fluid and proppant requirement was 47% and 70% less, respectively.