Exploration and production of unconventional reservoirs have been conducted in the Sichuan basin since the 1950s. In that time, the relatively thicker low-permeability (tight) gas reservoirs have been developed, and a very thin tight reservoir and a shale gas reservoir are now being targeted. An operator has planned to develop these unconventional reservoirs with long horizontal drilling combined with multistage hydraulic fracturing. However, the management of the subsurface uncertainties appears as the biggest challenge.
Since the basin rests in a major compressional tectonic area, the target reservoirs are very sensitive to abrupt structural dip changes and faulted standoffs. Precise landing and lateral placement of horizontal wells are critical to the success of this program. Advanced logging-while-drilling (LWD) acquisition and real-time data transmission have been applied to overcome these challenges. A new LWD imaging technology delivers high-resolution electrical borehole images, azimuthal gamma ray, and multidepth measurement of formation resistivity for well placement and fracture identification purposes in the thin tight gas reservoirs. A multifunction LWD formation evaluation delivers the elemental capture spectroscopy in addition to triple- combo measurements for well placement and real-time formation evaluation in the shale gas reservoir.
Based on these real-time data and advanced interpretation or analysis techniques while drilling, structural features including dips, faults, and fractures could be clearly identified. Improved elemental composition from elemental capture spectroscopy and enhanced formation grain density evaluation could also be obtained. As a result, the team has been able to accurately place the well and significantly reduce the probability of erroneous lateral placement and optimize the completion design and planning of the hydraulic fracturing staging and segmentations. The successful implementation of this solution has led to the conclusion that the very thin tight gas reservoir and shale gas reservoir can be profitably developed in Sichuan Basin.