Unconventional resources are considered to be a game changer for near-term and future energy, the huge resources of unconventional gas worldwide will be critical to the world economy. The JinQiu (JQ) block, joint operated by Shell and PetroChina, is located in the northwest of the Sichuan basin, with target reservoir in upper Triassic Xujahe formation (from T3x1 to T3x6). The play concept for the JQ block is a basin centered gas (BCG) play which consists of overpressured, stacked alluvial feldspathic litharenite reservoirs with a very high net-to-gross (N/G) and low porosity and permeabilityties in T3x2 and T3x4 members, and low N/G, low porosity and permeability calcarenites interbedded with calcareous coaly shales in T3x3 and T3x5 members. Major challenges that the operators face to produce these unconventional resources are identifying subsurface sweet spots and utilizing techniques such as wellbore stimulation to generate commercial projects. The process of sweet spot identification in the JQ block includes the following steps: 1) confirming and updating the play concepts from wells early in the play appraisal phase; 2) determining key geological, geophysical and petrophysical elements for the positive well results to define subsurface critical risks factors such as play concept model, reservoir properties, resource density, predicted facies distribution (i.e. channel orientation and distribution) and fracture geometries etc, and 3) follow play based exploration workflow by overlaying critical risk maps for each element to define areas of common risks segments (CRS). Using the results from these CRS maps and knowledge obtained from the positive well results enable us to identify sweet spots for future exploration, appraisal and development drilling. After this study was completed, one additional appraisal well used as a blind test was drilled and finally got an encouraging well testing result. Conclusions from this study are that, for unconventional plays, such as this BCG play, sweet spotting is important to define developable hydrocarbon resources, where all subsurface disciplines (geology, geophysics, petrophysics, reservoir engineering, completions and drilling) should be integrated to drive the decision making. In addition, the configuration relationship of fractures geometries, predicted facies distribution and resource density plays a critical role in the sweet spotting for BCG play exploration, appraisal and development.


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