Research On Reservoir And Fracture Prediction Of Xujiahe Formation In The Southern Puguang Gas Field

Continental Xujiahe Formation in the southern Puguang gas field belongs to low-porosity, ultra-low permeability and tight reservoir. Compared with domestic and overseas tight sandstone reservoirs, the densification degree of its reservoir ismuch higher. Tight gas reservoir has always been the focus and difficulty of exploration and development of domestic and overseas. The basic characteristics of such ultra tight gas reservoirs are: reservoir is thin and tight, the distribution of high-yield zones is jointly controlled by high-quality reservoir and fracture. The super-position of high-quality reservoir and fracture is the main reason for forming the storage-permeation body. Under the same reservoir forming conditions, the storage-permeation body with efficient penetration ability, in which features have large scale and developed relatively well, can obtain high and stable yield. Therefore, in such tight gas reservoirs, reservoir is the foundation while fracture is the key to high yield. Only considering synthetically the thickness of high-quality reservoir and the degree of fracture development, can we predict the high-yielding “sweet spot” of these tight gas reservoirs effectively.On the basis of the understanding of basic geological characteristics and reservoir characteristics, this paper combine with the actual data of Xujiahe Formation in the southern Puguang gas field, and has improved the resolution of seismic data. Then Starting from the geophysical method, mainly use post stack inversion technology(including sparse spike inversion and geostatistics inversion) to predict the thickness and physical properties of reservoir in the 2nd member of Xujiahe Formation quantitatively, and predict this layer’s favorable reservoir distribute on qualitatively. Moreover, fracture prediction technique has been optimized. By calculation of coherence cube and curvature cube, this paper completes the synthetical fracture prediction of the 2nd member of Xujiahe Formation, and reservoir connectivity is predicted as well as property. Then predict high-yielding enrichment zone in the 2nd member of Xujiahe Formation synthetically, and it provides a basis for subsequent well location demonstration and reserve calculation. This paper has made the following understanding through research:1、Xujiahe Formation in Puguang gas field is comprised of clastic sandstone and the degree of pore development is low. Sandstone reservoirs are general development, the whole structure contains gas. While the heterogeneity is still strong, transverse distribution is uneven, Vertical distribution regularity is poor. The 2nd member of Xujiahe formation in the southern Puguang gas field is the most developed;2、Continental strata of this study area has development faults which are all reverse faults. According to the trend characteristics, fault system can be divided into two groups of fractures—NW-trending and NE-trending fractures. These structural fractures can compose fracture-developed zone and improve the permeability of reservoir on a great extent, also can make some reformed dense layer to become a producing formation with commercial value;3、The storage-permeation body in Xujiahe Formation in the southern Puguang gas field has a large scale. Next to these faults within Xujiahe Formation, fault-bend fold developed area has storage-permeation body belongs to “sweet spot” type. We may obtain high yield when drilling in such storage-permeation bodies;4、Reservoirs with relatively high porosity are actually the “sweet spot” that reservoir research is looking for. Because high permeability zone is often closely related to the development of fracture, the prediction reservoir “sweet spot” and fractures is the key to tight sandstone gas reservoirs prediction. Therefore, the effective reservoir prediction technique and fracture prediction technology is the key technology in the exploration of tight sandstone gas reservoir.