The Volcaniclastic Sedimentary Rock Lithofacies Mode And Reservoir Significance Of Southern Songliao Basin

The prolific gas pool of volcaniclastic sedimentary rocks of Early Cretaceous of Shahezi Formation of well block CS6 in Wangfu Faulted in Songliao Basin was found in 2011. Its productivity of gas testing can reach to 15×104m3/d, and its controlled reserves up to 500×108m3. It shows that the volcaniclastic sedimentary rocks have a good exploration prospects in Songliao Basin. Drilling indicates the volcaniclastic sedimentary rocks is very developed in Wangfu, Yingtai and Dehui Faulted in Songliao Basion. It provide a study platform for facies models and its reservoir significance of volcaniclastic sedimentary rocks in basion.Based on geochronology study of those main studying objects, which are volcaniclastic sedimentary rocks of drilling indicates in Wangfu, Yingtai and Dehui Faulted in the south of the Songliao Basin. Using of the cores, well-loggings, seismices date, and combining with previous research achievements, the facies models of volcaniclastic sedimentary rocks in the south of the Songliao Basin is summarized. On this bases, we draw the reserving space type and its formation mechanism, reservoir characteristic of every facie and its reservoir significance of volcaniclastic sedimentary rocks in the south of the Songliao according to well cores, cast liquid photos and petrophysical data, as well as the date of NMR and pressure mercury. From the above research the following conclusions could be drawn:( 1) The lithology classification and petrogenetic type of volcaniclastic sedimentary rocks.The volcaniclastic sedimentary rocks can be divided into five categories including tuffites according to volume fraction of difference detrital grain(tuff, breccia and lapilli), sedimentary tuff breccia, sedimentary volcanic breccia, sedimentary tuff lapilli and reworked lapilli. It can be divided into single fraction and polymictic volcaniclastic sedimentary rocks. Furthermore the single fraction includes rhyolitic, andesitic and basaltic volcaniclastic sedimentary rocks, and the polymictic is transition of various single fraction volcaniclastic sedimentary rocks. There are four ways that can form the volcaniclastic sedimentary rocks:(1)Deposition after transition by lahor.(2)The volcanic materials fall into the watery environment from air.(3)Debris avalanches.(4)The breakage of volcanic rocks in autochthonous. The volcaniclastic sedimentary rocks in basin were mainly formed by the first three types, because the rocks were damaged easily and difficult to save forming by the latter two ways.(2) Characteristics and formation mechanism of volcaniclastic sedimentary rocks reservoirThere are three types reservoir of volcaniclastic sedimentary rocks in South Songliao basin, respectively are primary porosity, secondary porosity and secondary fractures. The primary porosity concludes debris vesicles and intergranular pores. Secondary porosity concludes moldic pores, sponge pores, sieve pores and intergranular pores. Secondary fractures mainly conclude tectonic fractures and alteration fractures. Among those, the intragranular primary pores are the significant difference between terrigenous clastic rocks. The formation mechanism of volcaniclastic sedimentary rocks reservoir mainly are volatile matter releasing effect, Particle supporting effect, organic acid dissolution and tectonism.(3) Lithofacies classification and reservoir significance of volcaniclastic sedimentary rocksBased on previous research results, cores data(hand specimen and thin sections) such as particle-size, rounding, bedding, cementation, logging curves of GR, DEN, AC and RLLS(RLLD), seismic section formation and seismic wave, as well as its generation formation, volcaniclastic sedimentary rocks can be divided into 3 lithofacies respectively are Lahar facies, Air fall facies and Analanche facies, and Lahar facies include 3 subfacies Flood plain, Lahar-related streamflow deposition, Lahar-related fan dalta deposition. Combining with reservoir types, reservoir formation mechanism, porosity and permeability and mercury characteristics of each lithofacies, high quality reservoir should be Analanche facies and Air fall facies, relatively-high quality reservoir should be Lahar-related streamflow deposition subfacies and Flood plain facies, possible reservoir should be Lahar-related fan dalta deposition subfacies.