| This thesis makes a recognition on mineral composition and rock structure type of Ordovician Yijianfang Formation carbonatite in the west of Tahe Oil Field, based on the theory of sedimentology, rock mechanics and reservoir geology. The author elaborates spacial distribution characteristics of different fabrics, probes its relationship with the development of reservoir and predicts beneficial sections which develops Yijianfang Formation reservoir.The author recognizes mineral composition and rock structure type of Ordovician Yijianfang Formation carbonatite by observing the rock core of the drilling and rock slice. After recognizing, the author names the carbonatite rock types of the region with the compositional characteristics of rocks, structure- genetic angle divided rock types method, probes into the electrical characteristics of part of rocks, and describes lengthways distribution characteristics of different rocks.By analyzing the dissolution of rock core in Yijianfang Formation, it could be known that the corrosion of this region include six types: dissolved pore, separate eroded pore, calcite corrosion holes along tectonic fissure, corrosion holes related to stylolite, corrosion holes in silicification concretion, large-scale karst cave. Among them, calcite corrosion holes along tectonic fissure is the main type. Corrosion holes happens in the earlier period of dissolution; calcite corrosion holes along tectonic fissure, corrosion holes related to stylolite, corrosion holes in silicification concretion and large-scale karst cave have their occurrence time in later period.This thesis studies the relationship between rock fabric and dissolution, on the basis of former research and simulation experiment on dissolution. The statistics of rock sample dissolution shows that, although dissolution develops in different rock types of Yijianfang Formation, dissolution happens most frequently in pure limestone layer and rock cores and microscopical corrosion degree is the strongest in this layer. dolomite limestone, siliceous concretion limestone and marlstone have lower frequency of dissolution; their rock samples are slightly corroded and holes scale is limited. The control of dissolution by rock structure is not very regular, but in generally, grain structure of carbonate rocks are in favor of dissolution occurred. Because granular carbonatite suffered intense or less intense seabed agglutination and atmosphere dissolution in syndiagenetic stage or early stage of diagenesis. Compared with silicification in burial period and dolomitization transformation, it is weaker, which is in favour of getting stronger dissolution and transformation latterly.By knowing the difference of potential dissolution of different fabric rocks, and combing the comprehensive dissection outcome of reservoir, this thesis explores the relationship between rock fabric and reservoir development, between rock fabric and reservoir type; and further understands the control effect exerted by rock fabric to reservoir type. The author analyzes the distribution regularities and controlling factors of reservoir development, with the consideration of transformation law and controlling factor of rock fabric. In conclusion, carbonatite fabric of the region controls reservoir development passively rather than actively; pure limestone is beneficial for the development of large-scale dissolution and is easily transformed into reservoir; places where crack highly develops could accelerate large-scale corrosion; karst opening reservoir which is made under the impact of corrosion and crack, is important reservoir stratum in the work area. Stylolite development is closely related to rock fabric and wide range of stylolite could inhibit large-scale corrosion and reservoir development. At last, the author puts forward the upside of Yijianfang Formation is the favorable layer for reservoir development. |
