The Silurian And Devonian Reservoir Characteristics In The Tarim Basin

The Tarim Basin is the largest petroliferous basin in China, with an area ofmore than 560,000 km2. The Silurian and Devonian clastic reservoir is one of thekey stratum series in the Basin. Since 1991, great achievements have been obtainedfrom well drilling and exploration. However, the large majority of the traps here aresubtle such as lithologic, stratigraphic and structural-lithologic, which makes itdifficult for the exploration. Therefore, it is necessary to make research into Silurianand Devonian reservoir characteristics.Based on the theories and technologies of sedimentology, reservoir geology,petrology, geochemistry and reservoir evaluation, researches are carried out onseveral aspects such as reservoir petrologic characteristics, reservoir sandbodygenesis types and distribution characteristics, diagenesis type, reservoir pore typesand evolution, physical property characteristics and its controlling factors. Theresults are as follows:(1) Devonian reservoir is mainly composed of mesograin or fine grain quartzarenite and lithic quartz arenite, with small ammount of litharenite. The main facieshere are shoreline, tidal flat and estuary. Among those facies, the foreshore andshoreface in the shoreline are favorable reservoirs. In the Silurian, the fine-grainedand very fine-grained litharenite and lithic quartz arenite constitute the reservoirs.The main facies are shoreline, tidal flat, shallow-marine shelf and braided river delta.The foreshore and shoreface in the shoreline and shallow-marine shelf are better thantidal flat facies as reservoirs. The sandstone in the distributary channel of the deltafront is also good as reservoirs.(2) In the Devonian, compaction is moderate in most areas. The residual primaryporosity is dominant. Quartz arenites constitute good reservoirs because of quartzovergrowth or clay rims. Carbonate cementation have had a significant impact onreservoir quality. In the Silurian, compaction becomes relatively strong. Thedominant porosity is secondary dissolved porosity which is controlled by theintensity of the dissolving process.(3) Silurian and Devonian reservoirs of Tarim basin are divided into 6 types ofdiagenetic facies. In the Devonian, the clay girdle cementation and quartzovergrowth diagenetic facies are favorable. In the Silurian, the favorable diageneticfacies are the unstable component's dissolution and pyrite cementation. Favorablereservoir belts are predicted by combining the sedimentary facies with thecorrelation research between the diagenetic facies and electrofacies.