Study On Volcanic Reservoir Characteristics And Acidizing Stimulation Technology For Block Xunshen8-9

Block Xu Shen 8-9 has features of large area, scattered distribution, complex geological conditions and difficult development. As the fast pace of the early exploration phase, each block had only a small number of exploration wells and superficial studies. Before entering into the development phase, the relevant reservoir characteristics parameters of the block was still not very clear. Reservoir Characteristics (reservoir lithology, physical properties, reservoir space, etc.) play an important role on blocks'development indicators determination and stimulation studies. This block has serious pollution caused by well drilling and completion; and some wells have problems of thin interlayer, poor stability, bottom water, gas and water exiting in the same layer with complex gas-water relationships, which easily results in water channeling in fracturing. Once the water is produced from gas well, gas recovery will fall significantly. Acidification technology has a better adaptability, acidizing fluid can not only effectively remove the pollution near wellbore area in volcanic reservoir, and can chemically dissolve the filling material in cracks and pores to improve reservoir flowing conditions, increase fluidity and boost productivity.Through macro and micro measures, such as the core observation, thin slice microscope identification, XRF fluorescent analysis, mercury intrusion method, whole rock analysis, CT and NMR, and so on, this paper researches and analyzes the volcanic lithology, reservoir space and petrophysical properties of the block based on core information and well logging data. The studied block is dominated by persilicic rock and intermediate- persilicic rock, as well as a small amount of basic eruptive rocks. Rock types are mainly tuff, welded tuff, rhyolite, andesite, dacite and volcanic breccia, etc. The composition of core mineral is mainly quartz, alkali feldspar, and plagioclase. Volcanic reservoir space is classified by two categories, primary and secondary storage space, and different types of rocks have different types of reservoir space, for example, rhyolite has gas cavity; welded tuff has micro-pore and matrix cavity; crystal tuff is the same as welded tuff; volcanic breccia is mainly intergranular pores; breccia lava has gas cavity and dissolved pore. Fractures are mainly structural fractures. The reservoir space of volcanic rocks in the studied block developed to pore, fracture-pore, pore -fracture and fracture, of which the fracture-pore and pore are the main types;average whole rock porosity is 7.10%, average logging porosity is 5.76%, average core permeability is 0.55mD, average logging permeability is 0.96mD, and it is mainly structural fracture, and diagenetic fracture followed, the average fracture width is 18.6μm, the average fracture permeability is 0.92mD; The volcanic reservoir are classified into four types in the studied block and the second is dominant.so it belongs to medium and low porosity and low permeability reservoir, pore structure has features of small pore throat, poorly gradation, high expulsion pressure, lower maximum intrusive mercury saturation.The main cause of pollution damage attributes to well drilling and completion in the studied block. Drilling damage is more serious, and the damage degree increases with the increasing permeability; completion damage is smaller, and the damage degree increases with the decreasing permeability. This volcanic reservoir has serious water sensitivity and salt sensitivity injury, speed sensitivity followed, relatively weak alkali sensitivity damage, and there is no acid sensitivity damage. According to analysis of reservoir pollution damage, the composite acid formula system is screened out through the orthogonal design method. The formula has strong mud dissolution ability, low corrosion rate, good complex effect, and low surface tension. Field tests showed that acid job had achieved the purposes of removing reservoir pollution, improving the liquid fluidity, and improving the whole well productivity. The comprehensive performance of the developed acidizing system can meet the need of field application for volcanic gas reservoir. The conclusion is that it not only provides important technical support for the efficient development of volcanic gas reservoirs, but also broadens the application areas of acidizing technology.